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DPSK-QAM Combination as a Signal Set for Spectrally Efficient Noncoherent Communication

A modulation scheme is presented that combines Differential Phase Shift Keying (DPSK) and Quadrature Amplitude Modulation (QAM). One or several QAM symbols are inserted between DPSK symbols, and the phase offset of QAM symbols is determined by the preceding DPSK symbol. Such signal can be treated as a transmission of overlapping signal blocks suitable for noncoherent reception. Along with Generalized Likelihood Ratio Test (GLRT) algorithm, simplified reception method is presented that is based on the use of demodulated DPSK symbols as pilot signals for demodulation of QAM symbols. Also, the technique is proposed for approximate theoretical calculation of the bit error probability for this scheme in the case of uncoded transmission. The simulation results show that, at the same spectral efficiency, proposed scheme provides significant power gain compared to DPSK (about 2.4 dB for spectral efficiency of 4 bits per symbol and about 6 dB for spectral efficiency of 6 bits per symbol). Theoretical approximation demonstrates reasonable agreement with computer simulation results.