wcdma rno call drop problem analysis guidance

Product name Confidentiality level WCDMA RNP For internal use only

Product version V100R001 Total 29pages

WCDMA RNO Call Drop Problem Analysis

Guidance

For internal use only

Prepared by URNP-SANA Date 2004-03-20 Reviewed by Date Reviewed by Date Granted by Date

Huawei Technologies Co., Ltd.

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WCDMA RNO Call Drop Problem Analysis Guidance For internal use only

2004-07-16 All rights reserved , Total29

Revision record

Date Revision version change Description Author

2003-09-03 1.00 Initial release Xie zhibin

2004-03-20 1.01 Modification based on the UAE experience Xie zhibin





Table of Contents

1 Overview ........................................................................................................................ 6 2 Common problem ........................................................................................................... 8 2.1 Neighbor list analysis................................................................................................. 8 2.2 Coverage analysis....................................................................................................12 2.3 Handover analysis....................................................................................................17 2.4 Signaling analysis.....................................................................................................22

3 Cause Classification.......................................................................................................24 3.1 Equipment Causes ...................................................................................................24 3.2 RF Causes...............................................................................................................25 3.3 Adjustment Suggestions ...........................................................................................25

4 Appendix .......................................................................................................................25 4.1 Normal Release Process ..........................................................................................25

4.1.1 CS services of 1 rate plus PS services of 0 rates ..................................................26 4.1.2 CS services of 0 rates plus PS services of 1 rate ..................................................27





List of Figures

Figure 1 Call drop analysis flow.......................................................................................... 6 Figure 2 Call drop location ................................................................................................. 8 Figure 3 Prior to the call drop, the information about the active set and monitor set............... 9 Figure 4 Prior to call drop, Radio parameters information .................................................... 9 Figure 5 CPICH EcIo compare between scanner and UE ...................................................10 Figure 6 CPICH RSCP compare between scanner and UE.................................................11 Figure 7 SC compare between scanner and UE.................................................................12 Figure 8 The measurement control message from cell SC358 ............................................12 Figure 9 Call drop location ................................................................................................14 Figure 10 Prior to the call drop, the information about the active set and monitor set.....14 Figure 11 Prior to call drop, Radio parameters information...........................................15 Figure 12 EcIo compare between scanner and UE......................................................15 Figure 13 CPICH RSCP compare between scanner and UE........................................16 Figure 14 Signal strength change...............................................................................17 Figure 15 Call drop location .......................................................................................18 Figure 16 Scanner Best Server Scrambling Code........................................................18 Figure 17 EcIo compare between scanner and UE......................................................19 Figure 18 SC compare between scanner and UE........................................................20 Figure 19 Prior to the call drop, the information about the active set and monitor set.....21 Figure 20 RSCP coverage from SC018 ......................................................................22 Figure 21 signaling records of UE at the call drop point ...............................................23 Figure 22 Signaling records of RNC at the call drop point ............................................23 Figure 23 RNC signaling record at the call drop point－RL FAIL_IND...........................24 Figure 24 Signaling process for CS services of 1 rate plus PS services at 0 rates .........26 Figure 25 Signaling process for CS services of 0 rates plus PS services of 1 rate.........27





WCDMA RNO Call Drop Problem Analysis Guidance

Key words：Call drop, power control, handover, coverage

Abstract：This guideline provides the general flow of the call drop analysis, the analysis method,

cause classification, parameter adjustment suggestions, and normal release signaling

flow.

List of abbreviations：

Abbreviations Full spelling SC Scrambling Code BLER Block Error Rate TPC Transmission Power Code SRB Signaling Radio Bearer





1 Overview Based on the present tools, the test tool and post processing tool for call drop analysis

related to this guideline is as following:

Qualcomm test UE（6200，6250）/MOTO A835 test UE/ LG test UE

Agilent scanner 6455c/ DTI Scanner

Agilent 6474A software/ TEMS /Probe

ACTIX Analyzer (V2.0 above)/ Assistant

The definition of call drop is:

Figure 1 Call drop analysis flow

Call drop analysis flow:

