03-wcdma radio network rf optimization technical guide(v1.0)

7/30/2019 03-WCDMA Radio Network RF Optimization Technical Guide(v1.0)

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Network Planning & Optimization

Department under ZTE Mobile Division

(Technical Guide)

WCDMA Radio Network RF

Optimization

Technical Guide

Version: V1.0

Released on 21.02.06 Implemented on 21.02.06

Released by Network Planning & Optimization Department

under ZTE Mobile Division


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For Internal Use Only

Contents

1 Scope............................................................................................................................................................ 1

2 Standards Quoted in this Guide................................................................................................................ 2

3 RF Optimization......................................................................................................................................... 3

3.1 RF Optimization Flow Chart............................................................................................................. 3

3.2 Single Site Spot Check...................................................................................................................... 3

3.2.1 Checking the Antenna Feeder System.................................................................................... 4

3.2.2 Checking Foreground and Background Configuration .......................................................... 4

3.2.3 Checking Single Site Functions ............................................................................................. 5

3.3 Coverage Test.................................................................................................................................... 5

3.4 Data Analysis and Troubleshooting................................................................................................... 6

3.4.1 Feeder Problem ...................................................................................................................... 6

3.4.2 Antenna and Environment Problems...................................................................................... 7

3.4.3 Pilot Pollution Problem.......................................................................................................... 8

3.4.4 Handoff Problem.................................................................................................................. 11

3.4.5 Other RF Problems............................................................................................................... 12

3.5 Making an Antenna Feeder Adjustment Scheme ............................................................................ 12

3.5.1 RF Optimization Methods.................................................................................................... 13

3.5.2 RF Optimization Influence................................................................................................... 13

3.5.3 Influence of RF Optimization on KPI .................................................................................. 14

3.6 Implementing Antenna Adjustment................................................................................................. 14

3.7 Optimization Verification................................................................................................................ 15

4 Optimization Cases .................................................................................................................................. 16

4.1 Inverse Feeder Connection Case 1 .................................................................................................. 16

4.2 Inverse Feeder Connection Case 2 .................................................................................................. 17

4.3 Antenna Downtilt Adjustment Case................................................................................................ 19

4.4 Calling Probability Optimization Case ........................................................................................... 20

Confidential and Proprietary Information of ZTE CORPORATION. 1


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5 WCDMA Antenna .................................................................................................................................... 25

5.1 Basic Antenna Knowledge.............................................................................................................. 25

5.2 Antenna Classification and Application .......................................................................................... 28

5.2.1 Omni Antenna ...................................................................................................................... 28

5.2.2 Directional Antenna ............................................................................................................. 28

5.2.3 Mechanical Antenna............................................................................................................. 29

5.2.4 Electrical Antenna ................................................................................................................ 29

5.3 Antenna Downtilt Adjustment Influence......................................................................................... 30

5.3.1 Antenna Downtilt Modes ..................................................................................................... 30

5.3.2 Relationship between CDMA Antenna Downtilt and Cell Coverage Radius ...................... 31

5.4 Introduction to Common Directional Antennas .............................................................................. 34

5.5 Summary......................................................................................................................................... 35

6 Electromagnetic Wave Propagation Theory .......................................................................................... 36

6.1 Electromagnetic Wave Space Propagation Model........................................................................... 36

6.2 Earth Reflection Model ................................................................................................................... 38

6.3 Energy Loss Through Medium........................................................................................................ 38

6.3.1 Introduction.......................................................................................................................... 38

6.3.2 Reflection and Transmittance Loss ...................................................................................... 38

6.4 Diffraction loss................................................................................................................................ 42

6.4.1 Fresnel Zone and Knife-Edge Diffraction Model ................................................................ 42

6.4.2 Multiple Knife-Edge Diffraction.......................................................................................... 43

6.5 Scattering Loss................................................................................................................................ 43

7 Annexes ..................................................................................................................................................... 44

7.1 Annex 1 WCDMA Radio Network Test Work Guide...................................................................... 44

7.2 Annex 2 WCDMA Radio Network Evaluation Work Guide........................................................... 44

7.3 Annex 3 WCDMA Radio Network Optimization KPI Analysis Guide........................................... 44

7.4 Annex 4 WCDMA Radio Network Optimization Work Guide ....................................................... 44

7.5 Annex 5 WCDMA Radio Parameter Configuration Guide ............................................................. 44



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7.6 Annex 6 WCDMA Radio Parameter Optimization Guide .............................................................. 44

7.7 Annex 7 WCDMA Radio Network Optimization Signaling Analysis Guide.................................. 44

8 Indexes ...................................................................................................................................................... 45



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1 Scope

This guide defines the workflow and precautions that the Network Planning &

Optimization Department under ZTE Mobile Division shall follow when performing

WCDMA radio network RF optimization. It can serve as standardized operations for

the site engineers to perform an RF optimization project.

This guide is applicable to both domestic and overseas WCDMA radio network

optimization projects performed by the Network Planning & Optimization Department.



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2 Standards Quoted in this Guide

This guide is written in strict compliance with the standard document specifications

defined in the TL9000 quality management system, and quotes the following enterprise

standards. For any enterprise standard indicating no year code, the latest version

released on the Internet should be used as the valid one.

Q/ZX 40.1010 Quality Manual

Q/ZX 75.1610 Engineering Specification

Q/ZX 75.1620 Engineering Quality Monitoring & Management Methods

Q/ZX 75.1851.1 International After-sales Service Work Procedure

International Market Project Management


Engineering Commissioning


After-sales Service Documentation Archiving

Management

Q/ZX D OX.OOX-200X Network Optimization Guide for the Network Planning &

Optimization Department



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3 RF Optimization

3.1 RF Opt imization Flow Chart

Figure 3-1 RF optimization flow chart

3.2 Single Site Spot Check

Purpose: To make sure the equipment is working normally, so as to prevent equipmentfailure from affecting overall network performance.

Person in charge: Equipment engineer

Input: Site Commissioning Report

Output: Single Site Spot Check Report

Work details:

Before network optimization is started, all sites should have been checked and should

be assuredly able to work normally. In an actual project, however, it is usual that some



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base stations fail to work normally due to lax or absent single site check, affecting

startup of subsequent optimization work. To ensure orderly performance of network

optimization, spot check is necessary for single sites. Single site spot check needs to

implement the following tasks:

1) Select sites for spot check according to project size and network situation.

Usually about 20% of the sites should be included. Moreover, the selected sites

must involve all site types, including sites in each area.

2) Put forth items that need to be checked according to the contents indicated in the

Site Commissioning Report. Make a spot check plan.

3) Accompany customer service engineers to check the selected sites as planned,

and put forth information that needs correction for any site with problems.

4) When all the selected sites are spot-checked, and over 20% of them are found

with problems, it is necessary to recheck other sites not involved in this spot

check. If no problem is found, skip the recheck.

5) Complete a Single Site Spot Check Reportbased on the single site check results

for the purpose of troubleshooting.

3.2.1 Checking the Antenna Feeder System

1) Ascend the rooftop to check the site longitude and latitude, antenna mount

height, antenna downtilt, and directional angle for consistence with the planned

values. For the towers that are not mountable, complete the check on the ground.

2) Turn on the power amplifier of one sector, and turn off the others. If the power

amplifier gives no alarm, measure the pilot signal strength beneath this sector.

Typically the Ec value is about 55dBm.

3) This step is performed simultaneously with Step 2 to check whether the cell

scrambling code is consistent with the planned value.

