Successful assignments show the number of successful TCH allocations at call setup.
At unsuccessful assignment, the Assignment Complete message, sent by the MS, was never received by the BTS.
The formula is defined as:
% TCH ASSIGNMENT SUCCESS RATE |
= |
TFCASSALL |
X 100 % |
|
|
TASSATT |
|
|
Probable Reason |
No dominant serving cell |
The serving cell cannot cope with the TCH traffic. |
Severe congestion on TCH |
Failing TCH allocation for assignment or handover due to congestion |
Low signal strength for call access |
The signal strength might be higher on the BCCH than on the TCH. |
Interference |
Disturbance on SDCCH or target TCH |
Faulty transceiver |
Faulty equipment |
The following procedure should be performed for TCH Assignment analysis:
For TCH assignment success rate, the first thing, check the TCH Time Congestion.
If there is congestion on TCH, it is recommend doing the dimensioning and adding TRU based on carried TCH traffic demand.
If there is no congestion on TCH, check the output power of the BTS. If the output power is low, increase the output power.
If the output power is ok, check the faulty BTS by extracting BTS error log.
If hardware fault found, swap or repair HW.
Perform drivetests to check the coverage and received RxLEV.
If no dominant cell or similar signal strengths of a few cells found during drivetests, it is recommended to add BTS.
If there is no problem on the dominant cell, check the interference whether co-channel or adjacent channel.
Check the disturbance whether it is on SDCCH or target TCH. If disturbance found, improve the frequency plan.
Mostly, the problems of low TCH assignment are TCH availability and interference.