2 g&3g planning & optimization

2G, 3G Planning & Optimization

ventinel


Part - 2


ventinel

Contents 2 GSM Radio Network Planning ............................................................................................................... 4

2.1 Overview ........................................................................................................................................... 4

2.2 Planning Foundation .......................................................................................................................... 5

2.2.2 Performance Target Confirmation ............................................................................................... 6

2.3 Coverage Analysis .............................................................................................................................. 6

2.3.1 Area Division ............................................................................................................................... 6

II. Define the field strength at coverage area edges .......................................................................... 7

2.4 Network Structure Analysis ................................................................................................................ 8

2.4.1 Middle-Layer Station ................................................................................................................... 8

II. Advantages .................................................................................................................................. 8

III. Distance between stations .......................................................................................................... 9

IV. Challenges .................................................................................................................................. 9

2.4.2 High-Layer Station....................................................................................................................... 9

II. Functions ..................................................................................................................................... 9

2.4.3 Low-Layer Station ....................................................................................................................... 9

II. Other considerations.................................................................................................................. 10

2.5 Traffic Analysis ................................................................................................................................. 10

2.5.1 Traffic Prediction and Cell Splitting ............................................................................................ 10

II. Cell splitting ............................................................................................................................... 11

2.5.2 Voice Channel Allocation........................................................................................................... 13

II. Relationship between carrier number and bearable traffic ......................................................... 14

III. Example .................................................................................................................................... 14

2.5.3 Control Channel Allocation........................................................................................................ 15

II. CCCH allocation.......................................................................................................................... 15

2.6 Base Station Number Decision ......................................................................................................... 16

2.6.1 Characteristics of 3-sector base stations in urban areas ............................................................ 16

2.6.2 References for Design of Base Station Parameters .................................................................... 17

2.6.3 Uplink and Downlink Balance .................................................................................................... 17

I. Link budget model ...................................................................................................................... 18

II. Bass station sensitivity ............................................................................................................... 19


ventinel

2.6.4 Cell Coverage Estimation........................................................................................................... 22

2.6.5 Base Station Address Planning .................................................................................................. 24

II. Planning methods ...................................................................................................................... 24

2.7 Design of Base Station Address ........................................................................................................ 25

2.7.1 Address design .......................................................................................................................... 25

I. Environment for antenna installation .......................................................................................... 28

II. Antenna isolation in GSM system ............................................................................................... 29

IV. Installation distance between antennas .................................................................................... 32

2.8 Location Area Design ....................................................................................................................... 34

2.8.1 Definition of Location Area ....................................................................................................... 34

2.8.2 Division of location areas .......................................................................................................... 35

II. Calculating coverage area and capacity of a location area .......................................................... 35

2.9 Dual-Band Network Design .............................................................................................................. 38

2.9.1 Necessity for Constructing Dual-Band Network ......................................................................... 38

2.9.2 GSM 1800MHz Coverage Solutions ........................................................................................... 38

2.10 Design of Indoor Coverage System ................................................................................................. 44

2.10.5 Traffic Control ......................................................................................................................... 48

2.11 Tunnel Coverage ............................................................................................................................ 49

2.11.4 Tunnel Coverage Based on Leaky Cable System ....................................................................... 53

2.12 Repeater Planning ......................................................................................................................... 57

2.12.2 Working Principles of Repeater ............................................................................................... 60

VII. Repeater adjacent cell planning ............................................................................................... 65

2.13 Conclusion ..................................................................................................................................... 66


ventinel

2 GSM Radio Network Planning 2.1 Overview The design of radio network planning (RNP) is the basis of the construction of a wireless mobile network. The design level of network planning decides the future layout of a network. During network planning, the documents concerning base station distribution, channel assignment, and cell data must be outputted. And the major tasks involved are as follows: 1) Analyze carriers’ requirements on network coverage, capacity and quality. 2) Analyze the coverage and capacity features of the candidate mobile communication systems and bands, and then analyze the investment feasibility through estimating the network scale. 3) Decide the network structure and base station type based on further analysis. First analyze whether to construct a layering network according to user distribution, propagation conditions, city development plan and existed network conditions, and then analyze the sites within this area to decide whether to use omni antennas or directional antennas to meet the requirements on coverage and capacity. 4) Estimate the number of base stations Before estimating the number of base stations, estimate the coverage distance of base stations of various types in various coverage areas. The factors deciding the effective coverage area of a base station include: - Valid transmit power of the base station - Working bands to be used (900 MHz or 1800 MHz) - Antenna type and installation position - Power budget - Radio propagation environment - Carriers’ indexes on coverage Then through calculating the coverage distance and dividing the coverage areas, you can obtain a rough number of base stations for various coverage areas. 5) Plan an ideal base station address according to cellular structures. According to geographic maps or administrative maps and with the help of on-the-spot surveys, you can have a full understanding of the areas to be planed, and then mark the area where the number of users is large as a target address. After that, mark the addresses of other base stations according to the ideal cellular structure and the result of link budget. 6) Calculate the number of channels of the cells of each base station - Estimate the traffic of a base station according to its ideal location, and then obtain the number of carriers and channels needed by each base station by checking Erl table according to the indexes of call loss rate. - Decide the frequency reuse mode according to band width, network quality requirement, and equipment supportability. - Estimate the maximum base station configuration type according to the frequency bandwidth and reuse mode provided by the construction carriers. If the system capacity in some areas cannot be met, you need to add more base stations or cells to the system according to cell splitting principles and actual conditions. After that, reselect an ideal base station address on the map and re-estimate the number of channels required by the base station. 7) Predict the coverage area and decide the project data, namely, perform the preliminary emulation. The specific tasks are as follows: - Select the design indexes


ventinel

Select the minimum received power and the penetration ratio index at the coverage area edge. - Select the design parameters, which includes: Antenna height (above the ground), antenna azimuth angle, antenna gain, antenna tilt angle, base station height above sea level, base station type, feeder length, antenna feeder system loss, combining and distribution modes, transmitter output power, receiver sensitivity, base station diversity reception, and diversity gains. - Predict the coverage area of each cell according to the propagation models in different areas, and then give the opinions on adjusting the base station address, antenna direction, antenna tilt angle, and antenna height in the areas where dead zones may be present and signals are poor. Finally, provide the project data. 8) Select actual base station address and decide base station type: Perform filed examination according to the ideal base station addresses, and then record the possible addresses according to various construction conditions (including power supply, transmission, electromagnetic background, and land taken over). Finally, recommend a suitable address based on integrated consideration of the deviation from the ideal base station address, the effect on future cell splitting, economic benefits, and coverage prediction. After the base station address is selected, decide the actual base station type according to the number of base station channels. After the base station type is decided, you need to make a scheme for antenna configuration. For moving a network, if you intend to provide a best combination scheme for the antenna feeders, you must fully investigate the combination of the antenna feeders of the original carriers, plan the future expansion of the base station, and design the combination of the antenna feeders supported by current equipments. 9) Plan frequency and adjacent cell Decide the frequency and adjacent planning according to the actual base station distribution and type. 10) Make cell data To ensure that the network runs stably, you must design the parameters relative to performance for each cell. These parameters include system information parameters, handover parameters, power control algorithm parameters, and so on. - Note: For the selection of handover bands, the handover algorithms to be enabled, and whether to use frequency hopping, power control, and DTX, they must be decided in coverage prediction and frequency planning, because the related parameters will be used in emulation. In addition, sections 2.9 and that later introduce the solutions to the planning of dual-band network and the planning in special occasions.

2.2 Planning Foundation

2.2.1 Coverage and Capacity Target Confirmation Before planning a network, you must confirm the network coverage and capacity target and relative

specifications from carriers. They are specified as follows:

- Definition of coverage areas

- Specific division of the service quality in coverage areas

- Grade of service (GoS) at Um interface

- Prediction of network capacity and subscriber growth rate


ventinel

- Available bands and restrictions on using bands

- Restrictions on base station address and the number of carriers

- Penetration loss in cars or indoor environment

- Performance and sensitivity of base stations

- Rules on base station naming and numbering

- Information of the base stations in the existing network

Engineers perform the network planning and guide the subsequent construction work according to the

previous technical specifications. Because any change of these specifications will affect network

construction, you must discuss these specifications with carriers and get their confirmation.

2.2.2 Performance Target Confirmation Carriers emphasize much on the future network quality. Therefore, network planning engineers must

judge the indexes concerning network performance according to construction difficulty and experience,

and then cooperate with carriers to design a reasonable solution.

Generally, the performance of voice services can be judged according to KPI indexes. The KPI indexes

vary slightly with carriers.

The mean opinion score (MOS) is divided into five levels.

- The call whose quality is above level 3 can access the mobile communication network.

- The call whose quality is above level 4 can access the public network.

2.3 Coverage Analysis

2.3.1 Area Division I. Types of coverage area

The signal propagation models are applied in accordance with the propagation environments in areas of

different types. The signal propagation models decide the design principles, network structures, grade of

services and frequency reuse modes for the radio networks in coverage areas. In order to decide the cell

coverage area, you can the radio coverage areas into the following four types:

- Big city

- Middle-sized city

- Small town

- Countryside

Big city

- Dense population

- Developed economy

- Large traffic

- Dense high buildings and mansions distributed in center areas

- Flourishing shopping centers


ventinel

Middle-sized city

- Relatively dense population

- Relatively developed economy

- Relatively large traffic

- Dense buildings distributed in center areas

- Active and promising shopping centers

Small town

- Relative large population

- Promising economic development

- Moderate traffic

- Relative dense buildings distributed in center areas

- A certain scale of shopping centers but with great potentiality

Countryside

- Scattered population

- Developing economy

- Low traffic

In addition, you must consider the coverage of the areas at the intersections and various transport

arteries, including:

- Express way

- National high way

- Provincial highway

- Railway

- Sea-route

- Roads in mountain areas

Generally, it is recommended to apply omni base stations in the countries plains and the areas with

restricted landforms. In big cities, middle-sized cities, and along expressways, it is recommended to

apply directional base stations.

II. Define the field strength at coverage area edges

When defining the field strength of the uplink edges of a service area, you must consider the factors:

Mobile station sensitivity -102 dBm

Fast fading protection 4 dB (3 dB for countryside)

Slow fading protection 8 dB (6 dB for countryside)

Noise (environmental noise and interfering noise) protection 5 dB

Remark:

- To ensure the indoor coverage in big and middle-sized cities, you can consider 15dB for the average

penetration loss between buildings and consider adding 5dB to the protection margin.

- Generally, the propagation loss of GSM 1800MHz signals is 8 dB greater than that of the GSM 900MHz

signals in average.


ventinel

- Radio links have two directions, namely, uplink direction and downlink direction, and the coverage

area is defined by the direction in which the signals are poor, so you must consider the uplink and

downlink balance. Therefore, if you intend to plan an ideal network, you must make a good power

control budget so that the uplink and downlink can be as balance as possible.

III. Define coverage probability

The definition of coverage probability varies with the coverage areas, and the coverage probability is

gradually improved along with the construction of the network.

Generally, a call must be ensured to access the network at 90% of the places and 99% of the time within

the coverage area.

- For the outdoor environment in big cities, the two ratios must be greater.

- For the areas in countryside, the two ratios can be lower.

- For transport arteries, different standards are applied, and the coverage probability can be defined in

accordance with the types of the arteries.

2.3.2 Radio Environment Survey Through surveying radio propagation environments, you can get familiar with the overall landforms,

estimate the rough antenna height, and select the proper radio propagation model, among which the

radio propagation model helps you estimate the number of base station when predicting the coverage.

If necessary, you must adjust the propagation model.

2.4 Network Structure Analysis When considering the layout of base stations, you must deeply analyze network structure. Generally,

according to network layers, a network can be divided into middle-layer, high-layer, and low-layer. The

base stations at the middle-layer bear the greatest traffic in a network

2.4.1 Middle-Layer Station I. Definition and application

A middle-layer station in big and middle-sized cities is defined as follows:

- The antenna is installed on building tops.

- The antenna height ranges from 25 to 30 meters, which is greater than the average height of the

buildings.

- It covers several blocks.

In small towns and countryside areas, except the high-layer stations are designed for controlling traffic

flow or for landform reasons, most of the base stations are middle-layer stations.

II. Advantages

Compared with high-layer stations, middle-layer stations can utilize frequency resources more

efficiently. Compared with low-layer stations, middle-layer stations can absorb traffic more efficiently.


ventinel

Therefore, the middle-layer stations bear the greatest traffic in a network.

III. Distance between stations

The average distance between most middle-layer stations range from 0.6 to 5 km except in countryside

areas. In big cities, the distance between some middle-layer stations is shorter than 0.6 km. However, it

is suggested that the distance between middle-layer stations in big cities cannot be shorter than 0.4 km.

If this distance is too short, the buildings will produce strong interference against the signals of the base

stations. In this case, to control the coverage area is quite demanding.

IV. Challenges

Because no suitable ground objective is available, to ensure the quality of service of a network is quite

demanding. According to the experience on project construction and maintenance, great challenge is

present in the selection of base station address, station design, project construction, network

maintenance, and network quality.

2.4.2 High-Layer Station I. Definition and application

A high-layer station in big and middle-sized cities is defined as follows:

- The antenna height ranges from 10 to 50 meters, which is far greater than the average height of the

buildings.

- Its coverage areas contain the areas covered by multiple middle-layer stations.

Because the high-layer stations make poor use of the frequency resources, they are mainly applied to

the traffic networks where people move fast in big and middle-sized cities.

In addition, to control construction cost and meet coverage requirements, you can install some high-

layer stations in suburban areas, highroads, small towns, and countryside areas.

II. Functions

The high-layer stations must be as fewer as possible but be as effective as possible. They mainly provide

services to the fast-moving subscribers in cities.

& Note:

The coverage of high buildings is realized by indoor distribution systems.

2.4.3 Low-Layer Station I. Definition and application

A low-layer station is defined as follows:

- The antenna height is shorter than 20 meters, which is shorter than the average height of the

buildings.

- The antenna can be installed on the outer walls of the lower floors of a building, on the top of lower


ventinel

roofs, or in the rooms of a building.

Generally, at the early stage of the network construction, signal network design is applied, so most of

the base stations are middle-layer stations. After the basic network is established, you must adjust the

base stations and add new base stations according to traffic and coverage requirements.

For populated commercial areas where the traffic is heavy, you can use low-layer stations, which are

constructed with micro cell layer and distributed antenna system. In this case, not only the

requirements on indoor coverage are met, but also the interference and difficulties of base station

selection caused by short distance between stations are avoided. With the development of the network,

the low-layer stations will develop into the layering network structure.

II. Other considerations

The coverage area of a low-layer station is small, so it can fully use frequency resources but cannot

absorb the traffic efficiently. As a result, ideal traffic cannot be ensured if the base station deviates far

away from the areas where the traffic is heavy.

Therefore, when constructing a low-layer station, you must consider whether the base station is used to

make up coverage or solve the problem of heavy traffic, because the construction purpose is directly

related to the selection of the address and type of the base station.

& Note:

A layering network cost much frequency resource, so it is not recommended for the networks where the

frequency resource is inadequate.

2.5 Traffic Analysis

2.5.1 Traffic Prediction and Cell Splitting I. Traffic prediction

The network construction requires the consideration of economic feasibility and rationality. Therefore, a

reasonable investment decision must be based on the prediction of the network capacity of the early

and late stage.

When predicting network capacity, you must consider the following factors:

- Population distribution

- Family income

- Subscription ratio of fixed telephone

- Development of national economy

- City construction

- Consumption policy

After predicting the total network capacity, you must predict the density of subscriber distribution.

Generally, base stations are constructed in urban areas, suburban areas, and transport arteries.

Therefore, you can use the percentage of prediction method.

At the early stage of construction, the subscribers in cities account for a larger percentage of the total

predicted subscribers. With the development of the network construction, the percentage of the


ventinel

subscribers in suburban areas and transport arteries grows. The traffic of each subscriber is 0.025 Erl in

urban areas and 0.020 Erl in suburban areas.

The formula calculating traffic is:

A = (n × T) / 3600

Here,

- “n” is the call times in busy hour

- “T” is the duration of each call, in the unit of second.

In this way, the number of voice channels needed for a base station can be obtained through predicting

the traffic.

& Note:

When estimating the number of voice channels needed for a base station in the future, you must

consider the effect caused by cell splitting.

In a GSM system, you can use Erl model to calculate the traffic density that the network can bear. The

call loss can be 2% or 5% depending on actual conditions.

Because restrictions on cell coverage area and the width of the available frequencies are present, you

must plan the cell capacity reasonably. If good voice quality is ensured, you must enhance the channel

utilization ratio as much as possible.

In actual networking, if the network quality is ensured at a certain level, two capacity solutions are

available, namely, a few stations with high-level configuration and multiple stations with low-level

configuration. Both the advantages and disadvantages of the two solutions are apparent, so which one

should be used depending on the actual conditions of an area.

For network construction, you can expand the capacity either through adding base stations or through

expanding the base station capacity. The expansion strategies adopted must be in accordance with the

traffic density in an area. For example, the strategies such as adding 1800 MHz base stations, expanding

sector capacity, adding micro cells, or improving indoor coverage can be used to expand network

capacity.

II. Cell splitting

Cell splitting is quite effective for the expansion of network capacity. An omni base station can split into

multiple sectors, and a sector can split into multiple smaller cells. In other word, you must plan cell

radius in accordance with the traffic density of an area.

Cell splitting means more base station and greater cost are needed. Therefore, when planning a

network, you must consider the following factors:

- The rules and diagrams of frequency reuse are repeatable.

- The original base stations can still work.

- The transition cells must be reduced or avoided.

- The cell can split without effect.

Cell splitting is quite important in a network. The followings further describe the cell splitting based on

1-to-4 splitting.


ventinel

Cell splitting is used to split a congested cell into multiple smaller cells. Through setting the new cells

whose radiuses are smaller than the original cells and placing them among the original cells, you can

increase the number of channels in a unit area, thus increasing channel reuse times. In this case, system

capacity is expanded.

Through adjusting the project parameters relative to antenna feeders and reducing transmitter power,

you can narrow the coverage area of a cell. Error! Reference source not found. shows that a cell splits

into four smaller cells by half of its radius.

Smaller cells are added without changing the frequency reuse mode. They are split proportional to the

shape of the original cell clusters.

In this case, the coverage of a service area depends on the smaller cells, which are 4 times outnumber of

the original cells. To be more specifically, you can take a circle with the radius R as an example, the

coverage area of the circle with the radius R is 4 times that of a circle with the radius R/2.

