06 GSM BSS Network KPI (Network Coverage) Optimization Manual

GSM BSS Network KPI (Network Coverage) Optimization Manual V1.0

Product Name G3BSC Product Version

INTERNAL

Confidentiality Level INTERNAL Total 20 pages

GSM BSS Network KPI (Network Coverage) Optimization Manual V1.0 For internal use only Prepared by

GSM&UMTS Network Performance Research Department

Xie Haibin

Date

Reviewed by

Date

Reviewed by

Date

Granted by

Date

Huawei Technologies Co., Ltd. All rights reserved

2008-6-3


INTERNAL

Contents 1 Coverage Capability.........................................................................................................................5 2 Analysis of Top Problems in Network Coverage Cases..................................................................6 2.1 Engineering Quality..............................................................................................................7 2.2 Network Planning and Optimization....................................................................................8 2.2.1 Network Parameter Settings......................................................................................8 2.2.2 CDU Configuration....................................................................................................9 2.2.3 Missing Configuration of Neighboring Cell Relations...........................................10 2.3 Non-Huawei Devices..........................................................................................................10 2.4 Equipment Faults.................................................................................................................11 3 Troubleshooting Process of Coverage Problems...........................................................................11 4 Typical Cases..................................................................................................................................15


INTERNAL

Revision Record Date 2008-6-3

Revision Version 1.0

Change Description

Author

Draft completed.

Xie Haibin


INTERNAL

GSM BSS Network KPI (Network Coverage) Optimization Manual Keywords: network coverage, optimization Abstract: This document analyzes the top problems in the cases submitted at http://support.huawei.com/support/, describes the troubleshooting procedures, and provides optimization methods. Abbreviations: Abbreviation

Full Spelling


INTERNAL

Preface This document compares the transmit power on top of the cabinet and receiver sensitivity between Huawei products and non-Huawei products. It also analyzes the top coverage problems in the collected cases. In addition, it provide the troubleshooting procedures and coverage optimization methods for the onsite engineers.

1 Coverage Capability Conclusion: The BTS312 and BTS3012 from Huawei can replace the BTSs from other vendors. After the replacement, the transmit power on top of the BTS cabinet is the same or even higher and thus normal network coverage can be ensured. With the large-scale commercial use of the BTS3012 and the development of the cavity combiner, the coverage capability of Huawei equipment is greatly enhanced. In addition, the DBS3900 GSM has a distributed structure. It can be mounted on a tower, thus reducing the feeder loss and expanding the coverage area without power boost. Our rich crisis handling experience proves that the decrease in the coverage area of a BTS is closely related to the engineering quality, network optimization parameters, geographical factors, and electromagnetic environment. The technical specifications, such as the frequency, sensitivity, and power of the system, do not degrade in performance and further cause decrease in the coverage area unless a board is faulty. Table 1 Comparison on the coverage capability between Huawei and non-Huawei products in the GSM900 band Cell Configuration

Maximum Transmit Power on Top of the Cabinet in the GSM900 Band (dBm) E(2202)/E(2206)

M (Horizon)/ II

N (Ultrasite)

S (BS240)

HW312*

S1–2, EDU

45.5

46.2/46.6

45.4

45.6

S1–2, CDU

42.3 (measured result)

43.2 (measured result)/43.5

42

S3–4, CDU

42.3 (measured result)

43.2/43.5

42

S5–6, SCU

　


38.6

S7–8, SCU

　


38.6

S4–S12, cavity

44.4 (measured result) –113 dBm (measured result)

43.7

44.2 (measured result) -110.5 dBm

Sensitivity (static)

–111 dBm (measured result)

44.8/46.2/47.8

HW3012 DTRU 46.8

HW3012 QTRU*** 47.8/49.0 (1 TRX)

42.5 (measured result) 42.5 (measured result)) 39.3 (measured result) 39.3 (measured result) 43

40.9/42.3/43.9

43.3

47/47.8 (2 TRXs)

40.9/42.3/43.9

43.3

44.8/46.0 (3 TRXs)

37.9/39.3/40.9

40.2

44/44.8 (4 TRXs)

37.9/39.3/40.9

40.2

43/44 (5 TRXs)

　


Normal: –111 dBm EDGE: –112 dBm

44.6 (typical value)** –112.5 dBm

40.8/43.0 (6 TRXs) –112.5 dBm

*Remarks: The three values in each cell of this column indicate the output power of the 40 W BTS312, 60 W BTS312, and 40 W+PBU BTS312 respectively. **Remarks: For the four-in-one cavity, the typical insertion loss is 2.5 dB and the maximum insertion loss is 3.5 dB; for the six-


INTERNAL

in-one cavity, the typical insertion loss is 3 dB and the maximum insertion loss is 3.5 dB. In this document, 3 dB is used as the typical value. ***Remarks: The output power of the QTRU varies according to the number of configured TRXs. The three values in each cell of this column indicate the normal output power, the enhanced output power, and the number of TRXs respectively.

