Joint Optimization of Rates and Regions for Optimum Performance of Adaptive Modulation

We present a method for exactly solving the optimization problem for a scenario of discrete rate adaptive modulation. The aim is to maximize the spectral efficiency based on the imperfect channel estimation condition, constant power and average bit error rate(BER) constraints for multilevel quadrature amplitude modulation MQAM over Rayleigh flat fading channels with band-limited feedback signal. Transmission rates are not assigned predetermined values before solving the optimization problem. We show that the general optimization solution entails constellation sizes shouldn´t be very large. Our proposed method is an iterative algorithm during which two sets of transmission rates and classification regions for signal to noise ratio (SNR) are updated alternately. The joint solution is a special case of Vector Quantization solution with minimum average cost function. We consider the case where channel is estimated by Pilot Symbol Assisted Modulation (PSAM) and Minimum Mean Square Error (MMSE) criterion.