I’m not a big fan of TA filtering neither, unless for troubleshooting purpose (for example, try to filter the faraway MS for few hours, see if it enhances the QoS or not).
you’ll always face phantom RACH. There are two facts that I gathered about those ghosts:
– they are usually produced by the BTS itself (electromagnetic noise) –> you can’t fight it.
– they don’t matter, as long as you don’t face SDCCH congestion. Think about it… a ghost rach will just load your system a little bit more. If it’s below a certain amount, then consider it as acceptable and move on to other topics.
Looking at your problem, can you give some numerical values per hour during a standard day?
sdcch assign unsuccess (# and %)
requests and success ?
split of sdcch requested for calls, sms, location update, or imsi detach, etc.