Gsm bss network kpi (sdcch congestion Rate) Optimization Manual

5.2SDCCH Congesiton Caused by Improper Configuration of LAC

Description
The SDCCH Congestion Rate of two cells in a BTS (S1/1/1) is up to 4.91%; however, the traffic of each cell is generally less than 3 Erl.
Handling Procedure
1. Query the counters of TCHs and SDCCHs and find that the traffic on TCH is not high with each cell less than 3 Erl. The number of SDCCH seizure requests is large, even reaching 3,032 times during busy hours. The traffic volume is up to 1.86 Erl, and the congestion rate is up to 4.91%.
The SDCCH is occupied in the following situations.
a. Transmitting the signaling before call setup
b. Transmitting the signaling of handover
c. Transmitting the signaling of location update in idle mode
3. Normally, the traffic volume on the TCH is 2.79 Erl (the number of available TCHs is 6).The number of TCH seizure requests (including handovers) is 318, which is within the normal range. The number of TCH handover requests is 146, which is also within the normal range. Therefore, the congestion may be caused by frequent location updates.
4. Check the LAC of this BTS and find that it is 0500. The LACs of the cells near this BTS are 0520. Change the LAC of this BTS into 0520. During busy hours, the number of SDCCH seizure requests becomes 298, the congestion rate becomes 0, and the traffic volume becomes 0.27 Erl.
Suggestion and Summary
1. Plan the LAC according to the geographical locations and habits of the MSs to minimize the location updates at the edge of a Lifer example, the traffic volume is high in urban areas. If there are more than two LAs, the mountains, rivers, or other natural resources should be set as the boundary of the LA to minimize coverage overlapping of different cells in two neighboring Lassie there is no mountain or river, the streets or the place with heavy traffic (for example malls) should not be set as the boundary of the LA. Generally, the boundary of the LA should not be parallel or vertical to the streets but beveled to the streets. Generally, in rural-urban fringe zone, the boundary of an LA should be set in the area with least traffic instead of in the area with high traffic to avoid frequent location updates. The value of LAC should not be set too great or too small. It is recommended that the number of TRXs be not more than 300.
2. When changing the LAC, note that the cells cannot have the same CGI. If the LAC is changed on the BSS side, the LAC should be changed on the MSC side accordingly.