chapter 1 mobile network comleted

8/6/2019 Chapter 1 Mobile Network Comleted

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Chapter 1 Mobile Network

Evolution of technologies used

Figure 1.1 shows the evolution of technologies used

The more common transmission schemes include FDMA (Frequency Division Multiple Access),

TDMA (Time Division Multiple Access), and CDMA (Code Division Multiple Access).

y FDMA (Frequency Division Multiple Access) is use in 1Gy TDMA (Time Division Multiple Access), is used in 2Gy CDMA (Code Division Multiple Access) is used in 3G

Frequency Division Multiple Access

Figure 1.2 shows Frequency Division Multiple Access

1 Generation 2 Generation 3 Generation


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FDMA divides the given spectrum into channels by the frequency domain. Each phone call is

allocated one channel for the entire duration of the call. In the figure above, each band represents

one call.

Time Division Multiple Access

Figure 1.3 shows Time Division Multiple Access

TDMA enhances FDMA by further dividing the spectrum into channels by the time domain as

well. A channel in the frequency domain is divided among multiple users. Each phone call is

allocated a spot in the channel for a small amount of time, and "takes turns" being transmitted. In

the figure above, each horizontal band represents the channel divided by the frequency domain.

Within that is the vertical division in the time domain. Each user then takes turns occupying the

channel.

Code Division Multiple Access


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Figure 1.4 shows Code Division Multiple Access

Unlike FDMA and TDMA, CDMA transmission does not work by allocating channels for each

phone call. Instead, CDMA utilizes the entire spectrum for transmission of each call. Each phone

call is uniquely encoded and transmitted across the entire spectrum, in a manner known as spread

spectrum transmission. In the figure above, each brightly colored pattern represents the encoded

phone call being transmitted across the spectrum.

GSM

GSM (Global System for Mobile communications) is an open, digital cellular technology used

for transmitting mobile voice and data services.

GSM offer

GSM supports voice calls and data transfer speeds of up to 9.6 Kbit/s, together with the

transmission of SMS (Short Message Service).

GSM operates in the 900MHz and 1800MHz bands in Africa region. By having harmonized

spectrum across most of the globe, GSMs international roaming capability allows users toaccess the same services when travelling abroad as at home. This gives consumers facility and

same number connectivity in more than 270 countries.

Terrestrial GSM networks now cover more than 80% of the worlds population. GSM satellite

roaming has also extended service access to areas where terrestrial coverage is not available.


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Introduction

A connection between two people is the basic service of all telephone networks. To provide this

service, the network must be able to set up and maintain a call, which involves a number of tasks

identifying the called person determining the location, routing the call, and ensuring that the

connection is sustained as long as the conversation last. After the transaction, the connection is

terminated and normally the calling user is charger for the service ha has used.

In a fix telephone network providing and managing connection is a relatively easy process,

because telephones are connected by wires to the network and their location is permanent from

the networks point of view. In a mobile network however, the establishment of a call is a far

more complex task, as the wireless connection enable the users to move at their own free will

providing the stay within the networks services area. In the practice, the network has to find

solution to three problems before it can even set up call:

y Where is the subscriber?y Who is the subscriber?y What does the subscriber want?

In other words, the subscriber has to be located and identified to provide him/her with the

requested services. To understand how to serve the subscribers, it is necessary to identify the

main interfaces, the subsystems and network elements in the GSM network, as well as their

functions.

One of the main purposes behind the GSM specifications is to define several open interfaces,

which then limit certain parts of the GSM system. Because of this interface openness, the

operator maintaining the network may obtain different parts of the network from different GSM

network suppliers.

When an interface is open, it also strictly defines what is happening through the interface, and

this in turn strictly defines what kind of actions, procedures, functions must be implemented

between the interfaces.


