wcdma rno special guide coverage problem analysis-20050316-a-2.0

WCDMA RNO Special Guide Coverage Problem Analysis Internal open

2005-07-13 All rights reserved , Total36

Document code Product name WCDMA RNP

Target readers Product version 2.0

Edited by WCDMA RNP Document version 1.0

WCDMA RNO Special Guide

Coverage Problem Analysis

(For internal use only)

Drafted by: WCDMA RNP Date: November 21, 20004

Reviewed by: Date:

Reviewed by: Date:

Approved by: Date:

Huawei Technologies Co., Ltd.

All rights reserved



Revision Records

Date Revised version Description Author

2004-11-21 1.00 First draft completed Chen Qi

2005-02-28 1.10 Revision based on review comments Chen Qi



Table of Contents

1 Overview of Coverage Analysis ................................................................................................................ 6

2 Coverage Problems Classifications ............................................................................................................ 6

2.1 Signal Dead Zone .................................................................................................................................. 6

2.2 Coverage Void ...................................................................................................................................... 7

2.3 Cross-cell Coverage .............................................................................................................................. 7

2.4 Pilot Pollution ........................................................................................................................................ 8

2.5 Imbalance of Uplink and Downlink ...................................................................................................... 9

3 Coverage Analysis Flow .......................................................................................................................... 10

3.1 Preparations for related Knowledge .................................................................................................... 10

3.1.1 Planning Scheme .......................................................................................................................... 10

3.1.2 Analysis Tools .............................................................................................................................. 11

3.1.3 Configuration Parameters Adjustment .......................................................................................... 11

3.2 Coverage Data Analysis ...................................................................................................................... 13

3.2.1 Drive Test Data Analysis .............................................................................................................. 13

3.2.2 Traffic Measurement Data Analysis ............................................................................................. 21

3.2.3 Trace Data Analysis ...................................................................................................................... 21

3.2.4 User Complaints Analysis ............................................................................................................ 21

4 Coverage Enhancement Strategies ........................................................................................................... 21

4.1 NodeB Configuration Adjustment....................................................................................................... 21

4.2 Coverage Enhancement Technology ................................................................................................... 26

5 Typical Coverage Problems ..................................................................................................................... 27

5.1 Coverage Void due to Inappropriate Site Planning ............................................................................. 27

5.1.1 Problem Descriptions .................................................................................................................... 27

5.1.2 Analysis ........................................................................................................................................ 28

5.2 Cross-cell Coverage due to Inappropriate Site Selection .................................................................... 29


5.2.2 Analysis ........................................................................................................................................ 30

5.3 Coverage Restricted due to Irrational Antenna Installation ................................................................ 31


5.3.2 Analysis ........................................................................................................................................ 32

5.4 Coverage Restricted due to Antenna Installation Failure .................................................................... 33


5.4.2 Analysis ........................................................................................................................................ 33

6 Concerns at the Network Optimization Phases ........................................................................................ 34

6.1 Single Site Test Phase ......................................................................................................................... 34

6.2 Evaluation Phase before the Optimization .......................................................................................... 34

6.3 RF Optimization Phase........................................................................................................................ 34

6.4 Parameter Optimization Phase ............................................................................................................ 35

6.5 Network Optimization Project Acceptance Phase ............................................................................... 35

7 Summary 35



List of Figures

Figure 1 Pilot strength distribution ............................................................................................. 14

Figure 2 Pilot Ec/Io Best Server distribution.............................................................................. 15

Figure 3 Pilot Ec/Io Best Server distribution.............................................................................. 15

Figure 4 Comparison and analysis between the Scanner coverage and UE coverage ................ 16

Figure 5 Downlink code transmit power PDF of Voice service in the case of 50% load .......... 17

Figure 6 UE soft handover ratio ................................................................................................. 18

Figure 7 Abnormal UL RTWP recorded in the NodeB .............................................................. 19

Figure 8 UE transmit power distribution (micro-cellular) .......................................................... 20

Figure 9 UE transmit power distribution (macro-cellular) ......................................................... 20

Figure 10 Coverage void due to irrational site distribution .......................................................... 28

Figure 11 Coverage prediction of XX pilot .................................................................................. 28

Figure 12 Site distribution ............................................................................................................ 29

Figure 13 Cross-cell coverage before the optimization ................................................................ 30

Figure 14 Cross-cell coverage after the optimization ................................................................... 31

Figure 15 Coverage restriction at the bottom of site without considering the shielding of platform

32

Figure 16 Optimization of antenna design implementation ......................................................... 33

Figure 17 Pilot RSCP coverage before and after the correction of antenna installation of

701640_ElzHse site .................................................................................................................................. 33

List of Figures

Table 1 Huawei serial NodeBs and features (V100R003) ……………………………………21



WCDMA RNO Coverage Problem Analysis Guide

Key words: Signal dead zone, coverage void, cross-cell coverage, pilot pollution, and imbalance of uplink

and downlink

Abstract: This document instructs the network optimization engineers to analyze and solve the pilot

coverage and service coverage problems that are present during the network optimization,

measure the network coverage performance and describes the coverage enhancement strategies.

Acronyms and abbreviations:

Acronyms Full spelling



1 Overview of Coverage Analysis

WCDMA radio network planning and optimization is a systematical project, including

from the site obtaining and antenna device indexes analysis to antenna type selection and

propagation mode research

from the pilot coverage and traffic distribution predication to static emulation and capacity

analysis

from the detailed design of engineering parameter and cell parameter to single site installation

and test

from the test route design and network performance test to system parameter adjustment

optimization and KPI evaluation

and the coverage analysis penetrates the whole process of network construction.

From the perspective of telecom operators, after the network planning and optimization, the service

quality provide by the network is the most concern, and the service coverage range of radio carrier is an

important aspect of service quality.

This document instructs the network optimization engineers to analyze and solve the pilot coverage

and service coverage problems that are present during the network optimization and measure the network

coverage performance. Analyzing and solving the problems found during the coverage verification of

planning result is not involved in the document. For details, see the related documents.