3.2.2 Checking Foreground and Background Configuration

1) Check whether the neighbor list configuration is consistent with the planned

value.

2) In the case of idling, the RTWP value (namely the uplink RSSI) of each cell on

Node B background should range from -107 ~ -104dBm.

3) Check the version number of each type of software in use.



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4) Set parameters in the search window. There are settings in both LMT and

OMC-R, and the setting in LMT is valid.

3.2.3 Checking Single Site Functions

Open all cells, and perform service tests for CS and PS domains respectively. Conduct

softer handoff test, and conduct soft handoff test again for the areas involved in soft

handoff.

3.3 Coverage Test

Purpose: To know the coverage range of each site in the network, and the

corresponding areas that can provide different rates of services

Person in charge: Test engineer

Input: None

Output: Drive test data

Work details:

The RF optimization phase needs no detailed special service test, and what should be

done is to have knowledge of the network coverage by the following means.

1) Cell cluster coverage test

2) Whole network coverage test

This coverage test uses Scanner plus test mobile phone to collect data simultaneously.

The test data collected by the mobile phone is helpful to judge the uplink coverage, and

know the change of signal in each section of the road if call hold is performed

simultaneously.

Different rates of services require different signal conditions. The table below lists the

pilot signal strength and quality reference values of border coverage corresponding to

common services.

Table 3-1 Reference values of border coverage corresponding to common services

Service Border reference value

CS12.2K voice -105dBm/-13dB

CS64K video -98dBm/-10dB

PS64K -100dBm/-11dB

PS128K -95dBm/-10dB

PS384K -85dBm/-8dB



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The data in this table is provided only for general reference, and the object of RF

optimization performed after site commissioning is usually an idle network, where the

service border will shrink with increasing number of users.

3.4 Data Analysis and Troubleshooting

Purpose: To analyze the test data to judge the network coverage level and locate the

areas with problems for troubleshooting.

Person in charge: Optimization engineer

Input: Drive test data

Output: Pre-optimization Test Report

Work details:

Network coverage judgment:

1) Cell cluster coverage test. Know the distribution of each cell in the context of

mutual signal inhibition in a cell cluster, and, in combination with site spacing

and network planning results, identify the cells that do not meet coverage

requirement.

2) Whole network coverage test. Know the distribution of signal throughout the

whole network, the same as 1.

Mastery of antenna knowledge is one of the prerequisites of RF optimization. For

information about antenna, please refer to chapter 5.

The problems common to RF optimization will be detailed in the following sections.

3.4.1 Feeder Problem

According to the result of single site coverage test, check whether the coverage signal

of each actual test area is consistent with that of the planned coverage cells. Analyze

whether there is incorrect feeder connection.

Cause:

Typically a directional site has three cells, each of which uses two feeders (one for both

receiving and transmitting and the other for only receiving) as its antenna. On the base

station side, the feeders are further connected to NODE B cabinet through a jumper.

This series of connections is prone to error during construction of the engineering team.

The two feeders connected to one antenna are likely to be connected to any one or two



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cells, so the symptom of incorrect feeder connection is that a signal transmitted by one

antenna of three cells could come from any one or two of the three cells in this site.

Analysis:

During optimization, it is necessary to check whether each coverage signal actually

measured in an area of each base station is consistent with the planned coverage cell.

Normally, the strongest signal in this direction near each antenna should be the cell

corresponding to this antenna. In the case of occurrence of a strong signal of other cells,

first check whether there is incorrect feeder connection.

Solution:

If incorrect feeder connection is found, contact an equipment engineer concerned to

ascend the site to check feeder connection.

3.4.2 Antenna and Environment Problems

According to the result of the whole network coverage test, check whether the

coverage signal of each actual test area contains any overshooting signal or any signal

with coverage obviously smaller than expected. For any problem area, ascend the site

to check whether the antenna directional angle, downtilt, and mount height are

consistent with the design. A further check can be conducted on whether there is any

obstruction in the main lobe direction, and whether the pole is vertical.

Cause:

The main cause of inconsistence of actual antenna directional angle and downtilt with

the design is that the engineering team fails to follow completely the workflow,

drawings, and planned data for construction. In addition, the precision of some devices

in use, such as a compass, may also cause some error. Generally, a five-degree

directional angle error is acceptable, while a downtilt error of over two degrees may

have an obvious effect on the coverage.

During optimization, sometimes obvious obstructions may be found in the main lobe

direction. Such a result may cause a certain coverage hole, but this problem can be

improved by proper adjustment of the antenna directional angle. The actual antenna

downtilt may sometimes deviate from the design. The possible cause is that the antenna

pole is not vertical to the ground or the measurement is not accurate.

Analysis:

An easy way to measure the downtilt is using the antenna-attached scale label provided

by the antenna manufacturer. This method needs first to paste a correct scale label to



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the antenna and then make fine adjustment against the scale. A more accurate method

to measure the downtilt is to use a gradienter directly. The prerequisite of these two

methods is that the antenna pole or support is installed vertical to the ground, ensuring

that the measured antenna downtilt is actually its downtilt relative to the ground.Therefore, for those antennas that are mounted on a tower or whose poles are mounted

on walls, it is a must to measure whether their poles are vertical to the ground.

Solution:

The problems above can be found by measurement with special tools. Upon finding

such a problem, notify the engineering team to correct it. If there is an obstruction or a

pole cannot be vertical to the ground, improvement is possible by adjusting the

directional angle and downtilt. Decrease of downtilt is liable to cause overshooting and

increase interference, while increase of downtilt tends to cause a coverage hole.

Moreover, excessive downtilt may also cause beam distortion, resulting in new

interference. Therefore, proper adjustment is very important to guarantee the whole

network performance.

Generally speaking, directional angle adjustment is helpful to solve the problem of

large-area weak coverage, while downtilt adjustment can solve a problem of coverage

distance. It is a prerequisite of quality assurance that the engineering team follows the

flow strictly for construction. Equipment engineers verification after installation is

also very important.

3.4.3 Pilot Pollution Problem

In a new site during optimization phase after commissioning, the network load is light,

so there are large overlapped areas between sectors and the signal is complex. This may

result in pilot pollution.

Formation of pilot pollution: Pilot pollution usually has three causes:

1)

High site overshooting. If the space link loss caused when an antenna pilot signalfrom a remote high site reaches a test point is the same as the link loss caused

when a pilot signal from a near low site reaches the same test point, it is probable

that several pilot pollution areas with close Ec/Io values are caused at this test

point. Furthermore, presence of a high site may usually cause a large antenna

downtilt, resulting in antenna beam distortion. And the coverage waveform may

squeeze against the side lobe, resulting in pilot pollution in the side lobe

coverage area.



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Base station

Base station coverage area

Neighbor base station

R1

R2

Figure 3-2 Schematic diagram of pilot pollution due to high site overshooting

2) Ring layout of base stations. As the base stations are arranged into a ring, the

ring center can receive a few pilot signals from around, and the pilot Ec/Io

values are close.

Figure 3-3 Schematic diagram of pilot pollution due to ring layout of base stations

3) Signal distortion caused by street effect and strong reflectors. Due to the

propagation characteristics near the WCDMA downlink 2000M frequency, thedownlink signal has strong reflection, and propagation of remote pilot signal

along tubular streets is likely to cause interference to coverage areas of other

cells. Moreover, strong reflection of signal by some buildings and walls may

also cause pollution to nearby pilot coverage.