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The GSM specifications define two truly open interfaces within the GSM network.

y The first one is between the Mobile Station (MS) and the Base Station (BS).This open-air interface is appropriately named the air interface. It is relatively easy to imagine

the need for this interface to be open, as mobile phones of all different brands must be able to

communicate with GSM networks from all different suppliers.

y The second interface is located between the Mobile services Switching Centre, MSC,(Which is the switching exchange in GSM) and the Base Station Controller (BSC).

This interface is called the A-interface. The system includes more than the two defined

interfaces, but they are not totally open, as the system specifications had not been completed

when the commercial systems were launched.

Legend

Um: MS - BTS (air or radio interface)

A: MSC BSC

Abis: BSC BTS (proprietary interface)

Ater: BSC TRAU (sometimes called Asub)

(proprietary interface)

B: MSC VLR

C: MSC HLR

D: HLR VLR

E: MSC MSC

F: MSC EIR

G: VLR - VLR.

Figure 1.5 shows the Interfaces in GSM


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When operating analogue mobile networks, experience has shown that centralised intelligence

generates excessive load in the system, thus decreasing the capacity. For this reason, the GSM

specification, in principle, provides the means to distribute intelligence throughout the network.

Referring to the interfaces, the more complicated the interfaces in use, the more intelligence is

required between the interfaces in order to implement all the functions required.

In a GSM network, this decentralised intelligence is implemented by dividing the whole

network into three separate subsystems:

y NetworkSwitching Subsystem (NSS)

y Base Station Subsystem (BSS)

y NetworkManagement Subsystem (NMS)

The actual network needed for establishing calls is composed of the NSS and the BSS.

The BSS is responsible for radio path control and every call is connected through the BSS.

The NSS takes care of call control functions. Calls are always connected by and through the

NSS.


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Figure 1.6 shows the three subsystems of GSM and their interfaces

The NMS is the operation and maintenance related part of the network and it is needed for the

control of the whole GSM network. The network operator observes and maintains network

quality and service offered through the NMS. The three subsystems in a GSM network are linkedby the Air-, A-, and O&M interfaces as shown in Figure 1.6

Mobile Station (MS)

The MS (Mobile Station) is a combination of terminal equipment and subscriber data. The

terminal equipment as such is called ME (Mobile Equipment) and the subscriber's data is stored

in a separate module called SIM (Subscriber Identity Module).

Therefore, ME + SIM = MS.

From the users point of view, the SIM is certainly the best-known database used in a GSM

network. The SIM is a small memory device mounted on a card and contains user-specific


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identification. The SIM card can be taken out of one Mobile and inserted into another. In the

GSM network, the SIM card identifies the user.

The SIM card contains the identification numbers of the user and a list of available networks.

The SIM card also contains tools needed for authentication and ciphering. Depending on the type

of the card, there is also storage space for messages, such as phone numbers. A home operator

issues a SIM card when the user joins the network by making a service subscription. The home

operator of the subscriber can be anywhere in the world, but for practical reasons the subscriber

chooses one of the operators in the country where he/she spends most of the time.

Subsystems and network elements in GSM

The GSM network is divided into three subsystems: Network Switching Subsystem (NSS), Base

Station Subsystem (BSS), and Network Management Subsystem (NMS). The three subsystems,

different network elements, and their respective tasks are presented in the following.

Network Switching Subsystem (NSS)The Network Switching Subsystem (NSS) contains the network elements MSC, VLR, HLR, AC

and EIR.


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Figure 1.7 shows The Network Switching Subsystem (NSS)

The main functions of NSS are:

Call control

This identifies the subscriber, establishes a call, and clears the connection after the conversation

is over.

Charging

This collects the charging information about a call that is the numbers of the caller and the called

subscriber, the time and type of the transaction, etc and transfers it to the Billing Centre.

Mobility management

This maintains information about the subscriber's location.

Signalling

This applies to interfaces with the BSS and PSTN.


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Subscriber data handling

This is the permanent data storage in the HLR and temporary storage of relevant data in the

VLR.

