wpo-16 principles and methods of rf optimization-58

7/25/2019 WPO-16 Principles and Methods of RF Optimization-58

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Principles and Methods of RF

Optimization

ZTE University


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Content

Principle of Antenna

Antenna and Radio propagation Features

WCDMA RF Optimization Data Analysis and

Problem Locating

WCDMA RF Cases


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Principles of Antenna (1)

What is antenna?

Antenna converts the electrical signals from the conductive

wire into radio wave and transmits it into the air

Antenna collects the radio wave and converts it into

electrical signals

Blahblah

blah bl ah


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Principles of Antenna (2)

When the conductive wire has alternating current, it can form radiationof electromagnetic wave, with the radioactive capacity related to thelength and form of the conductive wire.

When the length of the conductive wire increases to a degreecomparable to wavelength, the current on the conductive wire sharplyincreases, forming strong radiation. Generally the straight conductivewire above that can form noticeable radiation is called dipole .


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Outer View of Antenna (1)

--- Outdoor NodeB patch directional antenna


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Outer View of Antenna (2)

Indoor ceiling-mountantenna Indoor wall-mount antenna

--- Indoor antenna


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For example, 1 symmetrical dipole

Receiving power: 1mW

Antenna array of 4 symmetrical dipoles

Receiving power: 4 mW

GAIN= 10log(4mW/1mW) = 6dBd

The high gain of the patch antenna is formed by the antenna array of multiplebasic dipoles

Gain of Antenna


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Gain of Antenna

The definition of the gain of an antenna is related to the 1/2wavelength dipole or the omni radiator.

The omni radiator assumes that the radiation powers in all directionsare equal. The gain of the antenna in a certain direction is a value ofthe field strength generated in this direction over the intensity by theomni radiator in this direction.

Generally the gain of the antenna has two units: dBd and dBi.

dBi indicates the field strength in the direction of the largest radiationof the antenna, compared with the reference value of the omniradiator.

The gain of the antenna compared with the 1/2 wavelength dipole isindicated with dBd.

0dBd=2.15 dBi


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Difference of dBd and dBi

2.15dB

Pattern radiation of a

single symmetrical dipoleA omni homogeneous

radiator has the same

radiation in all directions

Gain of an antenna compared with a

symmetrical dipole is indicated with dBd.

Gain of an antenna compared with an omni

homogeneous radiator is indicated with dBi.

For example: 3dBd = 5.15dBi


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Gain of Antenna

BaseStationTransmitter

(20 watts)

Convert to dBm

10Log(20) + 30 = +43 dBm

jumper

Heliax

Cable

jumper

-0.5dB

-0.5dB

-3dB

Antenna Gain

= + 18 dBi

Ant Input

Power = + 39dBm

EiRP = +39 + 18 = +57 dBm EIRP

case


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Antenna Direction

The antenna direction refers to the capability ofradiating electromagnetic wave in a certain direction.

For the receiving antenna, pattern means thereceiving capability of the wave promulgated fromdifferent directions.

The characteristic curve of antenna direction isusually indicated with pattern.

Pattern is employed to describe the capability of

transmitting/receiving electromagnetic wave in alldirections in the space.


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Antenna Pattern

Top view


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120

(eg)Peak

- 10dB point

- 10dB point

60

(eg) Peak

- 3dB point

- 3dB point

15

(eg) Peak

Peak - 3dB

Peak - 3dB

32

(eg) Peak

Peak - 10dB

Peak - 10dB

Vertical pattern

3dB beamwidthHorizontal

pattern 10dB beamwidth

Beamwidth of Antenna


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Radio parameter-Beamwidth


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Work Frequency Range of Antenna

In disregard of transmitting or receiving antenna, it

always works within a certain frequency range. With the

considerations of out-of-band anti-interference capacity,

the usual practice is to select the bandwidth of the

antenna that just meets the frequency requirements.

At 850MHz, the 1/2

wavelength is best

At

890MHz Antenna

dipole

At

820MHz


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Polarization of Antenna

Vertical

polarization

Horizontal

polarization

+ 45

tilted polarization - 45

tilted polarization


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Dual-polarization Antenna

The dual-polarization consists of two Antenna with orthogonal poleswithin the same radome. The adoption of dual-polarization antenna cansharply reduce the number of Antenna, streamline the installation

engineering of antenna, lower cost, and save space in antennainstallation.

