A Principled Framework for Narrowband Mobile Digital Communications
This paper developes a model-based framework for narrowband communications. First, we derive the optimum (MAP) demodulation algorithm for M-QAM signaling in the frequency flat time-varying Rayleigh fading channel. This recursive structure allows for symbol-by-symbol data decisions to be made in an efficient manner. The complexity problem inherent to optimal detection schemes is addressed and approximations to optimal detection are considered which reduce complexity to practical levels yet still provide near-optimal performance levels. Reduced complexity algorithms are obtained through the use of decision feedback, thresholding and a novel state partitioning which allow for higher order modulations such as 16-QAM and 64-QAM to be implemented. The algorithms presented exhibit favorable advantages over pilot symbol assisted modulation techniques in performance, bandwidth efficiency and the necessary decoding delay. This principled approach to narrowband mobile digital communications provides a unified framework which incorporates diversity combining techniques, array signal processing, forward error control decoding and optimum demodulation in a single demodulation architecture. Performance characterizations of the algorithms presented are obtained via Monte Carlo simulation and the results show that near-optimal BEP levels are achieved.
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