8/18/2019 06 GSM BSS Network KPI (Network Coverage) Optimization Manual.pdf http://slidepdf.com/reader/full/06-gsm-bss-network-kpi-network-coverage-optimization-manualpdf 1/20 GSM BSS Network KPI (Network Coverage) Optimization Manual V1.0 INTERNALProduct Name Confidentiality Level G3BSC INTERNAL Product Version Total 20 pages GSM BSS Network KPI (Network Coverage) Optimization Manual V1.0 For internal use only Prepared byGSM&UMTS Network Performance Research Department Xie Haibin Date2008-6-3Reviewed by Date Reviewed by Date Granted by Date Huawei Technologies Co., Ltd. All rights reserved
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4. On the Local Maintenance Terminal (LMT) of the BTS3900 GSM and DBS3900 GSM, the
output power of the TRX is set the same as the transmit power on top of the cabinet, which is
different from the value before network replacement.
2 Analysis of Top Problems in Network Coverage Cases
To solve the coverage problems, the onsite engineers need to analyze them first and then
identify the problems by following the troubleshooting procedures.
Before network replacement, test the coverage of the original network, especially in the
important areas. After network replacement, compare the coverage before and after network
replacement. In addition, reasonably configure the BTS antenna according to the principles of
configuring the antenna before network replacement. Coverage comparison before and after the
network replacement provides valid evidence and is effective for locating the coverage problems.
Nearly 80% of the coverage problems are caused by the poor engineering quality, network
optimization problems, faults in non-Huawei devices, and equipment faults. The following section
analyzes the coverage problems from these aspects.
2.1 Engineering Quality
Incorrect
feeder
connections
Antenna
faults
Cable faults
Figure 1 Pie chart of engineering quality causes
During the deployment, capacity expansion, or replacement of a BTS, the feeders are
usually reversely connected, thus reducing the traffic volume and decreasing the
network coverage. You can identify this problem by performing a drive test and
checking the antenna and the feeder. A high voltage standing wave ratio (VSWR)
increases the power loss. You can use the SITEMASTER to test the VSWR, check the
VSWR alarm, and check the feeder connections for problem identification. The
GSM&UMTS Network Performance Research Department will develop a tool for
locating the problems of the antenna and feeder. For details, see Case 1.
The fault in the RX signal cable may deteriorate the uplink signals and decrease the
coverage. You can identify the problem by checking the cable connections, analyzingthe balance between the uplink and downlink, and querying the main and diversity
of the BTS is reduced. You are advised to lower the antenna or increase the tilt angle of the
antenna. When the coverage is poor, ensure that the transmit power level is 0.
RACH Min.Access Level
If this parameter is set to a smaller value, the MS can easily access the RACH and call drops
are more likely to occur. If this parameter is set to a larger value, some MSs may fail to make calls
even if they have strong signals. When the coverage is poor, ensure that the value of RACH
Min.Access Level is smaller than or equal to 1. For details, see Case 5.
RXLEV_ACCESS_MIN
If this parameter is set to a smaller value, the required access signal level is low; therefore,
many MSs attempt to camp on this cell, thus increasing the cell load and call drop rate. If this
parameter is set to a larger value, the coverage area of the cell decreases. Therefore, you need to
set this parameter to a reasonable value to balance the uplink with the downlink. When the
coverage is poor, set this parameter to a smaller value. For details, see Case 6.
Other parameters
Other parameters, such as the Cell Layer, CRO (cell reselection offset),
MS_TXPWR_MAX_CCH, and TMA Power Attenuation Factor, also affect the coverage. For
the settings of these parameters, see the Help on the LMT. For details, see Case 7.
Improper settings of network parameters are the important cause for the poor coverage. If
you increase the value of RACH Min.Access Level to increase the call completion rate and
decrease the call drop rate, the actual coverage area may become smaller. Therefore, in a
wide-coverage area, pay attention to the balance between the coverage area and the coverage
quality. During network replacement, ensure that the coverage quality does not decrease and then
ensure the KPIs using other methods.