V/H

(vertical/horizontal) Tilt (+/- 45

)


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Antenna Beam Downtilt

Applied to suppress coverage and reduce cross-

modulation Two modes: Mechanical downtilt and electrical

downtilt


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Impact of Down-tilt on Coverage


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Beam Downtilt

The purpose of the downtilt technology is to tilt the main beam toreduce the radiation level to the adjacent coverage cells. In the case,though the frequency level at the edge of the cell is reduced, theinterference level is much lower than the frequency level.

No downtiltElectrical

downtilt

Mechanical

downtilt


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Phase Shifter

Principle of Electrical Downtilt


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Electrical Downtilt and Mechanical Downtilt


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Front-to-Back Ratio

In the antenna pattern, the ratio of max. value of front andback lobes is called front-to-back ratio . The front-to-backratio of the outdoor NodeB antenna is preferably generallylarger than 25dB.

Front powerRear power


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Input Impedance of Antenna

The ratio of the signal voltage and the signal current of

the antenna and the feeder connection points, or the twoends of the feeding points, is called impedance ofantenna.

Input impedance has resistance component and

reactance component. For any antenna, within therequired work frequency range, we can make adjustmentof the antenna impedance, make the imaginary part of

impedance is very small and real part is very close to 50, so that the antenna impedance is Zin = Rin = 50 .This is necessary to ensure the impedance of antennaand that of feeder to be well matched.


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VSWR

The generation of VSWR (Voltage Standing Wave Ratio) : As theincident wave power is transmitted to the antenna input end and is not

completely absorbed. Reflection wave is generated and stacked togenerate VSWR.

The value of VSWR is between 1 and infinite. VSWR is 1, indicatingfull match. VSWR is infinite, indicating full reflection and full mismatch.

9.5 W80ohms

50 ohms

Forward: 10W

Backward: 0.5W


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Reflection coefficient :

||=|(Za-Zo)/(Za+Zo)|

Za: Input impedance

Zo: Antenna standard input impedance

VSWR=(1+||)/(1-||).

RL=-20lg||, ( Reflection Loss)eg:

if VSWR=1.5, then RL=-13.98dB.

VSWR

Principles of Antenna


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Side Lobe Suppression and Null Fill-in


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Side Lobe Suppression and Null Fill-in


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Content

Principle of AntennaAntenna and Radio propagation Features


Problem Locating

WCDMA RF Cases


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Antenna

There are multi kinds of antenna down-tilt such as mechanical down-tilt, fixedelectrical adjustment down-tilt, adjustable electrical adjustment down-tilt andremote control adjustable electrical adjustment down-tilt. Mechanical down-tiltis to tilt antenna when setting up it. So the price of it is cheaper. It is usually

used for the down-tilt with the angle less than 10 degrees. When furtherincreasing the angle of antenna down-tilt, there appears obvious concavepit right in the front of coverage area. The two sides of coverage area are alsopressed flat. The antenna pattern distortion causes that the front of antenna isnot sufficiently covered and the scrambling to the base stations on the side of it

increases. The other defect of mechanical down-tilt is that the antenna backlobe will turns up which make scrambling to neighbor sector. That will causethe call drop of the high floor user in the nearby cells.


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The Relationship between Antenna Down-tilt and


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The Relationship between Antenna Down tilt and

Cell Coverage Radius in Heavy Traffic Area

The heavy traffic area mentioned here is mainly the urban areas,especially the dense urban areas. The distribution of base stations inthese areas is intensive. And the scrambling is easy to form betweenthe base stations. In order to let the most of the energy radiate in the

covered area and reduce the scrambling to neighbor cells, we shouldmake the half-power points on the main lobe of the antenna aimed atthe border of the covered area.



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The Relationship between Antenna Down tilt and

Cell Coverage Radius in Heavy Traffic Area

The formula of down-tilt is shown below:

Where,

a is the initial mechanical down-tilt of antenna;

H is the effective height of the site which means thedifferent between the hung height of antenna and the averageheight of surrounding coverage areas;

L is the distance between the antenna of the site and the

border of the sector needed to be covered; ??? is the vertical beam width of the antenna;

??? is the angle of antenna down-tilt.

