Dear Pan,
For your point in reply to item 3. it is true that the 51 frame Idle is sliding against 24 frome SACCH MF. but how does the site synchronize with its neighbours. As the synchronization should be such that the MS knows which neighbour to measure to decode its FCH / SCH. As far as the standard says a neighbour’s info is measured in 10 secs.
As far as synchronization is concerned it is beleavable for PCM / GPS synchronized network that the sites might be synchronized with each other and know where in 51 MF which neighbour is. but what would be the case in free running network where BTSs are opperating on internal clocks.