An investigation of phase pulse shape diversity to generate parallel branches, increase data rate, and reduce the complexity of CPM modulation

Continuous phase modulation is a well understood modulation scheme which utilizes a constant envelope signal with inherent memory to create a bandwidth efficient waveform. The pulse shapes defined for CPM modulation influence the bandwidth, demodulation complexity, and power efficiency and can be spread across multiple symbols. This paper investigates a novel modulation scheme that is comprised of a family of pulse shapes which add parallel branches to the existing CPM trellis. The resulting modulation scheme maintains the power efficiency of the underlying modulation while increasing the data rate of the waveform. The spectral efficiency is not affected by the increase in data rate while the receiver complexity is reduced. The first part of the paper outlines the standard CPM modulation and a pair of complementary (non-orthogonal) phase pulse shapes is presented. The corresponding effect on bandwidth, power efficiency, and receiver complexity is analyzed and the advantages of this modulation technique are discussed. Then, a novel methodology for generating a family of optimal pulse shapes is discussed and various generation methods are compared. The spectral and power efficiencies of the resulting M-ary waveform are then compared to an equivalent, standard CPFSK modulation.