_e

2

)

L

H(arctg +=



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p

Cell Coverage Radius in Low Traffic Area

For low traffic areas such as suburbs, rural areas, highways,sea surface and so on, reducing the initial down-tilt to make thebiggest gain point of main lobe aimed at the border of coveragearea can make the coverage far as possible. The formula ofdown-tilt is shown below:

_e)L

H(arctg =

Antenna Down tilt Angle


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Antenna Down-tilt Angle

When adjusting the antenna direction angle, the horizontal half-powerbeam width of the antenna should be taken into consideration. If theangle of two directions of sector is too small, the coverage overlapswill be larger. This may cause frequent handover and be difficult to

guarantee the well coverage around the base station. However, biggerangle may cause the signal quality of handover area worse. Thecommon suggested direction angle is between 90 to 140 degrees.

When adjusting the antenna down-tilt angle, the vertical half-powerbeam width of the antenna should be taken into consideration. For

adjusting mechanical down-tilt, 1 to 5 degrees is the usual valuebecause the beam distortion is not very large with this value. 6 to 9degrees is suggested to used for large station height and densestation distance. 10 to 12 degrees is usually only used for high stationin urban area.

For antenna hung height, beyond the average height of the buildingsaround the station with 5 to 10 meters is the best value. Besides, theantenna hung height of the neighbor stations should not be differenttoo much. The base stations obviously unsatisfied with the above two

points need significant attention.

The Characteristics of Land Mobile Communication


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Environment

Complex radio transmitting environment Radio spread environment is affected by geographic and

geomorphic and artificial environment. A large amount ofreceiving signals is the overlay signals of refraction, reflection andscattering.

Mobility of MS MS is always on the state of movements. Although the MS doesnt

move, the environment around it keeps change continuously suchas the movements of people and vehicles, Wind blowing leavesand son on, This make continuous changes of spread routebetween base stations and MS. Besides the above reasons, theMS movement direction to base station and the speed all cancause the changes of signal electric level.

Random variation of signal electric level Signal electric level changes with the time and location which can

be described by probability distributions of random process. Serious signal scrambling

The scrambling of disorder and scattering, blocking,intermodulation and adjacent channel between differentequipments is a little more large. It should be controlled strictly.

The Characteristics of Land Mobile Communication


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Environment

Waveguide effects exists in the urban environment

The transmitting Forms of Radio Wave


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B

A

d

D

LOS NLOS

RFD

Pass-through of buildings and cars

Multipath transmitting

The transmitting Forms of Radio Wave

The main transmitting forms of radio wave includes direct wave,reflected wave, diffracted wave and scattered wave.

Sight distance and non-sight distance transmitting; Complex

multipath environment . Pass-through losses of buildings and cars

Received Power Attenuation


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Received Power Attenuation

On the condition of multipath transmitting, with the increasing distancebetween the transmitter and receiver, the received power attenuatesmuch more faster than in free space. In general, in the dense urbanareas and indoors, received power is not in inverse proportion to the

square of distance, but about the fourth power of distance. However,in suburbs, received power is in inverse proportion to the square ofdistance.

Reflection

Diffraction

transillumination

Indoor Loss


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Indoor Loss

Material Dielectric constant Material Dielectric constant

Wood -2 Plasterboard 3

Bakelite board 4 Class 410

Marble 12 Cement 46

Floor 530 Water 80

Content


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Content




Problem Locating

WCDMA RF Cases

The Purpose of RF Optimization


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The Purpose of RF Optimization

RF optimization is an important stage of WCDMAradio network optimization. It is the optimization ofRF.

Its purpose is to control the pilot frequency pollutionand soft handover rate with the optimization ofsignal coverage and guarantee that the distributionof radio signals is normal before the next step ofparameter optimization.

Its data analysis is mainly based on drive test data.The problem need to be solved is about coverage

and scrambling. The method of optimization is mainly based on

adjusting base station engineering parameters. All

the aboves are the characterastic of RF optimization.

The Main Contents of RF Optimization Work


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The Main Contents of RF Optimization Work

Single station check before optimization. Thepurpose is to guarantee that every sector of basestation runs normally.

Pilot frequency signal coverage optimization

Pilot frequency pollution optimization. Pilotfrequency pollution can bring a serials of problems

such as the increasing of downlink scrambling, calldrop caused by handover frequently and the reduceof network capacity. These problems need to be

solved by adjusting the engineering parameters. Handover problem optimization.

