## Dynamic Channel Multicarrier Access (DC/MA)

#### DC/MA is a proprietary two-way radio air-interface designed to be a direct upgrade for 25 kHz channelled FM analogue radio systems. The DC/MA approach is a further FDMA subdivision of the 25 kHz channel to give five voice or data channels within the same bandwidth as the original single FM voice channel.

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#### The downlink channel structure incorporates dual pilot tones for channel sounding and frequency/Doppler correction, and an additional dedicated data channel for system trunking, and so on. Each of the downlink channels is split into two sub-channels placed symmetrically about the channel centre – this has been termed the 'onion ring' approach. In data mode, each sub-channel pair can support 9600 bps data using a 16-QAM modulation format.

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#### The uplink channel structure differs from the downlink structure in that each uplink channel requires its own pilot tone so that the receiving base-station has an independent measure of the fading and frequency error from each mobile user. The additional bandwidth required to support the five pilot signals means that the uplink cannot support the sixth dedicated data channel found in the downlink.