2.2.2 CDU Configuration
BTS capacity expansion causes insertion loss. For example, when the BTS capacity increasesfrom two TRXs to three or four TRXs, 3 dB loss is introduced, thus deteriorating the coverage.
the antenna changes , because the mainand diversity of the BCCH omnidirectional
antenna may change the coverage area,thus decreasing the traffic volume.
Test the power on top of
the cabinet. If the power
and receive sensitivityare normal, exclude the
BTS fault from thecause.
Check whether additional losses are
introduced, such as the additional jumpers, added TMA, and surge
protector.
Possible cause
analysis 1
Possible cause
analysis 2
7. Find out
other possiblecauses
Check whether congestion occurs andwhether coverage is normal according to
traffic statistics, and check the uplink and
downlink receive quality.
Figure 5 Troubleshooting process of coverage problems
The troubleshooting process is as follows:
4.
Check the hardware configuration: Check whether capacity expansion is performed and
whether the combination mode changes according to the TRX configuration provided by
the customer. Checking the hardware configuration helps determine whether a TRX is
faulty or whether the TRXs are sufficient, because the number of TRXs may be smaller
than that before network replacement, which leads to congestion and traffic decrease.Objective: To solve the coverage problem caused by the combination loss due to
alarm, TRX board communication alarm, CDU level-1 VSWR alarm, and CDU
level-2 VSWR alarm.
Note: After network replacement, the output power of the TRX may be manually
decreased to clear the VSWR alarm. This only covers the problem but not solves the
problem. Meanwhile, the coverage shrinks and the traffic volume decreases.
ii) Clock alarms: clock reference abnormal alarm, frame or TS number alarm, TRX
clock major alarm, phase-locked loop critical alarm, and TMU clock alarm.iii)
Transmission alarms: LAPD OML fault alarm, E1 remote alarm, and E1 local
alarm.
The preceding alarms do not necessarily cause the coverage decrease; however, if
alarms are generated and cleared frequently, the coverage seems to be poor and the
signal seems to fluctuate for the customer. In problem identification, handle these alarms
first.
The measurement counters are related to KPI Measurement per Cell,
Incoming/Outgoing Internal/External Inter-Cell Handover Measurement per
Cell, Measurement of Power Control Messages per Cell, Receive Quality
Measurement per TRX, and Uplink-and-Downlink Balance Measurement per
TRX.
i)
Compare the number of SDCCH requests and the number of TCH requests
respectively before and after network replacement to check whether the number of
SDCCH requests and the number of TCH requests during paging response are
normal.
ii)
Check whether congestion occurs according to the congestion rate. If the
congestion rate is high, access to the network becomes difficult, thus causing
complaints.
iii)
Compare the traffic volume in busy hours before and after network replacement tocheck whether the traffic volume decreases. Traffic volume is an important
iv) Compare the number of incoming inter-cell handovers and the number of outgoing
inter-cell handovers respectively before and after network replacement to check
whether the cooperation with the neighboring BTS is normal.
v)
Check the average receive level and the average receive quality in the uplink and
the downlink.
Objective: To solve the coverage problem caused by the equipment faults by analyzing
the traffic statistics, which are important for problem identification.
7.
Compare the drive test data before and after network replacement: This method is
effective to solve the coverage problem and can provide valid evidence for coverage
decrease. If network replacement is performed by the customer, the drive test data
before network replacement may be unavailable; therefore, identifying the coverage
problem becomes more difficult. You can perform drive tests after network replacement
and check the BTS to identify the problems such as reverse connection of the feeder,
poor coverage of the antenna, and handover failure. In addition, you need to
communicate with the customer that makes the complaints and perform field tests to
obtain the firsthand data for future comparison.