Base Station Subsystem (BSS)

The Base Station Subsystem is responsible for managing the radio network, and it is controlled

by an MSC. Typically, one MSC contains several BSSs. A BSS itself may cover a considerably

large geographical area consisting of many cells. A cell refers to an area covered by one or more

frequency resources. The BSS consists of the following elements:

BSC Base Station Controller

BTS Base Transceiver Station

TC Transcoder

Figure 1.8 shows The Base Station Subsystem

Some of the most important BSS tasks are listed in the following:


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Radio path control

In the GSM network, the Base Station Subsystem (BSS) is the part of the network taking care of

radio resources, that is, radio channel allocation and quality of the radio connection.

Synchronization

The BSS uses hierarchical synchronisation, which means that the MSC synchronises the BSC,

and the BSC further synchronises the BTSs associated with that particular BSC. Inside the BSS,

synchronization is controlled by the BSC. Synchronization is a critical issue in the GSM network

due to the nature of the information transferred.

If the synchronization chain is not working correctly, calls may be cut or the call quality may not

be the best possible. Ultimately, it may even be impossible to establish a call.

Air- and A-interface signalling

In order to establish a call, the MS must have a connection through to the BSS.

Connection establishment between the MS and the NSS

The BSS is located between two interfaces, the air- and the A-interface. The MS must have a

connection through these two interfaces before a call can be established. Generally, this

connection may be either a signalling connection or a traffic that can be speech or data

connection.

Mobility management and speech transcoding

BSS mobility management mainly covers the different cases of handovers. These handovers and

speech transcoding are explained in later sections.

Base Station Controller (BSC)


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The BSC is the central network element of the BSS and it controls the radio network. It has

several important tasks, some of which are presented in the following:

y Connection establishment between the MS and the NSSAll calls to and from the MS are connected through the group switch of the BSC (GSWB).

y Mobility managementThe BSC is responsible for initiating the vast majority of all handovers, and it makes the

handover decision based on, among others, measurement reports sent by the MS during a call.

y Statistical raw data collectionInformation from the Base Transceiver Stations, Transcoders, and BSC are collected in the BSC

and forwarded via the DCN (Data Communications Network) to the NMS (Network

Management Subsystem), where they are post-processed into statistical views, from which the

network quality and status is obtained.

y Air- and A-interface signalling supportIn the A-interface, Common Channel Signalling System No. 7 is used as the signalling language,

while the environment in the air interface allows the usage of a protocol adapted from ISDN

standards, namely LAP-Dm (Link Access Protocol on the ISDN D Channel, modified version).

Between the Base Transceiver Station and the BSC (A-bis interface), a more standardized LAPD(Link Access Protocol - Channel D)protocol is used. The BCSU (Base Station ControllerSignalling Unit) in the BSC will therefore need to convert from LAP-D to SS7 and vice versa in

the uplink/downlink directions. The BSC also enables the virtual signalling connection needed

between the MSC/VLR and the MS.

y BTS and TC controlInside the BSS, all the BTSs and TCs are connected to the BSC(s). The BSC maintains the BTSs.

The BSC is capable of separating (barring) a BTS from the network and collecting alarm

information. Transcoders are also maintained by the BSC, that is, the BSC collects alarms related

to the transcoders.


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y Base Transceiver Station (BTS)The BTS is the network element responsible for maintaining the air interface and minimizing the

transmission problems. The air interface is very sensitive for disturbances. This task is

accomplished with the help of some 120 parameters. These parameters define exactly what kind

of BTS is in question and how MSs may locate the network while moving in this BTS area.

The BTS parameters handle the following major items: what kind of handovers paging

organization, radio power level control, and BTS identification. The BTS has several very

important tasks, some of which are presented in the following.

y Air interface signallingA lot of both call and non-call related signalling must be performed in order for the system to

work. One example is that when the MS is switched on for the very first time, it needs to send

and receive a lot of information with the network more precisely with the VLR before we can

start to receive and make phone calls.