1. Call drop location analysis: based on the location of the call drop event in the map window

in the post processing tool, following information need to be got:





l the place of the drop call

l in the edge of the 3G coverage or not

l which 3G cells related

l the distance between related 3G cells and the drop call point

l which 3G cell the call dropped on

2. Neighbor list analysis: to find out any cell not defined in the neighbor list, following

information need to be got:

l the best serving 3G cell before the call dropped

l the best serving 3G/2G cell after the call dropped

l the existing neighbor list of the best serving 3G cell (intra-freq HO neighbor list ,

inter-freq HO neighbor list , inter-RAT HO neighbor list )

3. Coverage analysis

l analyze the pilot coverage to get information about: CPICH transmission power,

whether following coverage events take place or not: Coverage limited, System

interference, Poor uplink coverage, Poor downlink coverage, pilot pollution

l analyze the service coverage to get information about: Service related Maximum

downlink transmission power, SIR before the call dropped, Max uplink transmission

power allowed for UE, Actual uplink transmission power before the call dropped

4. handover analysis to get information about:

l the signal strength change of the target call and the serving cell

l whether following cause exist or not: insufficient handover area, too late to start CM, too

late to add target cell, too early to delete serving cell, interaction problem among 3 type

of handover

l whether ping-pang handover exist or not

5. Signaling analysis: as for those call drop that still confused about the exact reason

through analysis mentioned above, the signaling must be analyzed. Signaling of different

interface including: Iu, Iub, Iur, Uu. Signaling of different layer including : NAS, RRC. In addition,

analysis signaling in UE side in conjunction with signaling in network side.

The structure of this document is as follows:

1. Overview, giving the analysis flow.

2. common problem, giving the detailed analysis methods for common problem

3. Cause classification, classifying call drop causes and giving analysis and modification

suggestions accordingly.

4. Appendix: Signaling in the process of normal release





2 Common problem

2.1 Neighbor list analysis

There maybe missing neighbor if the best serving cell is not the same one before and after

the call dropped. Prior to the call dropped, the best serving cell maybe not the signal strongest

cell. The best serving cell should be picked out by the latest measurement control message and

corresponding event measurement report.

The characteristic of the missing neighbor is: compare the scanner data with UE data,

l prior to the drop, the CPICH Ec/Io (and CPICH RSCP) degrades for UE ONLY while

scanner shows no degradation

l prior to the drop, the best server for the UE is not the same as that of the scanner

Figure 2 Call drop location

The position of the drop call was not in the edge of the 3G coverage. The call dropped on

cell SC358. The distance between cell SC358 was very far away from the drop call point.





Figure 3 Prior to the call drop, the information about the active set and monitor set

Prior to call drop, on the basis of the measurement results from UE, only sc358 in the active

set, no cell in the monitor set.

Figure 4 Prior to call drop, Radio parameters information

Prior to call drop, on the basis of the measurement results from UE, RSSI was not very low,

and SIR was negative.





Figure 5 CPICH EcIo compare between scanner and UE

Prior to the drop, the Ec/Io degrades for UE ONLY while scanner shows no degradation.





Figure 6 CPICH RSCP compare between scanner and UE

Prior to the drop, the RSCP degrades for UE ONLY while scanner shows no degradation1.

1 During the test, the antenna of the scanner is mounted on the top of the vehicle, and the UE is in the car, the car penetration loss is nearly 10 dB.





Figure 7 SC compare between scanner and UE

Prior to the drop, the best server for the UE was not the same as that of the scanner, the

best serving 3G cell before the call dropped is SC358, the best serving 3G/2G cell after the call

dropped is sc364.

MC358.txt

Figure 8 The measurement control message from cell SC358

Conclusion: cell SC364 should be defined in the neighbor list of cell SC358 to avoid the call

drop in this place.

2.2 Coverage analysis

Coverage analysis including: analyze the active set and monitor set information before call

drop from UE measurement results, analyze the radio parameter information before call drop

from UE measurement results, compare the best server SC, RSCP, Ec/Io from UE and

scanner.





Definition for coverage events:

• System Interference:

– Both scanner and UE, the signal strongest cell

– CPICH_EcNo_in_ActiveSet < -15 dB

– And, CPICH_RSCP_in_ActiveSet > -80 dBm

• Poor Uplink Coverage:

– Both scanner and UE

– CPICH_EcNo_in_ActiveSet > -15 dB

– And, CPICH_RSCP_in_ActiveSet > -95 dBm

– And, UeTransmittedPower > 15 dBm

• Poor Downlink Coverage:

– Both scanner and UE , the signal strongest cell


– And, CPICH_RSCP_in_ActiveSet < -95 dBm

– And, UeTransmittedPower < -15 dBm.