2 Coverage Problems Classifications

2.1 Signal Dead Zone

The signal dead zone refers to the coverage area whose pilot signal is lower than the minimum access

threshold of mobile phone (for example, RSCP threshold is -115dBm, and Ec/Io threshold -18dB), such

as valley, opposite of the sidehill, elevator well, tunnel, underground garage or basement and inside of the

high buildings.

If there are many users in the non-overlapped coverage areas of two neighbor NodeBs or the

non-overlapped coverage area is relatively larger, construct a new NodeB or add the coverage range of

peripheral NodeBs (increase the pilot transmit power and antenna height at the risk of capacity) to ensure

about 0.27R (R is the cell radius) of overlapped coverage depth and the soft handover area and concern the

same-neighbor frequency interference caused because the coverage range increases.

When the dead zone caused in the valley and the opposite of sideill is present, add the NodeB or

adopt the RRU or repeater to compensate effectively the dead zone and extension coverage range in the

coverage areas. In addition, the RF repeater may generate intermodulation interference. Therefore, the

engineering implementation must consider the interference.



When the dead zone caused in the elevator well, tunnel, underground garage or basement, and inside

of high buildings is present, adopt the RRU, repeater, indoor distribution system, leakage cable, or

directional antenna.

2.2 Coverage Void

The coverage void refers to the coverage area whose pilot signal is lower than the minimum

requirement of full-coverage services (such as Voice, VP and PS64K) but higher than the minimum access

threshold of mobile phone. For example, when the traffic distribution is relatively balanced, no RSCP in

some areas can satisfy the minimum requirement for full-coverage service due to the NodeB distribution

imbalance. In addition, all the RSCPs of pilot signal in some areas can satisfy the requirement, but the pilot

channel Ec/Io cannot satisfy the minimum requirement for full-coverage service because of

intra-frequency interference increase. For example, the cell breathing effect generated due to the increase

of the capacity of peripheral cells in the soft handover area results in the decrease of coverage quality in

the soft handover areas, that is, the coverage void.

The coverage void is from the perspective of the mobile phone services, different from the signal

dead zone, where the mobile phone fails to camp on the cell and originates the location update and

registration and the network drop is present.

During the network planning phase, the site distribution should be rational and an appropriate site can

ensure that:

The pilot RSCP strength of network is up to certain level (such as, the dense city: -65dBm and

common city: -80dBm).

The pilot Ec/Io of network under certain load should not be lower than the minimum

requirement for full-coverage service.

Out of the consideration of the restrictions of logistics and device installation, unideal site is

inevitable. When the coverage void is present, construct a new micro-NodeB or repeater to strengthen

the coverage. If the coverage void is not very critical, select the high gain antenna, increase the

antenna mounted height or reduce the mechanism tilt of antenna to optimize the coverage. If the RF

adjustment does not effectively improve pilot Ec/Io coverage, adjust the pilot power (increase the

strongest power and reduce others) to generate the primary cell.

2.3 Cross-cell Coverage

Cross-cell coverage means that the coverage areas of some NodeBs exceed the specified range but

the primary areas without continuously satisfying the requirement of full-coverage service are

generated in the coverage areas of other NodeBs. See two examples:

For the sites excessively higher than mean height of peripheral buildings, the transmission

signal spreads far along with the hills or road and primary coverage is present in the coverage

areas of other NodeBs to generate an “island”. When access the “island” area far away from a



NodeB but served by the NodeB and the cells around the “island” are not set to the adjacent

cells as setting the cell handover parameters, the call drop is present immediately if the mobile

station moves out of the “island”. Even though the adjacent cells are configured, not

immediate handover is easy to result in the call drop because the “island” area is over-small.

For the areas at both sides of V Harbor, if there is no special design for the NodeBs at the

Central and Coast of H Island, the cross-cell coverage is easily present to generate the

interference because two sides of the harbor are too close.

To reduce the cross-cell coverage must avoid the antenna propagation directed to the road or uses

the shield effect of peripheral buildings. Meanwhile, confirm whether the same-frequency interference to

other NodeBs is generated.

If there is a higher site, an effective method of reducing the cross-cell coverage is to change the site

address. Owing to the restrictions of logistics and device installation, an appropriate site around the

original site is unreachable, and the excessive adjustment of mechanism tilt of antenna also distorts the

antenna pattern. If necessary, adjust the pilot power or use the electrical tilt antenna to reduce coverage

range and eliminate the “island” effect.

2.4 Pilot Pollution

The pilot pollution means that too pilots are received in one point but there is no stronger primary

pilot. This document introduces the following method to judge whether the pilot pollution exists:

There are more than three pilots satisfying the condition dBmRSCPCPICH 95_

anddBRSCPCPICHRSCPCPICH thst 5)__( 41

Where, the absolute threshold judgement of pilot RSCP is to differentiate the coverage void and no

primary cell at the target coverage cell edge. Whatever the micro-cellular or macro-cellular coverage area,

if the pilot pollution is present, the interference to the useful signal is generated due to many strong pilots

to increase Io and BLER, reduce Ec/Io and easily form the ping-pong handover resulting in call drop.

The pilot pollution is contributed to:

Irrational cell layout

Too high site or antenna mounted height

Irrational setting of antenna direction angle

Antenna back lobe effect

Irrational setting of pilot power

Peripheral environment effect

Where, the peripheral environment effect can summarized as the block to the signal from high

buildings or mountains, relatively far propagation extension of signal from the streets or the reflection

of signal from high glass buildings. Therefore, besides adjusting the layout and antenna parameter and

reducing the pilot power, combining the NodeB sectors or deleting redundant sectors also can reduce

the pilot pollution if the capacity is not affected. The pilot pollution should be avoided at the planning



design phase to facilitate the later network optimization.

2.5 Imbalance of Uplink and Downlink

The imbalance of uplink and downlink means the uplink coverage restriction (representing that the

maximum transmit power of UE also cannot satisfy the uplink BLER requirement) or downlink coverage

restriction (representing that the maximum transmit power of downlink dedicated channel code still cannot

satisfy downlink BLER requirement) in the target coverage areas. The most concern of telecom operators

is the service coverage quality mapped to the traffic measurement indexes, and the good pilot coverage is

the precondition to guarantee service coverage quality.