Another example is the signalling required setting up both mobile originated and mobile

terminated calls. A third very important signalling in mobile networks is the need to inform the

MS when a handover is to be performed and later when the MS sends a message in the uplink

direction telling the network that the handover is completed

y CipheringBoth the BTS and the MS must be able to cipher and decipher information in order to protect the

transmitted speech and data in the air interface.

y Speech processingSpeech processing refers to all the functions the BTS performs in order to guarantee an error-free

connection between the MS and the BTS. This includes tasks like speech coding digital to

analogue in the downlink direction and vice versa, channel coding (for error protection),

interleaving to enable a secure transmission, and burst formatting (adding information to the

coded speech / data in order to achieve a well-organized and safe transmission).


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Figure 1.9 shows Speech in the BSS

Modulation and De-modulation

User data is represented with digital values 0 and 1. These bit values are used to change one of

the characteristics of an analogue radio signal in a predetermined way. By altering the

characteristic of a radio signal for every bit in the digital signal, we can "translate" an analogue

signal into a bit stream in the frequency domain. This technique is called modulation. In GSM,

Gaussian Minimum Shift Keying (GMSK), is applied.

The base station can contain several TRXs (Transceivers), each supporting one pair of

frequencies for transmitting and receiving information. The BTS also has one or more antennas,

which are capable of transmitting and receiving information to/from one or more TRXs. The

antennas are either Omni-directional or sectorized. It also has control functions for Operation and

Maintenance (O&M), synchronization and external alarms, etc.


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Figure 1.10 shows the Omni directional and sectorised cells

Transcoder and Rate Adaptation Unit (TRAU)

In the air interface (between MS and BTS), the media carrying the traffic is a radio frequency.

To enable an efficient transmission of digital speech information over the air interface, the digital

speech signal is compressed. We must however also be able to communicate with and through

the fixed network, where the speech compression format is different. Somewhere between the

BTS and the fixed network, we therefore have to convert from one speech compression format to

another, and this is where the Transcoder comes in.

For transmission over the air interface, the speech signal is compressed by the mobile station

to 13 Kbit/s (Full Rate and Enhanced Full Rate), 5.6 Kbit/s (Half Rate), or 12.2 Kbit/s (Enhanced

Full Rate). A more modern speech codec is the AMR (Adaptive Multirate Coding) which is more

flexible since it produces speech with bitrates similar to older solutions but adapted to link

conditions.


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However, the standard bit rate for speech in the PSTN is 64 Kbits/s. The modulation technique is

called "Pulse Code Modulation" (PCM). This requires the GSM network to perform bit rate

adaptation of speech.

Figure 1.11 shows the Location of Transcoder and Sub multiplexer

The TRAU thus takes care of the change from one bit rate to another. If the TC is located as

close as possible to the MSC with standard PCM lines connecting the network elements, we can,

in theory, multiplex four traffic channels in one PCM channel. This increases the efficiency of

the PCM lines, and thus lowers the costs for the operator. When we connect to the MSC, the

multiplexed lines have to be de-multiplexed. For that reason, the TRAU is called Transcoder and

Sub multiplexer (TCSM).

According to the standards, the TRAU functionality can be also implemented at the BSC and

BTS site. The most common case is the MSC site.

Another task for the TRAU is to enable DTX (Discontinuous transmission), which is used during

a call when there is nothing to transmit (no conversation). It is activated in order to reduce

interference and to save MS battery.


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Network Management Subsystem (NMS)

The Network Management Subsystem (NMS) is the third subsystem of the GSM network in

addition to the Network Switching Subsystem (NSS) and Base Station Subsystem (BSS), which

we have already discussed. The purpose of the NMS is to monitor various functions and

elements of the network.

The functions of the NMS can be divided into three categories:

y Fault managementy Configuration managementy Performance management

These functions cover the whole of the GSM network elements from the level of individual

BTSs, up to MSCs and HLRs.