• Coverage Limited

– Both scanner and UE , the signal strongest cell


– And, CPICH_RSCP_in_ActiveSet < -95 dBm

– And, UeTransmittedPower > 10 dBm.

• Pilot pollution:

– 4 or more pilots with their Ec/No above -15 dB are in the pilot pollution

relative threshold(for example:8 dB)

To analyze the coverage, need to:

l Analyze the pilot coverage in conjunction with the service coverage

l Analyze the uplink coverage in conjunction with the downlink coverage

l Analyze the scanner data in conjunction with the UE data

l Analyze the CPICH RSCP in conjunction with CPICH Ec/Io, SC






The position of the drop call was in the edge of the 3G coverage, the call dropped on cell

SC314, the distance between cell SC314 was very far away from the drop call point.


Prior to call drop, on the basis of the measurement results from UE, only sc314 in the active

set, no cell in the monitor set.





Figure 11 Prior to call drop, Radio parameters information

Prior to call drop, on the basis of the measurement results from UE, RSSI was very low, and

SIR was negative. In addition, the uplink transmit power from UE reaches the maximum2.

Figure 12 EcIo compare between scanner and UE

Prior to the drop, the Ec/Io degrades for both UE and scanner.

2 In the network, we defined 21dBm as ”Max uplink transmission power allowed for UE”, but here what we seen is above 21dBm, that’s measurement error, based on the specification 25.102, the tolerance can be +2 dB / -2 dB .





Figure 13 CPICH RSCP compare between scanner and UE

Prior to the drop, the RSCP degrades for both UE and scanner.

Conclusion: the coverage should be enhanced here to avoid the call drop in this place.





2.3 Handover analysis

Figure 14 Signal strength change

In the diagram, the graduation unit on the horizontal axis is 2 seconds. SC60 is the serving

cell and SC130 is the target cell. As the handover threshold of 1a event is 5dB, the delay is 3dB,

the delay trigger time is 640ms, the filter coefficient is 5 (2 seconds is required), so the

requirement for the handover area is: The lasting time when (Ec/Io of 60 cell – Ec/Io of 30 cell) <

2dB is about 3 seconds. The value in the circle as shown in the diagram cannot meet the

requirement.






The position of the drop call was not in the edge of the 3G coverage.

Figure 16 Scanner Best Server Scrambling Code





It shows that drop call 1 occurred at an area of frequent change of best server as shown by

the scanner scrambling code plot.

Figure 17 EcIo compare between scanner and UE

Compare Ec/Io from both scanner and UE at the time of the drop: the UE Ec/Io drop to < -21

dB while the scanner remained above -11 dB.





Figure 18 SC compare between scanner and UE

Comparing the best servers from the UE and the scanner at the time of drop: for the scanner

and UE SC009 is the best server prior to the drop. However, before the drop, the scanner

selected SC018 as the best server while the UE continued to have only SC009 in its active set

resulting in the drop call. Immediately after the drop, the UE camps on SC018.






Examining the UE Active and Monitored set: does not show SC018 to be measured by the

UE prior to the drop. This scenario resembles a missing neighbour problem, although in this case

the two cells in question are neighboured.

It seems that the best server’s changes from SC009 to SC011 and then to SC018 were too

fast for this UE to perform soft handoff on time. Although, other UEs may have succeeded in

performing soft handoff in such conditions, it is important to improve the cell dominance in the

affected area.3

3 Qualcomm UE has call drop here, but MOTO UE doesn’t.





Figure 20 RSCP coverage from SC018

At the location of the drop, SC018 should not be the best server. The cell is extending into a

large area. E.g. around the location of drop call, SC018 RSCP is > -75dBm. Cell SC018 clearly

requires some down tilting to control its interference into the area of Drop 1. Summary: The drop call

appears to be associated with unnecessary change of best servers caused by excessive

dominance of SC018. To improve the dominance in the affected area, SC018 should be

considered for down tilting.