Because WCDMA supports multi-service bearers, the target areas must ensure the balance of uplink

and downlink of continuous full-coverage service, and partial areas must support asymmetrical service of

discontinuous coverage (such as the service with 64K uplink and PS128K downlink and service with 64K

uplink and PS384K downlink).

Theoretically, the uplink coverage restriction can be thought that the maximum transmit power of UE

still cannot satisfy the receiver sensitivity requirement of NodeB. For example, the intermodulation

interference and signal leakage generated by the cell edge or co-located device and inappropriate uplink

gain setting of repeater generate the interference to NodeB RTWP uplink to increase the thermal noise

and uplink coupling loss. The downlink coverage restriction can be thought as the increase of noise

received by downlink mobile phone to deteriorate Ec/Io. For example, adding the users increases local

cell interference or adjacent cell interference and restricts the downlink power (such as the hybrid

network of 10W power amplifier and 20W power amplifier causes the imbalance of radio resource

configuration).

The imbalance coverage of uplink and downlink easily generates call drop. The imbalance of uplink

and downlink generated due to the uplink interference monitors RTWP alarms of NodeBs to detect the

problems and checks antenna installation and adds antenna configuration to solve the problem. See the

examples:

If 3G network shares the antenna with 2G network, add the band pass filter.

For the interference from the repeater, change the antenna installation location.

For the uplink coverage restriction of cell edge, adopt the mounted amplifier to increase NodeB

sensitivity under the condition of allowed downlink capacity loss.

For the imbalance of uplink and downlink generated by downlink power restriction, check the

congestion through the OMC traffic measurement data, or compare cell’s busy hour traffic

volume with the calculated capacity to judge the traffic congestion, or adopt sectorization, add

the carrier or construct a new cellular. If adopting the sectorization, the selected antenna type

should be of narrow beam and high gain to increase the system capacity and improve the service

coverage, but the inter-cell interference level and soft handover ratio must be controlled.



3 Coverage Analysis Flow

3.1 Preparation for related Knowledge

3.1.1 Planning Scheme

GSM planning scheme is based on the coverage range planning and frequency planning, which

conform to respectively the coverage range rule and capacity rule obtained from the typical environment

where earlier mobile communication system. In WCDMA, the network planning aims to improve the

capacity requirement and frequency spectrum efficiency. The initial cellular design density, size, and type

cannot use the pure coverage rule and must consider the capacity requirement and confirm the cellular

structure type of target area from the perspective of redundancy cellular or capacity enhancement

technology.

Compared with GSM, WCDMA has intra-frequency interference but no additional free of channel

number allocated in TDMA system, that is, if the density of initial resource allocation cellular over the

capacity restriction is irrational, the succeeding parameter adjustment cannot solve the problem

fundamentally. From the perspective of the resource allocation, readjust the resource based on the

network load. Therefore, the precondition of pilot coverage and reference service coverage analysis is to

understand the planning scheme of target area, including sites distribution, NodeB configuration, antenna

configuration, pilot coverage prediction, and service load distribution. For details, see the following:

1. Site distribution

Obtain the surrounding clutter, terrain features, site address, height, and site type of each site in the

area through the site survey report and obtain the site coverage target information.

2. NodeB configuration

Understand the installed NodeB type, sector distribution, the mapping between sector and cell, cell

transmit power, EIRP, cell channel power configuration, and cell primary scramble.

3. Antenna configuration

Understand the antenna type selection, antenna parameter (horizontal beamwidth, vertical beamwidth,

and antenna gain), and antenna installation (antenna mounted height, direction angle, and tilt angle).

4. Pilot coverage prediction

Understand the pilot coverage prediction result provided by the planning software and the service

coverage in the areas based on the pilot coverage threshold of services, and analyze whether the pilot

pollution, coverage void, signal dead zone, and cross-cell coverage.

5. Service load distribution

Understand the reference traffic distribution, soft handover area after the static emulation,

uplink/downlink capacity distribution and restriction of each cell.



3.1.2 Analysis Tools

The analysis of coverage data contains:

Drive test call and the BAM of pilot census data

Traffic measurement of current network

UL RTWP alarm of each cell

User call process traced by RNC

Using proficiently the analysis tools helps to detect the network coverage problems and perform the

planning and adjustment in combination with the planning tools.

1. Drive test BAM

The common drive test data BAM analysis tools are Actix and Huawei Genex Assistant. In addition,

TEMS also provides BAM analysis tools of data collected by the foreground. We can refer to the auto

analysis report of call event, soft handover, and drive test coverage performance provided by the tools, and

check the signal coverage in a specific area through the replay similar to the foreground.

2. Traffic measurement tools

The traffic measurement analysis tools based on the traffic measurement point secondary

development helps to grasp fast the traffic distribution and the cell performance indexes. After the network

commercial use, analyzing whether the network cellular density fits the traffic distribution of users plays

an important role.

3. UL RTWP alarm system

Monitor the uplink interference of network based on UL RTWP alarm reported by NodeB.

4. Testability log

Use RNC Debug Management System to analyze the testability log of records and the causes

triggering the drop call of users.

3.1.3 Configuration Parameters Adjustment

The following lists the adjusted radio configuration parameters aiming to solve the coverage

problems:

1. CPICH TX Power

This parameter defines the transmit power of intra-cell PCPICH. Setting the parameter should

consider the actual system environment, such as cell coverage range (radius) and geographical

environment.

In the cell where the coverage is required, setting the parameter aims to ensure the downlink coverage.

In the cell where the soft handover cell is required, setting the parameter aims to ensure the soft handover

area ratio required by the network planning. In general, the parameter value is 10% of the cell downlink

total transmit power.



2. MaxFACHPower

This parameter defines the maximum transmit power of FACH (the maximum transmit powers of two

FACHs in the MOD SCCPCH are FACH1MaxPower and FACH2MaxPower respectively), corresponding

to the transmit power of PCPICH.