After cell splitting, the number of cell clusters in the coverage area increases. Thus the number of

channels in this coverage area increases and the system capacity is expanded accordingly.

You can adjust the coverage area of the new cells through reducing the transmit power. For the transmit

power of the new cells whose radiuses are half of that of the original cell, you can check the power “Pr”

received at the new cell edge and at the original cell edge, and make them equal. However, you must

ensure that the frequency reuse scheme of the new micro cells is the same as that of the original cell. As

for Figure 5-1,

- Pr [at the edge of the original cell] = Pt1R-n, and,

- Pr [at the edge of the new cell] = Pt2 (R/2)-n

Here,

Pt1 and Pt2 are the transmit power of the base stations of the original cell and the new cell, and n is

path fading exponent. If make n = 4, make the received power at the edge of the new and original cell

equal, the following equation can be obtained:

Pt2 = Pt1/16

That is to say, if the micro cells are used to cover the original coverage area and the requirement of S/I is

met, the transmit power must be reduced by 12 dB.

Not all cells need splitting. In fact, it is quite demanding for carriers to find out a perfect cell splitting

scheme. Therefore, many cells of different scales exist in a network simultaneously. As a result, the

minimum distance among intra-frequency cells must be maintained, which further complicate frequency

allocation.

In addition, you must pay attention to the handover because success handover ensure the all

subscribers to enjoy good quality of service regardless of moving speed.

When two layers of cells are present within an area but their coverage scale is different, according to

the formula Pt2 = Pt1/16, neither all new cells can simply apply the original transmit power, nor all

original cells can simply apply the new transmit power.

If all cells apply great transmit power, the channels used by smaller cells cannot be separated from the

intra-frequency cells. If all cells apply lower transmit power, however, some big cells will be exclusive

from the service areas.

For the previous reason, the channels in the original cells can be divided into two groups. One group


ventinel

meets the reuse requirement of the smaller cells, and the other group meets the reuse requirement of

the bigger cells. The bigger cells are applied to the communication of fast-moving subscribers, which

requires a fewer handover times.

The power of the two channel groups decides the progress of cell splitting. At the early stage of cell

splitting, the channels in the low-power group are fewer. As the requirement grows, more channels are

needed in low-power group. The cell splitting does not stop until all channels within this area are applied

in the low-power group. In this case, all cells in this area have split into multiple smaller cells, and the

radius of each cell is quite small.

& Note:

Commonly, you can restrict cell coverage area through adjusting the project parameters of the base

station.

2.5.2 Voice Channel Allocation I. Voice channel decision

The base station capacity refers to the number of channels that must be configured for a base station or

a cell. The calculation of the base station capacity is divided into the calculation of the number of radio

voice channels and the calculation of the number of radio control channels.

According to the information of base stations and cells and the density distribution of subscribers, you

can calculate the total number of the subscribers. Then according to the radio channel call loss ratio and

traffic, you can obtain the number of voice channels that must be configured by checking Erl B table.

Generally, you can decide the number of voice channels as follows:

1) According to the bandwidth and the reuse mode allowed by current GSM networks within the areas

to be planned, you can obtain the maximum number of carriers that can be configured for a base

station.

2) Each carrier has 8 channels. You can obtain the maximum number of voice channel numbers that can

be configured for a base station by detracting the control channels from the 8 channels.

3) According to the number of voice channels and call loss ratio (generally 2% dense traffic areas and 5%

for other areas), you can obtain the maximum traffic (Erl number) that the base station can bear

through checking Erl B table.

4) Through dividing the Erl number by the average busy-hour traffic of subscribers, you can obtain the

maximum number of subscribers that the base station can accommodate.

5) According to the data of subscriber density, you can obtain the coverage area of the base station.

6) After the areas are specified based on the subscriber density, according to the area of an area and the

actual coverage area of the base station, you can calculate the number of needed base stations.

7) For important areas, you must consider back up stations and the cooperation between carriers. For

example, an important county needs at least two base stations and three important carriers.

8) For the areas where burst traffic is possible, such as the play ground and seasonal tourism spots, you

must prepare the equipments (such as carriers and micro cells) and frequency resources for future use.

9) The dynamic factors, such as roaming ratio, subscriber mobility, service development, industry

competition, charging rate change, one-way charge, and economic growth, must be considered.


ventinel

10) To configure a base station, you must consider the transmission at the Abis interface so that the

capacity can be met while saving transmission. For example, the application and concatenation of the

Abis interface 15:1 and 12:1 should be considered.

11) For indoor coverage and capacity, you can use micro cells and distributed antenna systems. For the

coverage in countryside areas and highroads, you can use economical micro base stations. For the

transmission in countryside areas and highroads, you can use HDSL because it is cost effective.

12) Prepare the some carriers, micro cells, and micro base stations for new coverage areas and future

optimization.

13) In some special areas, you can use the base stations consisting of omni and directional cells, but you

must consider the isolation between omni antennas and directional antennas. For traffic control, you

can use the algorithm in terms of network layers.

14) For some highroads which require a little traffic by large coverage, you can use the two networking

modes. They are:

- (A micro base station with single carrier) + (0.5 + 0.5 cell with two set of directional antennas)

- A micro base station with single carrier + 8-shaped antenna

II. Relationship between carrier number and bearable traffic

Erl traffic model can calculate the traffic that a network can bear. The call loss ratio can be 2% or 5%

according to actual conditions. Table 5-7 describes the relationship between the number of carriers and

the traffic that a network can bear according to Erl B table.

According to Erl B table, the larger the number of carriers and the call loss ratio are, the greater the

traffic that each TCH bear, and the greater the TCH utilization ratio is (the channel utilization ratio is an

important indicator of the quality of network planning and design). If the number of subscribers of a

base station is small, you can consider delaying the construction.

Because restrictions on the coverage area of a cell and the bandwidth of the available frequencies, you

must plan a reasonable capacity for the cell. If good voice quality is ensured, you must take measures to

enhance the channel utilization ratio as much as possible.

For the construction of the dual-band network, you can use the frequencies with wider bands to

enhance channel utilization ratio, which is helpful for traffic sharing.

In actual applications, when the traffic on each TCH accounts for 80-90% of total given by Erl B table (the

call loss ratio is 2%), the congestion ratio in this cell rise greatly. Therefore, we generally calculate the

traffic that a network can bear by taking the 85% of the traffic given by Erl B table as a reference.

III. Example

The capacity of a local network needs to be expanded. According to the service development,

population growth and mobile popularity, the subscribers in this area are expected to reach 100,000 in 2

years.

If only the followings are considered:

- Roaming factor (according to the development trend of traffic statistics) = 10%.

- Mobile factor (the subscriber moves slightly within the local network instead of roaming) = 10%.


ventinel

- Dynamic factor (with burst traffic considered) = 15%.

The network capacity = 100000 * (1 + 10% + 10% + 15%) = 135,000.

However, because the congestion is present, we generally calculate the traffic that a network can bear

by taking the 85% of the traffic given by Erl B table as a reference. As a result, the network capacity must

be designed as follows:

The network capacity = 135, 000/85% = 158,800, about 160,000.

2.5.3 Control Channel Allocation I. SDCCH allocation

Stand-alone dedicated channel (SDCCH) is an important channel in a GSM network. Mobile station

activities, such as location update, attach and detach, call setup and short message, are performed on

SDCCH. The SDCCH is used to transmit signaling and data.

It is difficult to induce a traffic model for the SDCCH; especially it even becomes impossible after the

large-scale application of layering networks and short messages. Moreover, the equipments of some

carriers support SDCCH dynamic allocation function. As a result, the traffic model for SDCCH must be

adjusted according to actual conditions.

The advantages of the SDCCH dynamic function are as follows:

- Adjusting SDCCH capacity dynamically

- Reducing SDCCH congestion ratio

- Reducing the effect of initial SDCCH configuration against system performance

- Making SDCCH and TCH configuration more adaptive to the characteristics of cell traffic

- Optimizing the performance of the systems under the same carrier configuration.

In conclusion, the SDCCH dynamic allocation function is divided into two types, namely,

- Dynamic allocation from SDCCH to TCH

- Dynamic recovery from SDCCH to TCH

II. CCCH allocation

Common control channels (CCCH) contain access grant channel (AGCH), paging channel (PCH) and

random access channel (RACH). The function of a CCCH is sending access grant message (immediate

assignment message) and paging message.

All traffic channels in each cell share the CCCH. The CCC can share a physical channel (a timeslot) with

SDCCH, or it can solely occupy a physical channel. The parameters relative to the CCCH include CCCH

Configure, BS AG BLKS PES, and BS PA MFRMS.

Here,

- CCCH Configure designates the type of CCCH configuration, namely, whether the CCCH shares one

physical channel with the SDCCH. If there are 1 or 2 TRX in a cell, it is recommended that the CCCH

occupies a physical channel and share it with the SDCCH. If there are 3 or 4 TRXs, it is recommended that

the CCCH solely occupies a physical channel. If there are more than 4 TRX, it is recommended to

calculate the capacity of the paging channels in the CCCH according to actual conditions first, and then

you can perform the configuration.


ventinel

- BS AG BLKS PES indicates that the number of CCCH message blocks reserved to the AGCH. After CCCH

configuration is done, this parameter, in fact, decides allocates the ratio of AGCH and PCH in CCCH.

Some carriers can set sending priority for the “access grant message and “paging message”. When the

former message set to be prior to the later one, the BS AG BLKS PES can be set to 0.

- BS PA MFRMS indicates the number of multi-frames that can be taken as a cycle of paging sub-

channels. In fact, this parameter decides the number of paging sub-channels that a cell can be divided

into.

& Note:

In CCCH configuration, the location area planning, paging modes and system flow control must be

considered.

2.6 Base Station Number Decision After traffic and coverage analysis, according to the selected base station equipments and parameters,

you can obtain the coverage areas of various base stations through link budget. The coverage area helps

you calculate the number of base stations required by each area. Then you decide the base station

configuration according to traffic distribution. Finally, you must perform emulation using relative

planning software so that coverage, capacity, carrier-to-interference ratio can be assured and

interference can be avoided.

2.6.1 Characteristics of 3-sector base stations in urban areas Cellular communication is named because the coverage areas of base stations are extruded through

small cellular-shaped blocks. In urban areas, for the purpose of capacity expansion and radio frequency

optimization, mainly 3-sector base stations are used. This section explains some basic concepts of a 3-

sector base station.

This is a standard 3-sector cellular layout. Thedistance between two 3-sector base stations is R + r, here

R = 2r. However, “R” is mainly used in cell radius estimation because the direction along “R” is the

direction of the major lobe of the directional antenna. In the design for cellular layout, however, “r”

indicates the cell radius.

In a cellular cell, if the included angle between a direction and the direction of the major lobe of the

antenna, the coverage distance along this direction is r = R/2, and the path loss along this direction is

about 10dB less than that along the direction of the major lobe of the antenna (for the deduction, it is

introduced in the following), namely, the equivalent isotropic radiated power (EIRP) along this direction

can be about 10dB less than that along the major lobe.

According to this feature, in the cellular layout of this kind, you can adopt the directional antenna whose

azimuth beam width ranges from 60 to 65 degrees because their horizontal lobe gain diagram also

meets this feature.

If “R” is the cell radius, the cell area is S = 0.6495 × R × R. Sometimes the “r” is used as cell radius, so the

cell area is S = 2 5981×r×r. Therefore, when calculating the cell area, you must make clear whether “r” or

“R” is used.

The followings deduce the EIRP required along “R” direction and “r” direction.


ventinel

As shown in Figure 5-3, the coverage distance along “r” direction is half of that along “R” direction,

namely, r = R/2. To keep even coverage, you must make the field intensity at the edges of the cell equal,

namely, RxlvelB = RxlevelC.

Suppose that the EIPR transmitted from cell A is EIRPR and EIRPr along “R” direction and “r” direction

respectively, and the city HATA mode is used for path loss, the path loss from point A and B is expressed

as equation (1) :

EIRPR – RXLEVB = 69.55 + 21.66lgf - 13.82lgh1 + (44.9 - 6.55lgh1) lgR (1)

And the path loss from point A to point C is expressed as equation (2):

EIRPr- RXLEVc = 69.55 + 21.66lgf - 13.82lgh1 = (44.9 - 6.55lgh1) lgr (2)

Subtract (2) from (1), the equation (3) is expressed as follows:

EIRPR - EIRPr =(44.9 - 6.55lgh1)×(lgR – lgr) =(44.9 - 6.55lgh1) × lg (R/r) (3)

Introduce R = 2r, the equation (4) is obtained as follows:

EIRPR - EIRPr = 0.3 × (44.9 - 6.55lgh1) (4)

When the antenna height “h1” increases from 5m to 100m, the values of (EIRPR - EIRPr) decrease from

12 to 9.5, which can be roughly treated as 10dB.

2.6.2 References for Design of Base Station Parameters When estimating the number of base stations, you must perform uplink and downlink budget. Based on

the coverage division and propagation environment survey, you can obtain some project parameters

and apply them to link budget.

2.6.3 Uplink and Downlink Balance After base station parameters are specified, you can perform link budget to estimate the coverage area

of the base station. In addition, you must consider the sensitivity of the base station equipments at this

time.

In a mobile communication system, radio links are divided into two directions, namely, uplink and

downlink. For an excellent system, you must perform a good power budget so that the balance is

present between uplink signals and downlink signals. Otherwise, the conversation quality is good for

one party but bad for the other party at the edges of the cell. If uplink signals are too bad, the mobile

station cannot start a call even if signals are present.

However, the because the fading for uplink channels and downlink channels is not totally the same and

the other factors such as the difference of the performances of receivers are present, the calculated

uplink and downlink are not absolute, but the there a fluctuation of 2 to 3 dB.

The measurement report on uplinks and downlinks at the Abis interface can tell whether the uplink and

downlink reach a balance. In addition, dialing tests in actual network can also tell whether the balance

between uplinks and downlinks are reached. If the conversation quality on downlinks uplinks becomes

poor simultaneously, it means that the downlinks and uplinks are balance.

& Note:

Some carriers provide the traffic statistics on uplink and downlink measurement, which can also tell


ventinel

whether the balance between uplinks and downlinks are reached.

I. Link budget model

When calculating uplink and downlink balance, you must consider the functions of the tower amplifier

first. In a base station receiving system, the thermal movement of the active parts and radio frequency

(RF) conductors cause thermal noise, which reduces the signal-to-noise ratio of the receiving system. In

this case, the receiving sensitivity of the base station is restricted and the conversation quality is

reduced. To improve the receiving performance of the base station, you can add a low-noise amplifier

under the receiving antenna. And this is the principle of the tower amplifier.

The contributions of the tower amplifier to uplinks and downlinks are judged according to the

performance of its low-noise amplifier and gain. In fact, it is the tower amplifier that reduces the noise

coefficient of the base station receiving system. The power amplifier can improve the coefficients for

the uplink receiving system (start from the output end of the receiving antenna). However, if the

functions of the tower amplifier are quantified by this, the uplink improved value can be represented by

the NFDelta (it is the reduced value of the noise coefficient of the receiving system) after a tower

amplifier is added to the system.

(1) No tower amplifier

When there is no tower amplifier, the sensitivity of the equipments at the duplexer input interface at

the top of the base station cabinet are taken as a reference.

For downlink signals, if,

Mobile station receiver output power = Poutm

Base station diversity received gain = Gdb

Base station receiving level = Pinb

Base station side noise deterioration = Pbn

Antenna receiving gain = antenna transmitting gain (according to reciprocity theorem)

The following equation can be obtained:

Pinb + Mf = Poutm + Gam – Ld + Gab + Gdb – Lfb – Pbn

Generally, Pmn is almost equal to Pbn, so the following equation can be obtained:

Poutb = Poutm + Gdb + (Pinm – Pinb) + Lcb

(2) With tower amplifier

If a tower amplifier is present, the improved value of the noise coefficients of the uplink receiving

system can be represented by NFDelta, so the equation Poutb = Poutm + Gdb + (Pinm – Pinb) + Lcb can

be developed into the following equation:

Poutb = Poutm + Gdb + (Pinm - Pinb) + Lcb + NFDelta

The two equations, Poutb = Poutm + Gdb + (Pinm – Pinb) + Lcb and Poutb = Poutm + Gdb + (Pinm - Pinb)

+ Lcb + NFDelta are used to calculate base station transmit power when the uplinks and downlinks are

balance. Here,

Pinb is the base station receiving sensitivity

Pinm is the mobile station receiving sensitivity

Gdb (antenna diversity receiving gain) is 3.5dB


ventinel

According to the requirements in protocols GSM05.05, the mobile station transmit power and the

reference receiving sensitivity of the mobile station and base station are specified in Table 5-10. At

present, however, the sensitivities in actual systems are greater than the reference values listed in the

following table.

II. Bass station sensitivity

This section further introduces the base station sensitivity and the functions of the tower amplifier.

Receiver sensitivity refers to the minimum signal level needed to by the input end of the receiver when

the certain bit error rate (BER) is met. The receiver sensitivity detects the performances of the following

components:

Receiver analog RF circuit

Intermediate frequency circuit and demodulation

Decoder circuit

Three parameters are used to measure the receiver bit error performance. They are frame expurgation

rate (FER), residual bit error rate (RBER), and bit error rate (BER). When a fault is detected in a frame,

this frame is defined as deleted one.

Here,

FER indicates the ratio of the deleted frames to the total received frames. For full rate voice channels,

the FER is present when the 3-bit cyclic redundancy check (CRC) detects errors or bad error indication

(BFI) is caused. For signaling channels, the FER is present when the fire code (FIRE) or other packet codes

detect errors. The FER is not defined in data services.

FBER indicates the BER that are not announced as deleted frames, namely, it is the ratio of the bit errors

in the frame detected as “good” to the total number of bits transmitted in “good” frames.

BER indicates the ratio of the received error bits to all transmitted bits.

Because BER occurs at random, the statistical measurement is mainly applied to measure receiver error

rate. That is, sample multiple measuring points on each channel and when the number of measuring

points is certain, if the BER of each measurement is within the required limit, the BER of this channel

meets the BER as required.

However, the number of sampled measured points and the limit value of the BER must meet the

following conditions:

For each independent sampled measuring point, the times for it to pass a “bad” unit must be as fewer as

possible, that is, the probability must be smaller than 2%.

For each independent sampled measuring point, the times for it to pass a “good” unit must be as more

as possible, that is, the probability must be greater than 99.7%.

The measurement has vivid statistical features.

The measuring time must be reduced to the minimum.

As a result, you can measure the receiver sensitivity through measuring whether the receiver BER has

reached the requirement while entering sensitivity level to the receiver.

