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first TDMA was widely used and then they used FDMA.... 2G of GSM used TDMA+FDMA for effective transmission.... i think 3G would introduce much more advancements....
TDMA system: users share the same frequency but not at the same time. They are allowed to receive and/or transmit within a defined time slot.
FDMA system: users are allowed to receive and/or transmit (depending on the duplex mode) at the same time but not on the same frequency.
GSM used BOTH (TDMA and FDMA) ..... In simple words TDMA is used to give different time slots in a GSM burst which is divided into 32 time slots .......of which 30 are used for the users and 2 for signalling....FDMA is used to alot different freq to users if the number of users is more than lets say 30.
In GSM, the frame is divided into slots (TS). A classical GSM frame, which has a duration of 4.16ms, is divided in 8TS of 577us and not 32...
In circuit mode, the users has only one TS to receive data and one TS to transmit with a time gap of 3 TS between them. You have one additionnal TS dedicated to signalling (BCCH).
In packet mode (GPRS or EGPRS), the users can be allocated several TS to transmit and or receive depending on the multi-slots capabilities of the MS.
Please correct me if I am wrong...
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