Rabu, 06 Juli 2011

Call failure caused by low paging channel gain

Call failure caused by low paging channel gain
Typical case:

In the beginning of origination, MS Rx power is normal, pilot Ec/Io is normal, reverse Tx power is normal;
In the call procedure, MS moves far away from BTS, when MS is some distance from BTS (inside the coverage), access is failed;
At the point of access failure, MS can not stay in the current cell or always is in initialization state, or stay in other cell whose pilot Ec/Io is very low;
At the point of access failure, test pilot strength, the Ec/Io of the origination cell PN is normal;
Use the equipment (like Viper) to test the power of code domain, and find this cell paging channel power is not enough.


Analyzing:
Paging channel gain is set in background. If it is too low, even if pilot power is high, but MS can not stay in this cell because it can not demodulate paging message.
In the above case, when MS starts origination, all the signals are normal. But when MS is far away from BTS and exceeds the paging channel coverage, MS will not receive paging channel message correctly and call will be failed finally. After call failure, MS can still not stay in the current cell. Use the equipment (like Viper) to test the power of code domain, and can find this cell paging channel power is not enough


Optimization method:
Check background parameters setting and adjust paging channel gain.

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