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Why Dropout often Occurs to Standalone Base Stations

Problem description

After the cutover of Jinwu GSM network in Gansu, the deployment personnel report that Minqin base

station is not in normal service, which is shown by the low handover success rate of various cells and

the dropout rate fluctuating between 1 - 11%.

Analysis and solutions

The traffic statistics of Minqin base station shows that the interference of Minqin is slight and all the

idle channels are in fringe 1. The personnel of network layout department perform the call test at the

place about 10km away from Minqin base station. The mobile phone displays the receiving level is

less than -85dBm at this test site, but as soon as a call is placed, the mobile phone fails to find the

network and the call can not be connected.

Trace Abis interface to find that the up link and down link of Minqin base station are in serious

imbalance, with the down link 20dB higher than the up link. Perform communication test in the route

test within 5 km around the base station. The communication between the mobile phone and fixed

phone, and that between mobile phones are normal at the place near the base station. At the place

about 5 km away from the base station, the voice in the fixed phone is not clear when the mobile

phone calls the fixed phone, but the mobile phone displays that the receiving level is OK and the voice

is clear. When the call between mobile phones is handed over from cell 1 to cell 2, dropout occurs to

one mobile phone, and a loud sound can be heard in the other mobile phone, but it does not drop out.

During the route test, observe the service cell, the frequency bands of two adjacent cells, the receiving

level and cell identification code. When the test route is between cells 1 and 2, and is far away from

the base station, it is found that the BCCH frequency band of service cell is No. 52 whose level is the

strongest, BCCH frequency band of adjacent cell is No. 56, and the level of BCCH frequency band of

No. 48 is the weakest. Unlike the parameters in the layout, Table 1 shows the layout data and Table 2

shows the test data.

00138256240Minqin 300126752120Minqin 2

001161480Minqin 1

CI HEXTCH frequencyband

BCCH frequencyband

Antenna directionSector

Table 1

00116148240Minqin 300138256120Minqin 2001267520Minqin 1

CI HEXTCH frequencyband

frequency bandAntenna directionSector

Table 2

It is obvious that the actual data of frequency band are incorrect. It is learned that the network data are

the same as those of layout. Therefore, the problem may be with the engineering installation. Later

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check shows all TX jumpers of three cells are connected incorrectly, while RX jumper is connected

correctly. After the connecting line is adjusted by BTS personnel, perform the route test again and it is

found that cells 2 and 3 are still connected reversely. The test after recheck and readjustment shows

everything is normal. Up and down powers are basically in balance, mobile phone access to network

is OK, and normal communication can be realized in the places about 20 km away east and north ofthe base station.

Conclusion

1. It is necessary to check the installation and data configuration of the base station at the beginning

of the optimization flow.

2. Other causes can be considered for the base station with slight interference, high dropout rate and

abnormal handover.

3. The correct sequence of Minqin cell TX jumpers is 1/2/3, but the sequence is 2/3/1 in the actual

engineering, which is first adjusted to 1/3/2 and then adjusted to the correct sequence. This also

shows the poor operability of the actual connecting line.

For example, there should be a common specification on whether the connectors should be numbered

from 0 or from 1.