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Abstract

A trellis coded modulation system comprises a source of successive 2-bit data symbols X.sub.1, X.sub.2 arranged in a frame format wherein each frame comprises a plurality of data segments each including a plurality of groups of interleaved data symbols. Each group of interleaved data symbols is separately coded by a precoder and convolution encoder to derive coded output symbols Z.sub.0, Z.sub.1, Z.sub.2, which are mapped to respective 8-level symbols for transmission together with periodically generated frame and segment sync symbols. The received signal may be filtered by a linear filter, e.g. a comb filter, to reduce co-channel interference and each group of filtered symbols is applied to a respective first Viterbi decoder for estimating data bits X.sub.1 X.sub.2. Each first decoder preferably comprises a reduced complexity Viterbi decoder responsive to a partial representation of the state of the linear filter. Each group of received symbols may also be directly applied to a respective second Viterbi decoder for estimating data bits X.sub.1 X.sub.2. Estimated data bits X.sub.1 X.sub.2 from the first or second decoders are selected for further processing.

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First Claim