Rate 3/4 convolutional coding of 16-PSK - Code design and performance study
Convolutional coding coupled with 16-PSK modulation is investigated for bandwidth efficient transmission. Rate 3/4, small memory codes are found which are optimized in the free-distance sense on the Gaussian channel. These codes provide up to 4.8 dB of coding gain with 32 states over uncoded 8-PSK, a scheme having the same spectral efficiency as the codes described. The performance is compared with earlier findings of Ungerboeck and some recent results on R = 2/3 coded 8-PSK. In addition, results of a channel transmission study to assess the performance of the four-state code on the band-limited nonlinear channel are presented, and it is found that performance of the coded scheme degrades comparably with uncoded 8-PSK, i.e., coding gain is roughly preserved.