Drop Call Analysis

MOS report for VMS

Drop Call No. 1 & 2

1. Drop Call No.1 & Drop Call No.2:

Serving Cell: CI=10471, LAC=113, BSIC=75, BCCH=88;

Time: 17:43:29 pm;

Date: Oct 9th.

Description: Both the outgoing and incoming call mobiles dropped at the same time.

2. Problem analysis:

The mobile received RxLevBCCH=-83dbm (within normal range) from the serving cell (CI=10471,

LAC=113, BSIC=75, BCCH=88); but Rx_Quality_Sub=7, which means the speech quality was very poor.

There was more Measurement Reports than usual appeared at the uplink, which means the mobile received

strong interference signal from adjacent frequency and caused high BER. In such cases, the mobile might not

able to demodulate the BSIC of neighbor cells; the serving cell cannot receive Measurement Reports correctly.

The above problems would result in interferences to network during a call then eventually caused poor speech

quality and drop call.

3. Advised solution

a) First check the frequency allocation around the serving cell to see if there is inappropriate allocation that

causes interference to the same or adjacent frequency.

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MOS report for VMS

b) Check interference caused by equipments. For example, self-excitation of carrier frequency device,

intermodulation interference of antenna, performance degradation of antenna, repeater station etc.

c) Check traffic statistics from OMC. For example, cells that have frequent handover failure, performance

measurements of interference spectrum, receive level, receive quality and drop call.

d) If the interference is external to the network, use sweep generator to search the source of interference.

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Drop Call No. 3

1. Drop Call No.3


Time: 17:46:30 pm;

Date: Oct 9th.

Description: The outgoing call mobile dropped.



LAC=113, BSIC=75, BCCH=88); but Rx_Quality_Sub=7, which means the speech quality was very poor.

There was serious interference to the cell and caused drop call.

3. Advised solution

First to check the frequency allocation around the serving cell (CI=10471, LAC=113, BSIC=75, BCCH=88).

If there is any mistake in the allocation, amendment is needed to eliminate inter-network interference. If the

allocation is correct, check around this area for any repeater or jammer that may cause external interference.

Drop Call No.4 (Adjacent frequency interference)

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MOS report for VMS

1. Drop Call No.4


Time: 11:42:11 pm;

Date: Oct 12th.




LAC=113, BSIC=75, BCCH=88); but Rx_Quality_Sub=7, which means the speech quality was very poor. The

neighbor cell information demonstrates that there was serious adjacent frequency interference from neighbor

cell. The interference caused high BER and poor speech quality then drop call.

4. Advised solution

Adjacent frequency re-allocation is advised for base stations around the serving cell.

Drop call No.5, caused by across-boundary coverage:

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3. Phenomenon

Log file name: LOG_2008-10-10_15-02-48-386.lg4

Time: 16:28:20 pm;

Date: Oct 10th.


4. Problem analysis

The mobile switched to the serving cell: CI=10133, LAC=132, BSIC=27, BCCH=90 at 16:28:20 pm.

RxLevBCCH=-60dbm (within normal range). At the same time the mobile received strong signal

(RxLevBCCH=-56dbm, greater than the serving cell) from Cell=HNI_BDH3_PHO_DUC_CHINH,

BCCH=89, BSIC=55 and caused drop call (RxQualSub=7).

5. Advised solution

We advise to examine the neighbor cell information of the cell CI=10133, LAC=132, BSIC-27, BCCH=90.

We advise on declination of the antenna of Cell= HNI_BDH3_PHO_DUC_CHINH, BCCH=89, BSIC=55.

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Drop Call Analysis

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