A Quantized PSK 8-State Decoder for Spectrally Efficient Communications

Trellis Coded Modulation [5] combines the Viterbi Algorithm [4] with PSK or QAM signalling to achieve a coding gain, using signal set expansion as an alternative to bandwidth expansion. Optimum detection of TCM requires the calculation of Euclidean distances in the signal set space. Circular Quantization of received signal vectors as an alternative to Euclidean distance calculation has been shown to result in minimal loss of performance when used with a 4-state trellis codes [1, 2, 3]. This paper investigates the effect of circular quantization on 2 different 8-state trellis codes. The 8-state codes showed a modest gain over the 4-state code, while the effect of circular quantization on the 8-state codes paralleled the effect on the 4-state code.