Table 1 Comparison on the coverage capability between Huawei and non-Huawei products in the DCS1800 band Cell Configuration

Maximum Transmit Power on Top of the Cabinet in the DCS1800 Band (dBm) E(2202)/E(2206)

M (Horizon)/ II

N (Ultrasite)

S (BS240)

Huawei312*

Huawei3012

S1–2, EDU

44.5

45.6/46

45.3

43.7

44.8/46.2/47.8

46.8

S1–2, CDU

41.3

41.9

43.3

41.3

40.9/42.3/43.9

43.3

S5–6, SCU

　

37.9/39.3/40.9

40.2

S7–8, SCU

　

39.6/38.4

37.9/39.3/40.9

40.2

S4–S12, cavity

42.1 dBm (measured result) –112 dBm (measured result)

43.1

40.5 (measured result) 40.5 (measured result) 37.3 (measured result) 37.3 (measured result) 41.2 dBm to 40.7 dBm –112 dBm

40.9/42.3/43.9

S3–4, CDU

42.6 (measured result)/42.4 42.6 (measured result)/42.4 39.6/38.4

Sensitivity (static)


41.9　 38.5 dBm (measured result) 38.5 dBm (measured result) 44.1 –113 dBm(measured result)

Normal: –111 Bm

-112.5 dBm

EDGE: –112 dBm

*Remarks: The three values in each cell of this column indicate the output power of the 40 W BTS312, 60 W BTS312, and 40 W+PBU BTS312 respectively.

Note: 1. The minimum transmit power on top of the cabinet of Huawei BTS is listed. The actually measured value may be slightly larger. 2. The transmit power on top of the BTS312 cabinet takes the surge protector loss into consideration. The BTS3012 uses the new surge protection design without the surge protector. 3. After network replacement, the coverage may change because of the introduction of additional losses, such as the additional jumpers, added TMA, and surge protector. 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


INTERNAL

optimization problems, faults in non-Huawei devices, and equipment faults. The following section analyzes the coverage problems from these aspects.

2.1

Engineering Quality Cable faults

Incorrect feeder connections

Antenna 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, analyzing the balance between the uplink and downlink, and querying the main and diversity alarms. For details, see Case 2.  Check whether the tilt and azimuth of the antenna change after network replacement. The change of the main BCCH antenna, especially the omnidirectional antenna, before and after network replacement also affects the coverage. That is, the area of good coverage may become an area of poor coverage and the area of poor area may become an area of good coverage; however, the customers have concern about only the latter situation and may make complaints. For details, see Case 3. Summary: The poor engineering quality is the main cause of the coverage problem. The use of double-antenna, transmit diversity, and COBCCH pose increasingly high requirements for the engineering quality in antenna installation. To solve the coverage problems, ensure that the feeders and connectors are securely and correctly connected. For details, see Case 4. 


2.2

INTERNAL

Network Planning and Optimization

Network planning problems Improper CDU configuration

Incorrect antenna type Improper network parameter settings

Missing configuration of neighboring cell relations

Figure 2 Pie chart of network planning and optimization causes

2.2.1

Network Parameter Settings

The parameters that have an impact on the coverage include Power Class, RACH Min.Access Level, and RXLEV_ACCESS_MIN. 

Power Class To suppress the co-channel interference and adjacent-channel interference, you can lower the

antenna, increase the tilt angle of the antenna, or reduce the transmit power of the BTS in planning the network in urban areas. Generally, the indoor coverage may become poor if the transmit power 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


INTERNAL

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 widecoverage 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 increases from two TRXs to three or four TRXs, 3 dB loss is introduced, thus deteriorating the coverage. Sometimes, network planning is carried out by the customer. During capacity expansion of a BTS after network replacement, the change in the combination mode increases the loss, thus deteriorating the coverage. In this case, the customer may misunderstand that the coverage problem is caused by Huawei products. To avoid the preceding situation, check and compare the TRX configuration and combination mode before and after the network replacement for prompt problem identification. For details, see Case 8. It is normal that the power level decreases after a combiner is added during capacity expansion. Use the recommended configuration to avoid the loss due to capacity expansion. If you have to use different combination modes, negotiate with the customer in advance to minimize the adverse


INTERNAL

impact. If the coverage problems are caused by the capacity expansion carried out by the customer, explain and clarify the situation to the customer.

