Call Setup Failure Analysis

Call Setup Failure the following reasons are:

1. Low Signal Strength2. Interference3. High Congestion on SDCCH4. High Congestion on TCH5. Transmission Fault6. Faulty TRU/Hardware7. Central Processor Overload8. Software File Congestion9. Cell is not defined in MSC

Possible Solutions:

• Low signal strength => Signal strength analysis.• Interference => Interference analysis.• High Congestion on SDCCH:

==> Define more SDCCHs.

==> Activate adaptive configuration of logical channel feature and immediate assignment to TCH.

• High Congestion on TCH:

==> Add capacity/Tune coverage array.

==> Activate assignment to worse cell.

Analysis :

• SDCCH Blocking

Multiple Channel Requests.

Successful Random Access after the third try.

==> Congestion in SDCCH.

• From plot, identify which & where in log file the dropped call occurs.• In the log file, Jump the drop call event.• Check the Radio environment just before drop:

–If High Rxqual for a longer period of time and RLINKT expire ==> Interference problem.

–If Low SS DL, SS DL < MS SENS (-104dBm) ==> low signal strength problem.

–If TA > 63 ==> too far from the cell.

• If DL radio is good, check the TX power. If there is MS power down regulation when the MS is close to the cell. If full power ==> suspect uplink interference or antenna, TMA problem.

• Verify or isolate the problem using STS (Drop call and reasons).• Congestion: Activate half rate, activate cell load sharing.

TCH Blocking :

TCH Blocking maybe due to the following reasons

1. Handover and Power budget margins

2. Cells too large

3. Capacity Limitations (Congestion)

4. Incorrect or Inappropriate Timer

Optimization for tips:

1. Handover and Power budget Margins

Handover Margins should be properly optimized to move the traffic to neighboring cell. Strict handover margins can results in lower handovers and ultimately congestion in cell.

TIPS:

6 dB handover margins are considered to be an appropriate margin for handover. A strict handover margin results in the strict criteria for Power Budget Handovers also. Setting a lower value of handover margin will initiate ping pongs handovers, which are not considered good for network health.

2. Cells too Large

If cell are too large meaning antenna too high or antenna too shallow, it will pull in out of area traffic again causing congestion in the cell.

TIPS:

Consider reducing antenna height to reduce the footprint of the site. Also increase the antenna tilt (the max tilt is 10)