Enter the reference sensitivity level to the receiver in various propagation environments. For the data

produced after receiver demodulation and channel decoding, the indexes for FER, RBER.


ventinel

The requirements on BCCH, AGCH, PCH, and SACCH are the same as that on SDCCH.

The value of “a” in this table depends on the channels. It is 1 for base stations, and 1 to 1.6 for mobile

stations.

III. Contributions of tower amplifier to base station sensitivity

In terms of technical principles, the tower amplifier reduces the noise coefficients of the base station

receiving system, which is helpful for improving the sensitivity of the base station receiving system.

In an actual system, to improve the receiving performance of the base station, you can add a low-noise

amplifier near the feeder of the receiving antenna.

In a mobile communication system, the receiver sensitivity = noise spectrum intensity (dBm/Hz) +

bandwidth (dBHz) + noise coefficient (dB) + C/I (dB).

Here the noise spectrum intensity, bandwidth, and noise coefficient are system thermal noise. C/I is the

signal-to-noise ratio required at the Um interface. In a narrow band system, C/I indicates the modulation

performance required by the receiver baseband, and it is a positive number.

In a spreading communication system, because spread spectrum gain is present, the value of C/I is far

beyond the requirement of the modulation performance of the receiver baseband, and it is a negative

number.

When there are n* cascaded receivers, the equivalent noise coefficient is as follows:

Here,

Gn indicates the receivers gain at each level (including the loss at each level).

Fn indicates the noise coefficient of the receivers at each level.

The noise coefficient of the passive device is equal to its loss, and the gain of the passive device is the

reciprocal of the loss.

According to the previous equation, the noise coefficient of the cascading system is determined by the

receivers at the first level.

It must be pointed out that the linear values of the parameters must be applied in the previous

equation, so the “F” is a linear value, which must be converted into a logarithm. Moreover, according to

this equation, the noise the cascaded receivers are determined by the noise coefficient (F1) of the

receivers at the first level.

However, when the tower amplifier stops working, because the loss is present on duplexer and bypass

connectors, about 2dB of redundant loss is introduced on reverse link.

According to the equation , the following two assumptions conclude the regularity of the effect of tower

amplifier on the base station system.

(1) Assumption 1

Hereunder is a series of assumptions:

F1 = 2.5 dB (1.7783), noise coefficient of the tower amplifier

F2 = 4.5 dB (2.8184), noise coefficient of the base station

G = 2 (15.849) dB, tower amplifier gain

Loss of the feeder and other passive devices = 3 dB (2)

Gain of the feeder and other passive devices G0 = –3 dB (1/2)

Noise coefficient of the feeder and other passive devices F0 = 1/G0


ventinel

When the tower amplifier is not added, the noise coefficient of the base station receiving system with

the antenna output end as reference point is as follows:

F = F0 + (F2–1)/G0 = 10*log (2 + (2.8184–1)/0.5) =7.5dB

When the tower amplifier is added, the noise coefficient of the base station receiving system with the

antenna output end as reference point is as follows:

F = F1 + (F0 – 1)/G + (F2 – 1)/(G*G0) = 10*log(1.7783 + (2 – 1)/15.849 + (2.8184 – 1)/(15.849 × 0.5) =

3.2dB

At this time, the added tower amplifier improves the noise coefficient, and FDelta is 4.3dB, that is, the

uplink is improved by 4.3 dB.

(2) Assumption 2


F1 = 2.2 dB (1.6596), noise coefficient of the tower amplifier

F2 =2.3 dB (1.6982), noise coefficient of the base station

G = 12 (15.849) dB, tower amplifier gain

Loss of the feeder and other passive devices = 3 dB (2)

Gain of the feeder and other passive devices G0 = –3 dB (1/2)

Noise coefficient of the feeder and other passive devices F0 = 1/G0

When the tower amplifier is not added, the noise coefficient of the base station receiving system with

the antenna output end as reference point is as follows:

F = F0 + (F2 – 1)/G0 = 10*log (2 + (1.6982 – 1)/0.5) = 5.3dB

When the tower amplifier is added, the noise coefficient of the base station receiving system with the

antenna output end as reference point is as follows:

F = F1 + (F0 – 1)/G + (F2 – 1)/(G*G0) = 10*log(1.6596+(2 – 1)/15.849 + (1.6982 – 1)/(15.849 × 0.5)) =

2.6dB

At this time, the added tower amplifier improves the noise coefficient, and FDelta is 2.7 dB, that is, the

uplink is improved by 2.7 dB.

According to the previous calculation, the following conclusions can be obtained:

The tower amplifier improves the noise coefficient of the base station receiving system, thus improving

the receiving sensitivity of the base station.

The tower amplifier improves uplink signals effectively, which is also helpful for improving the receiving

sensitivity of the base station.

The gain of the antenna amplifier reduces the effect of the components installed behind the tower

amplifier against noise coefficient.

When the feeder is long and the loss of the feeder is great, if the tower amplifier is added, the noise

coefficient of the base station receiving system and the uplink signals will be greatly improved.

The smaller the noise coefficient of the tower amplifier is, if the tower amplifier is added, the greater

the noise coefficient of the base station receiving system is improved. However, if the noise coefficient

of the tower amplifier is too great, it may cause the noise coefficient of the base station receiving

system to deteriorate.

When the receiving sensitivity of the base station is great and the feeder is short, the tower amplifier

makes a little improvement on the noise coefficient of the base station.


ventinel

If the tower amplifier improves the base station sensitivity, the base station is more sensitive to outside

interference.

2.6.4 Cell Coverage Estimation In actual project planning, the effective coverage area of a base station largely depends on the following

factors:

Effective base station transmit power

Working band (900MHz or 1800MHz) to be used

Antenna type and location

Power budget

Radio propagation environment

Carriers; coverage requirements

Based on the indexes of QoS for the mobile network and the actual applications, this section introduces

the coverage area of the base station in different environments theoretically.

If the following assumptions are present:

The antenna height of GSM 900MHz and GSM 1800MHz base stations are 30 meters.

The sensitivities of the GSM900 MHz 2W (33 dBm) mobile station and GSM 1800MHz 1W (30 dBm)

mobile station are -102 dBm and -100 dBm respectively.

The mobile station height is 1.5 meters and the gain is 0 dB.

When the combiner and divider unit (CDU) is used, the sensitivities of the 900MHz base station and

1800MHz base station are -110dBm and -108dBm respectively.

The CDU loss is 5.5dB, and the SCU loss is 6.8dB.

The gain of the 65-degree directional antenna is 13dBd for the 900 MHz mobile station and 16dBd for

the 1800MHz mobile station.

The feeder is 50m in length. For 900MHz signals, the feeder loss is 4.03dBm/100m. For 1800MHz signals,

the feeder loss is 5.87dB/100m.

In general cities, select Okumura propagation model.

No tower amplifier and the downlinks are restricted according to the calculation of the uplink and

downlink balance.

According to the previous assumptions, the calculated results are as follows:

(1) Outdoor coverage radius of the 900 MHz base station in urban areas

The minimum received level of the mobile station dBm. The coverage radius is calculated according to

the maximum TRX transmit power. The maximum TRX transmit power for the 900 MHz base station W

(46 dBm).

The EIRP of the base station antenna is:

(dBm)

Here,

LCOM indicates the combiner loss

Lbf indicates the feeder loss

Gab indicates the antenna gain of the base station


ventinel

And the allowed maximum propagation loss is:

(dB)

According to the Okumura propagation model introduces earlier,

Here,

indicates the antenna height of the base station.

indicates the antenna height of the mobile station.

“f” = 900 MHz.

(dB)

According to the previous known number, the outdoor coverage radius of the 900 MHz base station in

urban areas can be obtained, that is, d = 2.8km.

(2) Coverage radius of the 900 MHz base station in urban buildings

The minimum received level of the mobile station (dBm).

(dB)

Therefore, the coverage radius of the 900 MHz base station in urban buildings can be obtained, that is, d

= 0.75km.

If the previous assumptions are present, this indicates that the 900 MHz base station can cover the

outdoor areas 2.8 km away, but for the subscribers on the first floor of the buildings 750 m away, the

quality of the received signals is not satisfying.

(3) Coverage radius of the 900 MHz base station in suburban areas


(dB)

The Okumura propagation model in suburban areas must be modified as follows:

Therefore, the coverage radius of the 900 MHz base station in urban areas can be obtained, that is, d =

5.4km, so it is obvious that the coverage radius of the base station with the same configuration is larger

in suburban areas that in urban areas.

(4) Outdoor coverage radius of the 1800 MHz base station in urban areas

The minimum received level of the mobile station (dBm). Because the maximum transmit power of the

1800 MHz TRX is 40W (46dBm), the coverage radius is calculated based on this maximum transit power.

(dBm)

(dB)

For the 1800 MHz base station, the Okumura propagation model is:

In addition, f = 1800 MHz and (dB).

According to the previous known number, the outdoor coverage radius of the 1800 MHz base station in

urban areas can be obtained, that is, d = 1.7km.

(5) Coverage radius of the 1800 MHz base stations in urban buildings


(dB)

If the previous assumptions are present, this indicates that the 1800 MHz base station can cover the

outdoor areas 1.7km away, but for the subscribers on the first floor of the buildings 500m away, the

quality of the received signals is not satisfying.


ventinel

2.6.5 Base Station Address Planning I. Overview

When planning base station addresses, first you must estimate the number of the base stations needed

in various coverage areas according to the coverage distance and the divisions of the coverage areas. For

the convenience of prediction and emulation, you must plan an initial layout the base station addresses

with the help of maps and the estimated results.

II. Planning methods

The base station address can be planned based on standard girds, or it can be planned from a specific

area.

(1) Plan base station address based on standard grids

First you set the base stations in the coverage areas according to the distance of the standard grids, and

then adjust the address layout and project parameters according to the estimated coverage results to

meet the coverage requirement. After that, continue the planning according to the following

instructions:

If a satisfying address layout is obtained, you must analyze the capacity of the base stations to be

planned according to this layout, and determine the reasonable number of base stations. When

designing the capacity, you must calculate the number of TRXs needs to be configured for each base

station, and then analyze and adjust the configuration of the base station according to the number of

the configured TRXs.

The adjustment of the configuration of the base station is determined by subscriber distribution. If the

number of base stations in some areas does not meet capacity requirement, another base stations must

be added.

(2) Plan base station address based on a specific area

According to this method, you are required to start the planning from the areas where the subscribers

are most densely distributed or the planning work is quite hard to be performed. As a result, you must

fully survey the subscriber distribution, landforms, and ground objectives within the coverage area to

position the key coverage area where the center base stations should be planned. And these center

base stations function as ensuring the coverage and capacity in important areas.

After the layout of these center base stations is determined, you can plan other base station addresses

according to coverage and capacity target. And this is how the final layout of the base station addresses

come from. After the overall solution is determined, the subsequent steps are performed according to

the first planning method.

& Note:

The difference of the traffic intensity and the abnormality of the landforms and ground objectives result

in irregularity of the radio coverage. Therefore, the distance between base stations varies. Generally,

this distance is smaller in the areas where traffic intensity is great. In some hot areas, you can ensure the

system capacity by using micro cells and distributed antennas to provide multi-layer coverage.

For restrictions from frequency resources are present, you must consider avoiding interference while


ventinel

ensuring system capacity.

There is no standard available for the layout of the base station addresses. A good planning solution is

selected based on the integrated performance of the network.

2.6.6 Coverage Prediction The coverage prediction is to predict the coverage of the network to be constructed according to the

selected base station addresses, designed base station types, suitable electronic maps, and network

planning tools to judge whether the coverage meet the requirements of the subscribers.

The coverage of a base station is determined by the following factors:

Indexes of QoS

Output power of transmitters

Available sensitivity of receivers

Direction and gain of antennas

Working bands

Propagation environment (such as landforms, city constructions)

Application of diversity reception

If the predicted results of the network coverage fail to meet the requirements, you can take the

following adjusting measures:

When there are subscribers distributing beyond the cell coverage area, but it is not economical for you

to install a base station, you can use a repeater to ensure the requirement of those subscriber.

When the signals are weak or blind zones are present within the coverage area, you can consider

whether to use micro cells according to actual conditions.

If a large blank area is present between neighbor cells, you can increase the antenna height and add

base stations according to the principles of cell splitting.

When the cell coverage area fails to meet the co-channel interference index, you can adjust the

frequency configuration of the cell, adjust base station addresses, or adjust design of the parameters,

such as antenna specification, antenna height, azimuth angle, tilt angle, and transmit power.

& Note:

When taking these adjusting measures, you must consider the mutual effect between base stations.

2.7 Design of Base Station Address

2.7.1 Address design Generally, in GSM radio network planning, the base station address is designed according to the

following requirements:

The address must serve to the reasonable cell structure.

Based on the comprehensive analysis of the electronic maps and paper maps, you can select several

candidate addresses from the perspective of coverage, anti-interference, and traffic balance.

In actual conditions, carriers are required to discuss the selected addresses with owners. Generally, the

addresses must be located within the area 1/4 radius of the cellular base station.


ventinel

During the early construction stage when only a few base stations are installed, the base stations must

be located in the center of the areas where subscribers are densely populated.

For the selection of the base station addresses, the priority must be given to the important areas, such

as government offices, airports, train stations, news center, and great hotels so that good conversation

quality can be assured. Furthermore, overlapped coverage must be avoided in these areas.

For other coverage areas, the base station addresses are designed according to standard cellular

structures. For the suburban areas, highroads, and countryside areas, the design of base station

addresses has little relation with cellular structures.

Without affecting the layout of base stations, you can select the telecommunication buildings and post

offices as the base station addresses so that the facilities, such as the equipment room, power supplier,

and iron tower can be fully utilized.

The direction of antenna major lobe must be in accordance with the area where the traffic intensity is

great. In this case, the signal strength of the area can be enhanced, so does the conversation quality.

Meanwhile, the direction of the antenna major lobe must be deviated from intra-frequency cells so that

the interference can be controlled efficiently.

In urban areas, it is recommended that the overlapped depth of the antennas in adjacent sectors cannot

excel 10%. In suburban areas and small towns, the overlapped depth between coverage areas cannot be

too great, and the included angle between sectors must be equal to or higher than 90°.

In addition, for actual design, you must consider the mapping relationship between carrier number and

cells. Generally, more carriers are configured for the cells with high intensity.

The azimuth angle must be designed according to not only the traffic distribution in the areas around

the base stations, but also the performance of the overall network.

Generally, it is recommended to adopt the same azimuth angle for the 3-sector base stations in urban

areas so that the complicated network planning can be avoided after cell splitting in the future.

Moreover, the antenna major lobe cannot directly point to the straight streets in populated urban areas,

because it can cause cross-coverage.

In the areas connecting urban and suburban areas, and along transport arteries, you must adjust the

azimuth angle according to coverage target.

Generally, the base station address is not considered on the high mountains in urban and suburban

areas. To be more specifically, the high mountains are those over 200 to 300 meters higher than above

the sea-level). Otherwise, not only strong interference and weak signals may be present within the

coverage area, but also the base stations are hard to be installed and maintained on high mountains.

New base stations must be installed at the spots where the traffic is convenient, the power supply is

available, and the environment is secure. In contrast, new base stations must not be installed at the

spots near the radio transmit stations with high power, radar stations, and other equipments which

produces great interference, because the interference-field intensity cannot be greater than that

defined by the base station.

The base station addresses must be far away from forests or woods to keep the receiving signals from

fading.

The transmission between base station controllers must be considered in the design of the base station

address.


ventinel

When selecting a base station address from high buildings in urban areas, you can divide the network

into several layers with the help of the building height. The antenna height of major base stations must

be a little higher than the average height of buildings. Generally, the antenna height of the base stations

in populated urban areas ranges from 25 to 30 meters. In suburban areas (or the antenna points to

suburban areas), the antenna height ranges from 40 to 50 meters.

Along highroads or in mountain areas, the base station address is selected based on full survey of the

landforms. For example, the address can be determined in an open area or at the turns of the highroads.

When selecting a base station address from the cities characterized by mountains and hills and from the

areas where high buildings are constructed with metals, you must consider the effect of time dispersion.

In this case, the base station address must near reflected objectives. When the base station is far away

from reflected objectives, you must adjust the directional antenna to the reverse direction of the

reflected objectives.

Caution:

Time dispersion mainly refers to the intra-frequency interference arising from the time difference

between the master signal and other multipath signal arriving at the receiver in terms of space

transmission. According to the requirements in GSM protocols, the equalizer of the receiver must carry

the time window with 16μs (equivalent to 4.8 km). The multipath signal with time difference greater

than 16 μs is regarded as intra-interference signal. In this case, you must consider whether the level

difference between the master signal and multipath signal meet the carrier-to-interference ratio (C/I),

namely, the master signal is 12 dB greater than the multipath signal at least.

2.7.2 Project Parameter Decision After finishing designing a base station address, you must decide the project parameters needed for the

base station installation. These parameters include:

Latitude and longitude of the location of base station antenna

Antenna height

Directions of the antenna

Antenna gain

Azimuth angle

Tilt angle

Feeder specifications

Transmit power for each cell of the base station

And the previous parameters are decided through field survey.

Before beginning field survey, you must familiarize yourself with the overall project and collect the

materials and tools relative to the project. They are:

All types of project documents

Background information

Information about the existing network

Local map

Configuration lists required in contracts

Relative tools (including digital camera, GPS, compass, ruler, and laptop computer)


ventinel

& Note:

Make sure that all the materials and tools are usable before setting out.

The following items must be emphasized before field survey:

The GPS must be placed in an open land to position the latitude and longitude of a base station

Make a detailed record of the surroundings around the base station, such as the distribution of the

buildings, facilities with strong interference, and the equipments sharing the same base station address.

It is better to record the previous information with a camera.

Prevent the compass from magnetizing, because the magnetization will cause great deviation during the

measurement.

Field survey determines the layout of the base station addresses ultimately. The field survey for the base

station includes optical measurement, spectrum measurement, and base station address survey. They

are specified as follows:

Optical measurement

Measure if a barrier that may reflect electrical waves around the base station, such as high buildings.

Spectrum measurement

Check if the electromagnetic environments around the base stations are normal at present or in recent

days.

Base station address survey

Check the installation conditions of antenna and equipments, power supply, and natural environment.

The following sections introduce the design for antenna installation.

I. Environment for antenna installation

The environment for antenna installation can be divided into the environment near the antenna and the

base station. For the environment near the antenna, you must consider the isolation between antennas

and the effect of iron tower and buildings against the antenna. For the environment near the base

station, you must consider the effect the high buildings within 500 meters against the base station.