If the transmit power of FACH is too low, UE probably fails to receive the data packet of FACH or

receives an error data packet. If the transmit power of FACH is too large, the power waste is present.

Setting the maximum transmit power of FACH can ensure target BLER. When the Ec/Io accessed at the

edge cell is -12dB, set the parameter to -1dB (corresponding to the pilot).

3. Sintrasearch, Sintersearch, and Ssearchrat

The parameters contain intra-frequency cell reselection start threshold (Sintrasearch), inter-frequency

cell reselection start threshold (Sintersearch), and inter-RAT cell reselection start threshold (Ssearchrat).

When UE detects that serving cell quality (CPICH Ec/N0 measured by the UE) is lower than

“minimum quality standard (that is, Qqualmin) of serving cell + the threshold”, start the

intra-frequency/inter-frequency/inter-system cell reselection process.

Intra-frequency cell reselection should precede the inter-frequency/inter-system cell reselection.

When setting the three parameters, the Sintrasearch must be larger than Sintersearch and Ssearchrat.

Sintrasearch, Sintersearch and Ssearchrat are defaulted to 5 (that is, 10dB), 4 (that is, 8dB) and 2 (that

is, 4dB) respectively. Set the parameters based on different scenarios. For example, in the area with

dense cellular, set the Sintrasearch to 7.

4. PreambleRetransMax

This parameter defines the maximum retransmission times of preamble in a preamble ascending cycle.

If this parameter is too small, preamble power is not the required one and UE access fails. If the parameter

is too large, UE increase the power continuously and performs the access repeatedly to interfere with other

users. This parameter is defaulted to 8. If the connection ratio is worse, increase the parameter.

5. Intra-FILTERCOEF

This parameter means the measurement smooth coefficient adopted when layer-3 intra-frequency

measurement report filters. The layer-3 filter must filter the random impact capability to ensure the filtered

measurement value reflects basic change trend of actual measurement.

The measurement value of layer-3 filter has passed the layer-1 filter to eliminate basically the fast

fading effect. Therefore, layer-3 shall perform the smooth filter to shadow fading and seldom fast fading

burr to provide better measurement data for the event decision. The protocol recommends that the filter

coefficient value be set to 0, 1, 2,3,4,5, or 6.

The bigger the filter coefficient is, the stronger for the smooth capability of burr and the weaker the

capacity of tracing the signal is. The smooth capability and signal tracing capability should be balanced.

This parameter is defaulted to 5. Set the parameter based on difference scenarios. For example, in the area

with dense cellular, set the parameter to 2.



6. Intra-CellIndividualOffset

This parameter means cell CPICH measurement value offset of intra-frequency handover. Adding this

offset to actual value is used for event evaluation of UE. UE adds the original measurement value of the

cell to this offset as the final measurement result, which is used for intra-frequency handover decision of

UE. In the handover algorithm, it aims to move the cell edge.

Set the parameter based on actual environment of network planning. In the case of adjacent cell

configuration, to trigger the handover easily, set a positive value, otherwise, set a negative value. The

larger the parameter, the easier the soft handover and the more the UE located in soft handover status

but occupying many forward resources. The smaller the parameter, the more difficult the soft handover

is. The receiving quality also may be affected. This parameter is defaulted to 0, that is, neglect the effect

of the parameter.

7. RLMaxDLPwr and RLMinDLPwr (oriented to the service)

The parameters indicate the maximum transmit power and minimum transmit power of downlink

DPDCH symbol, represented by relative value to CPICH. The power control dynamic adjustment range

exists between the maximum transmit power and minimum transmit power, and it can be set to 15dB.

If the RLMinDLPwr is too small, the transmit power is too lower due to SIR estimation erro.If the

RLMinDLPwr is too large, the downlink power contorl may be affected.

Consider RLMaxDLPwr from the persepective of the capacity. If the full-coverage service is not

required, set and adjust the parameter based on actual Signal-Interference Ratio target value required by

capacity design and actual traffic measurement indexes.

3.2 Coverage Data Analysis

3.2.1 Drive Test Data Analysis

1. Downlink Coverage

I. Pilot coverage strength analysis

The received strongest RSCP downlink in the coverage area must be more than -85dBm. As shown in

Figure 1, the area with the RSCP ranging from -105dBm to -85dBm in the road is present. For the

coverage void, if the RSSI received by the downlink does not change dramatically, the Ec/Io fading is

generated, unable to satisfy the performance requirement of service coverage.

The pilot RSCP Best Server coverage also can measure whether site distribution is rational. During

the preplanning phase, use the coverage predication result of planning tools to evaluate and select the

site distribution to ensure the network coverage balance. Because the digital map may has no

information of some buildings and deviation from actual site address, the coverage result is inconsistent

with the planning coverage.

Under the conditions, adopt the coverage enhancement technology to improve the coverage. The



pilot RSCP is normal from the perspective of Scanner and UE. If the antenna of Scanner is mounted

outside the vehicle but the UE is in the vehicle, there is a difference of penetration loss ranging from

5dB to 7dB. Therefore, check the downlink coverage from the perspective of the data of Scanner. In this

way, avoid the incomplete pilot information measured by UE due to adjacent cell not configured.

Figure 1 Pilot strength distribution

II. Primary cell analysis

Currently, the cell reselection and soft handover set the threshold based on the change of Ec/Io.

Therefore, analyze the Ec/Io Best Server distribution of each cell by the Scanner when there is no user and

50% of users. If an area has multiple Best Servers and Best Server changes frequently, it may be thought

no primary cell.

Under normal circumstance, the cross-cell discontinuous coverage due to high site or pilot pollution

(as shown in Figure 2) and coverage void present in the coverage edge ( as shown in Figure 3) easily cause

no primary cell to generate the intra-frequency interference and ping-pong handover and affect service

coverage performance.

At the unloaded single site test and pilot coverage verification test phase before the optimization and

downlink loaded 50% of service test phase after the optimization, the primary cell analysis is required,

which provides the important basis for RF optimization measures.



