Nonlinear PSK and combined nonlinear PSK/FSK modulation

Two classes of constant envelope signals called, nonlinear PSK and combined nonlinear PSK/FSK are introduced. Nonlinear PSK signals select a constant phase angle during each interval depending on the state of the signal and the transmitted symbol. Combined nonlinear PSK/FSK signals select a linear phase variation during each interval and a discrete phase variation at the end of each interval depending on the current state and the transmitted symbol. Both classes of signals achieve the highest constraint length allowed by the number of states. The numerical results presented at preselected numbers of states show that these signals produce significantly high minimum distances. Distances higher than those found in the literature at the same number of states are reported. The spectra of nonlinear PSK signals are almost identical to the spectrum of BPSK signals, while those of combined nonlinear PSK/FSK signals are continuous but similar to that of BPSK signals