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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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
2.1 Signal Dead Zone .................................................................................................................................. 6
2.4 Pilot Pollution ........................................................................................................................................ 8
2.5 Imbalance of Uplink and Downlink ...................................................................................................... 9
6 Concerns at the Network Optimization Phases ........................................................................................ 34
6.1 Single Site Test Phase ......................................................................................................................... 34
6.2 Evaluation Phase before the Optimization .......................................................................................... 34
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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