Figure 2 Pilot Ec/Io Best Server distribution

Figure 3 Pilot Ec/Io Best Server distribution

III. UE and Scanner coverage comparison analysis

If the adjacent cells are not configured or soft handover parameter and cell reselection parameter are

irrational, the Best Server in the active set when UE is in the connection mode or camped cell under the

idle mode is inconsistent with Scanner primary cell. After the optimization, the Best Severs of Ec/Io of UE



must be consistent with that of Scanner. Meanwhile, ensure that UE coverage figure has a definite Best

Server borderline, as shown in Figure 4.

Figure 4 Comparison and analysis between the Scanner coverage and UE coverage

IV. Downlink code transmit power distribution analysis

Import the UE drive test data into BAM analysis software (Genex Assistant), and import the time

aligned downlink code transmit power data and the data binning can be performed. The downlink code

transmit power of NodeB can be recorded in the RNC BAM. For detailed operation method, see WCDMA

RNO Special Guide Call Trace Data Collection.

Import the data into an Excel table to obtain the probability density distribution. Although the

maximum values and minimum values of each service downlink code transmit power are different, and

if the UE downlink power control is normal and network coverage is good, the downlink code transmit

powers of most points of whole network drive test are similar. Only the transmit powers in seldom areas

are relatively high, as shown in Figure 5.



Figure 5 Downlink code transmit power PDF of Voice service in the case of 50% load

The mean downlink code transmit power obtained through the whole network drive test measures the

downlink path loss and intra-frequency interference of the coverage area. The drive test data mainly

analyzes the areas with the power higher than the mean and maximum downlink code transmit power for

long. Compared with UE drive test data, the BLER of downlink traffic transmission channel does not

converge the target value, resulting in directly relatively higher downlink code transmit power.

Analyze first the Best Server coverage of pilot RSCP in this area and the path loss increases due to

signal dead zone or coverage void. And then, analyze the Best Server coverage of pilot Ec/Io in this area

and the cell number in the active set and monitor set, and whether the downlink coupling loss increases

due to intra-frequency interference by the pilot pollution.

If no pilot pollution is present, concern further the change of downlink RSSI. If RSSI increases

dramatically, compare with the data collected by Scanner and primary cell and analyze whether adjacent

cell is neglected. The external interference also should be considered, although the frequency sweeping

test is performed during the site construction.

V. Soft handover ratio analysis

According to the Scanner drive test data, the soft handover area ratio is defined as follows:

The soft handover ratio is the ratio of soft handover area dimension in the network to the total

network coverage dimension, and cannot reflect the resource consumption from the soft handover and the

effect on the system capacity. Therefore, define the soft handover ration from the perspective of traffic.



For example,

During the network optimization, because there is no user, adopt the UE drive test data of the whole

network. After the binning, the ratio of drive test points in the soft handover state to all the drive test points

is the soft handover ratio and must range from 30% to 40%.

Adding soft handover ratio is contributed to:

Reduce the filter coefficient and trigger time, trigger threshold and hysteresis of 1A event

Increase the trigger time, trigger threshold and hysteresis of 1B event

Increase CIO

For the micro-cellular areas, the soft handover ratio is relatively high due to dense site, as shown in

Figure 6.

Figure 6 UE soft handover ratio

2. Uplink coverage

I. Uplink interference analysis

The uplink RTWP data of each cell in the NodeB can be recorded in the RNC BAM. For detailed

methods, see WCDMA RNO Special Guide Call Trace Data Collection. The uplink interference is a major

factor affecting the uplink coverage. Because it is similar to the design and installation of antenna and the

each carrier has different features, the causes for uplink interference are not described here.

This part describes how to examine the uplink interference through uplink RTWP record. As shown

in Figure 7, the antennas in the cell are space diversity receivers. Under normal conditions, the change



trends of receiving signals of two antennas are the same. The figure shows that the signal in the Tx/Rx

antenna does not fluctuate but 20dBm fluctuation is present in the Rx antenna, indicating that intermittent

interference is present in the secondary set. Similar to the downlink coverage restriction when downlink

code transmit power continuously reaches the maximum, the uplink interference also result in the uplink

coverage restriction, and network performance is worse.

Figure 7 Abnormal UL RTWP recorded in the NodeB

II. UE uplink transmit power distribution

The transmit power distribution of UE illustrates the distribution of uplink interference and uplink

path loss. Figure 8 shows that the transmit power of UE is lower than 10dBm, under normal conditions,

whatever micro-cellular or macro-cellular. Only when uplink interference or coverage area edge is present,

the transmit power increases dramatically and is up to 21dBm and the uplink is restricted. The uplink

coverage restriction is present in the macro-cellular more easily than in micro-cellular.



Figure 8 UE transmit power distribution (micro-cellular)

Figure 9 UE transmit power distribution (macro-cellular)



3.2.2 Traffic Measurement Data Analysis

Supplement later. (The methods of coverage analysis based on current network traffic data are still

under way.)

1. Traffic measurement indexes

The effect on access success ratio, congestion ratio, call drop ratio, and handover success ratio from

the coverage

2. Traffic distribution

The coverage problem due to traffic volume measurement and imbalance of service distribution

3. Excessive busy/idle cell

The effect on the coverage based on the load adjustment

3.2.3 Trace Data Analysis

Supplement later (the methods of coverage analysis based on CDL are still under way)

3.2.4 User Complaints Analysis

Supplement later (the methods of coverage analysis based on user complaints are still under way)

4 Coverage Enhancement Strategies

4.1 NodeB Configuration Adjustment

1. Serial NodeBs features

Table 1 describes Huawei serial NodeBs configuration and features.

