CDMA Call failure caused by too narrow MS search window and
Call failure caused by low paging channel gain
Call failure caused by too narrow MS search window
Typical case:
In call procedure, MS Rx power is normal, Tx power is normal also;
In call procedure, pilot Ec/Io is too low and can not maintain the requirement for
demodulation, finally call is failed;
Use PN Scanner to test pilot, the pilot Ec/Io of PN in active set is normal.
Analyzing:
MS Rx power and Tx power are all normal, use PN Scanner to test pilot: the pilot Ec/Io
of the PN in active set is normal, but MS received Ec/Io is too low. This indicates MS
can not distinguish some useful multipath signal. Usually it is caused by too narrow
search window of MS.
If MS search window is too low, MS can not find strong multipath signal. This will lead the useful signal dropping outside the search window;the Ec/Io will be too low;
the unuseful signal dropping outside the search window will become strong
interference. If MS can not demodulate forward signal, the call will be failed finally.
Note:
The above case is about MS search window problem. Also, for reverse signal BTS has
search window: they are access channel search window and traffic channel search
window, if they are too low, the reverse multipath signal will drop outside and call will
be failed.
Optimization method:
Check OMC wireless parameters and adjust the search windows.
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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