Fault management

The purpose of fault management is to ensure the smooth operation of the network and rapid

correction of any kind of problems that are detected. Fault management provides the network

operator with information about the current status of alarm events and maintains a history

database of alarms.

The alarms are stored in the NMS database and this database can be searched according to

criteria specified by the network operator.

Configuration management

The purpose of configuration management is to maintain up-to-date information about the

operation and configuration status of network elements. Specific configuration functions include


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the management of the radio network, software and hardware management of the network

elements, time synchronisation, and security operations.

Performance management

In performance management, the NMS collects measurement data from individual network

elements and stores it in a database. On the basis of these data, the network operator is able to

compare the actual performance of the network with the planned performance and detect both

good and bad performance areas within the network.

Network elements and connections

The diagram below shows an overall picture of the GSM network, where you can also see some

of the connections to external elements, such as SMSC and Billing Centre. The network picture

below contains equipment from a typical GSM network, some of which is not included in the

GSM specifications.


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Figure 1.12 shows the GSM network architecture

y Diagram of 2 G network

According to all the information I received, I was asked to represent GSM network architecture

for 2G using Microsoft Visio.

y GPRS (General Packet Radio Service)General Packet Radio Service is a kind of radio communication service based on packet. GPRS

make communication rate rise up from 56 Kbps to 114Kbps and support continuous connection

between the computers and the mobile users. High data throughput capability can make portable

equipment and laptop computers usable for TV conferencing, multimedia pages and some

similar applications.

GPRS is based on Global System for Mobile communication (GSM) and can complete some

existing services such as cell phone circuit-switched connection and SMS. Theoretically, the

expense of GPRS packet service is less than that of circuit-switched services. Channels are

shared, and packet comes into being only in case of necessity, which can save a large number of

resources when compared to special connection. GPRS provide simpler services for users,

because the buffering middleware which is added to adapt to the slow speed of terminal

equipments is no longer necessary.


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Figure 1.13 shows the GPRS system Structure

Interfaces in the GPRS network

Ga

The interface serves the CDRs (accounting records) which are written in the GSN andsent to the charging gateway (CG). This interface uses a GTP-based protocol, with

modifications that supports CDRs (Called GTP'orGTP prime).

Gb

Interface between the base station subsystem and the SGSN the transmission protocol

could be Frame Relay or IP.

Gi

IP based interface between the GGSN and a public data network (PDN) either directly to

the Internet or through a WAP gateway.

Gp

IP based interface between internal SGSN and external GGSNs. Between the SGSN and

the external GGSN, there is the border gateway (which is essentially a firewall). Also

uses the GTP Protocol


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The GPRS network is realized on the basis of the existing GSM network. Some nodes need to be

added to the existing GSM network, such as GGSN (Gateway GPRS Support node) and SGSN

(Serving GSN, Serving GPRS Support node)

The reference model for GPRS network is shown in the diagram. GSN is the most important

network node in the GPRS network. GSM have mobile routing management functions, which

can connect with various data networks and GPRS registers. GSN can complete data

transmission and format conversion between mobile stations and various data networks. GSN is

a kind of independent equipment similar to routers, which can be integrated with MSC in GSM.

GSM is divided into two categories, SGSN (Serving GSN) and GGSN (Gateway GSN). SGSN is

mainly used to record the current position information of mobile stations and complete

transmission and reception for mobile packet data between mobile stations and GGSN. GGSN is

mainly used as a gateway, which can connect with various data networks such as ISDN, PSPDN,

LAN, etc. According to some literatures, GGSN is called GPRS router. GGSN can conduct

protocol transformation for GPRS packet data in GSM network, so as to transmit this packet data

to TCP/IP or X.25 network at the remote end.

