– Physical channels are all the available TSs of a BTS, whereas every TS corresponds to a physical channel. Two types of channels need to be distinguished, the halfrate channel and the fullrate channel. For example,a BTS with 6 carriers, has 48 (8 times 6)
physical channels (in fullrate configuration).
– Logical channels are piggybacked on the physical channels. Logical
channels are, so to speak, laid over the grid of physical channels. Each
logical channel performs a specific task.
Another aspect is important for the understanding of logical channels: during a call, the MS sends its signal periodically, always in a TDMA frame at the same
burst position and on the same TS to the BTS (e.g., always in TS number 3.
The same applies for the BTS in the reverse direction.