We have already seen some examples of digital communication systems
exploiting combinations of multi-user access techniques. GSM, although primarily a TDMA
system, requires several 200 kHz frequency channels (each carrying eight time slots) in
order to provide a practical high capacity cellular system and can thus be viewed as an
FDMA system also. The TETRA (Trans European Truncked Radio Access) system exploits a three time slot TDMA structure with FDMA channels spaced at 25 kHz spacing. |
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