2.4 Signaling analysis

Here only signaling on the standard interface is listed. For signaling of various modules

inside the equipment, please refer to other documents.

For normal release signaling flow, please refer to the appendix. For normal handover

signaling flow, please refer to other documents.

The basic idea of signaling analysis is to make analysis from the upper layer of the protocol

down to the lower layer: NAS signaling, RANAP signaling, RRC signaling, NBAP signaling.

Compare the signaling of UE with that of RNC, and see whether there is any message that the

peer end does not receive.

UE signaling records in case of call drop are shown as follows:





Figure 21 signaling records of UE at the call drop point

The RNC signaling records in case of call drop are shown as follows:

Figure 22 Signaling records of RNC at the call drop point





In case of call drop, RNC will initiate Iu release or RAB release. Signaling plane abnormality

will cause RNC to send message RANAP_IU_RELEASE_REQUEST, Service plane abnormality

will cause RNC to send message RANAP_RAB_RELEASE_REQUEST

In case of call drop, there maybe message NBAP_RL_FAIL_IND at Iub interface. The failure

cause value maybe 'Synchronization Failure'. If all the cells in the active set send message

NBAP_RL_FAIL_IND and no NBAP_RL_restore_IND message has been received within

T_RLFAILURE, then. RNC will start the release process, as shown below.

Figure 23 RNC signaling record at the call drop point－RL FAIL_IND

3 Cause Classification The causes resulting in call drop may be classified into two categories. One is related to the

equipment, That is, call drop due to the equipment defects, such as UE , NODEB, RNC,CN; the

other is related to RF, that is, call drop due to coverage problem or unsuitable radio layer

parameters.

3.1 Equipment Causes

Equipment causes can seek help from R&D support engineer from related products.





3.2 RF Causes

1） Poor coverage (CPICH RSCP is low). Different services have different coverage

requirements. Refer to WCDMA RNP Special Study - Pilot Receiving Strength

Requirements Analysis under Given Power Ratio Relations.doc.

2） Strong downlink interference (CPICH RSCP is not low, but Ec/Io is low). Different

services have different coverage requirements. Refer to WCDMA RNP Special

Study - Pilot Receiving Strength Requirements Analysis under Given Power Ratio

Relations.doc.

3） Strong uplink interference. On the basis of the RSSI scanning result or analysis of

the SIB7, there is uplink interference.

4） Insufficient handover area

5） Missing neighbor

3.3 Adjustment Suggestions

1） If coverage is poor, we can reduce the downtilt and adjust the azimuth, or we can

increase the pilot transmit power or maximum downlink transmit power for service.

The negative effect: is other places maybe interfered, and soft handover ratio maybe

higher.

2） If downlink interference is strong, first make sure whether it is internal network

interference or external network interference. If it is internal network interference,

find the interference source cell, increase the downtilt and adjust the azimuth, or

reduce the pilot transmit power or maximum downlink transmit power for the service.

The negative effect is coverage in other places may become discontinuous, and soft

handover areas maybe shrink.

3） As for the handover area is insufficient, and if it’s too slow to add the target cell, we

can modify corresponding 1a event parameters. If it’s too fast to delete the serving

cell, we can modify corresponding 1b event parameters. The negative effect is other

places may be interfered and soft handover ratio maybe increase.

4 Appendix

4.1 Normal Release Process

The normal release process may vary based on the current services combination in UE. The

services may be CS services of 1 rate plus PS services of X rates. In this guideline, CS services

of 1 rate plus PS services of 0 rates, CS services of 0 rates plus PS services of 1 rate are given

first. CS services of 1 rate plus PS services of X rates will be discussed later.





4.1.1 CS services of 1 rate plus PS services of 0 rates

Figure 24 Signaling process for CS services of 1 rate plus PS services at 0 rates

The release process includes two phases: NAS layer release and AS layer release. The AS

layer release phase includes: IU interface release, RRC release and Iub interface release. The

signaling process is detailed as follows:

1. UE sends RRC_UL_DIR_TRANSF message to RNC, in which the nas message is 0325,

indicating that it is a disconnect message in the call control sub-layer.

2. RNC sends RANAP_DIRECT_TRANSFER message to CN, in which the nas pdu is 0325,

indicating that it is a disconnect message in the call control sub-layer.

