Comparison of Quotiently Coherent QAM, Differentially Coherent QAM and Coherent QAM over Rayleigh Flat Fading Channel

A quotient coded quadrature amplitude modulation system having only a finite number of transmitted signal amplitudes is proposed. The expression to estimate the Symbol-Error-Rate (SER) performance of the quotiently coherent demodulated QAM (QQAM) system over a multiplicative Rayleigh fading channel is obtained. The computed SERs are in close agreement with the results obtained from simulations and hence justifying the approximation made in modelling the noise at the output of the quotient decoder. We next propose a differentially coherent demodulated QAM (DQAM) system, and its performance is compared with the QQAM system through simulation. Finally, the performances of both the QQAM and DQAM systems are compared with the conventional coherent QAM system. Relative merits and shortcomings between the QQAM and the DQAM systems are discussed.