TDMA - Time Division Multiple Access. TDMA systems are able to transmit multiple voice circuits per channel. A TDMA channel is a single FDMA channel divided up in time into multiple time slots. Three users can take it in turn to share one radio channel. The channels can vary in bandwidth and depending on the type of system, the time slots can transmit all or part of a voice circuit. Each user's speech is stored, compressed and transmitted as a quick packet, using controlled time slots to distinguish them-hence the phrase 'time division'. Its uses 30 KHz channels and a vocoder rate of 8 Kbits/sec. At the receiver, the packet is de-compressed.
TDMA channel


30 KHz | Voice circuit #1|Voice circuit #2|Voice circuit #3|Voice circuit #4|


Depending on the type of system, slots 1, 2, 3, & 4 could each transmit a voice circuit. In this example, 4 telephone circuits are transmitted on a single 30 KHz channel, a 4X increase in capacity over the FDMA example.

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