A new class of modulation schemes with variable envelope

A novel class of linear modulation schemes is proposed. Excellent spectral efficiency is achieved only at the expense of a small envelope fluctuation in the transmitted signal. Extensive computer simulations have been carried out which show that for noncoherent limited-discriminator (LD) detection the three-phase scheme presented performs better than MSK (minimum-shift keying). A Viterbi detector for coherent detection of the three-phase scheme is described which provides an improvement of 1-2 dB over LD detection and so could be used in low signal level areas. Good performance for both noncoherent and coherent detectors is therefore possible, while also fitting the signal into a channel spacing of 1.5× the bit rate with minimal levels of adjacent channel interference. The results presented suggest that nonconstant envelope schemes should be considered very seriously for future communications systems