Influence of pilot pollution: Pilot pollution has a negative effect on network

performance. The symptom and analysis are detailed as follows:

1) Access is difficult, and call failure probability is increased: Before UE originates

a call, it has been performing cell reselection. Due to existence of several pilots



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with close Ec/Io and reselection lagging, UE will not immediately reselect the

cell with the best Ec/Io. Especially when UE is moving rapidly, it usually

originates a call in a cell with poor pilot Ec/Io. When a call starts, UE first

initiates random uplink access, and meanwhile waits for an ACK message. Ifsuccessful, UE will initiate RRC signaling exchange with UTRAN. In this

process, UE will not perform handoff as there is no interaction of measurement

control or measurement report. RRC interaction must be completed before RNC

can deliver a measurement control message and wait for a measurement report

submitted from UE. That is to say, during the above-described process until UE

submits a measurement report, UE performs operations with UTRAN within the

cell where the call is originated. Once UE starts moving, the signal of this cell

may go bad, and it is possible to prevent receiving and transmitting of

subsequent signaling and result in call failure.

2) The call failure probability of high-speed data service is increased obviously.

Generally speaking, high-speed data services need higher pilot Ec/Io and more

stable radio environment, but in the case of pilot pollution, it is hard to find a

pilot signal in the steadily strongest position, and this is extremely unfavorable

to cal access of high-speed services.

3) Handoff failure. When mobile stations move in this area, as there are many

strong pilot signals and mutual change occurs rapidly, frequent handoff occurs to

mobile stations as a result. In such a state of soft handoff, the mobile stations

need to communicate with multiple base stations simultaneously. Although

diversity gain can improve the call quality of this mobile station, according to

ZTE research, handoff gain is negative at the instant of handoff, that is, not only

there is no gain, but the possibility of handoff failure is increased.

4) Capacity loss: frequent handoff may decrease system capacity, especially the

downlink capacity being limited, and one UE communicates with multiple cells,

increasing downlink load on the base station, but decreasing system capacity.

Solution: The key of pilot pollution optimization is to form a main pilot. In the RF

optimization phase, the adjustment means available include:

1) First consider adjustment of the antenna directional angle and downtilt.

2) Adjust pilot signal power of some cells.

3) Adjust antenna mount height

4) Adjust antenna position



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5) Use electronic adjustable antennas

6) Add sources

3.4.4 Handoff Problem

Cause:

Handoff problems generally lie in length of the handoff area and strength change of

each signal in the handoff area. If the handoff area is too small, there may be no

sufficient time for completing handoff process in the case of driving too fast, and

handoff may fail as a result. A too large handoff area is likely to occupy excessive

system resources. Moreover, too frequent change (not a signal gradually weakening

and another gradually strengthening) of strength of each signal in the handoff area may

cause frequent handoff and ping-pong effect. This may occupy excessive system

resources, and increase probability of call drop.

Analysis:

For handoff problems, the key is to control the handoff area position and length, and

ensure the strength of signals involved in the handoff in the handoff area can change

smoothly. The handoff area position and length should be taken into preliminary

consideration in planning. During optimization, make adjustment based on actual

environment, and determine the handoff area length in consideration of the averagetime needed for one time of handoff and the usual driving speed in this area. Try to

keep the handoff area away from a corner, as the obstruction of a corner itself may

cause extra propagation loss and quick signal attenuation, thus reducing the handoff

area length. If impossible to keep away, try to ensure the signal strength around the

corner has sufficient margin to offset the loss at the corner. Also try to keep the handoff

area away from any crossroad, high-traffic area, and VIP service area.

For the relationship between antenna downtilt and coverage distance, please refer to

section 5.3.

Solution:

Change the handoff area position and signal distribution by adjusting the antenna

directional angle and downtilt. If the handoff area is too small, reduce the downtilt or

adjust the antenna direction properly. If the signals in the handoff area change too

frequently, consider adjusting the downtilt and directional angle to ensure signal

strength in individual cells changes smoothly.



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3.4.5 Other RF Problems

During RF optimization, it also should be noted to make sure the base station

transmitting power works normally from the base station RF end to the antenna side.

Standing wave ratio is an important index. Before optimization, it is necessary to make

sure the standing wave ratio in each cell of the base station is smaller than 1.3 on the

WCDMA operating frequency. This work should be implemented by an equipment

engineer with a standing wave ratio tester.

Meanwhile, the power output from each power amplifier port should be kept within a

stable range.

3.5 Making an Antenna Feeder Adjustment Scheme

Purpose: To provide a feasible adjustment scheme based on the analysis result of

coverage test data in combination with actual sites and ambient environment.

Person in charge: Optimization engineer

Input: Pre-optimization Test Report, and data analysis result

Output: Antenna Feeder Adjustment Scheme

Work details:

1) Identify any area of poor coverage according to the analysis result of test data;

2) Try to make a uniform adjustment scheme based on the cell cluster;

3) Ascend the site to observe actual radio environment;

4) Provide an adjustment scheme;

5) Review the adjustment scheme;



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3.5.1 RF Optimization Methods

z Adjust the antenna directional angle

z Adjust the antenna downtilt

z Adjust antenna mount height

z Adjust antenna position

z Adjust antenna feeder connection

z Use characteristic antenna

z Adjust accessories, such as a tower amplifier

3.5.2 RF Optimization Influence

RF optimization means to change the coverage distribution of downlink WCDMA

signal by adjusting each engineering parameter of antenna, and thereby change the

distribution of effective coverage areas, network handoff areas, and pilot pollution

areas. Another purpose is to increase the coverage distance, and reduce the interference

between users. Adding tower amplifiers is another important approach to RF

optimization.

z Improve downlink coverage quality

z Change handoff areas

z Change pilot pollution areas

z Improve base station work performance

z Change uplink coverage areas

Currently, the antenna model used most in each network is an Andrew directional

antenna Andrew umwd_06516_2d.

Antenna parameter characteristics determine the fact that the maximum directional

gain 17dbi can only be obtained in the main lobe direction of a directional antenna, and

the gain may decrease in the horizontal and vertical directions other than the main lobe,

so adjusting the antenna directional angle and downtilt will affect the quality of

downlink signals received in various areas. Similarly, adjusting the antenna position

and mount height will also affect the quality of downlink signals.

When the downlink coverage quality of some sites changes, the Ec/Io of corresponding

received signals will change as well. As network handoff is judged according to the



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size of Ec/Io of received signals, the network handoff area will also change even if the

handoff algorithm is not changed practically.

Pilot pollution typically means there are many signals with close Ec/Io values or there

are strong signals alien to the planning design, so changing downlink coverage quality

by adjusting engineering parameters of antenna can also eliminate some pilot pollution

areas.

Feeder connection adjustment can solve the problem of abnormal receiving and

transmitting of base station signals resulting from inverse feeder connection, and

normal standing wave ratio is another prerequisite for a base station to work normally.

Adding power amplifiers can increase effective coverage distance of a base station.

Generally, the reason for base station uplink coverage limitation is that the uplink

transmitting power of a WCDMA mobile phone is only 21dBm. A tower amplifier can

offset the loss of uplink signals along the feeder.

3.5.3 Influence of RF Optimization on KPI

RF optimization has an obvious effect on the following KPIs. As each cell has different

engineering parameters and environments, their signal coverage states are also different.

Therefore, the strongest cells and handoff areas in different places of a network have

different signal coverage quality, so RF optimization influences not only coverage, but

also several indexes directly related to strength (quality) of received signals.

1) Coverage ratio

2) Call success ratio

3) Call drop ratio

4) Handoff success ratio

For details about KPIs, please refer to appendix 3.