In addition, some manufacturers have proposed the concept of GR (GSM Register, GPRS

database). GR is GPRS service data base which is similar to HLR in GSM. GR can exist

separately or coexist with HLR, which can be realized through servers or programming control

switched. The name of GR is not specially referred to in ETSI suggestions.

Advantages of GPRS

Comparing to the former circuit switching data transmission mode of GSM dial mode for GSM,

packet switching technology is used for GPRS, which can make a number of users share some

fixed channel resources and provide a kind of connection between the mobile users and data

network (such as supporting TCP/IP, X25 and other networks) in the remote end, featuring

advantages of high speed and online forever.


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Technical Features of GPRS

y High Resource efficiency: In GSM network, GPRS first introduces a transmission modeof packet switching, essentially changing the GSM data transmission mode of circuit

switching mode, which is especially important in case of lack of radio resources.

y High Transmission Rate: GPRS provide a transmission rate of up to 115kbit/s (themaximum value is 171.2kbit/s).

y Short Access Time: The access time for packet switching time is shortened to less than 1second, rapid instant connection can be provided, the efficiency of some affairs (such as

credit card check, remote monitoring, etc) can be improved greatly, and operation for

existing internet applications (such as E-mail, webpage browsing, etc.) can become more

convenient and fluent.

y Support IP Protocol and X.25 Protocol: GPRS support IP Protocol and X.25 Protocolwhich are most vastly applied to internet.

EDGE (Enhanced Data Rate for Global Evolution)

Enhanced Data Rate for Global Evolution was named GSM 384 because of the fact that it

provided Data Transmission at a rate of 384 Kbps. It consists of the 8 pattern time slot, and thespeed could be achieved when all the 8 time slots were used. The idea behind EDGE is to obtain

even higher data rates on the current 200 KHz GSM carrier, by changing the type of the

modulation used.

Now, this is the most striking feature. EDGE, as being once a GSM technology, works on the

existing GSM or the TDMA carriers, and enables them to many of the 3G services.

Although EDGE will have a little technical impact, since its fully based on GSM or the TDMAcarriers, but it might just get an EDGE over the upcoming technologies, and of course, the

GPRS. With EDGE, the operators and service providers can offer more wireless data application,

including wireless multimedia-mail (Web Based), Web Infotainment, and above all, the

technology of Video Conferencing.

Now all these technologies that were named earlier were the clauses of the IMT-UMTS 3G


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Package. But, with EDGE, we can get all these 3G services on our existing GSM phones, which

might just prove to be a boon to the user.

The current scenario clearly states that EDGE will definitely score higher than GPRS. The

former, allows its users to increase the data speed and throughput capacity, to around 3-4 times

higher than GPRS.

Secondly, it allows the existing GSM or the TDMA carriers to give the sophisticated 3G

services.

Technology of EDGE/EGPRS

EDGE/EGPRS is implemented as a bolt-on enhancement for 2.5G GSM/GPRS networks,

making it easier for existing GSM carriers to upgrade to it. EDGE is a superset to GPRS and can

function on any network with GPRS deployed on it, provided the carrier implements the

necessary upgrade.

EDGE requires no hardware or software changes to be made in GSM core networks. EDGE-

compatible transceiver units must be installed and the base station subsystem needs to be

upgraded to support EDGE. If the operator already has this in place, which is often the case

today, the network can be upgraded to EDGE by activating an optional software feature. Today

EDGE is supported by all major chip vendors for both GSM and WCDMA/HSPA.

Transmission techniques

In Gaussian minimum-shift keying (GMSK), EDGE uses higher-order PSK/8 phase shift

keying (8PSK) for the upper five of its nine modulation and coding schemes. EDGE produces a

3-bit word for every change in carrier phase. This effectively triples the gross data rate offered

by GSM. EDGE, like GPRS, uses a rate adaptation algorithm that adapts the modulation and

coding scheme (MCS) according to the quality of the radio channel, and thus the bit rate and

robustness of data transmission.