The Flow of RF Optimization


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The Flow of RF Optimization

RF optimization includespreparation of test, singlestation check, datacollection, data analysis,problem analysis and planestablishment and plancarrying out. The steps ofdata collection, problemanalysis and plan

establishment and plancarrying out, should beexecuted repeatedlyaccording to the

optimization target andcurrent optimization statusuntill the situation of thenetwork reaches theoptimization target.

Single Station Check


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Single Station Check

Confirm site information

Longitude and latitude, configuration, height above sealevel and peripheral environments;

Confirm antenna feeder information Antenna type, azimuth, down-tile angle and height and so

on;

Check antenna feeder link

Standing wave ratio, primary set and diversity RSSI check,primary set and diversity lock balance and so on;

Confirm system parameters

List of adjacent areas, overhead channel transmitting power,

SC configuration, switching parameters; Check and test basic functions

Basic call process, soft switching, softer switching;

Check single station coverage

Data Collection


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Data Collection

Collecting data by SCANNER

Collect all the pilot frequency signal coverage data inthe optimization area by SCANNER. The data

includes the total received power of carrier wave (lo),Ec and Ec/lo of pilot frequency and so on.

Collecting data by UE Besides collecting the basic information of the first

level including Rx, Ec, Ec/Io and Tx, collecting data by

UE can also collect the BLER and PDU information ofthe second level and the signal message data of thethird level. The data is richer than those collected bySCANNER.

Parameter Analysis


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y

SCANNER data analysis

SCANNER data analysis is mainly used to analyzethe problems of pilot frequency coverage such as less

coverage, over area coverage and pilot frequencypollution and so on.

UE data analysis Besides the pilot frequency coverage analysis, UE

data analysis is used to analyze the service KPI,

signal flow, radio parameter setting, statistics dataand so on. The means is great rich.

RF Optimization Policy


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p y

Adjust the antenna directional angle

Adjust the antenna down-tilt angle

Adjust the antenna height Adjust the antenna location

Adjust the antenna feeder information

Use characteristic antenna Adjust the accessories such as tower amplification


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The Effects of RF Optimization


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p

The parameter characteristics of antenna determines that the maximumdirectional gain (17dbi) can only be obtained on the direction of main lobe ofdirectional antenna and the gains on the horizontal and vertical directionsoutside the main lobe will reduce. So adjusting the direction angle and down-tiltangle of antenna may affect the downlink signal quality received in differentareas. As well, changing the position and hung height of antenna can affect

downlink signal quality. After changing the downlink coverage quality of certain stations, the

corresponding Ec/lo receiving signals will change. Because the judgment ofnetwork handover is based on Ec/lo receiving signal, the handover area ofnetwork will change on the condition of keeping the handover algorithmbasically unchanging.

Pilot frequency usually occurs when there are many signals with closely Ec/loin a certain area, or there is a certain strong signal out of the planning. Sochanging downlink coverage quality by adjusting engineering parameters ofantenna can remove some of the pilot frequency pollution areas.

Adjusting feeder line connection can avoid the condition of abnormally

transmitting and receiving signal of base station caused by feeder lineconnection reversed. At the same time, standing-wave ratio being normal isalso the pre-condition that the base station runs normally.

Increasing tower amplification can increase the valid coverage distance ofbase station. Generally the reason of the limitation of base station uplink is thatthe uplink transmitting power of WCDMA mobile phone is only 21dBm. Tower

amplification can cancel out the loss of uplink signal on feeder line.

Feeder Line Problems


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To check and really test whether the coverage signals in the areas are thesame as planning according to the result of single station test. To analyzewhether there is the condition of error feeder line connection.

The reason of the problem: Generally for the three cells under a directional station, we use two feeder lines

for each antenna of the cells. One of them is used for receiving andtransmitting. The other is only used for receiving. On the station, the feeder lineconnects to jumper and than connects to the NODE B cabinet. During theworks of engineering team, this series of connecting may bring mistakes.Perhaps the two feeder lines connecting to one antenna are connected torandom two cells. So the appearance of feeder line connection error is that the

signals transmitted from three cells are from one or two of them. Problem analysis: During the optimization, we should check station one by one whether the test

coverage signals of every area is the same as planning. The normal situation isthat the strongest signal on the direction near each antenna is the cellcorresponding to the antenna. If strong signal of the other cells appears in this

cell, we should check whether there is feeder line connection errors firstly. Solving method: We should contact the equipment engineer to go up to the station to check the

feeder line connection if we find feeder line connection error.