Objective: To identify the coverage problem by comparing the coverage before and after
network replacement. If the drive test data before network replacement is unavailable,
drive tests can still be performed, which are important for problem identification.
8. Check the BTS antenna and feeder: With the drive test results, check the antenna and
feeder connections. If the drive test results show that the antenna coverage is poor, use
the SITEMASTER to test whether the VSWR is smaller than 1.5. If the VSWR isgreater than 1.5, check whether water runs into the antenna connector or feeder
connector and whether the surge protector is faulty. If there are complaints about poor
coverage after network replacement but the drive test results show that the coverage is
normal, the poor coverage in some areas may be concerned with the antenna, especially
the omnidirectional antenna, of the main BCCH changes, or the tilt or azimuth angle of
the antenna changes. If the TMA is installed, you need to check whether the TMA is
activated and functional.
Objective: To ensure that the link between the top of the cabinet and the antenna is
normal by checking the BTS antenna system.
9.
Test the transmit power on top of the cabinet: Ensure that the cables are securely
connected. Then, check whether the transmit power on top of the cabinet is normal. If
the transmit power is abnormal, use a power meter to check the power of the TRX and
combiner. If the TRX power decreases or the combiner loss is too high, replace the
faulty TRX or combiner. The receiver sensitivity can be tested by only the CMD57,
which is unavailable on site. Therefore, you can replace the faulty TRX.
Objective: To identify the coverage problem caused by the BTS. If the transmit power
on top of the cabinet is normal and is not lower than that of the non-Huawei equipment
before network replacement, the BTS fault can be excluded from the cause of poor
coverage.10.
Find out other causes: insufficient coverage, interference, poor electromagnetic
In April 2007, the traffic volume of a BTS decreased by 50% after network replacement.
Conclusion:
The check on the onsite network optimization parameters proves that the fault is not caused by the product
defects or improper settings of network optimization parameters. Instead, the onsite engineers did not follow the
guidelines for network replacement. Therefore, the main BCCH antenna changes after replacement. That is, the
omnidirectional antenna is used after network replacement; therefore, the traffic volume of the directional cells on
the two sides of the tower is different from that before network replacement.
Solution:
Change the BCCH antenna to the one before network replacement by exchanging the jumpers. The coverage
problem is solved. The traffic volume increases by nearly 40% compared with that before network replacement.
Case 4: Weak coverage in the GSM900 band in a dual-band network
Problem Description:
In March 2007, the traffic volume of a dual-band (GSM900&DCS1800) network decreased and the coverage
area shrunk after COBCCH is enabled.
Conclusion:
The comparison on the drive test data before and after COBCCH is enabled and the analysis of the related
traffic statistics show that the coverage of the GSM900 band is weak. After COBCCH is enabled, the main BCCH
is on the DCS1800 network. Therefore, the coverage decreases and the traffic absorption of the TRXs in theoriginal DCS1800 band decreases, thus decreasing the overall traffic volume.
Solution:
Before enabling COBCCH in a dual-band network, check the hardware and antenna of the BTS in the
network for correctness. Otherwise, the COBCCH-related KPIs are affected.
Case 5: Call access failure because the value of RACH Min.Access Level is too great
Problem Description:
A lot of complaints are raised concerning BTS M because of the call setup failure and high call drop rate.
BTS M with wide coverage is located in a mountainous area.
Conclusion:
Check the data of the existing network and find that the value of RACH Min.Access Level is 5. Check the
list of complaints and find that the complaints have been made since May 8. It is learnt that a BSC cutover was
performed in the early morning on May 8.Therefore, it is doubted that the data changes after the cutover. Compare
the data before and after the cutover and find that the value of RACH Min.Access Level is 0 before the cutover
and 5 by default in the current network.
Solution:
Change the value of RACH Min.Access Level to 0. The problem is solved and complaints about call setupfailure are no longer made. The call drop rate remains high because of the wide coverage. After communication,