Table 1 Huawei serial NodeBs and features (V100R003)

Version BTS3812 BTS3806 BTS3806A BTS3802C RRU3802C

Recei

ve

perfo

rman

ce

Static noise

coefficient 2.2dB 2.2dB 2.2dB 2.2dB 2.2dB

Static receiver

sensitivity

Better than

-125dBm

Better than

-125dBm

Better than

-125dBm

Better than

-125dBm

Better than

-125dBm

Receive adjacent

channel selectivity ≥52dB ≥52dB ≥52dB ≥52dB ≥52dB

Receive dynamic

range ≥35dB ≥35dB ≥35dB ≥35dB ≥35dB

Maximum receive

search radius

Single sector

≤ 180Km (it

is

configurable

and the unit

is 300m)

Single sector

≤ 180Km (it

is

configurable

and the unit

is 300m)

Single sector ≤

180Km (it is

configurable

and the unit is

300m)

Single sector

≤ 180Km (it

is

configurable

and the unit

is 300m)

Single sector

≤ 180Km (it

is

configurable

and the unit

is 300m)



Trans

mit

perfo

rman

ce

Transmit power

Under the

condition of

single

carrier

wave, the

set top port

output

≥2×25W

(diversity)

Under the

condition of

single

carrier

wave, the

set top port

output

≥2×25W

(diversity)

Under the

condition of

single carrier

wave, the set

top port

output≥2×25W

(diversity)

2×5W

(diversity) or

2×10W

(diversity)

2×5W

(diversity) or

2×10W

(diversity)

Spurious emission

Satisfy the

141

protocol of

3GPP

Satisfy the

141 protocol

of 3GPP

Satisfy the

141 protocol

of 3GPP

Satisfy the

141 protocol

of 3GPP

Satisfy the

141 protocol

of 3GPP

Static transmit power

control range ≥10dB ≥10dB ≥10dB ≥10dB ≥10dB

Dynamic transmit

Power control range ≥22dB ≥22dB ≥22dB ≥22dB ≥22dB

Transmit power

absolute accuracy

≤±2dB (all

the

temperature

s ),≤±1dB

(normal

temperature

)

≤±2dB (

all the

temperatures

),≤±1dB

(normal

temperature)

≤±2dB (all the

temperatures),

≤±1dB

(normal

temperature)

≤±0.5dB ≤±0.5dB

Capa

city

desig

n

specif

icatio

ns

Single cabinet

maximum sector

number

6 3 3 2 2

Single sector

maximum carrier

wave number

4 2 2 2 2

Single cabinet

maximum Cell

number

12 6 6 2 2

AMR12.2K

BLER=1%

CS64K BLER=0.1%

PS64K BLER=0.1%

PS144K

BLER=0.1%

PS384K

BLER=0.1%

128*12

(128*12)

32*12

(40*12)

32*12

(48*12)

16*12

(24*12)

8*12 (12*12)

128*6

(128*6)

32*6

(40*6)

32*6

(48*6)

16*6

(24*6)

8*6

(12*6)

128*6

(128*6)

32*6

(40*6)

32*6

(48*6)

16*6

(24*6)

8*6

(12*6)

64

(64)

16

(20)

16

(24)

8

(12)

4

(6)

128*2

(128*2)

32*2

(40*2)

32*2

(48*2)

16*2

(24*2)

8*2

(12*2)

Powe

r

consu

mptio

n

1 * 1 no diversity

708 (typical

value)762

(maximum

value)

668 (typical

value)722

(maximum

value)

159(5W

maximum

value),214(1

0W

maximum

value)

Power

consumption

1 * 1 diversity

1118 (typical

value)1212

(maximum

value)

1078 (typical

value)1172

(maximum

value)

235(5W

maximum

value),334(1

0W

maximum

value)250(fo

ur-antenna

receive a

maximum of

5W )358(fou

r-antenna

receive a

maximum of

5W)



3 * 1 no diversity

1633 (typical

value)1780

(maximum

value)

1593 (typical

value)1740

(maximum

value)

Air-condition

Type: under

the normal

temperature

In the

case of

cooling,

it is

2930W

(typical

value)/30

98W

(maximu

m value),

In the

case of

heating,

it is

4310W/4

478W;

Heat

exchanger

type:

In the

case of

cooling,

it is

2310W/2

478W,

In the

case of

heating,

it is

4310W/4

478W

3 * 1 diversity

3023 (typical

value)

3316

(maximum

value)

1663 (typical

value)1836

(maximum

value)

3 *2 no diversity

3023 (typical

value)

3316

(maximum

value)

1829 (typical

value)2017

(maximum

value)

Air-condition

Type: under

the normal

temperature,

in the

case of

cooling,

it is

3679W/3

892W,

in the

case of

heating,

it is

4579W/4

792W;

Heat

exchanger

type:

in the

case of

cooling,

it is

2579W/2

792W,



in the

case of

heating,

it is

4867W/5

080W

3 *2 diversity

3009 (typical

value)

3317

(maximum

value)

6* 2 no diversity

3515 (typical

value)

3828

(maximum

value)

noise

Sound power

lever(Bel) 7 6.85 7.5 null Null

Sound pressure

level(dBA) 60 58.5 65 null Null

STM-1 ANSI T1.105-1995,ITU I.432.2 G.703,ITU G.957

RRU

suppo

rt

RRU (maximum

distance between

RRU and NodeB is

40Km, and the

distance between

NodeB and RRU

transmission signal

cell is no more than

100Km)

Support

(each

interface

processing

unit supports

three

optic-fiber

interfaces

and single

optic-fiber

supports at

most four

main/diversit

y RF remote

modules, and

macro

NodeB

supports at

most 12

RRU

transmission

signal

coverage

cells)

Support

(each

interface

processing

unit supports

three

optic-fiber

interfaces

and single

optic-fiber

supports at

most four

main/diversit

y RF remote

modules, and

macro

NodeB

supports at

most six

RRU

transmission

signal

coverage

cells)

Support (each

interface

processing unit

supports three

optic-fiber

interfaces and

single

optic-fiber

supports at

most four

main/diversity

RF remote

modules, and

macro NodeB

supports at

most six RRI

transmission

signal

coverage cells)