2.2.3

Missing Configuration of Neighboring Cell Relations

During network replacement, pay special attention to the configuration of neighboring cell relations. Ensure that each cell in the local BTS is configured with neighboring cells in the neighboring BTSs and configured as a neighboring cell of other cells in the neighboring BTSs. The cells in the BTSs under the control of different BSCs must be configured as external neighboring cells with each other. The missing configuration of neighboring cell relations decreases the handover success rate, increases the call drop rate, and reduces the traffic volume. The BTS coverage seems to decrease; however, the coverage does not change actually. For details, see Case 9. It is easy to avoid the missing configuration of neighboring cell relations; however, it is difficult to solve the coverage problem caused by the missing configuration of neighboring cell relations. Therefore, great care is required in initial data configuration and data check in the case of problems to avoid subsequent ineffective input.

2.3

Non-Huawei Devices Surge protector faults Booster amplifier faults

Repeater faults TMA faults Figure 3 Pie chart of the non-Huawei devices that cause the coverage problem

To reuse the original antenna after network replacement, check whether the TMA is used before network replacement. If the TMA is used, ensure that the TMA matches the Huawei equipment. For the BTS312, ensure that the surge protector is properly installed. For details, see Case 10. Summary: The non-Huawei devices are difficult to monitor. In addition, the active devices such as booster amplifier, repeater, and TMA are liable to fail. Therefore, when a coverage problem occurs, carefully check the non-Huawei devices in use.


2.4

INTERNAL

Equipment Faults TRX faults

Combiner faults

Clock faults

Figure 4 Pie chart of the equipment faults that cause the coverage problem

Summary: The poor coverage is also caused by the clock fault, intermittent transmission disconnection, communication failure on a board, and radio link fault. You can learn the equipment fault through alarms and rectify the fault by replacing the faulty part with a new one. For details, see Case 11.

3 Troubleshooting Process of Coverage Problems In case of coverage problems, the onsite engineers can do as follows to handle the problems: 1. Analyze the hardware configuration, parameter settings, traffic statistics, and alarms. 2. Check the BTS hardware, test the TRX power and the transmit power on top of the cabinet, and perform drive tests on site. 3. Communicate with the customer that makes the complaints and perform field tests. Then, most coverage problems can be solved.


Check whether the BTS is an operational Huawei BTS

Possible cause analysis 1

INTERNAL

Possible cause analysis 2

1. Check the hardware configuration

Coverage decrease is caused by combination loss due to capacity expansion?

2. Check the parameter settings

Configuration of neighboring cell relations is missing?

Check the parameters: Cell Layer, Power Class, RACH Min.Access Level, RXLEV_ACCESS_MIN, and CRO.

3. Check the alarms and traffic statistics

Check for clock faults, radio link faults, intermittent disconnection, or TRX communication fault.

Check whether congestion occurs and whether coverage is normal according to traffic statistics, and check the uplink and downlink receive quality.

Compare the drive test data before and after network swapping. If the coverage is normal, the BTS fault is excluded from the cause.

Communicate with the customer that makes complaints and conduct field tests to obtain the first-hand data.

Check antenna and feeder connections, connectors, combiner, and VSWR. Check whether the antenna is aging.

Check whether the tilt or azimuth angle of the antenna changes , because the main and 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 sensitivity are normal, exclude the BTS fault from the cause.

Check whether additional losses are introduced, such as the additional jumpers, added TMA, and surge protector.

4. Compare the drive test data

5. Check the BTS antenna and feeder

6. Test the power on top of the cabinet

Check for TRX fault or TRX insufficiency, which may cause congestion and traffic volume decrease.

7. Find out other possible causes 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


5.

6.

INTERNAL

capacity expansion. Check the parameter settings: Check the PDCH configuration and settings of the parameters closely related to the coverage, such as Power Class (0), RACH Min.Access Level (≤1), RXLEV_ACCESS_MIN, and Cell Layer (same as the layer of the neighboring cell). In addition, check the configuration of the neighboring cell relations. Cells in the same BSC should be configured as bidirectional neighboring cells; cells between different BSCs should be configured as external neighboring cells. Note that the serving cell should be configured as the neighboring cell of other cells. Objective: To solve the coverage problem caused by the missing configuration of neighboring cell relations or by improper settings of the network optimization parameters. Check the alarms and traffic statistics:  The coverage-related alarms are generated mainly because the TRX is faulty. i) Hardware alarms: LAPD alarm, TRX configuration alarm, TRX processor running Alarm, radio link critical alarm, TRX power decrease alarm, TRX power amplifier shutdown alarm, TRX voltage abnormal alarm, TRX hardware alarm, TRX VSWR 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 to check whether the traffic volume decreases. Traffic volume is an important


INTERNAL

indicator of the coverage. 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 is greater 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


INTERNAL

environment, MS fault, SIM fault, or mistaken complaints due to the surrounding environment of the antenna, building in the cell, vegetation in the cell, transmission model, and emergence of new hotspot areas. Remarks: For other causes, see the Guide to Dealing With Wireless Coverage Problems. Objective: To identify the coverage problem by finding out possible causes.