3. CN sends RANAP_DIRECT_TRANSFER message to RNC, in which the nas pdu is 832d,

indicating that it is a release message in the call control sub-layer.

4. RNC sends RRC_DL_DIRECT_TRANSF message to UE, in which the nas message is

832d, indicating that it is a release message in the call control sub-layer.

5. UE sends RRC_UL_DIR_TRANSF message to RNC, in which the nas message is 032a,

indicating that it is a release complete message in the call control sub-layer.

6. RNC sends RANAP_DIRECT_TRANSFER message to CN, in which the nas pdu is 032a,

indicating that it is a release complete message in the call control sub-layer.

7. CN sends RANAP_IU_RELEASE_COMMAND message to RNC to start the release of

the Iu interface resources, including resources of RANAP layer and ALCAP layer.

8. RNC sends RANAP_IU_RELEASE_COMPLETE message to RNC.

9. RNC sends RRC_RRC_CONN_REL message to UE to start the release of RRC

connection.





10. UE sends RRC_RRC_CONN_REL_CMP message to RNC.

11. RNC sends NBAP_RL_DEL_REQ message to NODEB to start the release of the Iub

interface resources, including resources of NBAP layer, ALCAP layer and PHY layer.

12. NODEB sends NBAP_RL_DEL_RSP message to RNC, and the whole release process

is completed.

4.1.2 CS services of 0 rates plus PS services of 1 rate

Figure 25 Signaling process for CS services of 0 rates plus PS services of 1 rate

The signaling process is detailed as follows:

1. UE sends RRC_UL_DIR_TRANSF message to RNC, in which the nas message is 0a46,

indicating that it is the “deactivate PDP context request” message in the session management

sub-layer.

2. RNC sends RANAP_DIRECT_TRANSFER message to CN, in which the nas pdu is 0a46,

indicating that it is the “deactivate PDP context request” message in the session management

sub-layer.

3. CN sends RANAP_DIRECT_TRANSFER message to RNC, in which the nas pdu is 8a47,

indicating that it is the “deactivate PDP context accept” message in the session management

sub-layer.

4. CN sends RANAP_RAB_ASSIGNMENT_REQ message to RNC, which contains the





to-be-released RAB list, including to-be-released RAB ID.

5. RNC sends RRC_DL_DIRECT_TRANSF message to UE, in which the nas message is

8a47, indicating that it is the “deactivate PDP context accept” message in the session

management sub-layer.

6. RNC sends NBAP_RL_RECFG_PREP message to NODEB.

7. NODEB sends NBAP_RL_RECFG_READY message to RNC.

8. RNC sends RRC_RB_REL message to UE, to release RB service.

9. NODEB sends NBAP_RL_RECFG_COMMIT message to RNC.

10. UE sends RRC_RB_REL_CMP message to RNC, and RB service release is completed.

11. RNC sends RANAP_RAB_ASSIGNMENT_RESP message to CN, and RAB release is

completed.

Note:

Compare with the release process of CS services of 1 rate plus PS services of 0 rates.

Steps1 through 3 here are corresponding to steps1 through 6 for CS services of 1 rate plus PS services of 0

rates. That is NAS release.

Here steps 4 through 11 are particular.

Steps12 through 17 here are corresponding to steps 7 through 12 for CS services of 1 rate plus PS services

at 0 rates.

12. CN sends RANAP_IU_RELEASE_COMMAND message to RNC to start the release of

the Iu interface resources, including resources of RANAP layer and ALCAP layer.

13. RNC sends RANAP_IU_RELEASE_COMPLETE message to RNC.

14. RNC sends RRC_RRC_CONN_REL message to UE to start the release of the PRC

connection.

15. UE sends RRC_RRC_CONN_REL_CMP message to RNC.

16. RNC sends NBAP_RL_DEL_REQ message to NODEB to start the release of the Iub

interface resources, including resources of NBAP layer, ALCAP layer and PHY layer.

17. NODEB sends NBAP_RL_DEL_RSP message to RNC, and the whole release process

is completed.





List of reference ：

[1] 3gpp Protocol, 25.331




[5] GMCC-HUAWEI WCDMA Radio Network Optimization Report of the second phase in the

pilot of Dongguan

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