However, if the height of the buildings is properly used, you can obtain the intended coverage area.

If a directional antenna is installed on the wall, the radiation direction of the antenna is perfectly

perpendicular to the wall. If its azimuth angle must be adjusted, the included angle between the

radiation direction and the wall is required to be greater than 75°. In this case, if the front-to-back ratio

of the antenna is greater than 20 dB, the effect of the signals reflected by the wall in reverse direction

against the signals in the radiation direction is quite slight.

When installing an antenna, you must consider whether large shadows will be present within the

coverage area of the antenna. The shadows are produced mainly because the base station is surrounded

by some huge barriers, such as high buildings and great mountains. Therefore, the antenna must be

installed in the areas with no such barriers.

When a directional antenna is installed on building roofs, you must prevent the building edges from

barring the radiation of antenna beams. Therefore, to reduce or ease the shadow, you can install the

antenna near building edges.


ventinel

Because the building roofs are diversified and complicated, if an antenna must be installed far away

from building edges, the antenna must be installed higher than the roof. In this case, the wind load of

the antenna must be considered.

II. Antenna isolation in GSM system

To avoid inter-modulation interference, you must leave certain isolation between the receiver and

transmitter of the GSM base station, namely, Tx - Rx: 30 dB and Tx -Tx: 30 dB. They are applicable to the

situation that a GSM 900MHz base station and a GSM 1800MHz base station share the same address.

The antenna isolation depends on the radiation diagram, space distance, and gain of the antenna.

Generally, the attenuation introduced by the voltage standing wave ratio (VSWR) is not considered. The

antenna isolation is calculated as follows:

For vertical arrangement, Lv = 28 + 40lg (k/λ) (dB)

For horizontal arrangement, Lv =22 + 20lg (d/λ) – (G1+G2) – (S1 + S2) (dB)

Here,

Lv indicates the required isolation.

λ indicates the length of carrier waves.

k indicates the vertical isolation distance.

d indicates the horizontal isolation distance.

G1 indicates the gains of the transmitter antenna in the maximum radiation direction, in the unit of dBi.

G2 indicates the gains of the receiver antenna in the maximum radiation direction, in the unit of dBi.

S1 indicates the levels of the side lobes of the transmitter antenna in the 90° direction, in the unit of

dBp, and it is a negative value relative to the main beam.

S2 indicates the levels of the side lobes of the receiver antenna in the 90° direction, in the unit of dBp,

and it is a negative value relative to the main beam.

The followings introduce the requirements on the antenna mount in GSM 900MHz and GSM 1800MHz.

(1) Directional antenna

In one system, the following requirements must be met in terms of isolation:

The horizontal distance between two antennas in the same sector must be equal to or greater than

0.4m.

The horizontal distance between two antennas in different sectors must be equal to or greater than

0.5m.

In different systems, the following requirements must be met when two antennas are in the same sector

and direction:

The horizontal distance between the two antennas must be equal to or greater than 1m.

The vertical distance between the two antennas must be equal to or greater than 0.5m.

The distance between the bottom of the antennas and the enclosing wall of building roof must be equal

to or greater than 0.5m.

The included angle between the line connecting the bottom of the antenna to the antenna-facing roof

and the horizontal direction must be greater than 15°.


ventinel

The bands of the two systems are close to each other, the interference against each other will easily

occur. Mostly, the transmission of CDMA2000 1X base station will interfere with the reception of GSM

900MHz base station.

The disclosure signals of the CDMA band falling into the channels of the GSM base station receivers will

enhance the noise level of the GSM receivers. In this case, the GSM uplinks become weak, which will

reduce the coverage area of the base station and worsen the quality of the network.

If there is not enough isolation between base stations or the transmitting filter interfering base stations

does not provide enough out-of-band attenuation, the signals falling into the band of the interfered

base station receiver may strong, which will increase the noise level of the receiver.

The deterioration of the system performance is closely related to the strength of interference signals,

and the strength of interference signals is determined by the factors, such as the performance of the

transmitting elements of the interfering base stations, the performance of the receiving elements of the

interfered base stations, the distance between bands, and the distance between antennas.

The signal from the amplifier of the interfering base station is first sent to the transmitting filter, and

then it attenuate due to the isolation between the two base stations. Finally, it is received by the

receiver of the interfered base station. The power of the spurious interference arriving at the antenna

end of the interfered base station can be expressed by the following equation:

Here,

Ib indicates the interference level received at the antenna receiving end of the interfered base station,

in the unit of dBm.

PTX-AMP indicates the output power at the amplifier of the interfering base station, in the unit of dBm.

Pattenuation indicates the out-of-band suppression attenuation at the transmitting filer.

Iisolation indicates the isolation between the antennas of the two base stations, in the unit of dB.

WBinterfered indicates the bandwidth of the signals at the interfered base station.

WBinterfering indicates the measurable bandwidth of the interfering signals, or it can be understood as

the bandwidth defined by spurious radiation.

Regulate the previous equation and the following equation can be obtained:

Suppose the transmit channel number of CDMA2000 1X is the last one on its working band, that is,

878.49MHz, the spurious signal level on the band of 890-915MHz must be equal to or lower than -

13dBm/100kHz. If you intend to put this assumption into practice, you can filter and combine each

transmitted channel number by using band-limited filter with a bandwidth of only 1.23MHz. The band-

limited filter of this type has great out-of-band attenuation, which can reach 56 dB at 890 MHz and 80

dB at 909 MHz. Here you must consider the worst situation, that is, the frequencies at the highest end of

the CDMA system interfere with the frequencies at the lowest end of the GSM system.

In this case, Iisolation = (-13dBm/100kHz) - 56 - Ib + 10lg (200kHz/100kHz)

Here Ib indicates the highest interference level (dBm) allowed by the receiving end of the interfered

base station. If the receiving sensitivity of the interfered base station is ensured, the outside

interference level are required to be 10 dB lower than the back noise of the receiver. In this case, the

sensitivity affected only accounts to about 0.5 dB.

The back noise of the GSM receiver is the sum of the noise intensity, bandwidth, and noise coefficient. If

the noise coefficient is 8 dB, the back noise is -174+noise coefficient+10lg (200000) = -174+8+53 = -113


ventinel

(dBm). Therefore, the maximum spurious interference allowed is -113-10 = -123 (dBm/200kHz).

As a result, the spurious interferences from other systems falling at the GSM receivers are required to

be smaller than -123 (dBm/200kHz); otherwise, the spurious interferences will seriously affect the GSM

system.

Therefore, Iisolation = (-13dBm/100kHz) – 56 - Ib + 10lg (200kHz/100kHz) = -13- 56- (-123dBm/200kHz) +

10lg (200kHz/100kHz) = 57 dBm/200kHz.

That is, according to the assumption, the isolation between a CDMA antenna and GSM 900MHz antenna

must be at least 57dB regardless whether they share the address or not.

Many ways can be used to reduce the interference. For example, you can adopt the following ways:

Design enough distance between antennas

Filter the out-of-band interference of the transmitter

Add different equipments to the filter, such as receiver, duplexer, and divider.

According to the requirements in TIA/EIA-97 protocols, the spurious interference from the CDMA

antenna interface falling within the GSM 900MHz receiving bands must be less than -13 dBm/100kHz.

Therefore, the problems, such as mutual interference and co-address construction must be considered

in the initial design.

To be specific, you can filter and combine each transmitted channel number using a limited-band filter

with the bandwidth of only 1.23 MHz. The band-limited filter of this type has great out-of-band

attenuation, thus the space distance between the antennas of the CDMA system and GSM system must

be shortened.

In addition, to minimize the interference, you must keep suitable isolation between the antennas of the

CDMA system and GSM system.

The antenna isolation is calculated according to the following two formulas, which has been introduced

earlier:

For vertical arrangement, Lv = 28 + 40lg (k/λ) (dB)

For horizontal arrangement, Lv =22 + 20lg (d/λ) – (G1+G2) – (S1 + S2) (dB)

According to the two formulas, the requirements on the isolation between the antennas of CDMA

system and GSM 900 MHz system are specified in the following three circumstances.

The antennas of the CDAM system and GSM 900MHz system do not share the same address, with the

antennas horizontally opposite to each other, or the antennas of the two systems share the same

address, with the antenna type of omni antenna.

Suppose the effective gains of the antennas of the two systems in the maximum radiation direction are

10 dBi (with the feeder loss considered), and the interference signals are 890MHz, according to previous

analysis, the isolation between the CDMA system and GSM system is required at least 57dB.

Therefore, the following equation can be obtained according to the previous formula:

57 = 22 + 20lg (Dh/λ) – (10 + 10)

The antennas of the CDMA and GSM 900 MHz system share the same address (the antennas are

installed on the same platform and horizontally separated), with the antenna type of directional

antenna.

Suppose that the two antennas are horizontally placed, and their tilt angle is 65°, and that the effective

gains of the two antennas in the radiation direction are 15dBi.


ventinel

And if the side lobe of the 65°antenna is -18dB in the horizontal plane, the effective gain of the antenna

in this direction is (15 – 18) dBi = -3 dBi.

Therefore, 57=222+0lg (Dh/λ) - {(15+15) + [(-18) + (-18)]}.

According to the previous equation, the horizontal distance between the two antennas are d = 9.5m.

The antennas of the CDMA and GSM 900 MHz antennas share the same address (the antennas are not

installed on the same platforms of the iron tower and vertically separated), with the antenna types of

directional antenna and omni antenna.

In this case, the equation 57=28 + 40 lg (k/λ) is present.

According to this equation, the vertical distance between the two antennas is d = 1.8m.

& Note:

The previous descriptions are just theoretical detections. In actual networking, other types of antennas

may be installed at the same address. In this case, some equipment indexes must be considered, among

which the important ones are spurious radiation, the interference power of the interfering signals to

interfered signals, and the antenna isolation.

IV. Installation distance between antennas

Diversity technology is the most anti-fading effective. When two signals are irrelevant to each other, the

horizontal distance between the diversity antennas must be 0.11 times that of the valid antenna height.

The higher place the antenna is installed, the larger the horizontal distance between diversity antennas

is. When the distance between diversity antennas is equal to or greater than 6m, however, the antenna

is hard to be installed on an iron tower.

In addition, the distance required by vertical diversity antennas is 5 to 6 times that of the horizontal

diversity antennas when the same coverage is ensured. Therefore, the vertical diversity antenna is

seldom used in actual projects, but antennas are often vertically installed to meet isolation requirement,

especially omni antennas are vertically installed.

In addition, for highroad coverage, the line connecting two receiving antennas must be perpendicular to

the highroad. If space diversity is used, the diversity distance is the perpendicular. Isolation

requirement: Tx-Tx, Tx - Rx: 30 dB

The installation for GSM 900MHz and GSM 1800MHz antennas is flexible, but no matter what

specifications are used, they must meet the requirements on isolation and distance. In addition, in

actual projects, barriers are present between antennas. For example, a tower is always present between

two omni antennas, so you must shorten the horizontal distance between them.

V. Design of base station parameters in residential areas

A large number of residential areas are distributed in urban areas, so this section introduces the design

of base station parameters in these areas.

(1) Features of residential areas

Building intensity


ventinel

Great-intensity residential areas: the distance between buildings is within 10 meters.

Middle-intensity residential areas: the distance between buildings ranges from 10 to 20 meters.

Low-intensity residential areas: the distance between buildings is larger than 20 meters.

Construction material

The walls of the residential areas are constructed with concretes.

The walls of the residential areas are constructed with bricks and concretes.

The walls of the residential areas are constructed with hollow blocks.

Notes:

The thickness of the buildings varies with the regions and climates. Three specifications are available,

namely, 24m, 47m, and 49m. Generally, the walls are thicker in southern parts and thinner in northern

parts.

(2) Antenna installation in residential areas

The address where the antenna should be installed in residential areas is hard to be determined.

Generally, when adopting micro cells, you can install the antenna within a residential area near to the

target coverage area.

In this case, the antenna can be installed in the following spots:

On outer walls (not roofs) of a building

On pillars

Install a micro cell in underground garages

If the antenna is installed at a wall corner, the major lobe of the antenna can radiate the space between

buildings. Generally, the major lobe of the antenna cannot face the walls of the buildings nearby

directly.

If frequencies are reusable among these micro cells, the directions of antennas must be consistent with

each other. In addition, you can also use the cell splitter to enable a cell to coverage the areas in two

directions. In this case, however, the frequency utilization ratio may decrease and extra power splitter

will introduce loss of 3 dB.

For the residential areas with regular arrangement, the directional antennas whose horizontal beam

width is 90° to 120° and vertical beam width is greater than 30° are recommended.

Under certain conditions, the micro cell antenna can be installed on the pillars within a residential area.

For the residential areas with irregular arrangement, the antenna can be installed on the walls of a

building, so the reflected waves can coverage the walls of opposite buildings. In this case, the antennas

whose horizontal beam width is greater than 120°and vertical beam width is greater than 30°are

recommended.

(3) Antenna selection

When the walls of a building is selected as an installed position, you can use the build-in antenna of the

micro cell directly, or other antennas with small size. According to coverage features of residential areas,

when selecting the specifications for the micro cell antennas to be used, you must consider the

following factors:

Antenna gain

Horizontal beam width


ventinel

Vertical beam width

Polarization mode

Visual effect (antenna size, shape, and weight)

The antenna gain is recommended less than 9 dBi for micro cell antennas. Because the coverage area of

a micro cell antenna is small and the installed position is near to the coverage area, the antenna gain can

be adjusted to a smaller value, especially if the gain of an antenna is greater than 10dBi, its size is large,

which may cause opposition from residents.

The selection of the horizontal and vertical beam width for an antenna is related to radio environment.

If a micro cell antenna is installed on a wall, the antenna height is lower than the average height of

surrounded buildings. In this case, if both the indoor coverage of lower floors and higher floors can be

assured, you must select the antennas with greater vertical beam width. According to the height of

buildings, you can select the directional antennas whose vertical beam width ranges from 35°to 80°.

The selection of the horizontal beam width of the micro cell antenna and the installed position of the

antenna are related to coverage target. In this case, you can select the directional antennas whose beam

width ranges from 60° to 150°, or you can choose omni antennas or bi-directional antennas (8-shaped

antennas).

Both vertical polarization antennas and dual polarization antennas can be selected for a micro cell. The

coverage area of a micro cell in urban areas is small, so the diversity reception is unnecessary. In this

case, a vertical polarization antenna can meet the coverage requirements in residential areas. As for the

dual polarization antenna, however, it is expensive and large in size, so it is not recommended.

The visual effect must be emphasized for the micro cell antennas installed in residential areas. They

must be small and moderate. In addition, they must be light for installation convenience. If the contract

between the color of the antenna and that of the surrounded buildings is great, you must color the

antenna with the same color of the buildings.

In some cases, you should consider adopting dual-band antennas. When selecting a small-sized antenna,

you should consider whether its maximum output power can bear the micro cell output power. When

adopting short jumpers instead of 7/8 feeders, you should consider whether the antenna connector (N-

shaped male/female, 7/16 DIN header) matches the jumper connector.

2.8 Location Area Design

2.8.1 Definition of Location Area In GSM protocols, a mobile communication network is divided into multiple service areas according to

the codes of location areas. Thus the network pages a mobile subscriber through paging its location

area.

Location area is the basic unit of paging areas in a GSM system. That is, the paging message of a

subscriber is sent in all cells of a location area. A location area contains one or more BSCs, but it belongs

to one MSC only.

Figure 5-13 shows the division of service areas.


ventinel

Figure 5-1 Division of service areas

2.8.2 Division of location areas The coverage area of each GSM PLMN is divided into multiple location areas, in which an MS is

positioned. The size of a location area, namely, the area covered by a location area code (LAC), plays a

key role in a GSM system. Therefore, this section mainly introduces the principle for planning location

areas.

I. Dividing the location area according to the distribution and behaviour of mobile

subscribers

The distribution of location areas in cities and suburbs is different. Generally, suburban areas or counties

occupy independent location areas. In cities, the distribution of location areas is similar to a concentric

circle. (The areas in the internal circle can be divided into several location areas due to the requirements

on capacity. The concentric circle can be divided into several fragments.)

In addition, if two or more location areas are present simultaneously in a big city of great traffic, the

landforms, such as mountains and rivers within this city can be used as edges of the location areas. In

this case, the overlapped depth between the cells of the two location areas can be reduced. If no such

landforms available within this city, the areas (such as streets and shopping centers) with great traffic

cannot be used as edges of the location areas.

Generally, the edge of a location area is oblique instead of parallel or perpendicular to streets. In the

intersected areas of urban areas and suburban areas, to avoid frequent location update, you must

design the edges of location areas near the outer base stations instead of the base stations just installed

at the intersections.

II. Calculating coverage area and capacity of a location area

If the coverage area of a location area is too small, the mobile station will perform frequent location

update. In this case, the signaling flow in the system will increase. If the coverage of a location area is

too larger, however, the network will send a paging message in multiple cells until the mobile station is

paged. In this case, the PCH will be overloaded and the signaling flow at the Abis interface will increase.

The calculation of location areas varies with the paging strategies designed by different carriers. During

early network construction stage, the traffic is not great, so a location area can accommodate more

TRXs. However, it is still necessary for you to monitor the PCH load and traffic growth. When the traffic

grows great, you can enhance the PCH capacity by adding a BCCH to the system, but the number of

voice channels can be added is reduced by one accordingly.

Generally, the capacity of a location area is calculated as follows:

The number of paging blocks sent in each second × the number of paging messages sent in each paging

block = the maximum paging times in each second. As a result, the number of paging times in each hour,

the traffic allowed in each location area, and the number of carriers supported in each location area can

be deducted.

The followings introduce the items present in the previous paragraph respectively.

(1) The number of paging blocks sent in each second


ventinel

1 frame = 4.61ms, 1 multiframe = 51 frames = 0.2354s; suppose the number of access grant blocks is

AGB, the number of blocks, the number of paging blocks sent in each second is calculated by the

following formulas:

For non-combined BCCH, the number of paging blocks sent in each second = (9 – AGB)/0.2345 (paging

block/second).

For combined BCCH, the number of paging blocks sent in each second = (3 – AGB)/0.2345 (paging

block/second).

For non-combined BCCH, the AGB is 2 according to Huawei BSC. Therefore, the number of paging blocks

sent in each second is 29.7 (paging block/second); when AGB is 0, it is 38.2 (paging block/second).

For combined-BCCH, the AGB is 1, so the number of paging blocks sent in each second is 8.5 (paging

blocks/second); when the AGB is 0, it is 12.7 (paging block/second).