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GSM frequency bands

System Band Uplink (MHz) Downlink (MHz) Channel number

P-GSM-900 900 890.0915.0 935.0960.0 1124

E-GSM-900 900 880.0915.0 925.0960.0 9751023, 0-124

DCS-1800 1800 1710.21784.8 1805.21879.8 512885

Table 1.2 shows the GSM frequency bands

y P-GSM, Standard or Primary GSM-900 Bandy E-GSM, Extended GSM-900 Band (includes Standard GSM-900 band)y T-GSM, TETRA-GSM

In Africa most of the providers use 900 MHz and 1800 MHz bands. GSM-900 is most widely

used. Fewer operators use DCS-1800 and GSM-1800. A dual-band 900/1800 phone is required

to be compatible with almost all operators. At least the GSM-900 band must be supported in

order to be compatible with many operators


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UMTS Network

The WCDMA system consists of a number of logical network elements that each has a defined

functionally. In the standards, network elements are defined at the logical level, but this quite

often results in a similar physical implementation, especially since there are a number of open

interfaces. The network elements can be grouped into Radio Access Network (RAN) that handles

all radio-related functionally, and the external networks. To complete the system, the User

Equipment (UE) that interfaces with the user and the radio interfaces defined. Radio Access

Network (RAN) is a switched circuit network consisting of Radio Network Controller and Node

B. It is linked to Core Network via Iu interface. In 3GPP, RAN is referred to as UTRAN (UMTS

Terrestrial Radio Access Network). RNC is the radio controller which manages radio resources

and controls Node B, and controls handover, for example. Node B, a logical node which receives

and transmits radio signals, is the base station in the real world.

y 3G technologiesGSM technology was able to transfer circuit switched data over the network. The use of3G

technology is also able to transmit packet switch data efficiently at better and increased

bandwidth. 3G mobile technologies proffers more advanced services to mobile users. It can help

many multimedia services to function. The spectral efficiency of 3G technology is better than 2G

technologies. Spectral efficiency is the measurement of rate of information transfer over any

communication system. 3G is also known as IMT-2000.

3G technologies make use of TDMA and CDMA. 3G (Third Generation Technology)

technologies make use of value added services like mobile television, GPS (global positioning

system) and video calls. The basic feature of 3G Technology (Third Generation Technology) is

fast data transfer rates. Data rate of 384kbits/s are normally achieved on the 3G network while

speeds of 7Mbps or higher can be reached on 3.5G (HSPA/HSPA+).

ITU sell various frequency rates in order to make use of broadband technologies. Network

authentication has won the trust of users, because the user can rely on its network as a reliable


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source of transferring data.3G technology is much flexible, because it is able to support the 5

major radio technologies. These radio technologies operate under CDMA, TDMA and

FDMA.CDMA holds for IMT-DS (direct spread), IMT-MC (multi carrier).

TDMA accounts for IMT-TC (time code), IMT-SC (single carrier). FDMA has only one radio

interface known as IMT-FC or frequency code. Third generation technology is really affordable

due to the agreement of industry. This agreement took place in order to increase its adoption by

the users. 3G system is compatible to work with the 2G technologies. 3G technologies hold the

vision that they should be expandable on demand. The aim of the 3G is to allow for more

coverage and growth with minimum investment.

Explanation of the diagram

The interface between Node B and RNC is referred to as Iub, and the interface betweenRNCs is Iur. Node B covers one or more cells. When one base station is sectorized and

equipped with multiple directional antennas, each sector is sometimes called cell.

Node B is connected with mobiles via radio interface.