3.6 Implementing Antenna Adjustment

Purpose: To execute the antenna adjustment scheme

Person in charge: Equipment engineer

Input: Antenna Adjustment Scheme

Output: Antenna Adjustment Record

Work details:



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1) Contact the engineering team to determine the number of antennas that need

adjustment and the operation date;

2) Contact the operators person in charge to confirm necessary procedures and

acquire an equipment room key;

3) Monitor and verify adjusted parameters and engineering quality;

4) Necessary auxiliary background operations;

3.7 Optimization Verification

Purpose: To test and verify the result of optimization adjustment

Person in charge: Test engineer and optimization engineer

Input: Drive test data, andAntenna Adjustment Record

Output: XX Service Area RF Optimization Report

Work details:

1) Test engineers collect post-optimization whole network drive test data. Note that

the test conditions must be the same as before optimization;

2) Optimization engineers analyze the test data and evaluate optimization result;

3) If the whole network coverage fails to meet the requirement, return to the steps

in section 3.4 to test and analyze specially the areas still with problems, and

provide an analysis report and adjustment scheme;

4) If the coverage requirement is met, this time of RF optimization is completed;

5) Output anXX Service Area RF Optimization Report.



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4 Optimization Cases

4.1 Inverse Feeder Connection Case 1

Keyword: scrambling code, feeder

Symptom:

This is a test of a new site. SCANNER or High Pass was used to collect signals. When

the actual coverage areas of the tested signals were compared with the designed

coverage area of each cell in the base station, the scrambling code of the coverage areas

of the second and third sectors in the BERIBI site was found inconsistent with theplanned value, as shown in the following diagram:

Figure 4-1 Illustration (incorrect) of inverse feeder connection case 1

Troubleshooting:

In the Beribi_Industri site at the lower left corner, the southeast direction should have

been covered by the second cell 112, but according to the test, the scrambling code of

this area was signal 120 of the third cell, while the third cell was covered by signal 112

of the second cell. Therefore, it could be concluded that the antenna feeders of these

two cells were connected inversely. This was proved by the field test in the base

station.



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Solution:

Notify an equipment engineer to contact the engineering team to check and correct the

feeders.

Result evaluation:

Figure 4-2 Illustration (correct) of inverse feeder connection case 1

The actual coverage areas of signals 112 and 120 match the designed antenna direction.

4.2 Inverse Feeder Connection Case 2

Keyword: scrambling code, track, feeder

Symptom:

This was a commissioning test of the Seameo Votech base station during

commissioning. SCANNER or a test mobile phone was used to collect signals. The

analysis with RNA found there was a stretch of signals with track points appearing in

the two sectors (183 and 191) of one base station, as shown in the following diagram:



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Figure 4-3 Illustration (incorrect) of inverse feeder connection case 2

Troubleshooting:

This indicated the signals of these two cells were transmitted simultaneously through

one antenna. The antennas in cell 183 transmitted signals of both 183 and 191

simultaneously. Thereby it could be judged that the antenna feeders of cells 183 and

191 were not connected correctly. It was possible that two antennas for both receiving

and transmitting were connected to cell 183, while two antennas for only receiving

were connected to cell 191. As a result, the signals from these two cells were receivedsimultaneously in one sector.

Solution:

Notify an equipment engineer to contact the engineering team to check the problem

and correct the feeders.

Result evaluation:



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Figure 4-4 Illustration (correct) of inverse feeder connection case 2

The actual coverage areas of 183 and 191 match the designed antenna direction.

4.3 Antenna Downt ilt Adjustment Case

Keyword: downtilt, reflection

Symptom:

In the rooms on the fifth floor of CENTREPOINT Hotel near the CENTREPOINT site

in Brunei was received the signal of the second cell 206 in the GADONG PROP site

nearby. The signal strength was close to that of the two cells in the CENTREPOINT

site. As a result, the frequent handoff of multi-cell signals occurring in the rooms

affected the network performance. The rooms of this hotel were located on the back of

cell 206.There was no 206 signal on the lower floors, and there was a building of about

ten stories in the front direction of cell 206.



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Figure 4-5 Distribution of the sites near CENTREPOINT Hotel

Troubleshooting:

As there was no signal 206 received on the lower floors of the hotel, which was located

in the rear direction of the antenna, it should be suspected first that this was caused by

reflection from buildings in the front direction of 206.According to the base station

information table, the antenna was planned to have a one-degree mechanical downtilt,

and a two-degree electrical downtilt. However, the field check found the wall where the

206 antenna pole was mounted itself tilted inwards by two degrees, so the mechanical

tilt actually tilted upwards by one degree. That was why the reflection was so severe.

The mechanical downtilt was increased by three degrees, so the actual downtilt was

two degrees.

Solution:

Increase the mechanical downtilt by three degrees to resume an actual downtilt of two

degrees.

Result evaluation:

The interference of cell 206 to higher floors of this hotel was cleared.

4.4 Calling Probability Optimization Case

Keyword: Call success ratio, handoff area

Symptom:

In the calling probability test for Shenzhen test network, ten times of failure occurred

to Taolin Road and the turning of Nanhai Avenue in the Shenzhen University area. The



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call success ratio should be over 99% if the influence of coverage on call failure is not

considered. This turning was the softer handoff area of cells 356 and 324.

Analysis:

The distribution of the best scrambling code Ec measured by Scanner is illustrated as

follows:

The turnover area is too small

Figure 4-6 Schematic diagram of the strongest cells on Taolin Road and at the turning of

Nanhai Avenue

This diagram shows that the handoff area between cell 324 of Shenzhen University

dormitories and cell 356 of Shenzhen University is too small, because it is only about

10 meters long. ZTEs systems do not support signaling handoff at present, so a mobile

phone can start handoff only when RB assignment is completed. The mobile phone will

remain in the original cell for four or five seconds, which are needed for completion of

RB assignment after the mobile phone starts a call. Taking this test for example, even if

the test vehicle is driven at the constant speed of 30 km/hour, it could cover over 40

meters within five seconds. In most cases, the signal in the strongest cell can still

support a mobile phone to complete various services within 40 meters even if it

deteriorates in the process. However, in a special case, such as around a turning, the



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signal in the strongest cell will deteriorate quickly, as shown in the following diagram.

If a mobile phone starts a call near the handoff area, it will remain in cell 356 for five

seconds, when the received signal deteriorates quickly, so the call will be dropped due

to poor signal quality before the RB setup is completed. In this case, the key problemaffecting calling probability is that the overquick change of signal in cell 356 makes the

handoff area undersized. Extending the handoff area by increasing the signal strength

of cell 356 in the handoff area should be able to make the call proceed smoothly in this

area to complete the signaling process and then hand off to a new cell.

Signal 356 declines abruptly in the handoff

area, and probability is high that the call

process cannot be completed. This may

affect calling probability.

Figure 4-7 Signal change trend in the handoff area

As shown in the diagram above, the coverage of signal 356 is characterized by

occurrence of abrupt drop in the handoff area. As a result, the signal quality of

reselection during the call process in cell 356 declines, the process is not completed,

and the call fails. The usual symptom is that the base station cannot receive the

message radiobearer setup complete.

Solution:

Decrease the antenna directional angle of cell 356 by ten degrees to improve the signal

strength of cell 356 in the handoff area.



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356 coverage signal

The handoff area is lengthened obviously

after antenna adjustment.

324 coverage signal

Figure 4-8 Schematic diagram of the strongest area after adjustment

This diagram shows that the handoff area between cells 356 and 324 becomes longer

after the antenna is adjusted.



