A Low Complexity M-QAM Soft De-mapping Method in Alpha Stable Field of Interference

Wireless communication systems employing quadrature amplitude modulation (QAM) are impacted adversely by undesired disturbances that are modeled as the sum of Gaussian noise and co-channel interference generated by randomly dispersed interferers surrounding the victim receiver. Due to the lack of a closed-form probability density function (PDF) for the aggregate interference modeled by Symmetric-Alpha-stable distribution, optimal computation of log-likelihood ratio (LLR) for symbol de-mapping becomes too complex. We propose a low-complexity soft de-mapping method for M-ary QAM by using an alternative parametric solution for the interference PDF. After estimation of appropriate parameters, the closed form of the alternative solution is used to arrive at a simple approximation of the LLR values. We show that the performance of the reduced-complexity method stays close to the one achieved by using the exact PDF. The robustness of the proposed method is also investigated.