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Full duplex over a single channel

It is possible to design a full duplex radio system on a single channel, using Audio compression and the time division multiplexing technique (TDMA): if the radio network is managed by the terminals themselves, one obtains a system usable in any place for a conference mode approaching the "natural" human conversation. To this end, time is divided in as many "slots" as terminals:

  • On the Audio side, the terminals are in a permanent listening mode, where the microphone picks up a signal to be compressed and transmitted, while the data received, unpacked, can reproduce sounds from other terminals.
  • On the Radio, the channel is used alternately by each terminal to transmit its own compressed data in emission mode, and receives data from the other terminals the rest of the time.

When compression and decompression phases are synchronized to retrieve the audio samples in t good order, the “conference” conversations seem to be continuous.

An example of this temporal division is indicated by a group of three terminals simulating mode "full-duplex" on a single radio channel:

Example of a temporal division

The Radio channel is only used during emission slots, allowing interlacing several terminals, or even, several groups of terminals: the technological challenge is to maintain synchronization between all the terminals in the network.

One technique is to select a device to synchronize the other and play the conductor or “Master” role. This solution, however, shows the same drawback as using a "base": the loss of the Master (radio range, failure, etc.) stops the communication between the other terminals.