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Optimum discrete-power adaptive QAM scheme for Rayleigh fading channels

In this letter, the utilization of a finite number of power levels per constellation in adaptive QAM schemes for flat fading channels is analyzed. Assuming a maximum target BER, the optimum switching thresholds in order to maximize the spectral efficiency are found for Rayleigh fading. Both analysis and simulation results show that a small number of power levels per constellation allows to obtain a good compromise between high spectral efficiency and low feedback information rate.