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The attenuation of 356slows down obviously.

Figure 4-9 Signal change trend in the handoff area after adjustment

This diagram shows that the signal attenuation of cell 356 in the handoff area slows

down obviously, enabling the call signaling of reselection in cell 356 to be completed.

Result evaluation:

During the actual call test in this handoff area, the mobile call success ratio was

100% (there were more than 20 calls.)



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5 WCDMA Antenna

5.1 Basic Antenna Knowledge

The main parameters of antenna performance include pattern, gain, input impedance,

standing wave ratio, polarization, lobe width, and front-to-back ratio.

1. Antenna input impedance

Antenna input impedance is the ratio of input voltage to input current at the

antenna feeding end. The optimal result of antenna-feeder connection is that the

antenna input impedance is pure resistance and equal to characteristicimpedance of the feeder. In this case, there is neither power reflection on the

feeder terminal nor standing wave on the feeder, and the antenna input

impedance changes mildly with frequency. Antenna matching is to eliminate the

reactive component from the antenna input impedance, making the reactive

component as close to the characteristics impedance of the feeder as possible.

Matching quality is usually measured with four parameters: reflection

coefficient, traveling wave coefficient, standing wave ratio, and echo loss.

Between these four parameters there are fixed value relationships, so use which

one is a mere issue of habit. In routine maintenance, the frequently used ones are

standing wave ratio and echo loss. Typically, the input impedance of mobile

communication antenna is 50.

2. Standing wave ratio

Standing wave ratio is reciprocal of traveling wave coefficient, and ranges from

1 to infinity. When standing wave ratio is 1, it means perfect match; when it is

infinity, it means total reflection, that is, complete mismatch. In a mobile

communications system, standing wave ratio is usually required to be smaller

than 1.5, but in practice, VSWR (Voltage Standing Wave Ratio) should be

smaller than 1.2.Overlarge standing wave ratio may decrease base station

coverage and increase intrasystem interference, thus affecting base station

service performance.

3. Echo loss

Echo loss is reciprocal of the absolute value of reflection coefficient and is

represented with a decibel value. Echo loss ranges from 0dB to infinity. The

smaller the echo loss, the worse the match. The larger the echo loss, the better



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the match. 0 means total reflection, while infinity means perfect match. In a

mobile communications system, echo loss is usually required to be larger than

14dB.

4. Antenna polarization

Antenna polarization refers to the electric intensity direction resulting from

antenna radiation. When the electric intensity direction is vertical to the ground,

this electric wave is called vertically polarized wave; when the electric intensity

direction is parallel to the ground, this electric wave is called horizontally

polarized wave. Due to electric wave characteristics, the signal propagated in the

horizontal polarization mode may produce polarized current on the earth surface

when it travels close to the ground. This polarized current is affected by earth

impedance to generate thermal energy, resulting in quick attenuation of electric

signal. By contrast, the vertical polarization mode rarely produces polarized

current, thus avoiding immense attenuation of energy and ensuring effective

propagation of signals.

Therefore, in a mobile communications system, propagation is usually

implemented in the vertical polarization mode. In addition, a kind of

dual-polarized antenna is introduced recently with development of new

technologies. In terms of design conception, it is classified into two modes:

vertical & horizontal polarization and 45 polarization. The latter is generally

superior to the former in performance, so it is adopted currently in most cases.A

dual-polarized antenna combines two antennas that are in cross-polar directions

of +45 and -45 and work simultaneously in the receiving and transmitting

duplex mode, which can reduce the number of antennas needed in each cell.

Moreover, cross polarization in 45 directions can effectively ensure good

diversity reception.(Its polarized diversity gain is about 5dB, which is 2dB

higher than a single-polarized antenna.)

5. Antenna gain

Antenna gain is used to measure ability of an antenna to receive and transmit

signals in a specific direction. It is one of the most important parameters for

selecting a base station antenna.

Generally speaking, gain is improved mainly by reducing the lobe width of

radiation on the vertical plane, but maintaining omni radiation on the horizontal

plane. Antenna gain is extremely important for operation of a mobile

communications system, because it determines signal level of the cell edge.



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Increasing gain can enlarge the coverage range of a network in a specific

direction, or increase gain margin in a specific range. Any cellular system is a

two-way process, and increasing antenna gain can decrease the gain budget

margin of a two-way system. In addition, the parameters that represent antennagain are dBd and dBi. dBi means the gain relative to an isotropic antenna, with

uniform radiation in all directions; dBd means the gain relative to a symmetric

array antenna. The relationship between these two parameters is: dBi = dBd +

2.15. Under the same condition, the higher the gain, the further the electric wave

can travel. Typically, the antenna gain for a GSM directional base station is

18dBi, and 11dBi for an omni base station.

6. Antenna lobe width

Lobe width is another important parameter common to a directional antenna. It

refers to the width of an enclosed angle formed by the locations 3dB lower than

the peak in the antenna pattern (antenna pattern is an index for measuring ability

of an antenna to receiving and transmitting signals in each direction, and

typically represents the relationship between power strength and enclosed angle

in a graphic way.)

Vertical lobe width of an antenna is usually related to the coverage radius in the

direction corresponding to this antenna. Therefore, cell coverage quality can be

improved by adjusting the antenna verticality (pitch angle) within a certain

range. This is also a method frequently used in network optimization. This

method involves two aspects: horizontal lobe width and vertical lobe width. The

half-power angle on the horizontal plane (H-Plane Half Power beamwidth): (45,

65, 90, etc.) defines the beamwidth of the horizontal plane of an antenna. The

larger the angle, the better the coverage at the sector edge. However, increasing

antenna downtilt is more likely to cause beam distortion and overshooting. The

smaller the angle, the worse the coverage at the sector edge. Increasing antenna

tilt can improve coverage at the sector edge in terms of mobility, and relatively,

is less likely to cause overshooting across other cells.In an urban center, a base

station should adopt an antenna with a small H-Plane Half Power beamwidth as

the site spacing is small and the antenna tilt is large. For a suburb, an antenna

with a large H-Plane Half Power beamwidth should be adopted. The half-power

angle on the vertical plane (V-Plane Half Power beamwidth): (48, 33, 15, and

8) defines the beamwidth of the vertical plane of an antenna. The smaller the

half-power angle on the vertical plane, the quicker the signals attenuate when



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deviated from the main bean direction, the easier to control the coverage range

precisely by adjusting antenna tilt.

7. Front-to-back ratio

This parameter indicates how well the antenna can suppress the back lobe. If an

antenna with a low front-to-back ratio is selected, its back lobe is likely to cause

overshooting, resulting in disorderly handoff relationships and call drop. This

ratio usually ranges from 25dB to 30dB. An antenna with a front-to-back ratio of

30dB should be preferred.

5.2 Antenna Classification and Appl ication

According to its directivity, a mobile communication antenna can be classified into twotypes: directional mobile antenna and omni mobile antenna. For a WCDMA system, an

antenna can be subcategorized into mechanical antenna and electric antenna. The

following will analyze and compare these types of antennas in terms of influence of

change of mobile antenna downtilt on antenna pattern and radio networks.

5.2.1 Omni Antenna

An omni antenna can produce uniform radiation around 360 degrees in the horizontal

pattern, namely what is referred to as non-directivity, and also can produce a beam with

a certain width in the vertical pattern. Generally, the smaller the lobe width, the larger

the gain. In a mobile communications system, an omni antenna is typically applied to a

large-area site in a suburban county, for its coverage range is large.

