SD Block & SD Drop



       SD Block

 

SDCCH channel is a dedicated channel which is using for LAC updation, Call Setup, SMS in Ideal mode. It works in UL & DL
SD Blocking means that you are not getting SD resource for the call origination. When MS connects with Network then RACH and AGCH are provided. After AGCH, SDCCH is provided but if SDCCH is not provided at this time due to some problem or due to unavailable of SD by BSC.
Reason for SD Blocking:
·         LAC Boundary
·         High Volume of SMS
·         SD utilization is high
·         Time Slot faulty
·         Wrong SD Dimension
·         Hardware Issue

Solution for Removal of SD Blocking:

·       Check the no of SD channels available, if less, then increase SD channel while TCH Blocking should be taken care.
·         Check LAC boundary, if location update is more, then change the LAC of that site and set C2 and HYS.
·         Use of dynamic SDCCH (it is a BSC parameter)
·         Shift SD to new time slot
·         Adaptive configuration of logical channel switch ON
·         Check for T3212 value

SD Drop

 

                When SD is assigned for a mobile during call connection process and during this time due to any problem or any mismatch occurs by which SD loss occurs, It is between allocation of SD and before TCH allocation.

Reason for SD Drop:

·         Overshooting
·         Shift the SD time slot
·         Interference
·         HW Issue
·         Wrong parameter planning
·         Bad coverage
·         MAIO mismatch
·         High LAPD utilization
·         Wrong Power control settings
·         Check the Timer T 3101
·         Check the Timer T 200(20ms)

Solution for Removal of SD Drop:

Interference:
·         Check the BCCH Plan(C/I or C/A)
·         Co-BSIC & Co- BCCH
·         To find out proper frequency to reduce interference
Overshooting:
·         LAC Planning
·         If a cell is picking call from long distance, check the sample log according to TA
·         Cell orientation need to defined according to clutter
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.
Hardware Fault:
·         Check Alarms.
·         TRX condition.
·         Check Path Imbalance.
·         VSWR of the Cell.
·         Connector Connection.
·         Sometimes you will find issues on BCCH TRX. In this case BCCH shift from one to other TRX will reduce SD drop
 Wrong Parameter configuration:
·         Power control settings: Lack of good power control settings for SDCCH can lead to excess drop. Two types of power control 1.MS Power control 2.BTS Power Control
·         SDCCHREG: Function of this parameter Enable (1)/Disable (0), Enable the power control to minimize the drops.
·         INIDES (Initial desires signal strength): For the SDCCH UL and DL, Default value -70dbm, especially UL impact of drop rate, because extremely sensitive to interference, for INDIES from -70 dbm to -85dbm this will reduce the cumulative power emitted by mobile closer to base station (which need not transmit at very high power to communicate with the BS) and this will reduce the interference

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