Problems of Antenna and Environment


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According to the result of the whole network test, we can check whether thereis the situation of signal of over area coverage or the coverage being less thanexpectation obviously among the real test coverage signal in every area. Forthe cell with problems, we should go up to the station to check whether thedirection angle, down-tilt angle and hung height of the antenna are the sameas design. In additional, we can check whether there is any block on the main

lobe direction of the antenna, whether the pole direction is vertical and so on. The reason of the problem: The main reason of wrong direction angle, down-tilt angle different with the

design is that the engineer team doesnt work completely according to theblueprint and planning data. On the other hand, the precision of equipments

such as the compass can also bring some errors. Generally the direction angleof 5 degrees can be accepted. But if the error of down-tilt is beyond 2 degrees,it will bring more obvious effects to coverage.

Sometimes we find that there is obvious block on the direction of main lobe ofthe antenna when optimizing. This result will bring some blind coverage areas.Properly adjusting the direction angle of the antenna can improve this kind of

situation. Sometimes the real down-tilt angle of antenna may be different withthe design because the pole of the antenna is not vertical with ground or themeasurement is not exact.

Problems of Antenna and Environment


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Problem analysis: A simple method of measuring down-tilt angle is to use the paper with scale stuck on the

antenna applied by the manufacturer. With this method, we need stick the correct paperwith scale on the antenna, and then adjust it exactly according to the scale. Another moreexact method measuring down-tilt is to use gradienter to measure it. Both of the premisesof these two methods are that the pole and support of the antenna are installed vertical toground. Only this can guarantee that the down-tilt angle measured from antenna is justthe down-tilt angle to ground. For some antennas installed on the iron tower or installed onthe wall through pole, we must check whether the pole is vertical with the ground.

Solving method: The above problems can be found through special measurement tools. If we find those

kinds of problems, we should notify the engineering team to modify them. For the situationthat there is block or pole cannot be vertical with ground, we can improve it by adjusting

the direction angle and down-tilt angle. The reduction of down-tilt angle may easily causeover area coverage and scrambling increasing. Increasing down-tilt angle may easilycause blind coverage area. At the same time, too large down-tilt angle may cause wavebeam distortion and bring new scrambling. So adjusting the down-tilt properly is veryimportant for guaranteeing performance of the whole network.

Generally, adjusting direction angle can help to solve the problem of weak coverage overlarge areas. And adjusting down-tilt angle can help to solve the problem of coverage

distance. Engineering team constructs according to the flow strictly is the premise ofquality assurance. The check of equipment engineer after installation is also veryimportant.

Coverage Problem Analysis and Optimization

Coverage Test


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Coverage Test

Collecting data through scanner and UE is usuallyused for coverage test. The sensitivity and samplingrate of scanner is better than that of UE. It can

obtain more sampling point; Scanner can only testEc and Ec/Io index. However UE can test Ec, Ec/Ioand transmitting power of BLER and UE. It has

complete signal messages. The test indexes of UEare more completely. Scanner is used for collectingthe completely coverage information of radionetwork, completing pilot frequency analysis test,spectrum analysis test and so on.

Coverage Problem Analysis and Optimization Pilot

Frequency Strength Analysis


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Pilot frequency strength analysis

Weak

coverage area

Frequency Strength Analysis

Generally, the strongestRSCP received by scanner inthe coverage area need to beabove -95dBm. Entering

WiNOM RNA, analyzingBest Ec in PNscanner andBest Ec/Io in PNscannerbased on scanner can obtainthe distribution of weak

coverage area. Ec of pilotfrequency can be seen on bothscanner and UE. Duringcoverage analysis, we suggestto use the data of Scanner.

This can avoid incompletelypilot frequency informationmeasured by UE because ofthe neighbor cell missing.


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Coverage Problem Analysis and Optimization

Comparison between UE and Scanner Coverage


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Comparison of coverage between UE and Scanner

p g

If the neighbor cellconfiguration is missing or theparameter of soft handover,cell selection and reselectionis not reasonable, the BestSC in the active set when UEis on the mode of connectionand the resident cell on idlemode will be different with thedominant cell of scanner.


