SDCCH DROPS

What we measure in Drive Test – Uplink or Downlink radio properties? Need to know as a fresher…

I’m a BSS Engineer in a GSM company. There was congestin on TCH and a high value of SDCDR(SDCCH Drop Rate) on one of our site configured 1/1/1. I then added one TRX on the first sector making the configuration 2/1/1. I noticed the congestion on TCH is resolved but the value of SDCDR remained as high as before.

What could be the cause of that problem? Will the add of an SDCCH channel to the second added TRX solve the issue?

Thanks,

Jerrys,

in radio, there are mny possible causes for one problem. For instance a SDCCH drop can be caused to interference, low coverage (uplink, downlink), by wrong settings of radio parameters, wrong settings of nss parameters, or even a BTS failure or an Abis failure.

The impact on subscriber is simple : he will feel like the call setup was not completed. He pushed the green button, but the call failed in the first few seconds.

Hello Nazmul,

2 possibilities :

either the NSS has detached the IMSI of that subscriber, because the perioic location update (T3212) wasn’t performed before the expiry of another timer that controls the IMSI detach on the NSS side.

or the cell in which the subscriber is doesn’t allow IMSI ATTACH (it is a cell parameter, ATT = ENABLE). Therefore when the subscriber switches on the mobile, the mobile is still not attach to the network. Only after it originates its first call, his IMSI will be attached to the network. But before his 1st call, the IMSI is not attached, so he can’t receive a call.

regards,

Hi Kwesi,
Mobile in this problematic area has to measured good RXlev (downling), as a good candidate for neighbour. HO will be tried to perform. But due to wrong LNA there will be too low RXlev (uplink). Thehe will be also problem to setup call (SDCCH will be too low) and problem with TCH asigment.
BR
Tomar

if nothing was changed RF wise, could be a problem with signalling back to core. Too much location updates may cause increased signalling traffic.
Maybe a bunch of filipinos decided to move into the area and started sending too many sms messages. hehehehe. How is the SDCCH Blocking anyway. Is it high too? I assume it is.. so check ghost siezures. if it is also high, run a BCC plan check.

BTW, in general, the way to reduce most SDCCH drops is the following.. proper power budget, BTS TX should be properly set (drops due to insufficient uplink rxlev in most cases), rxlevaccmin (drops due to insufficient C/N margin), and proper frequency plan (drops due to interference).

All the site’s SDCCH stats are almost perfect. The only KPI that is high is the incoming handover failures. The strange thing is that incoming handovers were working fine and something caused it to rise from 2% to 40% failures. This means something went wrong suddenly. This site is a rural site. I am stumped.

I am Working in operation area of the telecom company, we have GSM Ericsson System 850 Mhz, we are experimet high SDCCH drop rate in some sectors of the BTSs, somebody can help my to get an idea of this problemen cause.