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Improving GPRS KPI through Cell Reselection Parameter Optimization

Our Story:

1. Background

Mobility management plays a crucial role in the user tracking process in the GSM network. The Mobile Station (MS) performs cell selection and reselection when it moves around the coverage area. It also sends the location update message to the Serving GPRS Support Node (SGSN) so that the network can be always aware of the MSs current location.

Frequent cell reselections result in an increase of location updates and present three main drawbacks with negative impacts on 2G services: Firstly, the MS cannot respond to the paging during the location update, decreasing the call completion rate in the system. Secondly, ping-pong location updates increase the signaling load on the Stand-alone Dedicated Control Channel (SDCCH). Lastly frequent cell reselections and location updates decrease the PS Accessibility and increase the PS call drop rate as a result of frequent cell updates

In August 2014, the UL PS Accessibility was degraded in H BSC due to an increase of Establishment failures caused by MS no reply.

2. Root cause Analysis:

After investigations, two cells located on the Highway were identified as main contributors due to ping-pong cell reselection.

3. Solution: Cell Resection Parameter Optimization

The Cell Reselection Offset was modified on the affected cells in order to create dominance by reduce the frequent cell reselections and hence improve the 2G PS accessibility.

4. Results and Summary

The Number of UL GPRS Establishment Failures due to MS No reply were reduced

The number of cell reselection were reduced as a result of Cell Reselection Parameter adjustment

The Network UL PS Accessibility was recovered

Lessons Learned:

Cells at high traffic location, Location Area (LA) are to be carefully be monitored in order to reduce the risk of KPI degradation as a result of ping-pong cell reselection .A proper LA planning is always required as a preventive method.

2014-10-01

Huawei Proprietary - Restricted Distribution

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