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Call failure reasons analyzing

 

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Call failure caused by equipment problems
Strictly speaking, equipment problems should be solved before network optimization, but actually a lot of equipment problems are found in optimization.
Typical phenomena
The problems are sudden: the previous network works normally, and the problems happen suddenly.
The problems are universal: after DT test, it can be found that the problems happen in large area.
Analyzing:
Inquire if there is hardware changing recently, like boards replacing or transmission changing and so on; Inquire if there is software changing recently, like the software version updating or parameters adjustment;

If there are software and hardware adjustment, check the adjustment and consider resuming these adjustments, observe if the problem will happen;

If there is no adjustment recently, start single cell checking and judge if there is problem in hardware;
Single cell checking can find the obvious equipment problem, but some secluded problems are hard to find. At this time, boards resetting and replacement can be used to locate the problem.

Solution:
Because the reason is equipment problem, so the solution can not be called as “optimization”, it is just like troubleshooting.
In troubleshooting, TRX, CHM, CCM, and antenna feeder system are the key points we should care for.
Note:
The operation for software and hardware should be very cautious. For commercial network, the operation should be carried out by operator’s engineers after operator’s permission;
All the operation for equipment should be after midnight, if there is problem in operation, everything should be resumed in time.

 

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.

 

 

 

 

 

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