Concatenated Structure of EP and Turbo Equalizer for Overloaded Massive MIMO Detection

This paper proposes a novel Bayesian receiver design for uplink signal detection in overloaded massive multi-user multi-input multi-output (MU-MIMO) systems. Iterative detection schemes are roughly classified into two types: iterative detection and decoding (IDD), in which log-likelihood ratios (LLRs) are exchanged between the detector and the channel decoder, and self-iterative detection (SID), in which a message passing algorithm (MPA) is operated without involving the channel decoder. In either scheme, the most vital mechanism of iterative signal detection is to decouple the self-feedback across iterations and propagate extrinsic values. As a receiver design to achieve an excellent performance-complexity trade-off while adhering to this mechanism, a concatenated structure of SID based on expectation propagation (EP) and IDD based on turbo equalization is proposed. Numerical simulations show that the proposed method outperforms the state-of-the-art alternatives in terms of bit error rate (BER) performance in coded systems, especially when the overloading ratio is high. In addition, the iterative behavior is analyzed by extrinsic information transfer (EXIT) chart to verify the efficacy of extrinsic value exchange.