C09 WCDMA RNO Call Drop Problem Analysis

WCDMA Call Drop Problems Analysis

Course Contents

Definition of call drop problems Call drop problems analysis process Case study on call drop problems

Definition of call drop problems Definition of call drop problems :

Course Contents


Call drop problems analysis process

 General

call drop analysis flow

 Categories

for call drop reasons

Call drop problems analysis process General call drop analysis flow:

Call drop problems analysis process Call drop location analysis: based on the location of the call drop event in the map window in the post processing tool Neighbor list analysis: to find out any cell not defined in the neighbor list Analyze the pilot coverage to make sure whether following coverage events take place or not: Coverage limited, System interference, Poor uplink coverage, Poor downlink coverage, pilot pollution Handover analysis to make sure 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 Signaling analysis is used for those call drops that are still confused about the exact reason through analysis mentioned above

Call drop problems analysis process

 General

call drop analysis flow

 Categories

for call drop reasons

Call drop problems analysis process Categories for call drop reasons: 1.

RF problems

2.

Equipment problems RF problems usually can be find out by neighbor list analysis 、 coverage analysis 、 handover analysis, while signaling analysis is helpful to equipment problems.

Course Contents


Case study on call drop problems



RF concerned problems

1.

3.

Neighbor missing Coverage Limited Handover problems



Equipment concerned problems

1.

UE problem

2.

Data configuration problem

2.

Neighbor list analysis To analyze Neighbor list: to find out any cell not defined in the neighbor list. the best serving 3G cell before the call dropped the best serving 3G/2G cell after the call dropped 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

Neighbor list analysis There maybe missing neighbor if the best serving cell is not the same one before and after the call dropped. Before the call dropped, the best serving cell maybe not the signal strongest cell Before the call dropped, the best serving cell should be picked out by the latest measurement control message and corresponding 1d event measurement report. Compare the scanner data with UE data prior to the drop, the CPICH Ec/Io (and CPICH RSCP) degrades for UE ONLY while scanner shows no degradation prior to the drop, the best server for the UE is not the same as that of the scanner

Neighbor missing Call drop location-1-ScannerRscp:

Neighbor missing Call drop location-2-ScannerEc/I0 :

Neighbor missing Call drop location-3-ScannerBestserver :

Neighbor missing Before call drop, SC489 goes poor, while SC504 is good the moment before drop, according to the measurements by UE shown below; but SC03 which is not measured by UE is becoming good gradually :

Neighbor missing SC03 is becoming good gradually measured by Scanner:

Neighbor missing Further investigation shows different performance between UE and Scanner. Before the drop, the Ec/Io degrades for UE ONLY while scanner shows no degradation.:

Neighbor missing Before the drop, the RSCP degrades for UE ONLY while scanner shows no degradation:

Neighbor missing Before the drop, the best server for the UE is not the same as that of the scanner :

Corresponding measurement control shows there’s no neighbor relation between SC489 and SC03:

C:\ NeighborMissingSC03FromSC489.txt


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1.

3.





1.

UE problem

2.


2.

Coverage analysis To analyze the coverage: the pilot coverage CPICH transmission power Coverage limited System interference Poor uplink coverage Poor downlink coverage pilot pollution the service coverage 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

Coverage limited General definition of “coverage limited” : The signal of strongest cell should be in ranges: CPICH_EcNo_in_ActiveSet < Threshold1 And, CPICH_RSCP_in_ActiveSet Threshold3. Theshold1~3 is “-15 dB” 、 “ -95 dBm” 、 “ 10 dBm” respectively in our analysis

Coverage limited Call drop location-1-ScannerEc/I0 :

Coverage limited The strongest cell’s Cpich_Ec/I0 and Cpich_RSCP (shown in next page) is poor, while UE TxPower reaches the threshold of 21dBm:

Coverage limited The strongest cell’s Cpich_Ec/I0 and Cpich_RSCP is poor :





1.

3.





1.

UE problem

2.


2.

Handover analysis To analyze the handover: the signal change Source cell Target cell insufficient handover area Too late to add new cell Too early to delete old cell ping-pang handover

Handover problem Call drop caused by handover problems, is helpful for us to get solutions to parameters’ optimization. Here’s an example. Call drop place is shown below:

Handover problem Call drop location-ScanneEc/I0:

The UeTxPower is not high:

Handover problem The drop call occurred in the area of frequent change of best server shown by the scanner :

Handover problem Compare Ec/Io from both scanner and UE at the time of the drop: the UE Ec/Io drop to < -18 dB while the scanner remained above -6 dB :

Handover problem Comparing the best servers from the UE and the scanner at the time of drop: for the scanner and UE SC506 is the best server prior to the drop. However, before the drop, the scanner selected SC505 as the best server while the UE continued to have only SC506 in its active set resulting in the drop call. Immediately after the drop, the UE camps on SC505:

Handover problem It seems that the best server changes from SC506 to SC505 too fast for the UE to perform soft handover on time. As the handover threshold of 1a event is 4.5dB, the delay is 0dB, the delay trigger time is 320ms, the filter coefficient is 3 (1 second is required), so the requirement for the handover area is: the lasting time when (Ec/Io of 506 cell – Ec/Io of 505 cell) < 4.5dB is about 2 seconds :

Handover problem Uu_Interface messages that 1a event of SC505 was triggered at 54:04:

Handover problem But SC506 went bad too severe for the procedure of “Active Set Update” to be finished:





1.


2. 3.




1.

UE problem

2.


Equipment concerned problems During tests, problems caused by UE happen occasionally, we’ll give an example that we met with when testing with Motorola A835. Call drop place is shown below :

Equipment concerned problems Call drop location-ScannerEc/I0 :

Equipment concerned problems Call drop location-ScannerBestserver :

Equipment concerned problems Before call drop, SC507 went poor, and SC473 was becoming good according to the measurements by UE :

Equipment concerned problems Further investigation shows that UE reports event 1b of SC500 before drop instead of reporting event 1a of SC473 :

Equipment concerned problems Ec/I0 of SC500 before drop measured by UE :

Equipment concerned problems Ec/I0 of SC500 before drop measured by scanner :

There must be something wrong with the performance of UE’s measurement. Further reliability of UE is required .





1.


2. 3.




1.

UE problem

2.


Equipment concerned problems Problems caused by data configuration are always indiscoverable, here is an example. Call drop place is shown below :

Equipment concerned problems Call drop location-ScannerEc/I0 , The position of the drop call was at the border of two RNCs :

Equipment concerned problems Before call drop, SC473 went poor, and SC31 、 SC16 were becoming good according to the measurements by UE :

Equipment concerned problems Further investigation shows that UE reports event 1a of SC31 、 SC16 before drop:

Equipment concerned problems That active set updating about adding Sc31 was successful :

Equipment concerned problems While active set updating about adding Sc16 failed for the neighbor RNC cell configuration mistake:

Summary We’ve discussed of several kinds of call drop, so typical they are as mentioned above. Engineers may meet with call drops that seem more puzzling. Taking no account of equipment problems, RF problems can be solved by suggestions below mostly:

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 may be interfered, and soft handover ratio maybe higher.

2.

If the 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.

C09 WCDMA RNO Call Drop Problem Analysis

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