Not support

Diver

sity

Open loop transmit

Diversity Support Support Support Support Support

Closed loop transmit

diversity mode 1 Support Support Support Support Support

Closed loop transmit

diversity mode Support Support Support Support Support

Two-antenna receive Support Support Support Support Support



diversity

Four-antenna receive

diversity Support Not support Not support Support Support

Chan

nel

S-CPICH/Cell Not support Not support Not support Not support Not support

DSCH Not support Not support Not support Not support Not support

CPCH Not support Not support Not support Not support Not support

Other

s

TTA Support

(12dB)

Support

(12dB)

Support

(12dB) Not support Not support

OTSR Support Support Support Not support Not support

Electrical antenna

support Support Support Support Not support Not support

Cell breathing Support Support Support Support Support

2. Sectorized configuration

Use the sectorization to improve the system capacity, meanwhile, the service coverage performance

also improves. The most importance factor for affecting the sectorization performance is the antenna

selection. Widely speaking, it determines inter-cell interference level, soft handover area ratio and allowed

maximum propagation path loss, which directly affect the system capacity. The service coverage is

affected by allowed maximum propagation path loss.

Under the normal condition, micro-cellular sectorization does not exceed two sectors. Pay enough

attention to the antenna selection to ensure the appropriate inter-cell separation. The radio propagation

feature of micro-cellular is to mount the antenna in different directions and cannot ensure sufficient

separation between the primary cell and other cells in the coverage cell.

From the perspective of macro-cellular, each NodeB also can be expanded to six sectors. While

adding the sectors, the antenna gain and adjacent cell interference increase. In addition, for most

directional antennas, the side lobe of antenna also increases. Adjust the RRM algorithm parameters (such

as active set size and soft handover threshold) to maintain about 40% of soft handover ratio.

When NodeB expands to three sectors from one sector, the NodeB capacity is 2.8 times of original

capacity. When the NodeB expands to six sectors, the capacity is 1.8 times of three-sector capacity, that

is, the added NodeB sectors help improve the capacity. When the NodeB transmit power does not exceed,

reduce appropriately the maximum path loss of cell and the NodeB can support more users. In this way,

further reduce the maximum path loss of cell or adding NodeB transmit power does not improve the

NodeB capacity unlimitedly. At that time, optimize the parameters involved in the downlink load formula

to improve the NodeB capacity. For example, reduce the Eb/No or adjacent cell interference through the

optimization methods to improve the downlink capacity of NodeB.

For 3G NodeB co-located with 2G, the sector selection focuses on the antenna installation. When the

sector adds, the antenna increases and the separation must consider.



4.2 Coverage Enhancement Technology

1. Tower mounted amplifier

Tower mounted amplifier (TMA) reduces the total noise coefficient of NodeB receiving subsystem to

improve the uplink coverage performance and the coverage gain depends on the mechanism of receiving

subsystem and the feeder loss. If the system capacity is restricted downlink, the TMA reduces the system

capacity. Typically, the capacity loss ranges from 6% to 10%.

2. Transceiver diversity

In the downlink, provide the Time Switched Transmit Diversity (TSTD) and Space Time Transmit

Diversity to add the RAKE receiver number of UE and improve the quality to increase the coverage range,

improve the system capacity and reduce the NodeB number.

In the uplink, adopt four-antenna receiving diversity to decrease the Eb/No requirement by

demodulation. Under the condition of LOS, compared with two-antenna two receiving diversity, the gain

of two-antenna four receiving diversity is about 2.5-3.0dB. Improve the uplink sensitivity by 2.5-3dB, and

reduce the site quantity by 25%-30%.

3. Repeater

The repeater expands the coverage range of primary cell. WCDMA repeater is similar to the analog

repeater and the noise and signal are expanded at the same time.

The repeater increases the Eb/No required by uplink/downlink demodulation, and most repeaters do

not adopt uplink receiving diversity technology. In this way, Eb/No requiredby the uplink demodulation

increases dramatically.

If the uplink of system capacity is restricted, use the repeater to reduce the system capacity. If the

downlink of system capacity is restricted, the effect on the system capacity from the repeater depends

on:

Link budget between primary NodeB and repeater

Repeater power transmission setting

Maximum path loss related to repeater coverage area

Service allocation between host cell and repeater

Meanwhile, the indoor depth coverage of repeater is also an effective way.

4. Remote RF amplifier

The remote RF amplifier allows the physical separation of NodeB RF module and baseband module

and RF module is placed far away without using long feeder. The uplink/downlink budget improves and

remote coverage through RRU means that coverage performance increases but the capacity does not

reduce. Compared with the remote coverage through the RRU, the TMA adds the maximum path loss and

introduces insertion loss to reduce the EIRP of NodeB.



5. Micro-cellular

The city and dense areas require high NodeB density and the site selection is also difficult. At that

time, the micro-cellular can solve the high capacity and applicable for city and dense city.

The micro-cellular can effectively use blockings of buildings to reduce the interference ratio of

adjacent cell and improve the downlink capacity.

6. Omni Transmission Sectorized Receive Technology

Omni Transmission Sectorized Receive (OTSR) transmits in the omni-direction and receives with

three sectors. Because the gain of directional antenna is higher than that of omni-directional antenna, the

coverage radius is farther. It is applicable for wide coverage and low user density. At the earlier stage of

network construction, lower capacity requires and OTSR can reduce the network construction cost and

improve the coverage range.

5 Typical Coverage Problems

5.1 Coverage Void due to Inappropriate Site Planning

5.1.1 Problem Description

In partial sites of coverage area, the pilot signal strength is less than -90dBm, and is less than the

signal coverage level of peripheral area and the coverage void is present.



Figure 10 Coverage void due to irrational site distribution

5.1.2 Analysis

The drive test data and coverage simulation prediction of actual network construction in Figure 11

show that the pilot signal strength Ec in some areas is less than -90dBm. The inter-site distance also

illustrates the cause of lower coverage level in the central areas. For the areas with mean traffic, the

cellular density also should be average. In this way, the signal fluctuation is basically not present in the

coverage area, that is, avoid the area with signal fading from the perspective of network design.