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Common Coverage Problem and Its Solutions

Coverage Standard


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Coverage Standard

Network coverage is the key element of WCDMAnetwork quality. The situation of network coveragereflects in not only Ec received by UE, but also Ec/lo

and Tx power. The coverage is valid only when all ofthem meet the pre-defined conditions.

Standard for normal

urban area

Standard for Suburb

Ec/Io>= 12db

Ec/Io>= 15db

Ec>= 85dBm

Ec>= 95dBm

Tx power


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g

Phenomenon: Ec and Ec/Io are all lower.

Possible reasons: Cell coverage borders orengineering parameters of cell are set illogically.

The antenna is blocked. The setting of powerparameter is illogically.

Solutions: Check the parameter settings of base

station, determine whether the antenna is blockedon the spot, adjust the engineering parameters ofantenna (direction angle, down-tilt angle, hung

height of antenna , installation of antenna and soon), use high gain antenna, use coverageenhancement technique, add new base stations.


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Without Dominant Cell


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Phenomenon: In a certain area, the cell signals arealmost the same. This causes the dominant cellchanging frequently. Ec is normal, but Ec/lo is very

low. This may cause frequently handover in theseareas.

Possible reasons: Loop distribution of base station,

coverage border Solutions: Strengthen the coverage of a strong

signal cell and weaken the coverage of the other

poor signal cell by adjusting the engineeringparameters of antenna such as down-tilt angle,direction angle and so on. Adding base stations or

adjust the distribution of base stations.


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Optimization Cases


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Coverage

area is

different

with

planning,

over

coverage

Before optimization

After optimization

The coverage areas of cell (353) of

Xinya Hotel is different with planningcoverage areas. The antenna feeder

between cell (353) and cell (337) is

wrong. Its signal has over area

coverage which brings scrambling to

cell (267).

Analysis and Optimization of Pilot Frequency

Pollution Definition of Pilot Frequency Pollution


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Definition of pilot frequency pollution:

Pilot frequency pollution forms when the differencebetween a certain pilot frequency signal and the best

cell signal is within a certain range (generally equal to5dB) and the signal is not in the active set. The typicalappearance is that Ec is high, but Ec/lo is very low.

Two key points: difference, not in the active set

Pilot Frequency Pollution


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On the stage of optimization after new site launched, the overlaps of sectorsare usually a little large and the signals are complex because of the light loadof network. This may cause pilot frequency pollution.

Forms of pilot frequency pollution: Over area coverage of high station. If the space link loss of antenna pilot

frequency signal from far and high station to the test point is the same as thatfrom near and low station to the same test point, it has much possibility tocause several pilot frequency pollution areas with nearby Ec/lo at the test point.Otherwise, because of the existence of high station, the down-tilt angle of theantenna is usually a little large. This can make the antenna beam distortion.The coverage wave form is pressed to the direction of minor lobe. This cancause the pilot frequency pollution of minor lobe coverage area.

Loop distribution of base stations. Because of the loop distribution of basestation, on the central of the loop, several nearby pilot frequency signals can bereceived, and pilot frequency Ec/lo of them is closed.

Signal distortion cause by canyon effect, strong reflector and so on. Because ofthe transmitting characteristics nearby the downlink 2000M frequency ofWCDMA, the reflecting power of downlink signal is stronger. Far pilot frequency

signal transmits along the street looks like a tube. This may forms scrambling tothe coverage areas of other cells. Otherwise, some buildings and walls alsohas strong reflection to signals which can bring pollution to nearby pilotfrequency.


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Analysis and Optimization of Pilot Frequency

Pollution - Solutions


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The core principle of solving pilot frequency is to form mainpilot frequency in the areas with pilot frequency pollution. Theusual optimization method is shown below:

Adjust the engineering parameter of antenna such asdirection angle, down-tilt angle, antenna hung height andinstallation position.

Adjust the pilot frequency transmitting power of the cell

such as increasing the power of a certain cell anddecreasing the others.

Adjust the distribution of base stations. Lead strong mainsignal into the cell by adding new signal source in the area

with pilot frequency pollution. If necessary, the parameters of cell selection and

reselection can be adjusted in order to improve callconnection rate.

Handover Problem


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Cause of problem :

The cause of handover is usually the length of handover regionand the strong and weak changing of signals in the handoverregion. If the handover region is too small and the car speed istoo fast, UE may have not enough time to complete thehandover flow. That will cause handover failure. However, toolarge handover region may occupy too many system resources.Besides, if signals in handover region change frequently whichis not the universal changing as one signal turning weak andthe other turning strong, handover will happen frequently. Thatwill bring ping-pong effect which occupies too many system

resources on the one hand and increases the probability of calldrop on the other hand.