Figure 1.14 shows the architecture of 3G network


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Description of the Network Elements

Core Network

y GMSC: Gateway Mobile Services Switching Center Switches circuit switched (CS) datato the external network.

y MSC: Mobile Services Switching Center Switches circuit switched (CS) data.y VLR: Visitor Location Register Stores copy of visiting users service profiles.y HLR: Home Location Register Stores users service profiles.y GGSN: Gateway GPRS Support Node Handles packet switched (PS) data to the external

network.

y SGSN: Serving GPRS Support Node Handles packet switched (PS) data.UTRAN

y RNC: Radio Network Controller Controls radio resources.Node-B

y Converts Data flow between Iub and Uu interface.UE (User Equipment)

y ME: Mobile Equipment Radio terminal used for radio communication.y USIM: UMTS Subscriber Identity Module Smart card that stores subscriber identity.

Base Stations

Base stations may be stand alone transmission systems or part of a cell site and is composed of

an antenna system (typically a radio tower), building, and base station radio equipment. Base

station radio equipment consists of RF equipment (transceivers and antenna interface

equipment), controllers, and power supplies.

Base station transceivers have many of the same basic parts as a mobile device. However, base

stations radios are coordinated by the mobile systems BSC and have many additional functions

than a mobile device.

The radio transceiver section is divided into transmitter and receiver assemblies. The transmitter

section converts a voice or data signal to RF for transmission to wireless devices and the receiver

section converts RF from the wireless device to voice or data signals routed to the MSC or

packet switching network. The controller section commands insertion and extraction of signaling

information. Unlike end user wireless devices such as a mobile telephone or laptop computer, the


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transmitter, receiver, and control sections of an access point may be grouped into equipment

racks.

Operating

Band

Frequency

Band

Common

Name

ULFrequencies

UE transmit (MHz)

DL

Frequencies

UE receive

(MHz)

Channel

Number

(UARFCN)

UL

Channel

Number

(UARFCN)

DL

I 2100 IMT 19201980 21102170 9612 - 9888 10562 -

10838

Table 1.3 shows the Frequency range of 3G network

Data rates

ITU has not provided a clear definition of the data rate users can expect from 3G equipment or

providers. Thus users sold 3G service may not be able to point to a standard and say that the rates

it specifies are not being met. While stating in commentary that "it is expected that IMT-2000

will provide higher transmission rates: a minimum data rate of 2 Mbit/s for stationary or walking

users, and 384 Kbit/s in a moving vehicle, the ITU does not actually clearly specify minimum or

average rates or what modes of the interfaces qualify as 3G, so various rates are sold as 3G

intended to meet customer expectations of broadband data.

y Shifting from 2G to 3G


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2G was deliberately designed to be very power-efficient only for low-data rate voice services.

3G was designed to be more spectrally efficient and to delivers higher-rate data services, but at

the expense of using more power.

Specifically:

2G uses 200 kHz channel vs. 5MHz for WCDMA (25x more). Power is roughly proportional to

bandwidth. GSM used a very power-efficient constant envelope modulation scheme (GMSK).

3G uses CDMA and higher order modulation (up to 16QAM or even 64QAM), which needs

much better linearity and hence the radio draws far more power. 2.5G (GPRS) and 2.75G

(EDGE) use QAM, which deliver more data and are more spectrally efficient (bps/Hz) so they

converge with 3G somewhat.

Battery life can be improved significantly by turning of 3G and only using 2G if you stick to

voice but if you are going to web-surf then the better data-rate (bps) and data efficiency probably

make 3G more efficient.

y Security in 3G3G networks offer greater security than their 2G predecessors. By allowing the UE (User

Equipment) to authenticate the network it is attaching to, the user can be sure the network is the

intended one and not an impersonator. In addition to the 3G network infrastructure security, end-

to-end security is offered when application frameworks such as IMS are accessed, although this

is not strictly a 3G property.

Applications

The bandwidth and location information available to 3G devices gives rise to applications not

previously available to mobile phone users. Some of the applications are:

Mobile TV a provider redirects a TV channel directly to the subscriber's phone where it canbe watched.

Video on demand a provider sends a movie to the subscriber's phone.


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Video calls subscribers can see as well as talk to each other.

chapter 1 mobile network comleted

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