CDMA Call failure caused by wireless link fading and
Call failure caused by forward and reverse imbalance
Call failure caused by wireless link fading
Typical case:
In the beginning of origination, MS forward and reverse signal are normal, but finally
the call is failed;
In this period MS received signal fades greatly ( MS is in the corner of street or goes
into subway).
Analyzing:
When MS is in the corner of the street or goes into subway, the radio environment will
change greatly and signal fade very fast. Usually both forward and reverse link will
fade at the same time. If MS starts access at this time, it is very possible to meet access failure for signal losing.
Note:
For the signal losing, MS and BTS sides will transmit again. If the fading time is short,
access procedure can be continued; but if the fading time is too long, the retransmitted
signal may be lost and the access will be failed.
Solution:
Optimize network topology structure and decrease the area where signal fades greatly.
Call failure caused by forward and reverse imbalance
Typical case:
MS received power and strongest pilot Ec/Io maintain in good state, such as Rx
Power>-100dBm, Ec/Io>-15dB;
After MS origination, reverse Tx power is increasing continuously, until 23dBm, but
access is failed;
After access failure, MS will stay in previous pilot;
When MS is nearer to BTS, MS call can be successful. Observe Tx_Adj, it is a positive
value. (Note: only when MS acquires F-TCH and reverse closed-loop power control
starts working, Tx_Adj value will be efficient)
Analyzing:
In the above case, MS Rx power and pilot Ec/Io are all good, and this means the
forward link is good. But in MS origination procedure MS is increasing transmitting
power until maximum, and this means the reverse link is bad.
That is forward and
reverse imbalance. Tx_Adj>0 also means forward is better than reverse.
Because forward is better than reverse, so in the edge of coverage BTS can not receive
the signal from MS correctly and call is failed.
Optimization method:
Find the rootstock of imbalance:
Judge if the cell power configuration is too high:
Judge if the pilot gain is too high:
Judge if there is reverse interference;
Back to CDMA Menu