Jumat, 03 Desember 2010

Poor Coverage

Poor Coverage

Another problem related with coverage is Poor Coverage. Poor coverage means that received level from any base station is not sufficient to guarantee a stable connection. Poor coverage area will have high risk to drop call. To identify areas suffering from bad coverage, the correlated received level to received quality and received level to timing advance measurements are used. An indication for bad coverage is that the received level is low and at the same time the received quality is poor or UE distribution is near the BTS (low Timing Advance). This can be analyzed for both directions (uplink and downlink) separately.

However, the same symptoms can indicate wrong neighbor cell list, which may lead to confusion. Therefore, it is significant to check each cell not only against coverage problem but against interference and wrong neighbour list as well.

Correlated power and quality or power and timing advance measurements give the operator good view of the cell coverage. After the cell is identified, the user can perform a geographical analysis of the identified cells and its neighbor relations.

Another indicator, which brings valuable information about poor network performance caused by lack of coverage, is handover problem due to lack of coverage. If the cell suffers from poor coverage it may have many rejected HO indications due to empty neighbor list. This cause is very much related with lack of coverage because BA list is transmitted in SACCH, which can be unreadable due to insufficient signal level or low C/I. In case of coverage problem in the same time there are many handover attempts due to low level or distance.

There are several possible causes of poor coverage that are:
1. HW failure/faulty
- RF transmitter part can’t transmit full power.
- Antenna faulty
- High VSWR due to incorrect termination of RF Cable, RF Jumper
- Damaged connector or cable contribute to additional losses
2. Antenna Configuration
- Antenna configuration (Type, Height, Tilt, Direction) isn’t configured properly
3. Wrong Parameter Setting
- Parameter Maximum Power isn’t set properly
- Wrong setting of handover parameter may cause cell dragging due to no candidate for handover
4. Missing Neighbor
- Missing neighbor may cause MS is handled by serving cell can’t be handed over to other cell due to no measurement can be performed at dedicated mode. MS will be served until its border cell with poor coverage and finally will be dropped

Another way that can be done to identify poor coverage is plotting drive test result into Google Earth. From this visualization we can see whether there is terrain or building block that cause poor coverage.

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