OK, the TDMA and FDMA are implemented in the GSM. By using FDMA we have 124 carriers.
Each of these carrier frequencies is divided in 8 timeslots, using a TDMA scheme.
The fundamental unit of time in this TDMA scheme is called a burst
period and it lasts approx 0.577 ms. 8 burst periods are grouped
into a TDMA frame (approx 4.615 ms), which forms the basic unit for
the definition of logical channels.
One physical channel is one burst
period per TDMA frame.
Channels for speech and data traffic (TCH) use 26-frame multiframe. Other control channels (such as BCCH, RACH, PCH,…) use 51-frame multiframe.
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Brgds