wcdma rno special guide coverage problem analysis-20050316-a-2.0
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WCDMA RNO Special Guide Coverage Problem Analysis Internal open
2005-07-13 All rights reserved Page 1 , 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
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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
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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
5.2.1 Problem Descriptions .................................................................................................................... 29
5.2.2 Analysis ........................................................................................................................................ 30
5.3 Coverage Restricted due to Irrational Antenna Installation ................................................................ 31
5.3.1 Problem Descriptions .................................................................................................................... 31
5.3.2 Analysis ........................................................................................................................................ 32
5.4 Coverage Restricted due to Antenna Installation Failure .................................................................... 33
5.4.1 Problem Descriptions .................................................................................................................... 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
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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
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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
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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.
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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
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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
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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.
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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.
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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.
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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.
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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
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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.
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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
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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.
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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.
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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
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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.
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Figure 8 UE transmit power distribution (micro-cellular)
Figure 9 UE transmit power distribution (macro-cellular)
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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)
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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)
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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,
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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
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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.
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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.
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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.
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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
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Figure 12 Site distribution
5.2 Cross-cell Coverage due to Inappropriate Site Selection
5.2.1 Problem Description
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.
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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.
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Figure 14 Cross-cell coverage after the optimization
5.3 Coverage Restricted due to Irrational Antenna Installation
5.3.1 Problem Description
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.
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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.
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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.
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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
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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.
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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