Maximum-Likelihood Array Signal Decoding in the Presence of Block-Wise Stationary Cochannel Interference

Abstract

We address the demodulation and decoding of array signals in the presence of fluctuating cochannel interference (CCI). The maximum-likelihood decoder is formulated for the case of N receive antennas and stationary, temporally white Gaussian CCI within blocks of K samples, where K ≥ N . The pairwise error probability (PEP) is utilized to quantify the degradation in performance resulting from the absence of side information about the CCI. For pairs of code words that differ over a large number of blocks, an asymptotic PEP performance degradation of 10 log 10 (K/(K −N )) decibels is found.An iterative maximization of the log-likelihood function leads to an alternative suboptimal receiver with reduced complexity, including a block-wise adaptive beamforming via a sample matrix inversion (SMI) and a nearest-neighbor decoding. From the statistics of the spatially filtered signals we find the asymptotic PEP performance, and see that the presence of the desired signal, which is known to adversely affect the output of SMI-based beamformers with small sample support, is gradually mitigated in the iterative procedure.Index Terms-Cochannel interference, maximum-likelihood estimation, adaptive beamforming.