SDCCH Drop

When we assigned SD for call origination and at that time due to some problem or any mismatch comes by which SD loss occurs, it is called as SD Drop.

It occurs between allocation of SD and before TCH allocation. Sometimes SD drop occurs because queuing is not activated in the system.

If SD drop is high plz look on parameters likeovershooting, shift the SD timeslot , may be hardware issue, interference, change the values of RXP, PMAX, may be issue of uplink or downlink issue in that cells for UL put a TMA in that cell and for DL provide tilt ,re orient that antenna.

If SD Drop is high:
If SD drop is high plz look on parameters like-
Overshooting
Shift the SD time slot
Hardware issue
Interference
Change the values of RXP PMAX
It may be uplink or downlink issue in which cells for UL put a TMA in that cell and for DL provide tilt Re orient that antenna.

Reasons of SD Drop:
Hardware Fault.
Interference.
MAIO mismatch.
Bad Coverage.
High TR Fail.
Outage.
Overshooting.
Abis Drop.
High Path Loss.
Wrong Parameter Planning.
Due to ICM Band(CDMA)
High LAPD Utilization
Heavy blocking and DR feature being used extensively

Solutions for removal of SD Drop:

Interference:

Check the BCCH Plan (C/I or C/A).
Co-BSIC & Co BCCH.
Use latest ND 111 and MapInfo to find out proper frequency to reduce interference.

Arrange Drive Test:

The best way to find the real issues for Interference makes DT.
Check interference by Interference scanning.
Check clean BCCH by frequency scanning.

Overshooting:
LAC Planning.
If a cell is picking call from long distance,Check the sample log according to TA.
Cell orientation need to be defined according to clutter.
Mount position
Effective Tilt

High TR Fail:
Check and clear TR fail from OSS end.

Bad Coverage:

If the drop call is due to low signal strength uplink, check the receive path of this particular TRX. Check receiver sensitivity, VSWR, feeder connection and etc. Drops due to Low Signal Strength.
If the drop call reason is due to low signal strength downlink, then, check the transmit path. Check cards, feeder and etc.
Use MapInfo or Google Earth to find location of sites.

High LAPD Utilization:

Check LAPD util report from OSS, and define 32 kbps signaling instead of 16kbps.

Hardware Fault:
Check Alarms.
TRX condition.
Check Path Imbalance.
VSWR of the Cell.
Connector Connection.
Some times you will find issues on BCCH TRX.In this case BCCH shift from one to other TRX will reduce SD drop.

Check for parameter:
Check the Timer T 3101
Check the Timer T 200(20ms)
T11 Expired(10 s)
MAIO check.


Useful Reports for SD Drop:
Use report ZEOL to find the alarms.
Use 208 for Path loss analysis.
Use 196 for UL-DL Interference.
Use 163 report for SD drop.
Use report 216 for detail SD Drop.
232 report for TA report.
62 for Adj cell having same or adj freq.
ND 111 for freq plan.
204 for BTS and cell report.