According to the previous analysis, the larger the number of AGB, the smaller the number of the paging

blocks sent in each second and the smaller the paging capacity is. Moreover, the paging capacity of the

combined BCCH is far less than that of the non-combined BCCH.

& Note:

Generally, a combined-BCCH cell and a non-combined-BCCH cell are not configured simultaneously

within a LAC, and the number of AGB must be consistent with a location area; otherwise the paging

capacity of the location area will decrease (now the paging capacity of the cell with the least paging

capacity is the paging capacity of the location area).

However, if the capacity of a location area is small and the LAC resource is scarce, you can configure the

combined-BCCH cell and non-combined-BCCH cell within a LAC to enlarge the number of traffic channels

for O1 and S111 base stations.

(2) The number of paging messages sent in each paging block (X)

According to section 9.1.22 of GSM0408 protocols, each paging block has 23 bytes, and can send 2 IMSI

pages, or 2 TMSI and 1 IMSI pages, or 4 TMSI pages.

According to the paging strategies of Huawei MSC, if the IMSI paging mechanism is adopted, the number

of paging messages sent in each paging blocks is 2 (paging times/paging block); if the TMSI paging

mechanism is adopted, it is 4 (paging times/paging block)

(3) The maximum paging times in each second (P)

The maximum paging times in each second is calculated by the following two formulas:

For non-combined BCCH, P = (9 – AGB)/0.2345 (paging block/second) × (paging times/paging block).

For combined BCCH, P = (3 – AGB)/0.2345 (paging block/second) × (paging times/paging blocks).

If the IMSI paging mechanism is adopted, for non-combined BCCH, when AGB = 2, P = 59.47 (paging

times/second); when AGB = 0, P = 76.47 (paging times/second). For combined-BCCH, when AGB = 1, P =

16.99 (paging times/second); when AGB = 0, P = 25.49 (paging times/second).

If the TMSI paging mechanism is adopted, for combined BCCH, when AGB = 2, P = 118.95 (paging

times/second); when AGB = 0, P = 152.93 (paging times/second). For combined BCCH, when AGB = 1, P =

33.98 (paging times/second); when AGB = 0, P = 50.98 (paging times/second).

According to the previous analysis, the paging capacity under IMSI paging mechanism is half of that

under TMSI paging mechanism.


ventinel

(4) The traffic allowed in each location area (T)

When designing the capacity for a location area, you must be attention that the paging capacity of a

location area cannot break its limit. For network expansion, you can collect the times of the busy-hour

paging orders delivered by BSC from OMC, and then convert the times into the number of paging orders

sent in each second.

If no traffic measurement data is available, such as in the case of new network construction, you can

calculate the traffic allowed in each location area by assuming a traffic model.

For example, if the average conversation duration is 60s and the ratio of the times for the mobile station

to be successfully paged to the times of total pages is 30%, the 60s of conversation duration matches

1/60 calls (in the unit of second. Erl), and 30% of calls is generated by the called parties. Therefore, the

successful calls of the 30% mobile stations are 0.05 times (that is, 1/60*30% = 0.005), in the unit of

second. Erl.

If the 75% of the mobile stations respond to the first page and 25% respond to the second page, the

mobile stations responding to the third page can be neglected. (It is just an assumption, which may be

different from actual conditions.). Therefore, 1.25 pages are needed if a mobile station is successfully

called each time (25% of the pages must be resent). In this case, the following equation is present:

Y = 0.005*(1+25%) = 0.00625 paging times/(second. Erl)

Suppose the congestion on paging channels will occur when the paging capacity is 50% greater than

maximum theoretical paging capacity, the original paging messages are still present even the paging

queue is full in the BTS. In this case, the paging capacity in one second is P*50%.

Therefore, the traffic allowed in each location area can be calculated according to the formula T =

P*50%/Y.

(5) The number of carriers supported by each location area (NTRX)

Each TRX had 7.2 TCHs in average, so the maximum traffic of each TRX in each hour is 7.2.

Therefore, the number of carriers supported in each location area can be calculated according to NTRX =

T/7.2 and the specific values are listed in

All the previous assumptions do not include the effect of the point-to-point short messages against on

paging capacity. If the conversation times of a subscriber are equal to the number of the short messages

to be sent, and if the sent ratio and received ratio are consistent with each other, the paging

times/second. Erl will double in busy hour and the capacity of the location area will reduce by half.

Therefore, some common short messages must be sent on CBCH.

2.8.3 Others This section introduces some other information about location area design.

The capacity of a location area is closely related to paging mechanism, and is directly related to the

combinations of AGB and BCCH. When the combinations of AGB and BCCH are inconsistent with each

other in a location area, the capacity of the location area is determined by the cell with the smallest

capacity. Therefore, the combinations of AGB and BCCH must be designed to be consistent in location

area planning.

If the number of point-to-point messages grows large immediately, the number of paging messages will


ventinel

increase, but the number of supported subscribers will decrease. In this case, you must control and

protect the flows in the system.

Because the traffic density varies with location areas, it is recommended that the combined-BCCH cells,

non-combined-BCCH cells, and multi-BCCH cells form a location area respectively. When a cell with

BCCH/SDCCH combination, the location area can be as large as possible when the paging capacity of the

BTS does not reach the limit. However, because all paging messages will be broadcasted in all cells

within a location area, the cell with BCCH/SDCCH combination is the bottleneck of the location area.

The LAC is a kind of number resource. Therefore, you must cooperate with carries to plan location areas.

2.9 Dual-Band Network Design

2.9.1 Necessity for Constructing Dual-Band Network The earlier GSM mobile communication network is constructed on the 900 MHz band. With rapid

growth of subscribers, the network capacity also grows rapidly. Therefore, the lack of frequency

resources and radio channels is a major concern for mobile telecommunications.

Many methods can be used to expand the capacity of a GSM system, including:

Adding macro cell base stations to the system

Reducing distance between base stations

Adopting aggressive frequency reuse technologies (such as MRP and 1×3)

Adding micro cells to the system

Applying half rate to the system

However, all these methods cannot thoroughly solve the problems concerning network capacity. As a

result, the GSM 1800MHz network is introduced (uplink: 1805–1880 MHz; downlink: 1710–1785 MHz).

And the network integrating GSM 900MHz and GSM 1800MHz can meet the growth of network

capacity.

The application of GSM 1800MHz can bring the following advantages:

It does not occupy the bands of GSM 900MHz and has a communication bandwidth of 75M. Therefore,

it breaks the bottleneck of GSM 900MHz in terms of frequency resources.

The system networking, project implementation, network planning, and network maintenance of a GSM

1800MHz network are almost the same with that of a GSM 900MHz network.

The GSM 1800MHz and GSM 900 MHz can share a base station, so a GSM 1800MHz network can be

finished in a short time, which is quite helpful for network expansion.

Dual-band mobile phones now accounts for a major part of the total, so a GSM 1800MHz network can

provide services to the dual-band subscribers. In this case, the capacity pressure on GSM 900MHz can be

greatly eased.

2.9.2 GSM 1800MHz Coverage Solutions I. Propagaiton features of GSM 1800MHz

The propagation features of the electromagnetic waves of 900 MHz and 1800 MHz are different in the


ventinel

following aspects:

The propagation loss in free space

The propagation loss of the 1800 MHz signals is 6 dB greater than that of the 900 MHz signals in free

space.

Penetration loss

The penetration loss of the 900 MHz signals is greater than that of the 1800 MHz signals, but their

difference is slight.

Diffraction loss

The longer the waves, the smaller the diffraction loss is. The diffraction ability of the 1800 MHz signals is

poorer than that of the 900 MHz signals.

II. Dual-Band Networking Mode

There are three dual-band networking modes, namely, independent MSC networking, co-

MSC/independent BSC networking, and co-BSC networking, among which the former two are called

independent networking, and the later is called hybrid networking.

III. Coverage requirements on GSM 1800 MHz

Outdoor coverage

The outdoor coverage can be easily realized when the distance between base stations are not large. In

necessary cases, you can add a GSM 1800MHz base station at the address of the original GSM base

station. And in some places, you should consider add a new base station.

Indoor coverage

To ensure that the indoor coverage of GSM 1800MHz is good, you must control the distance between

the base stations installed in urban areas within 1000 meters. In China, however, the buildings in most

cities are constructed by concretes and metals, so the penetration loss is great. As result, the distance

between base stations in urban areas of China ranges from 500 to 800 meters.

IV. Coverage mode of GSM 1800MHz

(1) Scattered coverage in hotspot areas

At the early network construction stage, the GSM 1800MHz base stations are scattered in hotspot areas.

When the capacity configured for a GSM 1800 MHz base station is small, you must solve the problems,

such as SDCCH congestion, TCH congestion, and frequent update between GSM 1800MHz and GSM

900MHz. The cost in early construction stage is small.

Scattered coverage of GSM 1800MHz in hotspot areas

The coverage of the dual-band network of this mode is based on the original GSM 900MHz network. The

GSM 1800MHz base station is constructed in some hotspot areas, so the seamless coverage of GSM

1800MHz is not available in this case.

If a dual-band mobile phone starts conversation in an area covered by GSM 1800MHz, after leaving this

coverage area, it hands over to the GSM 900MHz cell where it originally was. And the handover of this

type is called the inter-band handover caused by coverage.

If a dual-band mobile phone starts the conversation in an area covered by GSM 900MHz, but because

the traffic in this area is great, the mobile phone will hand over to an area covered by GSM 1800MHz.

And the handover of this type is called the inter-band handover caused by capacity.

The scattered coverage in hotspot areas only relieves capacity problems in a short term. Moreover,


ventinel

frequent inter-band frequency handover increase the signaling load, which results in the loss of system

capacity.

(2) Seamless coverage in hotspot areas

If the coverage of this mode is available; the GSM 1800 MHz network can share greater traffic for GSM

900MHz network and expand the system capacity. In addition, it is cost-effective.

(3) Perfect seamless coverage

If a GSM 1800MHz network adopts the coverage of this type, the advantages are as follows:

The seamless coverage area within a city can be realized.

The GSM 1800MHz network can share the traffic load for GSM 900MHz network as much as possible.

The system capacity can be greatly expanded.

The ratio of the handover between layers is small.

The quality of the network is quite satisfying.

The frequencies can be planned by patch.

The carriers can be expanded step by step.

However, there are still disadvantages. They are as follows:

The number of base stations is large.

The work load of network planning and optimization is huge.

The investment is large.

The base station addresses cannot be decided once.

(4) Perfect coverage of GSM 1800MHz in hotspot areas

If a GSM 1800MHz network adopts this coverage mode, it can be easily expanded to meet future

coverage.

Compared with the scattered coverage in hotspot areas, the perfect seamless coverage is characterized

by great intensity and large area. Therefore, the ratio of inter-band handover under this coverage mode

is far smaller than that under scattered coverage mode. As a result, the signaling load is reduced greatly.

Therefore, this coverage mode is an ideal coverage solution. If a GSM 1800MHz network adopts this

coverage mode, it does not necessarily attach to the GSM 900MHz network, instead, it can form an

independent network.

2.9.3 Location Area Division for Dual-Band Network The location area division for dual-band network is suggested as follows:

If 1800 MHz cells and 900 MHz cells are under the control of two MSCs respectively, their location areas

are different. Therefore, you must set related parameters to maintain the mobile stations stay in the

1800 MHz cells where the traffic is absorbed. In this case, the times for the mobile station to handover

between the two bands and reselect cells will decrease. Meanwhile, when designing signaling channels,

you must fully consider the load resulted from location update.

If 1800 MHz cells and 900 MHz cells share a MSC, at the early network construction stage, they are

suggested to use the same location area without affecting the network capacity. If the restriction on

paging capacity is present, two location areas must be divided for them either in terms of band or

geographic location, as shown in Figure 5-17 and Figure 5-18.


ventinel

Location area division based on geographic location

If the location area is divided in terms of band, because frequent location updates are resulted from

inter-band handover and cell reselection, you must set related parameters to maintain the mobile

stations stay in the 1800 MHz cells where the traffic is absorbed. In this case, the times for the mobile

station to handover between the two bands and reselect cells will decrease. Meanwhile, when designing

signaling channels, you must fully consider the load resulted from location update.

If the location is divided in terms of geographic location, the frequent location updates resulted from

inter-band handover and cell reselection can be avoided. However, you need to modify the related data

of the original 900 MHz network. In addition, at the edges of the location areas, because the location

updates caused by intra-band and inter-band handover and cell reselection is present simultaneously,

the signaling flow is huge at these edges. As a result, you must carefully design the edges of the location

areas.

2.9.4 Traffic Guidance and Control Strategies of Dual-Band Network I. Traffic guide of Dual-Band Network

At early construction stage of a dual-band network, traffic control concerns how to use the new GSM

1800MHz network to share the traffic flow for the GSM 900MHz network. According to the original

intension of the GSM 1800MHz network, the traffic can be guided according to the following principles:

1) At the early construction stage of a dual-band network, the GSM 1800MHz network is mainly applied

to absorb the traffic of the dual-band subscribers so that the load of the GSM 900MHz network can be

eased.

2) When the number of dual-band subscriber grows large, each band must share the traffic so that the

inter-band handover times can be reduced.

(1) Process of traffic guide and control strategies.

The various traffic control strategies can be realized through adjusting parameter settings as follows:

1) In idle mode, when the mobile station is selecting cells after it is switched on and reselecting cells

when it is in standby state, you can set higher priorities for the 1800 MHz cells by designing the system

parameters, including CBQ, CBA, CRO, TO, and PT. In this case, subscribers are more likely to stay in the

1800 MHz cells. As a result, their calls are established on the 1800 MHz cells.

2) If traffic congestion is present in the service cell when a mobile station is setting up a call, the system

applies directed retry function to assign the mobile station to a TCH in the neighbor cells of the service

cell and adjust the traffic allocation.

3) In conversation state, the traffic must be guided to the 1800 MHz cells in lower layers and levels

according to the hierarchy cell structure. In addition, you can use Huawei dual-band handover

algorithms so that the traffic load can be allocated more properly.

II. Hierarchical Cell Structure

According to the hierarchy cell structure of the dual-band network, a GSM system covering an area can

be divided into four layers, as listed in Table 5-25.

To enable the network to develop smoothly and flexibly, you can divide each of the four layers into

multiple levels, and then you can set multiple priority classes (for example, 16 classes) for the levels in

each layer. This method is not only helpful for adjusting the traffic load in part of the areas. Therefore,


ventinel

the hierarchical cell structure enhances the cooperation of the current network equipments and meets

the devolvement of the future network.

In terms of traffic priority, the cells in lower layers and levels has higher priorities, namely, the cells in

lower layers has the priority to absorb the traffic.

2.9.5 Dual-Band Networking Engineering Implementation During network construction and optimization, a dual-band network is debugged and commissioned

step by step, which facilitates debugging the new GSM 1800 MHz networks and the original GSM

900MHz networks that has been expanded respectively. After each signal network is perfectly adjusted,

you must debug each base station in the dual-band network. And you cannot stop the debugging until

the whole dual-band network is finished.

The construction of a whole dual-band network can be divided into three stages, namely, deployment

preparation, signal 1800 MHz network debugging, and 900/1800 MHz dual-band network debugging.

I. Deployment preparation

The coordination of dual-band technologies and network planning must be finished in this stage. The

coordination of dual-band network technologies is a prerequisite for the cooperation of different

carriers’ networks. Network planning is the first step in network construction and involves many tasks,

including base station address survey, channel number planning, electromagnetic background test,

coverage test, and so on.

The followings must be emphasized in dual-band cooperation:

The customers, the third party (the designing institute or the original equipment supplier), and the new

equipment supplier must be cooperate with each other well.

If one party meets a tough problem during the debugging of the dual-band network, the engineers from

a third party must be present in site and help position the problem.

The 900 MHz BSC and 1800 MHz BSC must synchronize their clocks with the same source clock.

Meanwhile, the clock of each base station in the existing GSM 900 MHz network can lock the clock of

the BSC, and the clock of the BSC can lock the clock of the MSC.

When modifying the parameters related to dual-band handover (such as modifying the parameters at

the BSC side or MSC side), you must notify that to other two parties.

If the some problems concerning the cooperation of dual-band network arise, a meeting must be

organized, in which each party discuss with each other on how to solve the problems.

Both the designing institute or the original equipment supplier and the new equipment supplier must

provide the project implementation plan, cutover plan, and precise cell information.

II. Signal 1800 MHz network debugging

At this stage, you need not modify any data of the original GSM 900 MHz network, but it is still the GSM

900MHz network provides services to subscribers. The GSM 1800MHz network does not absorb traffic.

When debugging the GSM 1800MHz network, you must adjust the following parameter so that the

existing subscribers can be least affected.

In the system message data list, set the parameter “CBA” to “NO” to prevent general subscribers from

selecting and reselecting the 1800 MHz network. Theoretically, general subscribers can hand over to the

1800 MHz network, but in fact, the handover relationship is not configured with the dual-band network,


ventinel

so the general subscribers cannot enter the 1800 MHz network.

After that, you use the testing mobile phone which can access the network by force to perform dialing

test in each cell. If all goes normal, you can test coverage, handover, power control, interference,

downlink and uplink balance, power adjustment, the coverage of the GSM 900MHz network, and the

coverage of the GSM 1800MHz network.

Through these tests, you can not only discover the problems present in the networks, but also adjust the

channel number, power, tilt angle, and parameter setting and optimize the parameter configuration for

the GSM 1800MHz cell. In this case, the coverage and operation of the single GSM 1800MHz network

can be ensured.

III. 900/1800 MHz dual-band network debugging

After finishing the single GSM 1800MHz network debugging, you must change back the parameter

“CBA” to “YES” and configure the data for dual-band handover. The tests involved into the dual-band

network debugging include:

Cell reselection and location update

Traffic load control

Continuous conversation mode

Automatic dialing and scan

Dual-band network handover

Calls and handovers initiated on major streets

Calls and handovers initiated on edge areas

Dialing tests in poor coverage areas and indoor environment

Dialing tests in outdoor and indoor environments in key areas

The data includes neighbor cell relationship, layer and level setting, handover type, and handover

threshold. In this case, when a mobile phone is in idle mode, it can reselect an 1800MHz cell, the GSM

1800MHz network can absorb the traffic of dual-band subscribers, and the subscribers can perform

handover between 1800MHz cells and 900MHz cells.

At the beginning, you can control the GSM 1800MHz network to absorb only a small part of the traffic of

subscribers through adjusting the setting of CRO and handover threshold. When good cell reselection

and dual-band handover are ensured, you can take measures to enable the GSM 1800MHz network to

absorb more traffic, with the prerequisites that no congestion is present among cells and the network

quality is ensured.