Appendix: Check Items in Locating Coverage Problems Check Item BTS TRX configuration Transmit power

Remarks Capacity expansion provided by the customer

Objective information

Power consistency before and after network replacement

Data configuration

*.dat file

Alarm information

Hardware, clock, and transmission alarms (self-check) KPI Measurement per Cell

Traffic measurements

Intra-cell Handover 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

Drive test data Others

Uplink-and-Downlink Measurement per TRX *.log (*.cell) or *.ant file Engineering parameter electronic map

To check whether the TRX capacity is expanded. If the TRX capacity is expanded, check whether the combination mode changes. To ensure the power consistency before and after network replacement. Higher power may cause interference and lower power may decrease the coverage. To check the settings of the network optimization parameters, neighboring cell relations, and power configuration. To check whether these alarms are generated in the cell. Handle the alarms if they are generated. To check whether the paging and coverage are normal by comparing the number of SDCCH requests and the number of TCH requests respectively and comparing the traffic volume before and after network replacement. To 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. To check whether the receive quality in the uplink and the downlink is normal respectively.

Balance

table

and

To identify the coverage problem by comparing the coverage before and after network replacement. To check the geographical information through the NASTAR software.

4 Typical Cases Case 1: BTS coverage decrease caused by the loose connection of the jumper on the antenna side

Problem Description: The customer complains that the coverage of a BTS decreases and call setup is difficult; however, no alarm is found on the LMT. Conclusion: The receive level at the site with complaints ranges from –75 dBm to –95 dBm. Sometimes the signal level fluctuates greatly and the call connection is abnormal. The local customer reports that the BTS operates normally during initial deployment, the signal level is stable, and no interference exists. Check the hardware and cable connections of the BTS. No problem is found. Use the power meter to test the transmit power of the TRX. The transmit power of the TRX is normal. Test the VSWR of the antenna. The VSWR of the antenna is 1.5, which is a


INTERNAL

little big. It is found that the VSWR on the antenna side is bigger. Then, climb up the tower for checking and find that the connectors of the two feeders are securely connected. The jumper on the antenna side is too long, and the waterproof curve on the jumper is too deep and is wobbling. It is doubted that the jumper and the antenna are in loose contact. Pull the jumper and find that the jumper and the antenna are in loose contact. Solution: Reinstall and wrap the connectors of the jumper and the antenna and reinstall the antenna. Then, make the curve slighter. Wrap the jumper with straps. The jumper is no longer wobbling. Restart the BTS and perform a test at the site with complaints. The signal level becomes normal and the problem is solved. Case 2: Imbalance between the uplink and the downlink caused by the RX cable fault Problem Description: The signals of a BTS deteriorate remarkably. The local residents complain about call setup failures. The onsite test result shows that the call cannot be set up; however, the signal level in the cell is –70 dBm, which is not weak. Conclusion: If the signal in the cell is strong, then call setup failure is caused by the uplink faulty. Check the data configuration and the cable connections on the top of the cabinet. The antenna and feeder are securely connected and the connectors are in good contact. Exchange the TX/RX feeder with the RX feeder on top of the cabinet and then perform the test again. The fault persists, which proves that the antenna and feeder connections are normal. The analysis of traffic statistics shows that the uplink and the downlink of this cell are not in balance. Replace the TRX and perform the test again. The fault persists, which proves that the TRX is normal. Finally, it is found that the RX cable is faulty. Solution: Replace the faulty RX cable and perform the test again. The test result and traffic statistics show that the fault is rectified. Case 3: Traffic volume decrease caused by the change of the main BCCH antenna Problem Description: 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.