Handover Problem


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Analysis of problem: The key method solving handover problem is to control the position and length

of handover areas and to guarantee the signal intensity in the handover areacan change smoothly as far as possible. The position and length of handoverarea should be considered during planning and be adjusted according to thereal environment during optimization. We should determine the length of

handover area by the average time for completing one handover and thegeneral speed of a motor vehicle in the area. We should try to avoid to choosethe corner to be the position of handover area because the block of cornerbrings additional transmitting loss, causes the rapid attenuation of signal, andthen shortens the length of handover area. If we cannot avoid this kind ofsituation, we also should guarantee to remain enough allowance of signal

intensity for the corner to deal with the loss. We also should not take thecrossroad, heavy traffic area and VIP service area as the handover area. Please refer to chapter 5.3 to see the relationship between the antenna down-

tilt angle and coverage distance. Solutions:

We can change the position and the signal distribution of handover area byadjusting the direction angle and down-tilt angle of the antenna. If the handoverarea is too small, we can decrease the down-tilt angle or adjust antennadirection properly. If the signals change frequently in the handover area, wecan consider to adjust down-tilt angle and direction angle properly to guaranteethe signal strength of single cell to change smoothly.

Analysis and Optimization of HandoverNeighbor

Cell Optimization


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Use the data of scanner and the neighbor cell configuration data ofRNC to analyze. We can import the data of scanner and neighbor cellconfiguration data into WiNOM RNA. The neighbor analysis tool ofWiNOM RNA can generate neighbor cell configuration reportautomatically. The report includes one-way neighbor configuration and

the neighbor cell configuration need to be added. Analyze the UE test data generated by WiNOM RNT. Firstly by

comparing the active set Ec/lo distribution figure of UE and scanner,we can find the areas in which the Ec/lo of UE is much worse but the

Ec/lo of scanner is very nice or the areas in which call drop occurswhen handover. And then we combine the signals and the dataplayback of these areas with the above data to determine the missedconfiguration of neighbor cells.

If we have no data of scanner, we can firstly determine all the cell

scrambling of active set and monitoring set tested by mobile phonebefore call drop. And then we can determine the cell scrambling of thenew cell in witch the mobile phone stay in after call drop. We cancompare the above two kinds of data. If the latter cell is not included inthe former cells, that cell may be a missing neighbor cell.

Analysis and Optimization of HandoverNeighbor

Cell Optimization Case


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Call drop

Monitor set 267&283 arestrong

Analysis and Optimization of Handover Analysis

and Optimization of Soft Handover Rate


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The definition of DT soft handover rate: DT softhandover rate can be defined as the rate betweenthe number of sample points with the number of

cells bigger than 1 in the active set and the totalnumber of sample points. It can be obtained by theanalyzingActive pilot path countof UE test data

through WiNOM RNA.

Analysis and Optimization of HandoverSoft

Handover Principle and Method


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The soft handover optimization on the stage of RF optimizationis used to control the handover position and the length ofhandover area.

Try to avoid to put the position of handover on the corner orcrossroad.

Can be solved by adjusting handover parameters if necessary.

If the soft handover rate is too high, we should decrease or

change soft handover areas by increasing down-tilt angle,adjusting direction angle, lower the height of antenna, lowerpilot frequency power and so on which are the method ofdecreasing the coverage area range. The premise of adjusting

is not to bring new blind coverage areas and pilot frequencypollution.


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Content


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WCDMA RF Optimization Data Analysis andProblem Locating

WCDMA RF Cases

Case of Feeder Line Connection Error


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Test the new launched site. Collect signals by SCANNER orHigh Pass. Compare the coverage areas of test signals withthe designed coverage areas of cells in the base station. Thecoverage area scrambling of the 2nd sector and 3rd sector

under the base station, BERIBI, is different with planning.



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Problem location: Under the left and below base station, Beribi_Industri, the

coverage towards the direction of southeast should be therange of the 2nd cell (112). But during the test, the scramblingof the area is the signal of the 3rd cell (120). And in thecoverage area of the 3rd cell, the scrambling is the signal ofthe 2nd cell (112). So we can take the conclusion that thefeeder lines of the two cells are connected on the contrarycompletely. After entering the base station to check, thecondition is the same as analysis before.

