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This paper proposes a novel layered belief propagation (BP) detector with a concatenated structure of two different BP layers for low-complexity large multi-user multi-input multioutput (MU-MIMO) detection based on statistical beams. To reduce the computational burden and the circuit scale on the base station (BS) side, the two-stage signal processing consisting of slow varying outer beamformer (OBF) and group-specific MU detection (MUD) for fast channel variations is effective. However, the dimensionality reduction of the equivalent channel based on the OBF results in significant performance degradation in subsequent spatial filtering detection. To compensate for the drawback, the proposed layered BP detector, which is designed for improving the detection capability by suppressing the intraand inter-group interference in stages, is introduced as the poststage processing of the OBF. Finally, we demonstrate the validity of our proposed method in terms of the bit error rate (BER) performance and the computational complexity.

We propose an information-optimum approximate message passing (AMP) for quantized massive multi-input multi-output (MIMO) signal detection. A well-known strategy for realizing lowcomplexity and high-accuracy massive multi-user detection (MUD) is AMP-based belief propagation (BP). However, when internal operations are conducted with double-precision arithmetic, large memory occupancy and severe processing delay are inevitable in the actual massive MIMO implementation. To address this issue, we replace all operations with a simple look-up table (LUT) search where all messages exchanged between each iteration process are unsigned integers. That is, the proposed signal detection is performed using only simple integer arithmetic. The LUT is designed offline using an informationbottleneck (IB) method, and the probability distribution of messages at each iteration step is required for determining the quantization threshold tracked by discrete density evolution (DDE). Computer simulations demonstrate the validity of the IB LUT-based AMP in terms of bit error rate (BER) performance and memory occupancy. The proposed method allows quantizing the AMP detector with fewer bits while maintaining similar performances, such as that of a typical AMP with double-precision.