INTERNAL

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 the original 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 setup failure are no longer made. The call drop rate remains high because of the wide coverage. After communication, the customer expresses understanding of call drops at the site. In this case, the complaints about call setup failure are the major problem while the call drops caused by the environment are the minor problem. Case 6: Disconnection of the MS from the network because the value of RXLEV_ACCESS_MIN is too great Problem Description: Customers complain that the signal level in the rural area covered by a BTS fluctuates frequently and the MS is frequently disconnected from the network indoors. The result of the field test on site with the network optimization engineer of the customer proves that the symptom is true. Conclusion: Query the alarms, analyze the traffic statistics, and perform dialing tests and frequency scanning tests on site. As a result, the hardware fault and interference are excluded from the cause. Checking the CGI data at the MSC shows that the CGI data is consistent between the BSC and the MSC. Then, check the settings of the


INTERNAL

parameters that may affect the MS access, such as RXLEV_ACCESS_MIN and RACH Min.Access Level. The value of RXLEV_ACCESS_MIN is 12, which is too great. Solution: Change the value of RXLEV_ACCESS_MIN to a smaller value. The problem is solved. Case 7: Improper setting of MS_TXPWR_MAX_CCH Problem Description: A customer complains that the coverage of some BTSs, including the GSM900 BTSs and DCS1800 BTSs, becomes smaller than before. Conclusion: Check the network parameters and find that the customer sets MS_TXPWR_MAX_CCH of some GSM900 cells to 0 and sets MS_TXPWR_MAX_CCH of some DCS1800 cells to 5. The improper setting of MS_TXPWR_MAX_CCH causes the network coverage decrease. Solution: Set MS_TXPWR_MAX_CCH to 5 (33 dBm) in the GSM900 cell and 0 (30 dBm) in the DCS1800 cell. Then, perform a test in the network. The problem is solved. Case 8: Coverage decrease due to combination loss introduced by capacity expansion Problem Description: At the end of March 2007, local office Y reported that the BTS312 started operating at the end of 2006. Late in March 2007, the customer started to complain about the defects of the BTS312. The decrease in the BTS coverage was the main problem. Conclusion: The problem is not concerned with the product quality. According to the statistics, the areas with decreased coverage are all the cells where capacity expansion is performed. Generally, the capacity increases from two TRXs to three TRXs. In this case, cable connections need to be changed. After the main BCCH TRX signals are processed by the CDU and then transmitted by the duplexer, the loss increases by 3 dB and the coverage decreases. Solution: The customer agrees that the BTS312 functions well and the coverage decrease caused by capacity expansion is reasonable. To solve the problem, the customer decides to add BTSs to increase coverage. Case 9: Missing configuration of neighboring cell relations Problem Description: In May 2007, the customer complained that the coverage became smaller after an Ericsson BTS was replaced by a Huawei BTS. Cause Analysis: The coverage decreases because the BTS is not configured with neighboring cells. During the coverage test,


INTERNAL

the call made near the BTS cannot be handed over to this BTS. Therefore, the customer misunderstands that the coverage decreases. After the BTS is configured with neighboring cells, the problem is solved. Conclusion: Actually, the problem is not coverage decrease. Instead, the problem occurs because the BTS is not configured with neighboring cells. Thus, the handover cannot be performed and the traffic volume decreases. In this case, the problem is subjectively conceived as coverage decrease. Case 10: Faults in the third-party booster amplifier Problem Description: A BTS works in S2/1/1 configuration mode after network replacement and works in S4/1/1 configuration mode after capacity expansion. After capacity expansion, the subscribers in the area covered by cell A complain that the signal strength indicator of a mobile phone is full when no call is made but the signal strength drops sharply when a call is made. Cause Analysis: It is found that the booster amplifier of one TRX is burnt out. In addition, the cable connections of the other two TRXs are incorrect; therefore, the signal cannot be sent out from the antenna. Only the signals on the main BCCH TRX can be sent out while the signals on the other three TRXs cannot, thus causing heavy congestion. The signals on the main BCCH TRX are strong; therefore, when the TCH on the non-main BCCH TRX is assigned to a call, the signal level fluctuates. Conclusion: The problem is caused by the third-party booster amplifier of poor performance. Replace the booster amplifier and connect the cables correctly. Then, the problems of congestion and signal fluctuation are solved. Case 11: No response to paging due to clock faults Problem Description: When initiating a call, the calling party is informed that "The number you dialed is out of service now." Cause Analysis: After initiating a call, the calling party is informed that "The number you dialed is out of service now.", indicating that the called party makes no response. Check the BTS clock and find that the clocks of multiple BTSs are in free-run mode, because the BSC clock is not in locked mode. Conclusion:

After the clock fault is rectified, the called party can normally respond to the paging. This proves that the problem is caused by the clock fault.

06 GSM BSS Network KPI (Network Coverage) Optimization Manual

Recommend Documents