Trellis-coded modulation with high-speed low complexity decoding

A concatenated coding scheme that is particularly suitable for high-data-rate communications is described. The proposed coding scheme consists of a set of n convolutional codes multiplexed into an inner code and an outer (n, n-1) single-parity-check code. Each of the inner codes is independently maximum-likelihood decoded via n parallel implementations of the Viterbi algorithm. The output symbols of the inner decoders, together with the analog demodulator output samples, form the input of the outer soft-decision single-parity-check decoder, which is able to correct one erroneous Viterbi decoder output. The coding structure can be applied to conventional codes as well as to trellis coded modulation (TCM). It is shown, considering n=12 and Ungerboeck´s 4-state trellis-code for coded 8-PSK, that with the proposed coding scheme an asymptotic coding gain of 5.64 dB compared to uncoded 4-PSK is obtained, which is about 0.5 dB more than the asymptotic gain of a 128-state TCM code