you are making things too complicated : let the technology works for you 🙂
a TRX is 8PSK-capable when it can transmit GMSK and 8PSK bursts. For instance :
TS0 : BCCH (always GMSK)
TS1 : SDCCH (always GMSK)
TS2/3/4 : PDCH (can be alternatively GMSK or 8PSK)
TS5/6/7 : TCH (only GMSK available, as per today)
TS2/3/4 are defined dynamically as PDCH : you actually define them as TCH, and they’ll be defined as PDCH if some users need PDCH.
1 PDCH can serve several users (max is around 10). There is a multiplexing of the radio blocks. One block for user A can be in GMSK, while the next block for user B will be in 8PSK.
(in my example :
User A does not support 8PSK
User B supports GMSK)