64-state TCM for spectrally efficient space communications

Rate 2/3 8-PSK codes of 4, 8, 16, and 64 states were tested by simulation. The codes used are those found in Ungerboeck's original search. The results found were in close agreement with those predicted by analytical means in current literature. The Ungerboeck codes of 8, 16, and 64 states show coding gains of 0.2, 0.3, and 0.86 dB, respectively, relative to the four state code. In general, worthwhile gains are obtained in increasing the number of states of the encoder up through 64.