Call failure caused by poor coverage

Typical case:
MS Rx power is about -100dBm or less;
MS Tx power tends to 23dBm;
The strongest pilot Ec/Io is <-15dB;
After MS sends origination message, it is hard to access successfully, finally it is shown: call failure;
Analyzing:
MS call failure caused by poor coverage is normal phenomenon. In the edge of coverage, MS receive power is very low and usually Rx power is about -100dBm or less, the strongest pilot Ec/Io is -15dB or less; MS Tx power will tend to the maximum 23 dBm.

When MS starts origination in the edge of coverage, the signal transmission between BTS and MS can not be received correctly for the bad air link and the call will be failed.
In addition, even if MS starts origination in good coverage area, it will take some time to access for MS. When MS moves fast to outside or cell (cars or railway stations), MS may have reached outside of the coverage before access completion, this will lead to call failure.

Note:
In CDMA protocol MS maximum Tx power is 23dBm (0.2W). But MS is produced by different manufactures; the real maximum Tx power may exceed 23 dBm in practice.

Optimization solution:
The ultimate way for this kind of problem is add new BTS or repeater in blind coverage area or poor coverage area.
If adding new BTS is not possible, other methods also can be used to improve coverage, like increase antenna height, select large gain antenna, and adjust antenna azimuth and down tilt. But these methods can not solve problems ultimately, and it should be very careful when change these parameters.