Time Division Multiple Access (TDMA)

With Time Division
Multiple Access (TDMA), radio channels are divided into a number of time
slots, with each user assigned a given timeslot. For example, on a given
radio frequency, user A might be assigned timeslot number 1 and user B
might be assigned time slot number 3. The allocation is performed by the
network as part of the call establishment procedure. Thus, the user’s device
knows exactly which timeslot to use for the remainder of the call, and the
device times its transmissions exactly to correspond with the allocated time
slot. This technique is depicted in Figure 1-8.
Typically, a TDMA system is also an FDD system, as shown in Figure 1-8,
although TDD is used in some implementations. Furthermore, TDMA systems
normally also use FDMA. Thus, the available bandwidth is divided
into a number of smaller channels as in FDMA and it is these channels that
are divided into timeslots. The difference between a pure FDMA system and
a TDMA system that also uses FDMA is that, with the TDMA system, a
given user does not have exclusive access to the radio channel.
Implementing a TDMA system can be done in many ways. For example,
different TDMA systems may have different numbers of time slots per radio
channel and/or different time slot durations, and/or different radio channel
bandwidths. Although, in the United States, the term TDMA is often used
to refer to IS-136, such a usage of the term is incorrect because IS-136 is
just one example of a TDMA system. In fact, GSM is also a TDMA system.