Solutions:

Notify equipment engineer to ask engineering team to checkthe antenna feeder and modify the connection.



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Execute the test when the base station, SeameoVotech, was launched. Use SCANNER or testmobile phone to collect signals. After analysis using

RNA, we found the condition that the signals of twosectors (183, 191) in the same base stationappeared in the same sheet of track points.



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Problem location: This phenomenon explained that the signals of two

cells were transmitted from the same antenna. All

the antennas of cell (183) transmitted the signals ofcell (183) and cell (191). So we made the conclusionthat the connections of the antenna feeder lines of

cell (183) and cell (191) were wrong. Perhaps thecell (183) connected two transmit-receive antennasand cell (191) connected two receive. This causedthat there were the signals of two cells in one sector.

Case of Adjusting Antenna Down-tilt Angle


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The signal of the 2nd cell (206) in GADONG PROP could be received in therooms on the 5th floor of CENTREPOINT hotel near the station of Brunei,CETTREPOINT. The strength of the signal was similar with that of cells inCENTREPOINT. So there was frequent handover between cells in the roomwhich affected the performance a lot. The rooms of the hotel located on the

back direction of the cell (206). The lower floor couldnt receive the signal ofcell (206). In front of cell (206), there was a building with about 10 floors.

Case of Adjusting Antenna Down-tilt Angle


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Problem location: Because the lower floor couldnt receive the signal of cell (206),

and the point was on the back direction of the antenna, wedoubted that it was caused by the reflection of the building infront of cell (206). Through querying the base stationinformation table, we knew the planning mechanical down-tiltangle of the antenna was 1 degree and the electronic down-tiltangle was 2 degrees. During the scene check, we found thatthe wall hanging the antenna pole of cell (206) tilt inwardly for 2

degrees. So the mechanical tilted angle was up-tilt for 1 degreein fact. That caused the reflection seriously . We increased thedown-tilt angle to 3 degrees which is 2 degrees in fact.

Solutions: Increase the mechanical down-tilt angle to 3 degrees which is

2 degrees in fact. Effect evaluation: The scrambling of cell (206) in the higher floor of the hotel had

been cleaned up.

Case of Call Completion Rate Optimization


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Problem description: During the test of call completion rate of the Shenzhen test network,

we called failed for ten times at the corner of the Taolin Road andNanhai Road in the area of Shenzhen University. If we didnt consider

the effect of coverage, the call completion rate should be above 99%.This corner is the softer handover area of cell (356) and cell (324).

Problem analysis:

Ec distribution figure of best scrambling code generated by Scanner:

Case of Call Completion Rate Optimization

Th fi h th t th h d b t th ll (324) i th f d f


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The figure shows that the handover area between the cell (324) in the area of dorm ofShenzhen University and the cell (356) in the area of Shenzhen University is too small.The distance is only 10 meters. The system of ZTE doesnt support signal handovercurrently. Mobile phone can start handover only after completing RB assignment. However,during the 4 to 5 seconds from the mobile phone starting call to RB assignment completing,the mobile phone will stay in the original cell. Take the test as an example, although thespeed of test car is kept at 30km/h, it will run 40 meters. On most conditions, the strongest

cell signal within 40 meters can support the mobile phone completing various servicesalthough it becomes worse. But on the corner, the strongest cell signal will become worserapidly (see the following figure). So if the mobile phone begins to set up call near thehandover area, it will stay in the cell (356) for 5 seconds. The receiving signal will becomeworse rapidly. So call drop will occur before completing RB assignment because thequality of signal is too bad. On this condition, the signal of cell (356) changes too fast andthe handover area is too small is key reason to affect the call completion rate. Increasing

the signal strength of cell (356) in handover area and extending the handover can makethe call completing the signal process smoothly and then handover to the new cell. Thesignal of cell (356) has the characteristics of becoming worse rapidly in the handover area.This causes the quality of signal for call flow of reselection in cell (356) becoming worse.The flow can not be completed the call failed. This usually appears with radiobearer setupcomplete.

Solutions:

Decrease the antenna direction angle of cell (356) for 10 degrees to improve the signalstrength of cell (356) in handover area.


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wpo-16 principles and methods of rf optimization-58

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