A bandwidth-efficient class of signal-space codes

A new class of codes in signal space is presented, and their error and spectral properties are investigated. A constant-amplitude continuous-phase signal carries a coded sequence of linear-phase changes; the possible signal phases form a cylindrical trellis in phase and time. Simple codes using 4-16 phases, together with a Viterbi algorithm decoder, allow transmitter power savings of 2-4 dB over binary phase-shift keying in a narrower bandwidth. A method is given to compute the free distance, and the error rates of all the useful codes are given. A software-instrumented decoder is tested on a simulated Gaussian channel to determine multiple error patterns. The error parameter is computed for a somewhat more general class of codes and is shown to increase rapidly when mere phases are employed. Finally, power spectral density curves are presented for several codes, which show that this type of coding does not increase the transmitted signal bandwidth.