You have three main possible cases for TCH seizures failures:
– Congestion of TCH channels
– Poor radio quality (interference, poor coverage or TRX / Combiner hardware issues)
– Abis link failures / BSC failures
Because you have about 50% failure and you’re saying there is no congestion, I would assume it is probably a hardware issue.
You could check those points first :
– interference (intra-site, intra-cell ?). Try changing the frequencies.
– hardware (reset all TRE. If still failures : lock all TRE except one, and test all the TRE one by one this way. Finally, exhange the combiner…)
– Abis link availability and quality
Note : you have a very high amount of call drops also, isn’t it ?
What is your average call duration ? (= mean holding time)