Pix, correct me if I’m wrong.
The GSM standard say that it’s normal to have SDCCH failure up to 10% per day.
It’s based to the number of RACH subTSs per day, the probability the noise to be decoded as Channel Request ( Ghost RACH )and the probability to have a valid request reason…
It’s clear visible during the night ( when the radio interface is “not loaded”).
1.The BSIC is not involved in the Channel Request. Optimize the BCCH freq.
2. I’m not a fan of the TA Filtering and I don’t know someone who uses this approach efficient.
Downtilt could prevent Ghost RACH in my opinion but may be whit other consequenses…