Figure 11 Coverage prediction of XX pilot



Figure 12 Site distribution

5.2 Cross-cell Coverage due to Inappropriate Site Selection


In the XX pilot, the site of XX road is 60 meters high and 20 meters higher than peripheral average

buildings. Therefore, the cross-cell coverage is present easily and the intra-frequency interference with

other sites is generated.



Figure 13 Cross-cell coverage before the optimization

5.2.2 Analysis

For the high site problem, replace the 2° of fixed electrical tilt antenna with 6°. Because the XX road

is at the network coverage edge, adjust the antenna directional angle and tilt angle to reduce the

interference with other sites. Therefore, this optimization does not change. Add the mechanism tilt angle

and adjust the directional angle to solve the cross-cell coverage.

Figure 14 shows that the cross-cell coverage in most areas is solved, but some cross-cell coverage is

still present in the road, especially in the primary cell of NodeB in the XX road.

Because the city construction speeds up and the digital map does not contain the features of new

buildings to result in the inaccurate pilot coverage prediction in some areas, the cross-cell coverage

problem is not found at the planning phase.



Figure 14 Cross-cell coverage after the optimization

5.3 Coverage Restricted due to Irrational Antenna Installation


The Pilot Network: 701070_ParkLaneHotel site of S project covers the V Park and the antenna is

mounted on the platform (10 meters high), as shown in Figure 15. At the optimization phase after the

network construction, before the traffic light under the antenna, Video Phone mosaic adds and image

quality is worse and PS 384K service is reactivated.



Figure 15 Coverage restriction at the bottom of site without considering the shielding of platform

5.3.2 Analysis

From the perspective of planning, 3G network and 2G network co-locate. Compared with 2G

coverage test data, 2G network has not large signal fluctuation under the road and site, that is, if the

antennas of 3G network and 2G network are in the same location, the road’s 3G coverage should be

caused by 701070_ParkLaneHotel_Podium site. Therefore, 3G antenna is close to the platform and the

wall blocks the signal to not satisfy the installation conditions of antenna.

Meanwhile, 2G antenna and installation components affect the 3G antenna patter. From the

perspective of antenna installation scenarios, it is difficult to change 3G antenna location. After the

discussion with 2G network engineers, change at least the solution without affecting the 2G coverage and

connect the transceiver feeders of 3G and 2G respectively with two antennas of external broad frequency

polarization antenna, and connect other transceiver feeders of 3G and 2G with two antennas of internal

broad frequency antennas, as shown in Figure 16.



Figure 16 Optimization of antenna design implementation

5.4 Coverage Restricted due to Antenna Installation Failure

5.4.1 Problem Descriptions

In the Pilot network of S project, 701640_ElzHse1 site has only one cell and combined by transmitter

A, B and C (It is not OTSR, and is the combination of three antenna receiving signals and distribution of

NodeB transmission signal).

During the antenna installation at the NodeB construction phase, all the transmission feeders are

combined to sector A by mistake, so sector B and C have no signals to transmit and the coverage effect

is worse. The problem is found after RF engineers test RTWP interference at the site. Before the

problem is found, the single site test is passed and the problem is not found in the later network

optimization test. Figure 17 shows the comparison of pilot RSCP before and after the antenna

installation correction.

Figure 17 Pilot RSCP coverage before and after the correction of antenna installation of 701640_ElzHse site

5.4.2 Analysis

The pilot RSCP before the antenna correction in the Figure 17 shows that the signals close to the

bottom of the site are below -76dBm. Compared the coverage of three sectors, obviously, the coverage of

sector A is 20dB stronger than that of sector B and sector C. From the perspective of current single site test

Checklist, it is difficult to find the pilot RSCP is larger than -85dBm, especially for the micro-cellular site.



Most sites of S project share 2G sites location or sector. Therefore, use the 2G coverage distribution

to check whether the 3G coverage is normal. For example, compare the distribution area ranging from

-90dBm to -80dBm. Currently, the minimum working level of 2G network is about -60dBm, and only

when the minimum working level at the bottom of 3G sites also should reach about -60dBm, the sites are

basically normal.

6 Concerns at the Network Optimization Phases

6.1 Single Site Test Phase

1. Signal dead zone

Concern the major coverage target of each transmitter and confirm whether the signal dead zone is

present based on the specified target.

2. Coverage void

Concern whether the continuous coverage of full-coverage service can be guaranteed.

3. Planning verification

Concern the difference between the digital map and actual environment, and perform a comparison

and verification between the coverage prediction and actual drive test data.

6.2 Evaluation Phase before the Optimization

1. Uplink/downlink interference

Concern the change of uplink RTWP of each cell, Scanner in the drive test or RSSI of UE.

2. Ec/Io mean

Under the unloaded downlink and loaded downlink, concern whether the areas less than the mean

value affects continuous coverage of full-coverage service

3. RSCP mean

Concern whether areas with the mean value affect continuous coverage of full coverage service.

6.3 RF Optimization Phase

1. Cross-cell coverage

Concern the repeated coverage due to inconsistent site height.

2. Pilot pollution

Concern whether the ping-pong handover exists in the soft handover area to reduce the



intra-frequency interference.

6.4 Parameter Optimization Phase

1. Soft handover ratio

Concern the capacity restriction due to over-high soft handover ratio.

6.5 Network Optimization Project Acceptance Phase

1. Traffic measurement indexes

Concern the inconsistency between the specified coverage target and actual user traffic distribution.

7 Summary

The network optimization can improve the whole network quality by the mobile users and utilizes

effectively network resources, and WCDMA experience (personnel, technology, and tools) plays a vital

role. Although the coverage indexes are not reflected in the KPI, the coverage optimization is the basic

requirement for improving the network performance. Only the radio performance optimization based on

the requirement takes effect.



List of reference

1. Huawei WCDMA R & D Caliber Summary 20040302.xls

2. WCDMA Radio Network Optimization---RF Optimization Guidelines V1.00 by Jamal.doc

wcdma rno special guide coverage problem analysis-20050316-a-2.0

Documents

coverage data analysis

coverage analysis flow

coverage void

analysis tools

crosscell coverage

typical coverage problems

trace data analysis

user complaints analysis