5.2.2 Directional Antenna

A directional antenna can produce radiation within a certain angle in the horizontal

pattern, namely what is referred to as directivity, and also can produce a beam with a

certain width in the vertical pattern. Like an omni antenna, the smaller the lobe width,

the larger the gain. In a mobile communications system, a directional antenna is

typically applied to a small-area site in an urban, for its coverage range is small, but

with high user density.

According to networking requirement, build different types of base stations, for which

different types of antennas can be selected as needed. The basis of selection is the

technical parameters described above. For example, an omni station uses an omni

antenna with practically the same gain in all horizontal directions, while a directional

station uses a directional antenna whose horizontal gain changes obviously. Typically,



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an antenna with horizontal beamwidth (B) of 65 is selected in an urban, while an

antenna with horizontal beamwidth (B) of 65, 90 or 120 can be selected in a suburb

(depending on site type configuration and local geographic environment). In a rural, it

is the most economic to select an omni antenna that can provide large-scale coverage.

5.2.3 Mechanical Antenna

A mechanical antenna refers to a mobile antenna whose downtilt is adjusted

mechanically.

When a mechanical antenna is mounted vertical to the ground, it is necessary to change

the antenna tilt by adjusting the position of the rear support if network optimization is

required. During the adjustment, the coverage distance of its main lobe direction is

changed obviously, but the maximums of its vertical component and horizontal

component remain unchanged, so the antenna patter is likely to be distorted.

The following facts have been proved in practice: the optimal downtilt of a mechanical

antenna ranges from 1 to 5; when its downtilt changes between 5 and 10, the

antenna pattern is distorted a bit but changes not much; when its downtilt changes

between 10 and 15, the antenna pattern changes much; when it tilts downwards by

15 or more, the antenna pattern changes a lot, from the pre-tilt pear shape to the

post-tilt spindle shape, and although the coverage distance of the main lobe direction is

shortened obviously, the antenna pattern does not completely fall into the sectors of this

base station, and the neighbor base station sectors can also receive the signals of this

base station, thus resulting in severe intrasystem interference.

Moreover, to adjust downtilt of a mechanical antenna in routine maintenance, first

power off the whole base station. Monitoring cannot be performed when adjusting the

antenna tilt. It is troublesome to adjust downtilt of a mechanical antenna, because the

service personnel usually need to clime up to the antenna location for adjustment. The

downtilt of a mechanical antenna is a theoretical value calculated with simulation and

analysis software in a computer, and may deviate to some extent from the actual

optimal downtilt. The tilt of a mechanical antenna is adjusted by step of 1, and the

third-order intermodulation index is -120dBc.

5.2.4 Electrical Antenna

An electrical antenna refers to a mobile antenna whose downtilt is adjusted electrically.

The electrical downtilt principle is to tilt vertical antenna pattern by changing the phase

of antenna elements in the same array, changing the maximums of vertical component

and horizontal component, and changing the field strength of synthetic components. As



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the field strength in all directions of an antenna increases or decreases simultaneously,

this can ensure the antenna pattern varies not much after the tilt is changed, and the

coverage distance of the main lobe direction is shortened. At time same time, the

coverage area of the whole antenna pattern is reduced in the sectors of the service cell,but without causing interference. The following facts have been proved in practice:

when electrical antenna downtilt changes between 1and 5, the antenna pattern is

basically the same as that of a mechanical antenna; when its downtilt changes between

5and 10, the antenna pattern is improved a bit in comparison with that of a

mechanical antenna; when its downtilt changes between 10and 15, the antenna

pattern changes much in comparison with that of a mechanical antenna; when its

downtilt reaches 15, the antenna pattern is different obviously from that of a

mechanical antenna, but does not change much in shape, the coverage distance of the

main lobe direction is shortened obviously, and the whole antenna pattern falls into the

sectors of this base station. Increasing downtilt can reduce sector coverage area, but

will not cause interference. Such an antenna pattern is desirable, so an electrical

antenna can be used to reduce call loss and interference.

Moreover, an electrical antenna allows the system, without closedown, to adjust the

downtilt in the vertical pattern and monitor adjustment result in a real-time manner.

The tilt can be adjusted by a finer step (0.1), so fine adjustment is possible for the

network. The three-order intermodulation index of an electrical antenna is -150dBc,

with a difference of 30dBc from that of a mechanical antenna, and this is helpful to

eliminate adjacent channel interference and spurious interference.

5.3 Antenna Downtil t Adjustment Influence

5.3.1 Antenna Downtil t Modes

Antenna downtilt modes include: mechanical downtilt, fixed electrical downtilt,

tunable electrical downtilt, and remote-controlled tunable electrical downtilt.

Mechanical downtilt means to just tilt an antenna during setup. It is inexpensive and

often applied when a downtilt angle is less than 10. When the antenna downtilt angle

is increased further, dents appear in the front of coverage, and both sides are pressed

flat. That is, the antenna pattern is distorted, resulting in insufficient coverage in the

front of this antenna and aggravated interference to base stations on both sides. Another

defect of mechanical downtilt is warping of the rear lobe, which may cause

interference to adjacent sectors, resulting in call drop of high-level users in nearby

areas.



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No downtilt Electrical downtilt Mechanical downtilt

Figure 5-1 Comparison between base station antenna downtilt modes

The electrical downtilt principle is to tilt vertical antenna pattern by changing the phase

of antenna elements in the same array, changing the maximums of vertical component

and horizontal component, and changing the field strength of synthetic components. As

the field strength in all directions of an antenna increases or decreases simultaneously,

this can ensure the antenna pattern varies not much after the tilt is changed, and the

coverage distance of the main lobe direction is shortened. At the same time, the

coverage area of the whole antenna pattern is reduced in the sectors of the service cell,

but without causing interference.

Although electrical downtilt is relatively expensive, its downtilt angle has a wider

range (larger than 10), its antenna pattern has no obvious distortion, and the rear lobe

is also tilted simultaneously, without causing interference to near-end high-rise users.

Antenna downtilt modes can be selected according to customer and coverage

requirements. You may select a fixed electrical downtilt, tunable electrical downtilt, or

remote-controlled tunable electrical downtilt antenna. A fixed electrical downtilt

antenna with small angles plus a mechanical downtilt scheme for the commissioning

site are advantageous in performance and cost, while a remote-controlled electricaldowntilt antenna is effective to solve the coverage and interference problems in a dense

urban.

5.3.2 Relationship between CDMA Antenna Downti lt and Cell Coverage Radius

Antenna downtilt: when an antenna is mounted vertically, its transmitting direction is

horizontal. In view of co-channel interference and time dispersion, an antenna of a

small-area cellular network usually has a downtilt angle. Antenna downtilt modes

include mechanical downtilt and electrical downtilt.



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An overlarge mechanical downtilt angle may result in severe distortion of the antenna

pattern, thus bringing about many uncertain factors to network coverage and

interference, so antenna downtilt angle is recommended not larger than 25 degrees, and

mechanical downtilt angle should not exceed 15 degrees.

As shown by the vertical antenna pattern curve, when the main lobe maximum drops to

3dB, namely approaching to the part of antenna pattern where gain attenuation between

rays changes most, the co-channel interference to the affected cells is minimized.

For simple and effective implementation of the this part where gain attenuation

changes most, it is of obvious significance in physics and geometry to use half-power

angle rays of the main lobe to analyze the change areas of antenna downtilt angles.

This handling process matches the current design requirement, and makes analysis and

calculation operable, for half-power lobe width is one of the required electrical

performance indexes.