At this stage, the following parameters must be configured:

The parameters related to cell selection and reselection, including CBA, CBQ, ACCMIN, CRH, and CRO.

The parameters related to neighbor cell relationship, layer and level setting, and handover.

The configuration of the previous parameters must be based on the prerequisite that the cooperation of

the GSM 1800MHz cells and GSM 900MHz cells is normal.

After the GSM 900MHz and 1800MHz dual-band network is enabled, you must do the followings:

1) Find out the problems present in the network through multiple means, such as drive test.

2) Adjust and optimize the network according to the problems so that the dual-band network can run

stably.

3) Check if the dual-band network runs stably, analyze all the traffic statistic data, and check the


ventinel

network operation indexes.

4) Make sure the problems and take effective measures according to the analysis of the drive test and

traffic statistics.

5) Adjust the related parameters and retest the network till the network indexes meet the design

requirements.

Thus, a dual-band network is constructed and optimized according to the three stages as introduced in

this section.

2.10 Design of Indoor Coverage System

2.10.1 Characteristics of Indoor coverage With the rapid development of economy, hotels, commercial centers, large-scale flats, underground

railways, and underground parking areas are arising by batch. As a result, mobile stations are more

frequently used in indoor environment. Thus, they require better indoor mobile communication

services.

Generally, the following problems are present in indoor mobile communication systems:

From the perspective of coverage, the complex indoor structure and the shielding and absorbing effect

of the buildings cause great radio wave transmission loss. As a result, the signals in some areas may be

weak, especially the signals in the first and second floors in the underground are quite weak, or even

there are dead zones. In this case, mobile stations cannot necessarily access the network, there is no

paging response, or subscribers are not in service areas.

From the perspective of network quality, the factors interfering radio frequencies are probably present

in upper floors of high buildings. In this case, the signals in service areas are not stable, so “ping pong

effect” may occur and conversation quality cannot be ensured.

From the perspective of network capacity, if mobile stations are frequently used in buildings, such as

large-scale shopping centers, conference halls, some areas in the network cannot meet the

requirements of subscribers. In this case, congestion may occur on radio channels.

If the indoor coverage is realized by a repeater, an outdoor high-power base station, or a great-height

outdoor antenna, the following problems may arise:

The penetration loss is great, so the indoor coverage is not satisfying. In this case, a large number of

dead zones are present, so subscribers cannot keep conversation.

If a repeater is adopted, the level of original signals must be high. In addition, the cross-modulation and

intra-frequency interference is great, so the conversation quality is weak and call drop ratio is high.

The network capacity is limited and the call connected ratio is low.

The frequency planning is hard to be performed for the network and the network capacity is hard to be

expanded.

The “detached island effect” is great.

The value-added services are restricted for group subscribers due to network quality and capacity.

To enhance the grade of service, we must improve indoor coverage immediately. When designing an

indoor coverage system, we must make the following considerations:

A new indoor coverage system cannot affect the existing network.


ventinel

Enough capacity of an indoor system must be ensured.

An indoor system must support new services and functions.

The chapter analyzes the design of indoor coverage system from the following aspects:

Indoor Antenna System Design

Capacity Analysis and Design

Frequency Planning

Traffic Control

2.10.2 Indoor Antenna System Design I. RF design

(1) Link budget

In an indoor coverage system, the link budget formula is as follows:

Here,

Pant = antenna input interface power

RFmarg = Raleigh fading margin

IFmarg = access margin (depends on environment)

LNFmarg = design margin (generally, it is 5 dB)

BL = body loss (900MHz: 5 dB; 1800/1900MHz: 3 dB)

MSsens = mobile station sensitivity

Lpath = path loss

Here, Lpath = 20logd (m) + 30logf (MHz) - 28 dB + α. When there no barrier loss, Lp = 20logd (m) + 30logf

(MHz) - 28 dB. The “α” indicates the loss caused by other bariers.

Because the penetration in cylindrical tunnels is great, leaky cables are applied in cylindrical tunnels.

When performing link budget, you must consider the followings:

In an indoor multi-antenna system, the link budget for test points must be in accordance with the link

with the minimum loss.

Under the same converge area, the EIRP at each antenna interface must be consistent, and the error

must be controlled within 10 dB.

The uplink signal must be designed to a high value, so antenna diversity is unnecessary.

To reduce uplink interference, you must properly set the maximum transit power of the mobile station

and enable the power control function of the mobile station.

A certain margin must be leaved for error correction and future system expansion.

The estimation and design for interference margin vary with the distance from the outer wall. The

smaller the distance, the larger the interference margin is designed.

(2) Service quality design (interference degree)

The actual interference level changes with network layout and frequency re-planning, and it can be

tested according to actual situations.

(3) Service quality design (interference margin design)

The greater the interference in an area, the greater the interference margin (IFmarg) is designed, and

the higher the level the mobile station needs to receive.


ventinel

When a dual-band system is adopted in the indoor environment, the indexes of mobile station receiving

level are designed according to the 1800 MHz system standard.

II. Antenna system design

When designing an indoor distribution system, you must first survey the building type, structure,

interference environment, customers, and then analyze the path loss. Finally, decide the antenna type,

number, and installation location according to the requirements of an area.

This section introduces the antenna design guidelines in some typical cases.

(1) Single cell

If the indoor coverage is realized by a signal cell, each antenna must be designed to ensure that signals

are evenly distributed in the coverage area. Generally, it is recommended to install the antenna in a

zigzag way.

(2) Multi-cells

If the indoor coverage is realized by multiple cells, a certain distance must be leaved between intra-

frequency reuse cells. Each antenna must also be designed to ensure that signals are evenly distributed

in the coverage area of each cell. If the frequencies are reused frequently, it is recommended to install

the antennas on different layers at the same position of the layer.

(3) Closed building

A closed building has the characteristics, such as thick outer wall, great signal attenuation, and little

leakage. In addition, it is little affected by outdoor intra-frequency cells. Therefore, the frequency

between floors is easily to be planned. For the antenna design guideline in a closed environment.

(4) Half-open environment

For a half-open building, the outer wall is made of glasses, so the signal attenuation is small. Within the

building are the open conference halls, which are greatly affected by outdoor intra-frequency cells, so

you must plan dedicated frequencies or adopt the multi-antenna system with low output power to limit

the edges of the indoor cells within the building.

(5) Frame-structure building

For a frame-structure building, the number of internal walls is large and they are thick. Therefore, if the

antenna is installed at the corridors, the antenna output power must be high so that good coverage can

be ensured. In this case, signals will leak at the windows near the corridor, so you must plan dedicated

frequencies for the building. The distance of the intra-frequency cells between floors is larger than that

in other environments. For the antenna design guideline in frame-structure building.

(6) Office building

The indoor environment of office buildings requires high grade of services, so its coverage is realized by

several directional and omni antennas. You can control the coverage area easily through properly

designing the effective radiation power in the cell. For design guideline, see (7) Parking area

Parking area has no special requirement on capacity and mobile station receiving level (-90 dBm). For a

parking area, the elevator, escalator, entrance and exit are key coverage areas.

(8) Supermarket

Supermarkets have certain requirements on coverage and capacity. The antennas can be designed

according to actual structure of the buildings.


ventinel

III. Survey

The antenna design and installation is finally decided according to the survey, which includes the

following aspects:

Detailed coverage area and signal quality and converge requirements

Distribution of the signals in coverage areas

Composition of buildings in coverage areas

Signal access location and mode

Installation position

According to the survey, you must output the final topological structure diagram, antenna cabling

scheme, and list of materials. Generally, the omni antenna is installed at the ceiling center. The small

directional antenna is hung on the inner side of the outer wall, with the radiation directed to indoor

part. In this case, the effect of the antenna against the outdoor system can be reduced to the minimum,

so the C/I requirement of the outdoor system can be met.

If possible, you can test the coverage and adjust the antenna design according to the test result, or re-

plan the frequency to ensure the voice quality. Generally, if the radiation power at the antenna interface

is 10 dBm, the 2 dBi small indoor omni antenna is used. In this case, if the walls are densely distributed

in the areas within 30 meters from the antenna, the coverage level can reach -70 dBm.

2.10.3 Capacity Analysis and Design Before analyzing the capacity, you must define the type of the indoor service area.

Definition of indoor service area type

Indoor service area type

Characteristic

Example

Public service area

The traffic is hard to be predicted.

The population number varies with day and night.

The capacity characteristics, such as uneven distribution and bursting must be considered.

The grade of service and the traffic of each subscriber are similar to that for outdoor cells.

Airport, shopping center, and play ground.

Commercial service area

The existed fixed networks are frequently used.

The traffic is relatively fixed and easy to be calculated.

High service quality is required.

Generally, the grade of service (GoS) is 1%, the traffic of each subscriber can reach 0.1 Erl.

Office building and commercial hotels of high ranks.

There are two cell organization modes of distributed antenna system, namely, single cell and multiple

vertical split cells. The single cell is applied to the indoor environment which requires smell coverage

area. The multiple vertical split cells are applied to the indoor environment with dense traffic.

Likewise, a single cell will split when the capacity does not meet the requirement, with vertical splitting


ventinel

the splitting mode. Generally, a cell will vertically split into at least three cells so that frequency reuse

can be ensured. Four layers must be present between two intra-frequency cells . To avoid interference

between frequencies, you must take measures to prevent a cell from horizontally splitting.

2.10.4 Frequency Planning If the dedicated frequency is adopted in indoors, the frequency planning is relatively simple. Generally,

the frequency reuse mode in business service areas is almost the same as that in pubic service areas. If

the frequency resource is adequate, you must try best to use dedicated band for indoor coverage. If not,

you can search the available channel numbers with relatively small interference through scanning the

channel numbers. If the frequency resources of the 900 MHz cannot meet requirements, you can

introduce the 1800 MHz frequency; namely, use a dual-band system.

If you steal frequency resource for indoor system due to no available dedicated frequency, you must pay

attention to the followings:

Do not select the frequencies of the neighbor cells.

Ensure that the BCCH frequencies are not interfered.

The interference on the TCH frequencies can be reduced with the help of radio frequency hopping.

Search the available uplink frequencies through using BTS equipments to scanning the uplink channel

numbers.

Search the available downlink frequencies through using drive test equipment to scanning the downlink

channel numbers.

If the hierarchical cell structure is not used, the cell with the strongest signal level is the service cell, and

the interference from neighbor frequencies can be neglected.

If the hierarchical cell structure is used, the cell with the strongest signal level cannot necessarily be the

service cell, so you must take measures to reduce the interference from neighbor frequencies.

Because the environment is urban areas is quite complicated, especially the effect of the antenna back

lobe is present, the service areas for high buildings are greatly interfered, so you must carefully plan the

frequencies for the indoor coverage of high buildings. Generally, for the lower floors, you can plan the

frequencies according to general method. For the higher floors where the interference is strong, you can

use dedicated channel numbers. However, the final frequency planning must be based on practical

tests.

2.10.5 Traffic Control The indoor coverage system for high buildings can be taken as a system independent of outdoor systems

if the coverage of the indoor system is good. Theoretically, you can only consider the cell selection and

reselection, handover relationship, and the compact on outdoor networks at the entrances and exits of

the building.

However, the actual conditions are quite complicated. For example, the signals outside of the building

may be strong. In this case, if a mobile station is powered off, it may camp on an outside cell. Therefore,

when optimizing the network, you must set the one-way adjacent cell and two-way adjacent cell


ventinel

according to actual conditions and set the parameters, such as CRO and TO to a proper value according

to the regularity of cell selection and reselection. In addition, you can set the indoor cells to a high

priority so as to reserve more traffic. And the inter-layer handover threshold and hysteresis are defined

and adjusted according to actual conditions.

2.11 Tunnel Coverage

2.11.1 Characteristic of Tunnel Coverage At present, most of the tunnels are dead zones, so you must make out special solutions for tunnel

coverage. The tunnel types include railway tunnel, highroad tunnel, and underground railway tunnel.

Each tunnel has its characteristics, and they are specified as follows.

For the highroad tunnel, it is wide. The coverage in the highroad tunnels is relatively stable. When there

are vehicles passing by, you can select the antennas with a larger size to obtain a higher gain, so the

coverage distance is larger.

For the railway tunnel, it is narrow, especially when there is a train passing by; only a little room is left in

the tunnel, so the radio propagation is greatly affected. Moreover, the train has great effect on radio

signals. Since the antenna installation room is quite limited, the antenna size and gain are greatly

restricted. In addition, because general cars cannot be driven to such tunnels, the tunnel coverage is

hard to be tested. Therefore, the planning for highroad coverage is different from that of the railway

coverage.

The length of tunnels ranges from several hundred meters to several kilometers. For short tunnels, you

can adopt flexible and economical means to realize the coverage. For example, you can install a general

antenna near one end of the tunnel, with the radiation directed to the inside. For long tunnels, however,

you must adopt other means. Actually, the coverage solution varies with tunnels, so it is designed

according to actual conditions.

Cross section of the single-track railway tunnel and multi-track railway tunnel: The smaller the area of

the cross section, the greater the loss when a train passes through the tunnel. The related calculation

and analysis are based on the multi-track railway tunnels and highroad tunnels. For the calculation and

analysis for single-track tunnels, the protection margin can be 5 dB greater than that of multi-track

railway tunnels.

Before planning tunnel coverage, you must prepare for the following data:

Length of the tunnel

Width of the tunnel

Number of tunnel holes (1 or 2)

Needed coverage probability (50%, 90%, 98% or 99%)

Structure of the tunnel (it is constructed with metals or concretes)

Number of needed carriers (1–30)

Minimum receiving level in the tunnel (generally, it ranges from -85 dBm to -102 dBm)

Distance between tunnel holes

Whether AC/DC is available


ventinel

Whether the hole can be punched in the tunnel wall

Signal level at the tunnel entrance

Existed signal level in the tunnel

2.11.2 Tunnel Coverage Solution I. Link budget

Indoor radio link loss is mainly decided by path loss medium value and shadow fading. A tunnel can be

taken as a tube. The signals are transmitted through the reflection of walls and straight transmission,

with straight transmission the major form. ITU-R suggests an indoor propagation model on page 1238,

which is also effective for tunnel coverage. The formula is as follows:

Lpath = 20 lg f + 30 lg d + Lf (n) - 28 dB

Here,

“f” indicates frequency (MHz)

“d” indicates distance (m)

“Lf” indicates penetration loss factors between floors (dB)

“n” indicates the number of floors lying between the mobile station and antenna.

The Lf (n) can be neglected in tunnel coverage, so the following equation can be applied in the

calculation of the radio propagation in tunnels. That is:

Lpath = 20 lgf + 30 lg d - 28 dB

II. GSM signal source selection

A GSM signal source and a set of distributed antenna system are a must for tunnel coverage. For tunnel

coverage, the GSM signal source is selected according to the radio coverage, transmission, traffic, and

the existing network equipments near the tunnel. A macro cell base station, a micro cell base station, or

a repeater can work as a GSM signal source for the tunnel coverage.

For the coverage of railway tunnels and highroad tunnels, the indoor macro cell base station is seldom

used as signal source, but it can be used for an underground railway which requires the coverage of

platforms and entrances. In this case, the capacity of the signal source must be great. In most cases,

however, the tunnel coverage is realized by micro cell signals.

For the areas to be covered, if the nearby network capacity is adequate, the capacity expansion is

unnecessary. And if there are good GSM signals available, namely, the donor signal level meets the

requirements of a repeater (for example, -70 dBm); a repeater can work as the signal source for the

tunnel coverage. With the increase of traffic, however, you must use GSM base stations to replace the

repeaters.

Adequate isolation must left between donor antenna and retransmission antenna, though it will cause

difficulty in antenna installation. Generally, the log-periodical antenna with great front-to-back ratio is

used as the retransmission antenna.

The general antenna (wireless repeater), coaxial cable, and optical fiber (optical repeater) can connect a

repeater to a donor cell.

For tunnel coverage, the installation space and auxiliary equipments are quite limited, so micro cell base

stations and repeaters instead of macro cell base stations are often applied in tunnel coverage.


ventinel

In mountain areas, repeaters are more likely used because strong signal level often exists at the

mountain tops near the tunnel. In this case, the antenna isolation requirement can be easily met. If the

signal level of the existed network near the tunnel is not strong enough, you can use a micro cell for the

tunnel coverage.

III. Antenna feeder system selection

After deciding the GSM signal source, you must configure the antenna feeder system for the tunnel

coverage according to actual conditions. Three types of configuration are available, namely, coaxial

feeder passive distributed antenna, optical fiber feeder active distributed antenna, and leaky cable.

Hereunder introduces the tunnel coverage based on coaxial feeder passive distributed antenna and

leaky cable.

2.11.3 Tunnel Coverage Based on Coaxial distributed antenna system In a coaxial distributed antenna system, the following RF components are used:

Feeder (3/8", 1/2", or 7/8") and jumper

Power splitter

Power splitter

Antenna

This section introduces three tunnel coverage solutions based on the coaxial distributed antenna

system.

I. Solution 1

Tunnel coverage solution based on the bi-directional passive distributed antenna system.

Tunnel coverage solution based on bi-directional passive distributed antenna system

According to this solution, if the needed minimum signal level is -85dBm (the location probability is

50%), you must add a margin of 8 dB if the want to enhance the location probability to 90%.

If the gain of the bi-directional antenna is 5 dBi, the loss of the equal probability power splitter and the

jumper is 2 dB, and the feeder with the specification of 7/8" is used, the path loss in 100 meters is 4 dB

and the output power of the equipment is 39 dBm.

Suppose that the level of the signals transmitted by the first bi-directional antenna is -85 dBm at the

tunnel entrance, you can calculate the distance between the antenna and the tunnel entrance using the

following equation:

Pout- Lpath (d) – Lcable (d) – Ljumper + Gant = -85dBm + 8dB90%_loc.Prob

Here,

Pout indicates the output power (39dBm).

Lpath (d) indicates the path loss from the first bi-directional antenna to the tunnel entrance.

Lcable (d) indicates the cable loss.

Ljumper indicates the jumper loss (2 × 2 dB).

Gant indicates the antenna gain (5 dBi).

If introducing the previous data to the equation, you can obtain the sum of the Lpath (d) and Lcable (d),

that is, 117 dB.

For the relationship between distance “d” and Lpath (d) and Lcable (d), see Figure 5-34, in which the

curve indicates Lpath (d) and the slant line indicates Lcable (d).


ventinel

1 You can obtain that d = 301m through estimation.

If a power splitter is adopted for the first antenna, a loss of 3dB must be added. In this case, the sum of

Lpath (d) and Lcable (d) is 114 dB.

