SDCCH blocking is high

hi vijay,
please also try the following :
1. CELL-RESELECT-HYSTERESIS for Location Area selection can be fine tuned.

2.Check how much traffic the site is taking,if the site is carrying low traffic this can be the case of PHANTOM RACH which can make the SDCCH blocking high.

is it a “satellite abis” BTS ? if yes, then … well, i don’t know, that can create some delay on the sdcch signalling. what is the average time of sdcch dialogs ?

– try removing the adaptative configuration of logical channels and set 2 full timeslots for SDCCH (or 3, or 4, test different configurations out)

– try changing the frequencies

– try reducing the timing advance filter (instead of 64 (32km), set it to 15 (= 7.5km) for a few hours .

For info, the RXLEV MIN is different from the RXLEV ACCESS MIN. Beware. First one : for HO. Second one : for Call Setup. Be sure you set the latter to

hi kaluan,

most of the time, i find that SD drop is linked to interference from other cells or is caused by a large cell coverage (many subscribers at the cell border, with low RXLEV)

sdcch HO should be disabled, unless you want to make your life complicated. It will not improve the QoS in the end, so you’d rather leave it off.

if you want to make a better diagnostic : keep only on SDCCH timeslot, disable frequency hopping, and move your SDCCH timeslot on different TRX. Maybe only one frequency is interfered, or one TRX is faulty, causing trouble on the SDCCH timeslot.

hi nishant,

sd abis drops… mmm.. i’d say that the trx which is carrying your SDCCH timeslot is faulty. you don’t see any TCH abis drops ?
how much traffic does the cell carry ? what is the average call duration ?

Check CHAP make it 1 or 6

Hi Danish,

People get up for work, take their car at 8:30am and go towards the main city at 8:45am. So between 8am and 9am, a lot of location updates occur because many people cross the LAC borders at the same time.

No parameter or LAC design can fight this (AFAIK !). Be sure to optimize the dimensioning of SDCCH.

Regards,

Hi Danish,

I am very convinced with Pix idea. but you can take into consideration that there is a logical parameter to make the MS execute location update if the MS was in IDLE state for 3 or 4 hours (configurable by the this parameter); Example: subscribers sleep at 12:00 midnight after 4 hours the subscribers MS will start generating these Location Updates, which implies in the SDCCH. But truly, that wasn’t a reason for SDCCH Blobking in my network… this return us back to Pix idea, wich is more convincible for your case. you must redimension SDCCH for cells that are on LAC borders.