An Adaptive Digital Beamformer for Multi-User Communications Using Blind CMA - AMA

Abstract

We present an adaptive digital beamformer for QAM signals transmitted by multiple users to a base station equipped with a uniform linear array (ULA) antenna. The channel is modeled using the Rician distribution with a dominant line-of-sight (LOS) path and multiple non-line-of-sight (NLOS) paths for each user, with focus on millimeter-wave carrier frequencies. With no knowledge of the signals transmitted from each user aside from the modulation type, the blind adaptive system uses a modified joint CMA and AMA cost function to perform both signal recovery and uplink channel estimation for each user. The performance of the adaptive CMAAMA beamformer system is evaluated over varying signal-to-noise (SNR) ratio of the transmitted signal, and over varying number of antenna elements on the ULA at the base station. The singletap and multi-tap channel cases are tested to determine the symbol error rates (SER) and mean square error (MSE).