Concatenated trellis/high-rate Reed-Solomon and projection codes

A concatenated coding scheme consisting of trellis-coded modulation (TCM) and either Reed-Solomon (RS) or projection outer code is considered. TCM alone, employing M-ary phase-shift keying (PSK) offers the same spectral efficiency as baseline uncoded M/2-PSK at greatly improved error-rate performance. The Viterbi decoder performs a soft decision on data corrupted by Gaussian noise for the inner code. Two different outer codes are considered. One is a low-redundancy RS code with code length of 255 symbols. The RS decoder complements the error-correcting capabilities of the inner code with its ability to correct bursts of bits in error presented at its input. Another outer code is projection code that offers flexibility in code rate and is capable of correcting both random and burst errors. If high-rate outer code is chosen, the combined scheme will have almost the same spectral efficiency as the baseline uncoded system. The concatenated system provides more dramatic improvement, up to 2 dB, in additional coding gain at moderate SNR values.