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Optimum receiver for QAM signals based on EM algorithm over fading channel

This paper studies an optimum quadrature amplitude modulation (QAM) receiver based on the estimation of the information sequence of the noisy QAM signal received through a fading channel. The developed receiver uses an iterative algorithm based on the expectation-maximization (EM) algorithm instead of using the standard maximum likelihood (ML) procedure. Direct application of the ML procedure to this problem results in a complex and unpractical receiver due to the unavailability of an efficient way to perform the maximization of the likelihood function. The iterative algorithm used in the receiver reduces the complexity and performs the task that has previously been too complex to perform. Simulations are performed to validate the theoretical developments and to measure the performance of the algorithm. The performance of the algorithm is measured in terms of the normalized mean square estimation error.