2 You can also obtain that d = 261m through estimation.

For railway tunnels, train filling will affect signal propagation, so a protection margin of 5dB must be

considered when the antenna is installed in the tunnel. In this case, d = 240m. That is, if a bi-directional

antenna is installed in the tunnel, it can coverage a distance of 480m.

If a power splitter is adopted for the second antenna, the coverage distance between the first antenna

and the second antenna will be shortened unless an amplifier is used.

The followings analyze the coverage when no amplifier is adopted for the second antenna.

The total power output by the first power splitter (it is installed at the first antenna) Pout1 is expressed

as follows:

Pout1 = Pout – Lcable (d) - Ljumper - Lsplitter = 39dBm –Lcable (261m) - 2dB - 3dB= 23.56 dBm. (The

cable loss in 261m is about 10.44 dB, jumper loss is 2 dB, and the power splitter intersection loss is 3dB).

Suppose the overlapping level between the two antennas is -85 dBm, the distance between the second

antenna and the first antenna is: d2 = d + x. Here, “d” indicates the coverage distance of the first

antenna (261m), and “x” indicates the coverage distance of the second antenna in the single direction.

According to the previous analysis, the following two equations can be obtained:

Pout1 – Lcable (261m) – Lcable (x) – Ljumper + Gant – Lpath (x) = - 85dBm + 8dB90%_loc.Prob

Lpath (x) + Lcable (x) = 108.56dB

Plus the two equations, you can obtain the value of x, that is, 100m. This means that when no amplifier

is adopted, two antennas can coverage a tunnel distance of 722m, namely, 2*(261 + 100) m = 722m.

If you adopt cascaded antennas, the transmit power is relative low due to the coaxial cable loss. In this

case, you can use the amplifier to amplify the power.

II. Solution 2

If a tunnel is not long, you can adopt a simpler coverage mode.

Tunnel coverage solution based on a single antenna

According to this solution, a directional antenna is installed at the tunnel entrance, with the radiation

directed to the inside. The following analyze this coverage solution.

In this solution, Pout = 39 dBm (suppose that the output power of the GSM signal source is 8W).

If the Lpath (d) indicates propagation loss, the sum of Lcable (d) and Ljumper is 5dB, the antenna gain

Gant is 8 dBi, and the needed received level is -77dBm, the Lpath (d) is expressed as follows:

Lpath (d) = 39dBm - 5dB + 8dBi – (-77dBm) = 119 dB

According to the equation Lpath (d) = 20 lg10f + 30 lg10d - 28 dB, the value of “d” can be obtained, that

is, 858m.

The previous analysis is applicable to highroad tunnels. For railway tunnels, you can consider a margin of

10 dB due to the effect of train filling, but the coverage distance of the antenna in railway tunnels is

calculated the same as that in highroad tunnels. According to the calculation, d = 398m.


ventinel

2.11.4 Tunnel Coverage Based on Leaky Cable System If adopting leaky cables to realize the tunnel coverage, you must find the specifications of the leaky

cables and complete the leaky cable design according to the following steps:

1) Decide coverage factor

2) Calculate the gain of the bi-directional amplifier

3) Estimate the length of the leaky cable between the feeder source and the first amplifier

4) Estimate the length of the leaky cable between the amplifiers

5) Decide the number of needed amplifiers

The followings describe these steps in details.

I. Decide coverage factor

The following information is needed for deciding the coverage factor:

Coupler loss

Number of carriers

Coverage probability

Coverage factor indicates the loss in the areas 2 meters beyond the leaky cable (along the vertical

direction). This loss includes the coupler loss of the leaky cable and protection margin required by the

coverage probability. If 90% of coverage probability is required, you must add 8dB to the medium level.

Some leaky cables specify the relationship between the coverage probability and coupler loss.

The coverage factor is determined by the parameters, such as coupler loss, RF carrier number, coverage

probability, and tunnel type. For the decision of coverage factor in concreter tunnels. For the decision of

coverage factor in metal tunnels. When deciding the coverage factor, you can fix a point in the graph

and mark a horizontal line through this point, and this line intersects required coverage probability. This

intersection point is the coverage factor.

Coverage factor in metal tunnels:

For example, if the leaky cable with a coupler loss of 71 (900 MHz) is used, the RF carrier number is 18,

and the coverage probability is 90, the coverage factor in a concrete tunnel is -77

II. Decide cable length between GSM signal source and the first amplifier

Before deciding cable length between GSM source and the first amplifier, you must obtain the following

information:

Transmit power of the signal source (dBm)

Jumper loss: 1 dB

Connector loss: 1 dB

Leaky cable loss: 2 dB

Transmit power at the feeder source (dBm)

When calculating the power at a point of the feeder, you must subtract the feeder propagation loss

from the GSM signal source. If a wireless repeater with an output power of 18 dBm (18 carriers) is used

as the GSM signal source, and the attenuation from the jumper to feeder, and from the feeder to the

leaky cable is 7 dB (That is, the power from the repeater is transmitted from a jumper to a feeder, and

then from the jumper to a leaky cable, so four connectors are needed. Generally, the attenuation is 2 dB

for each jumper, 1 dB for each feeder, and 0.5 dB for each connector, so the total attenuation is 7 dB.),

the transmit power at this point is 11 dB. For the connection of leaky cable.


ventinel

Connection scheme of leaky cable:

Suppose the needed signal level in a tunnel is -85 dBm, the signal level at the first amplifier must be

equal to or greater than -85 dBm. The coupler loss and longitudinal propagation loss of the leaky cable

are present between the signal feeder point and the first amplifier. They are calculated according to the

following equation:

LossLong = 11dBm – (-85dBm) + Losscoup. Here, Losscoup indicates the coverage factor, and it is -77dB

when 90% coverage is ensured. Therefore, the LossLong is 19 dB (that is, 11dBm + 85dBm -77dB =

19dB).

The cable length between the signal feeder source and the first amplifier can be obtained according to

Figure 5-39 and Figure 5-40. For example, suppose that the attenuation is 4.3dB/100 for the leaky cable,

you can mark a plumb line at the point indicating 4.3dB. This plumb line will intersect the curve

indicating 19 dB at a point, and then you mark a horizontal line starting from this point. The horizontal

line will intersect the right vertical axis at a point. And this point shows the cable length. According to

this example, the distance between the signal source and the first amplifier is 440m (that is, 19/4.3 =

440m).

Cable length between amplifiers in concrete cables:

According to the previous figures, the left vertical axis indicates “Required RADIAMP Gain”, which can be

replaced by the radial loss of the leaky cable, but it makes no difference.

III. Needed amplifier gain

Before calculating the maximum amplifier gain, you must collect the following information:

The minimum acceptable signal level (dBm)

Coverage factor (dB)

The maximum output loss allowed by a single carrier (dBm)

If the amplifier is not added, the signal level output by the leaky cable for the longest transmission

distance is equal to the difference of the minimum acceptable signal level and the coverage factor.

The signal level at the leaky cable beyond the longest transmission distance may be lower the minimum

acceptable level, so an amplifier must be added to amplify the signals to the maximum output power

allowed by a single carrier. The amplification of this power is related to the specifications of the

amplifier and the number of carriers. If the maximum output power allowed by a single carrier is known,

the amplifier gain can be calculated as follows:

Needed amplifier gain = the maximum output power allowed by a single carrier (it depends on the

number of carriers) – (the minimum acceptable signal level – coverage factor)

Along the leaky cable, the maximum output power allowed by each carrier of a bi-directional amplifier is

related to the number of carriers that have been amplified. This is considered mainly for the

intermodulation interference is present, because the intermodulation interference will increase with the

total number of carriers that have been amplified.

Relationship between the maximum output power allowed by a single carrier and the number of carriers

that have been amplified:

Needed amplifier gain = the minimum acceptable signal level – coverage factor + the maximum output

power allowed by a single carrier.

According to the previous equation, if the minimum acceptable signal level is -85 dBm, the coverage


ventinel

factor is -77, and the maximum output power allowed by a single carrier is 5 dBm, the needed amplifier

gain is 13 dB.

IV. Decide cable length between amplifiers

Before deciding the cable length between amplifiers, you must know the needed amplifier gain and the

cable loss (dB/100m). Figure 5-39 and Figure 5-40 help you decide the cable length between amplifiers.

For example, in a concrete tunnel, if the amplifier gain is 13 dB and the cable attenuation is 4.3dB/100m,

the cable length between two amplifiers is 300m.

V. Decide the number of needed amplifiers

Before deciding the number of needed amplifiers, you must know the following information:

The cable length between the feeder source and the first amplifier

The cable length between amplifiers

The tunnel length

If the previous information is known, the following formula can be used to calculate the number of

needed amplifiers. That is:

The number of amplifiers ≥ (the tunnel length – the cable length between the feeder source and the first

amplifier)/(the cable length between amplifiers), rounding up to the nearest integer.

According to the formula, if the tunnel length is 1000m, the cable length between amplifiers is 300m,

and the cable length between the feeder source and the first amplifier is 420m, 2 amplifies are needed.

That is, (1000 – 420)/300 = 1.93, so the nearest integer is 2.

After deciding the number of needed amplifiers, you can optimize the distance between amplifiers. That

is, you can obtain the distance between the two amplifiers by dividing the remaining distance by the

number of needed amplifier. According to the previous example, it is 580/2 = 290m, namely, the

distance between the two amplifiers is 290m.

VI. Remarks on leaky cable installation

The leaky cable must not touch any metal. Generally, a leaky cable must be installed at a spot 5m away

from concrete walls and at least 10m away from metal walls. In addition, a leaky cable must be installed

near to the coverage area. You cannot necessarily consider the line-of-sight propagation, because the

signals leaking from the cable will fill the space nearby.

This section introduces the coverage solutions to tunnels in different length. In actual networking, the

following coverage solutions may be used:

Micro base station (or repeater) + a single antenna

Micro base station (or repeater) + distributed antenna system

Micro base station (or repeater) + leaky cable

Before deciding which coverage solution should be adopted, you must consider the followings:

Is the GSM signal near the tunnel entrance strong enough?

Is there any available transmission link near the tunnel?

Generally, if the existed signal level near the tunnel entrance (including nearby mountains) is lower than

-80 dBm, the micro base station is recommended. If it is greater than -80 dBm, the micro base station or

the repeater is recommended. If problems concerning transmission are present, the repeater is

recommended. When using the repeater, you must consider that certain isolation is required between

repeaters.


ventinel

1. Coverage solution to short tunnels

Generally, the tunnels shorter than 100m are defined as short tunnels. When planning the coverage for

these tunnels, you must consider the coverage areas near the tunnels. If several tunnels are close to

each other, you can install a base station or a repeater between the tunnels. If adopting a micro base

station, you must adopt the bi-directional antenna. If the antenna gain is 5 dBi, you should install the

antenna at the tunnel entrance so as to ensure coverage.

When designing tunnel coverage solutions, you must fully consider that fact that cars and trains move at

a high speed, so how to ensure normal handover after the cars or trains steering into the tunnels is of

vital importance.

If the repeater is used as the GSM signal source and the signals outside the tunnel and the signals within

the tunnel belong to the same cell, no handover problem will occur. If the micro cell is used as the GSM

signal source and the signals outside the tunnels and the signals within the tunnel belong to different

cells, the signals in the outside cell will drop dramatically when the train steers into the tunnel. In this

case, handover failure may occur and call drop will be resulted in.

To solve this problem, you can consider adopting the following methods:

Adopt the bi-directional antenna for the tunnel coverage, because it can provide enough overlapping

area for handover.

Enable special handover algorithms, such as fast level fall handover algorithm. In this case, a mobile

station can hand over to another cell when the signal level falls fast.

Select the directional antenna with small front-to-back ratio.

2. Coverage solution to middle-length tunnels

This section introduces several typical coverage solutions to railway tunnels.

The followings are a series of assumptions:

The Huawei BTS3001C (the maximum output power is 8W) is used as the GSM signal source.

The repeater with 1 amplified carrier and a maximum output power of 2W is considered.

The lowest receiving level is designed to -85 dBm, and the coverage probability is 90% (with a protection

margin of 8 dB).

For railway tunnel coverage, because the train will affect signal transmission, if the antenna is installed

at the tunnel entrance, the protection margin must be increased by 10 dB. If the antenna is installed in

the tunnel, the protection margin must be increased by 5dB.

The dedicated directional antenna with the specification of DB771S50NSY, the horizontal half power

angle of 60°, and the antenna gain of 8 dBi is used at the tunnel entrance.

The bi-directional antenna with the specification of K738446 and antenna gain of 5 dBi is used within the

tunnel.

According to these assumptions, if a micro base station (39 dBm) is used as the GSM signal source, the

coverage distance is 400m when the antenna with a gain of 8 dBi is installed at the tunnel entrance, and

the coverage distance is 480m when the bi-directional antenna with a gain of 5 dBi is installed in the

tunnel.

If a repeater (33 dBm) is used as the GSM signal source, the coverage distance is 250m when the

antenna with a gain of 8 dBi is installed at the tunnel entrance, and the coverage distance is 360m when

the bi-directional antenna with a gain of 5 dBi is installed in the tunnel.


ventinel

Therefore, for the tunnels shorter than 500m, you can use the combination of a micro base station and a

single antenna (or a repeater) for the tunnel coverage. For curve tunnels, you can install a bi-directional

antaean in the tunnel.

According to on-site survey on the cross-section, the available antenna size, and the tunnel length, you

can use the antenna with a higher gain to coverage the tunnels a little longer than 500m.

3. Coverage solution to long tunnels

For the tunnels longer than 500m, you need to use the distributed antenna system or the leaky cable for

the coverage. The followings introduce the coverage realized by the combination of a micro base station

and a leaky cable (or a repeater).


The Huawei BTS3001C (the maximum output power is 8W) is used as the GSM signal source.

The repeater with 1 amplified carrier and a maximum output power of 2W is considered.

The lowest receiving level is designed to -85 dBm, and the coverage probability is 90% (with a protection

margin of 8 dB).

The leaky cable with the specification of SLWY-50-22 and the radial loss of 5dB/100 m is used.

The coupler loss may be 77 dB when the 90% of signals are received.

According to these assumptions, if a micro base station (39 dBm) is used as the GSM signal source, the

coverage distance is 800m when only the leaky cable but no amplifier is used. If a repeater (33 dBm) is

used as the GSM signal source, the coverage distance is 680m when only the leaky cable but no

amplifier is used. The coverage distance will be larger if leaky cables with smaller loss are used.

For the coverage of still longer tunnels, you must use amplifiers to amplify signals. That is, you can use

either the distributed antenna system or the leaky cable for the coverage solution. In terms of technical

indexes and installation space, coverage solution based on leaky cable is recommended. In terms of

cost, you must select a suitable coverage solution base on actual conditions.

2.12 Repeater Planning

2.12.1 Application Background With rapid development of mobile communication networks, people have higher requirements on

service quality. They hope to enjoy mobile services anywhere and anytime. As for telecommunication

carriers, they cannot enable a base station in some dead zones due to the reasons such as cost and

transmission conditions. In this case, a repeater can provide an auxiliary and economical means to

coverage the dead zones.

I. Repeater types

A wireless repeater adopts a set of donor antenna to receive the signals from the base station. After

amplifying the signals, it adopts a set of retransmission antenna to forward the signals in another

direction. Generally, a wireless repeater has only one receiving path, so the diversity antenna is

unnecessary.

Optical repeater

An optical repeater transmits signals using optical fibers, so the repeater side and base station side must

have the optical transmission capability.


ventinel

Channel bandwidth

Bandwidth selection repeater

A bandwidth selection repeater is also called wideband repeater, and it can select a frequency (for

example, the frequency with a bandwidth of 6M, 19M, or 25M) and amplify it.

Channel selection repeater

A channel selection repeater is also called narrow band repeater or frequency selection repeater. It

amplifies the selected channel numbers only. It is a narrow band repeater and amplifies a limited

channel numbers.

New style

Solar energy repeater

A solar energy repeater is of the wideband type. It is similar to a general wideband repeater except that

its power is solar energy.

Product type

Wireless frequency selection repeater

Currently, the types of the repeaters listed in the left column are in commercial use.

Optical frequency selection repeater

Wireless wideband repeater

Optical wideband repeater

II. Comparison between repeater and micro cell

Many equipments and a long period are needed for constructing a micro cell.

A repeater is installed in a flexible way and the base station equipments and transmission equipments

are unnecessary.

A micro cell can expand the system capacity. When the cells near a base station are busy, a micro cell

can be used to ease the congestion.

A repeater can absorb traffic. When a cell is idle, it brings the traffic to this cell, thus enhancing the

utilization ratio of the equipments. A repeater does not expand the capacity for a system.

The system needs to allocate channel numbers to a micro cell, but this is hard to be realized in the areas

where the frequency resource is scarce.

The system does not need to allocate channel numbers to a repeater, but it must prevent the repeater

from interfering with other cells.

Note:

The filter of an intra-frequency repeater will produce a delay of about 5μs. Theoretically, the maximum

effective coverage distance of a GSM cell will be smaller than 35km in this case.

A GSM system must enable the dynamic power control function, which is transparent to a repeater.

Generally, you must adopt the automatic level control technologies (ALC) for a repeater.

& Note:

When the ALC technology is applied to a repeater, if a mobile station is too near to the repeater, the

repeater will reduce the gains for all the mobile stations within its service area. In this case, the

conversation quality of some mobile stations will become poor, or even call drop may occur; especially


ventinel

the mobile stations far away from the repeater are greatly affected.

III. Application characteristics

Repeaters are mainly used to cover the dead zones in vast open land, and they are the extension of the

base stations. A repeater improves the coverage but does add up to the traffic capacity of a network.

However, because it enlarges the coverage of the base station, the total traffic volume increases.

A wireless repeater applies the radio transmission mode, with short construction period and effective

cost. An optical repeater adopts optical fiber as transmission medium, so the transmission loss is small

and transmission distance is large, but construction cost is greater than that of the wireless repeater.

The application advantage of the wireless repeater lies in low transmission requirement. If you plant the

optical fiber, there is no price advantage against the construction of a micro cell base station. In this

case, considering the network quality, you are recommended to select the micro cell base station.

Compared with wideband repeater, a narrow band repeater has better performance and provides

better signal quality. However, the following problems are still present in application:

The carriers of a narrow band repeater must outnumber the carriers configured for the source base

station; otherwise the repeater cannot capture a channel.

The number of paths of many repeaters is set to 4, so the base stations outnumber 4 carriers cannot

work as the signal source.