5.3.2.1 Relationsh ip between Antenna Downtilt and Cell Coverage Radius in a High TrafficArea

H

L

Figure 5-2 Schematic diagram of antenna downtilt in a dense urban and urban

A high traffic area here refers to an urban, especially a dense urban, where base stations

are dense and likely to interfere with each other. To enable most energy to radiate

within the coverage area and reduce interference to neighbor cells, it is necessary to

align the half power points on the main lobe with the coverage area edge when setting

an initial downtilt angle, as shown in Figure 5-2. The calculation formula of a downtilt

angle is as follows:



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_e2

)L

H(arctg += (1)

In this formula, is an initial mechanical downtilt angle;

is effective height of this site, namely the difference between

antenna mount height and average height of ambient coverage areas;

H

is the distance from the antenna of this site to the edge that needs

to be covered in this sector;

L

is vertical lobe width;

_e is an electrical downtilt angle.

5.3.2.2 Relationship between Antenna Downtilt and Cell Coverage Radius in a Low Traffic

Area

H

L

Figure 5-3 Schematic diagram of antenna downtilt in a suburb and rural

For a low traffic area, like a suburb, rural, road, and sea, to extend coverage as far as

possible, it is workable to reduce the initial downtilt angle and align the maximum gain

point of the main lobe with the coverage area edge, as shown in Figure 5-3. The

calculation formula of a downtilt angle is as follows:

_e)L

H(arctg =

(2)



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5.4 Introduct ion to Common Directional Antennas

During RF optimization, it is an important method to adjust antenna downtilt angle and

horizon angle. Such adjustment aims to change antenna transmitting gain in some

directions and thus change reception gain in some areas on the basis that the same

environment road loss remains unchanged. Therefore, before such adjustment, it is very

important to learn about the transmitting gain in the horizontal and vertical directions

of antenna transmission.

In a radio communications system, the transmitting end is the antenna side of a base

station. A base station in a city usually uses a three-sector directional antenna. The gain

of a directional antenna determines it can obtain more power in the main lobe direction

than an omni antenna. Horizontal beamwidth and vertical beamwidth respectively

define the horizontal and vertical angles that are 3dB weaker than the main lobe.

At present, ZTE mainly uses a directional antenna Andrew umwd_06516_2d in

WCDMA networks throughout China.

Table 5-1 Andrew umwd_06516_2d antenna performance parameters

Name Value

Central frequency 2110.0 MHZ

Antenna gain 17.0dBi

Electrical downtilt 2 degrees

Front-to-back ratio 30dB

Horizontal 3dB width 61.5 degrees

Vertical 3dB width 6 degrees

Polarization Vertical polarization

Figure 5-4 Horizontal antenna pattern



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Figure 5-5 Vertical antenna pattern

The gain in the main lobe direction is 17dBi, and from these two antenna patterns wecan find out the difference between antenna transmitting gain in each horizontal and

vertical direction and the main lobe direction. For example, when the difference

between a direction and the antenna transmitting direction is 90 degrees, from the

horizontal pattern we can find out the value corresponding to 90 degrees is 22, so the

antenna transmitting gain in this direction is 17 - 22 = -5dBi.

5.5 Summary

z When adjusting antenna directional angle, we should consider the horizontal

half-power angle of this antenna. An undersized enclosed angle between two

sector directions and a large overlapped coverage area are likely to cause

frequent handoff and can hardly ensure proper coverage around base stations.

An overlarge enclosed angle is likely to degrade signal quality of the handoff

area. Normally, a recommended enclosed angle between directional angles

ranges from 90 degrees to 140 degrees.

z When adjusting antenna downtilt angle, we should consider the vertical

half-power angle of this antenna. Regarding adjustment of mechanical downtilt

angle, 1-5 degrees adjustment will not cause much beam distortion and is a

common range; 6-9 degrees adjustment is recommended for high sites or dense

sites; 10-12 degrees adjustment is usually applied to high sites in an urban.

z The antenna mount height is optimal when the antenna is 5-10 meters higher

than the average height of the buildings around the base station. Besides, the

antenna mount height in neighboring base stations should not differ much. Any

base station that does not satisfy these two points is liable to have coverage

problems, and needs special attention.



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6 Electromagnetic Wave PropagationTheory

When electromagnetic wave is traveling in space, the occurring power loss is mainly

the path loss resulting from space spread of electromagnetic wave, and the reflection

(transmittance), diffraction, scattering losses resulting from obstruction on the

transmission route. The factors that may influence these losses include distance

between a transmitter and a receiver, height of these two devices, material, height and

relative positions of obstructions, and electromagnetic wave frequency. These factors

describe field strength change in a long distance between a transmitter and a receiver,

which is also called a large-sized propagation model. On the other hand, the

propagation model that describes quick fluctuation of reception field strength in a short

distance or short time is called a small-sized attenuation model. Multipath transmission

is a major factor that may influence a small-sized attenuation model. As this chapter

describes only space transmission characteristics, and will not consider multipath

transmission. The following will provide a detailed analysis of various losses of a

large-sized propagation model under different conditions.

6.1 Electromagnetic Wave Space Propagation Model

Regarding electromagnetic wave space transmission, the simplest case is free space

propagation. The free space propagation model is used to predict the reception signal

field strength when a line of sight path without any obstruction exists between a

receiver and a transmitter. In this model, the reception power satisfies formula 1.1.

2)4

)(()(d

GGPP RTTR

=

(1.1)

Therefore, path loss can be obtained from formula 1.1.

= c/f

PL = Gr + Gt + 22 + 20 log (R/) = Gr + Gt + 22 + 20 log (Rf/c)

As indicated in these formulas, when electromagnetic wave is propagating in free space,

the reception power is in inverse proportion to the square of propagation distance and

frequency. However, this free space model has a small effective range. When line of



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sight electromagnetic wave exists between a transmitter and a receiver, this model is

similar to an actual transmission model.

Obviously in a radio communications system, a base station will cover a complex area

populated with a large number of users. There is no line-of-sight electromagnetic wave

between most UE and NODE B. Line of sight propagation is subject to obstruction by

various buildings, trees, hills, and vehicles. Then a lot of non-line-of-sight

electromagnetic waves are generated from reflection, refraction, and diffraction by

these obstructions. This is how well-known multipath transmission comes.

Reflection

Diffraction

Transmittance

During multipath transmission, reception power attenuation is much faster than that

during free space propagation with increase of the distance between a transmitter and a

receiver. Generally speaking, in a dense urban or a room, reception power is in

inverse proportion no longer to square of the distance, but approximately to the

fourth power of the distance. In a suburb, it is in inverse proportion to the third

power of the distance.



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6.2 Earth Reflection Model

Among mobile radio channels, a single line of sight path between a base station and a

mobile station is rarely a unique route for propagation. Therefore, only a free space

model cannot reflect accurately the actual situation. Then a dual-line earth reflection

model based on geometric optics can be applied in more cases. An earth reflection

model takes into consideration the earth reflection path between a transmitter and a

receiver, so it can be used accurately within a range of several kilometers. This model

supposes that, during electromagnetic wave transmission, apart from a line of sight

path, there is only one earth reflection path.

Pr = PtGtGrht2hr

2/d

4

This model provides a simple indication that space path loss is in inverse proportion to

the fourth power of this path in a city, and when the distance is large:

d > 20 hthr/, and reception power is irrelevant with frequency. It is noteworthy that in

a WCDMA system, wavelength is about 15cm, coverage distance does not exceed

1.5km, and antenna height is 30m+ and 1m+ respectively, so this condition is not

completely met.

6.3 Energy Loss Through Medium

6.3.1 Introduction

The transmission path of electromagnetic wave between a transmitter and a receiver is

very complex. In addition to path propagation, there are reflection, transmittance,

diffraction, and scattering resulting from influence by various environments.

Electromagnetic wave is reflected, together with transmittance, when encountering an

object that is much longer than its wavelength, such as ground, buildings, and wall

surface.

Diffraction occurs when a radio path between a receiver and a transmitter is obstructed

by established edge, such as hilltop and building top.

Scattering occurs when the wave transmission media contain objects that are smaller

than the wavelength and there are a great number of obstructions in a unit volume, such

as leaves and street nameplates.

6.3.2 Reflection and Transmittance Loss

When electromagnetic wave passes by a medium, some part is reflected. According to

the energy conversation law, the sum of the energy of reflected wave and transmittance



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wave should be equal to the energy of incident wave. Moreover, when electromagnetic

wave passes through a medium, energy loss occurs due to dissipation resulting from

polarization.

To calculate reflected and transmitted energy, it is necessary to calculate reflection and

transmittance coefficient of field strength or power. This coefficient depends on

medium characteristics, and is defined as electric permittivity r. Usually the insulation

constant of an ideal dielectric (without loss) should be = 0r.If energy loss occurs

during transmittance, the insulation constant takes the form of a complex, in which the

imaginary part represents the energy loss when electrical wave passes through the

medium.

= 0r+ ir

The reflection and transmittance coefficient depends on the entrance angle and

polarization of the incident wave.

Material Electric Permittivity Material Electric Permittivity

Wood -2 Gypsum plank 3

Plywood 4 Glass 4-10

Marble 12 Cement 4-6

Earth 5-30 Water 80

The smaller the electric permittivity, the larger the transmittance power, and the smaller

the reflection power. The larger the electric permittivity, the smaller the transmittance

power, and the larger the reflection power. When the electric permittivity is 3 (in

wetland), only half of energy is transmitted, and the other half is reflected. That is to

say, the smaller the electric permittivity, the closer to line of sight propagation the

electromagnetic wave is. At that time, the multipath influence is small.

Indoors transmittance loss during indoors coverage in a city depends on, to a large

extent, average height, density, material, structure, and wall thickness of buildings, and

base station signal path. As is known, due to underdeveloped economy and poor social

security in China, the buildings in small and medium sized cities, especially their lower

floors, are all equipped with doors and windows with metal burglar-resisting webs,

which make penetration loss reach 20~30dB. And the front stores along streets are

commonly equipped with aluminum alloy doors without a window, so the penetration

loss is also high.



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z Building transmittance loss

Building transmittance loss means the attenuation of electrical wave when

passing through external structures of a building. It is the difference between the

field strength without and within this building.

Building transmittance loss is largely related to building structure, door and

window types and sizes, and floor number. Generally, there is the largest loss on

lower floors of a building. The loss may decrease by about 1.9dB when acceding

to a higher floor.

The following is a group of data specific to the band of 900MHz, with foreign

test results incorporated.

z In an urban of a medium-sized city, ordinary reinforced concrete buildingshave a transmittance loss median of 10dB, with a standard deviation of

7.3dB; the same type of buildings in a suburb have a transmittance loss

median of 5.8dB, with a standard deviation of 8.7dB.

z In an urban of a large city, ordinary reinforced concrete buildings have a

transmittance loss median of 18dB, with a standard deviation of 7.7dB; the

same type of buildings in a suburb have a transmittance loss median of

13.1dB, with a standard deviation of 9.5dB.

z In a suburb of a large city, a building with a metal enclosure or a special

metal framework has a transmittance loss median of 27dB.

As the environment of cities in China is greatly different from that in foreign

countries, the same type of loss is 8-10dB higher in China than in foreign

countries.

Regarding the band of 1800MHz, its wavelength is shorter than that of 900MHz

and stronger in penetration, but with higher transmittance loss. Therefore, a

building adopting 1800MHz actually has higher transmittance loss than

900MHz.The GSM specification 3.30 mentions that buildings in a city generally

have the transmittance loss of 15dB, and 10dB in the rural. The transmittance

loss on 1800MHz is typically 5-10dB higher than that in the same type of areas

on 900MHz.



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z Indoors transmission loss

This diagram shows the loss characteristics in the case that both transmitter and

receiver are located indoors. The loss ranges from 50dB to 80dB when the

spacing is 10M.

For 2.4GHz, path loss (in dB) = 40 + 35 * [LOG (D in meters)]

That is, the indoors transmission loss is about 35dB/10 multiples of thread.

z Body loss

For a handset, the received signal field strength will be 4-7dB or 1-2dB lower

when it is attached to the waist or shoulder of a user than when the antenna is a

few wavelengths away from the body.

Generally body loss is set to 3dB.

z In-vehicle loss

The in-vehicle loss caused by a metal-structured vehicle cannot be ignored.

Especially in an economically developed city, people spend part of their time in

a vehicle.

z Typically in-vehicle loss ranges from 8dB to 10dB.

For a WCDMA system, where the operating frequency is close to 1800MHz and

wavelength differs little, transmittance loss is also close.For those modern

buildings with large glass windows, transmittance loss typically ranges from

7dB to 10dB.



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6.4 Diff raction loss

In a radio communications system, signals may have additional loss when encountering

obstructions during radio propagation. This loss is diffraction loss.

6.4.1 Fresnel Zone and Knife-Edge Diff raction Model

Diffraction loss can be explained by a Fresnel zone. A Fresnel zone refers to a group of

ellipses formed by all the points where the secondary wave path length is n/2 larger

than line of sight path length from a transmitter to a receiver. This group of ellipses

with the transmitter and receiver as focuses form a Fresnel zone. If radius is

represented by rn,

rn = [nd1d2/(d1+d2)]1/2

In a mobile communications system, diffraction loss results from obstruction of the

secondary wave transmitted from a Fresnel zone. Generally speaking, as long as the

first Fresnel zone is not obstructed, the diffraction loss remains the least. When

obstruction is zero, there is loss of 6dB. In fact, as long as 55% of the first Fresnel zone

is not obstructed, obstruction of other Fresnel zones has little effect on diffraction loss.

A diffraction model can be simplified into the following diagram.

Fresnel diffraction parameter v = h [2 (d1+d2)/d1d2]1/2

Diffraction loss Gd (dB) can be calculated from diffraction parameters:

Gd (dB) = 0 v


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The number of Fresnel zones being obstructed (n) can be obtained from this formula: n

= v2/2.

The Fresnel diffraction parameter is in direct proportion to 1/2 power of frequency.

This means diffraction loss increases with frequency.

Then it is known that diffraction loss depends mainly on obstruction height and

position relative to a transmitter and a receiver when electromagnetic wave is

obstructed on the propagation route during space propagation. If the relative height (h)

is smaller than or equal to zero, it means the loss is very small, and it is allowed to

neglect obstruction position (h=0, loss=6dB).On the contrary, the further an obstruction

is away from the center of line of sight path, the smaller the Fresnel zone, namely the

larger the influence on radio links by the obstruction. In this case, it is necessary to

consider the influence of the obstruction position. As a transmitter is normally much

higher than a receiver (outdoors), the diffraction loss of high buildings near a receiver

on the transmission route is larger than that of equally high buildings near a transmitter.

6.4.2 Multip le Knife-Edge Diffraction

If there are multiple obstructions on the propagation path, diffraction loss needs

recalculation.

03-wcdma radio network rf optimization technical guide(v1.0)

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