For the base stations with radio frequency and frequency hopping, if the frequencies in the frequency

hopping set outnumber the paths selected by the repeater, the conversation cannot be maintained.

When the channel number of the donor cell of the repeater changes, you must adjust the channel

number, otherwise the problems such as channel assignment failure, call drop, and interference will

occur.

The wideband repeater allows the base station to adopt frequency hopping, and you do not have to

adjust the channel number of the repeater after the channel number of the donor cell changes if the

channel number is within the bandwidth of the repeater. However, the wideband repeater will amplify

all the signals within the band, so it causes great interference against other cells.

No matter whether the optical fiber or wireless repeater is applied, the sum of the radius of the service

area of the repeater and the distance between the repeater and base station cannot break the TA

limitation. For general base stations, the distance between a repeater and the base station must be

shorter than 35 kilometers.

The optical repeater can be used in the areas where the GSM radio signals cannot reach and no space is

left for a repeater. Because the transmission loss of optical fiber is small and its bandwidth is wide, the

optical repeater is quite helpful for transmitting RF signals.

Either an omni antenna or a directional antenna can be selected for an optical repeater according to the

actual landforms. For an optical repeater, its transmission does not have to be isolated from the

reception. In addition, the address of an optical repeater is easy to be decided. Generally, an optical

repeater is applied in the dead zones within countryside, highroads, touring areas, factories, and urban

areas.

In remote mountain areas and along highroads, you can also consider using a solar energy repeater.

In conclusion, the repeater is used for the following purposes:


ventinel

Enlarge coverage area and eliminate dead zones.

Strength the field strength and enlarge converge of the base stations in urban areas.

Ensure the coverage along the highroads and tunnels.

Realize indoor coverage.

2.12.2 Working Principles of Repeater I. Wireless frequency selection repeater

Figure 5-45 shows the working principles of a wireless frequency selection repeater. The repeater

receives the RF signals from the selected base station (donor antenna) and amplifies and forwards the

signals. The antenna receiving the signals from the base station is called donor antenna, the other

antenna is called retransmission antenna.

Working principles of a wireless frequency selection repeater are as follows:

1) The low-noise power amplifier processes the signals (received by the donor antenna) from downlink

carriers.

2) The signals (900 MHz RF signals) are down converted into 71 MHz intermediate frequency (IF) signals.

3) The IF filter (with a bandwidth of 200 KHz) amplifies the 71 MHz IF signals and up converts the signals

into the 900 MHz RF signals.

4) The retransmission antenna (service antenna) transmits the signals to the coverage areas.

The uplink signals are also processed according to the previous procedures.

II. Wireless wideband repeater

The wireless wideband repeater works as the same way as the wireless frequency selection repeater

except the filter part. The bandwidth of the filter of the wireless wideband repeater is fixed. Generally, it

is 6M, 19M, or 25M.

III. Optical repeater

The difference between the optical frequency selection repeater and the optical wideband repeater lies

in the coverage end. The former adopts the frequency selection components, but the later adopts the

variable bandwidth options.

Compared with the wireless repeater, the optical repeater does require isolation between donor

antenna and retransmission antenna.

2.12.3 Repeater Network Planning I. Repeater address selection

There is no special requirement on the repeater address selection except the following items:

A repeater address must lie between the donor base station and the dead zone, and the azimuth angle

between the donor antenna and the retransmission antenna cannot be smaller than 90°, as shown in

the following figure.

If the service antenna is a directional antenna, the repeater must be installed about 200 to 500 meters

beyond the dead zone. If the repeater is installed within the dead zone, the coverage quality cannot

reach the best, as shown in the following figure.


ventinel

When the repeater is used to coverage the dense residential areas at the edges of the urban area, it

cannot face the buildings, because great penetration loss will be caused. In this case, the repeater must

be installed at the one side of the building, as shown in the following figure.

The areas to be covered must meet the requirement of line-of-sight transmission.

The repeater address must ensure the received signal level required by the repeater. Generally, the

received signal level ranges from -50 dBm to -80 dBm.

No strong carrier whose channel number is the same as that of the donor base station is present at near

the repeater address.

The landforms, buildings, or towers where the donor antenna and retransmission antenna can be

installed. (The donor antenna must be directed to the base station and the retransmission antenna must

be directed to the service area of the repeater. In addition, the isolation between the two antennas

must be greater than 170 dBc.)

II. Antenna selection

When selecting the antenna for a repeater, you must consider the followings:

Select the proper antenna gain according to the signals and coverage condition

Do not adopt the omni antenna because the wireless repeater is affiliated to the intra-frequency relay

system, otherwise the system will perform self-excitation.

The communication between the donor antenna and the donor base station antenna is point-to-point

communication, so you must select the antenna with high gain or narrow horizontal beam width. For

example, to reduce interference, you can select the reflector antenna or the log-periodical antenna.

Select retransmission antenna according to the characteristics of a coverage area. For a large coverage

area, you can select the general directional antenna with high gain. For tunnel coverage, you can select

the Yagi antenna or the spiral antenna. For indoor coverage, you must select the antenna specially

designed for indoor use. No matter in what occasions, you must control the transmit direction of the

retransmission antenna to prevent the retransmitted signals from feeding in the donor antenna.

The front-to-back ratio of the antenna must be as great as possible (it is better to be greater than 30 dB)

so that a better isolation between the donor antenna and retransmission antenna can be ensured.

III. Requirements on antenna isolation

The isolation between repeater antennas depends on the host gain, but the host gain cannot excel the

isolation coefficient for self-excitation. According to the requirements in GSM protocols 03.30, the

isolation must be at least 15 dB greater than the host gain. In actual project design, you can judge

whether the installation position meets the requirements on antenna isolation according to on-site

measurement.

According to the formulas calculating the antenna horizontal isolation, the following formula can be

deducted:

AH = 31.6 + 20 lgd – (Gt + Gr) dB (900 MHz)

AH = 37.6 + 20 lgd – (Gt + Gr) dB (1800 MHz)

Here, “d” indicates the distance between the donor antenna and retransmission antenna, in the unit of

meter. Gt and Gr indicate the antenna gain relative to the major lobe in the direction of the two

antennas. If the two antennas are back-to-back installed, Gt and Gr indicate the front-to-back ratio of

the antenna.


ventinel

Horizontal isolation of repeater antennas:

The formula calculating the vertical isolation of repeater antennas is as follows:

Av = 47.3 + 40 logd dB (900 MHz)

Av = 59.3 + 40 logd dB (1800 MHz)

Vertical isolation of repeater antennas:

If the horizontal isolation and vertical isolation are present simultaneously, the total isolation can be

calculated by the following formula:

AS = (AV - AH) a/90 + AH, here AV indicates the vertical isolation; AH indicates the horizontal isolation;

and “a” indicates the antenna included angle.

Donor antenna and retransmission antenna are installed on the top of the building. Suppose the host

gain is 100 dB, the isolation between the two antennas can be 120 dB. If the front-to-back ratio of the

donor antenna and the retransmission antenna is 30 dB, when no barriers are present between the two

antennas, the requirement on the isolation can be met.

If the space loss of the signals between the two antennas is 60 dB, the horizontal isolation distance can

be obtained, that is, d = 26m.

During project implementation, you must select the antenna installation position according to on-site

measurement. You can use a signal source and a receiver for the repeater. If the signal attenuation

between the signal source and the receiver reaches 60 dB, it means that the antenna installation

position meets the requirement on antenna isolation.

When installing the antenna for a repeater, you must pay attention to the following items:

If the antennas are horizontally installed, the host of the repeater must be installed between the donor

antenna and the retransmission antenna (it must be nearer to the donor antenna.)

A good isolation must be ensured regardless that the antennas are horizontally or vertically installed.

When they are horizontally installed, it is better that there are some barriers lying between the donor

antenna and the retransmission antenna, because you do not have to particularly design a large

installation space to ensure antenna isolation in this case.

IV. Uplink and downlink balance calculation

For a GSM repeater, the link balance is realized by four links, namely, the uplink and downlink between

the donor base station and repeater, and the uplink and downlink between the repeater and mobile

station.

This section employs the wireless repeater applied in outdoors as an example to calculate the link

balance. To simplify the calculation, we introduce the effective donor path loss (EDoPL), which includes

all the loss and gain from the output end of the base station combiner or the input end of the multi-path

coupler to the input end of the repeater.

The link balance is calculated according to the following two formulas:

For downlinks, Pbout - EDoPL + GRD - LRF + GRA - Lpass - Pmn = Pmin.

For uplinks, Pmout - Lpass + GRA - LRF + GRU - EDoPL - Pbn = Pbin.

Here,

Pbout indicates the output power of the base station.

Pmout indicates the output power of the mobile station.


ventinel

GRD indicates the downlink gain of the repeater.

GRU indicates the uplink gain of the repeater.

LRF indicates the feeder loss of the retransmission antenna.

GRA indicates the gain of the retransmission antenna.

Lpass indicates the path loss the mobile stations from the repeater to the service area.

Pbn indicates the attenuation margin of the mobile station.

Pbin indicates the receiving level of the base station.

Pmin indicates the receiving level of the mobile station.

BTSsens indicates the base station sensitivity.

MSsens indicates the mobile station sensitivity.

If the uplink EDoPL and downlink EDoPL are equal to the uplink path loss and the downlink path loss

from the repeater and mobile station, the attenuation margin of the base station is equal to that of the

mobile station. Therefore, if you subtract the formula calculating uplink balance from the formula

calculating downlink balance, you can get Pbout - Pmout + GRD - GRU = Pmin - Pbin.

If the links are balance, the equation Pmin - Pbin = Dsens = MSsens- BTSsens is present. In this case, the

formula calculating link balance is Pbout - Pmout + GRD - GRU = Dsens.

Therefore, the Dsens is fixed after the base station equipments are selected. Moreover, the output

power of the base station and mobile station may be decided in GSM system planning. As a result, to

achieve the balance of the whole links, you need to adjust the uplink gain and downlink gain of the

repeater only.

The followings employ the repeater system installed in outdoors as an example to calculate the whole

link balance.

For downlink budget of the outdoor repeater , output power of the transmitter (+43dBm) – loss of the

combiner (4dB) – EdoPL (90dB) = input power of the repeater (-51dBm) + downlink gain of the repeater

(80dB) = downlink output power of the repeater (+29dBm) – feeder loss of the retransmission antenna

(3dB) + gain of the retransmission antenna (18dBi) – path loss of the repeater in the coverage area

(127dB) = input level of the mobile station (-83dBm) – attenuation margin (20dBm) = the mobile station

sensitivity (-103dBm).

& Note:

To obtain the value of EDoPL, you can measure the input level of the donor repeater and output level of

the base station combiner first, and then obtain the difference between the two, and the difference is

the value of EDoPL. In addition, the gain of the mobile antenna must be converted to 0 dBi.

For uplink budget of the outdoor repeater, output power of the mobile station transmitter (+33dBm) –

path loss of the repeater in the coverage area (127dB) + gain of the retransmission antenna (18dBi) –

feeder loss of the retransmission antenna (3dB) = input power of the repeater (-79dBm) + uplink gain of

the repeater (80dB) = output power of the repeater (+1dBm) –EdoPL (90dB) = input level of the base

station (-89dBm) – attenuation margin (20dBm) = base station sensitivity (-109dBm).

& Note:

Because you do not have to consider the diversity function, the attenuation margin on uplinks is the

same as that on downlinks. According to the previous link budget, the downlinks are restricted by the


ventinel

output power of the repeater, the uplinks are restricted by the output power of the mobile station, and

the noise restricts the maximum gain (EDoPL-10 dB), so the link balance is present. However, this is the

most common situation. Actually, you must calculate the margin for all links when installing or

optimizing the repeater system. The latest repeater supports the uplink gain and downlink gain to be set

respectively.

Hereunder is an example.

There is a base station covering parts of a highroad. Its coverage radius is about 20 km.

The measured signal strength at the edges of the base station cells is -93dBm.

The microwave link tower on the top of the hill near the base station is selected as the address of the

repeater.

In the areas (including mountains) 350m below the top of the tower, the received level of the mobile

station is -71 dBm.

The log-periodical antenna with a gain of 18dBi and an azimuth angle of 35°is used as the donor

antenna.

The antenna is installed at 15 meters under the tower top and faces the base station.

If the previous conditions are present, the signals output by the repeater are -54 dBm. If a plane

antenna with a gain of 17 dBi and a horizontal azimuth angle of 60 degrees is installed at the top of the

tower and the antenna radiates to the reverse direction of the donor antenna, the requirements on

antenna isolation can be met even if the gain of the repeater reaches 85 dB. In this case, the output

power of the repeater is 30 dBm. And the level of the signals in the areas along the highroad which are

20 km beyond the tower can reach -90 dBm. Therefore, the radius of the cell along the highroad is

enlarged by 50%.

& Note:

If a retransmission antenna is installed at the top of the tower, you must ensure that the received signal

level in the zero point filling areas near the tower.

V. Repeater output power control

When adopting a repeater, you must pay special attention to the effect of the intermodulation products

against the system. The intermodulation products of the repeater depend on the number of the

amplified carriers, the output power of each carrier, and the linearity of the amplifier.

Linearity of the amplifier:

Third order intermodulation will increase with output power due to the nonlinearity of the amplifier.

Therefore, you must control the output to a certain degree to ensure that that the indexes on third

order intermodulation meet the requirements. The following formula shows the relationship between

the output power of each carrier of the repeater and the requirements on third order intermodulation.

Po = IP3 + (PIMP/2) +10 lg (N/2)

Here,

Po indicates the output power of each carrier (dBm)

IP3 indicates the third order section of the amplifier (dBm)

PIMP indicates the level of the third order intermodulation (dBc)

N indicates the number of carriers


ventinel

If the third order section of the amplifier of a typical repeater is 50 dBm, and the intermodulation level

must be lower than -45 dBc according to the requirement of the wireless communication institutes in

Britain.

VI. Repeater gain setting

The gain of the early repeaters must be set manually, but the latest gain of the latest repeaters can be

automatically set. For the repeaters whose gain is set manually, the sum of the repeater gain and the

protection margin must be equal to or smaller than the repeater isolation; otherwise, the self-excitation

of the repeater will be caused. Here the repeater isolation indicates the isolation between the donor

antenna and the retransmission antenna of the repeater. Generally, the protection margin ranges from

10 dB to 15 dB.

VII. Repeater adjacent cell planning

The coverage areas of a repeater may overlap other donor cells, so you must configure the

corresponding adjacent cell relationship for the repeater to ensure normal handover. In addition, you

must pay attention that the frequencies in the coverage areas of the repeater and that in the donor cells

cannot be the same frequency and neighbor frequency.

VIII. Effect of delay processing against repeater planning

If only one repeater cannot fully cover an area (such as a narrow and long tunnel), you can use several

cascaded repeaters to provide the coverage. The selection of the address and antenna for the repeater

of each level is the same as that for a single repeater.

However, the repeater will amplify the same frequency and it takes some time for the repeater to

process the signal, so there is a delay for each signal segment. If the delay is greater than the time for

the GSM system to identify the time window, the intra-frequency interference will occur. Therefore, you

must consider the effect of the delay when adopting cascaded repeaters, because the delay will also

accelerate the time dispersion and shorten the coverage distance.

If adopting the optical repeater, you must consider that the transmission speed of the signals in optical

fibers is 2/3 that of in free space, namely, if the extension cell technology is not used, the maximum

transmission distance of the signals in optical fiber is 35 km multiplies 2/3 (about 23.3 km) due to the

restriction on transmission delay.

In addition, if one of three synchronous cells adopting the optical repeater, the TA of two cells will be

different due to the difference of transmission mode and rate. In this case, the synchronous handover

failure will occur. Therefore, you must adopt the asynchronous handover to obtain the TA of a new cell,

which works as the handover target cell.

The delay processing varies with repeater types. Some take 2 to 3 μs and some takes 5 to 6μs. In a GSM

system, the delay of two signals cannot be greater than 16μs. For the effect of repeater delay processing

against time dispersion.

Distance between point A and the repeater “d” is 2.1km. The delay for the mobile station at point A to

receive the signals from the repeater and the cell is as follows:

(2.1km + 2.1km)/c (light speed) + 3μs = 14μs + 3μs = 17μs > 16μs.

In this case, the intra-frequency interference may be present. If the difference of the levels of the two


ventinel

signals is equal to or lower than 12 dB, the conversation quality will be affected.

The time dispersion will cause intra-frequency interference, and the time dispersion is caused by the

overlap of the signal source cell and the repeater coverage area. Therefore, you must select the signal of

the secondary cells in the coverage areas of the repeater instead of the signals of the major service cell

as the source signal of the repeater. In this case, the time dispersion caused by overlap can be avoided.

IX. Effect of background noise against repeater planning

Suppose that the maximum received noise level allowed by the base station is DN, if the uplink

background noise level of the repeater host is too great, the base station channels will be congested

when the noise level at the base station is greater than DN. However, how to set the repeater without

affecting the base station? They are introduces as follows.

If the following assumptions are present:

The transmitted signal strength of the base station is Tb.

The received signal strength of the base station is Rb.

The received downlink signal strength of the base station host is Dr.

The transmitted uplink signal strength of the base station host is Ut.

In this case, the path loss between the base station and the repeater is Tb-Dr, so Rb = Ut – (Tb-Dr). As a

result, if the repeater does not affect the base station, Rb < DN, so the following two inequities are

present:

Ut – (Tb - Dr) < DN

Ut < Tb-Dr + DN

According to the previous analysis, the repeater does not affect the base station if the uplink

background noise level output by the repeater host is lower than (Tb-Dr+DN). From this perspective of

review, the background noise must be particularly emphasized in repeater planning because it is easier

to bring interference than other types of base stations.

2.13 Conclusion Network planning is the foundation of a mobile communication network, especially the wireless parts in

a mobile communication network costs great and is of vital importance to network quality, so you must

make a good planning at earlier stage, which is helpful for network expansion and service update in the

future.

Network planning requires engineers to analyze coverage, decide network layers, and analyze traffic

based on relative technologies and parameters, and finally output the results of RF planning, including

base station layout and scale.

RF planning, as well as the application of cell parameters, determines the cell coverage. The cell

coverage must be properly designed so that the mobile station can always enjoy the best service at the

best cells. In addition, the cell coverage must be designed in a way conducive to network capacity

expansion.

This chapter also introduces the solutions to dual-band network, indoor coverage, tunnel coverage, and

so on. Last, this chapter introduces the repeater application.

2 g&3g planning & optimization

Education

planning foundation

traffic analysis

coverage analysis

gsm radio network planning

middlelayer station

highlayer station

lowlayer station

bearable traffic