Phase-Noise-Aware LLR Calculation for mmWave MIMO Systems with High-Order Modulation

This paper proposes a high reliable demodulation method via phase-noise-aware log-likelihood ratios (LLRs) in millimeter-wave (mmWave) multi-user multi-input multi-output (MU-MIMO) systems with higher-order quadrature amplitude modulation (QAM). When using high-order QAM schemes in mmWave wide-band wireless communication systems, the phase noise severely degrades the demodulation performance at the operating point in the high signal-to-noise ratio (SNR) region. Typical two-stage processing, which consists of MIMO signal separation (i.e., multi-user detection (MUD)) and phase noise compensation via LLR calculation, cannot properly solve this inherent problem, because the spatial fading correlation in mmWave channels causes phase noise enhancement during MUD. To circumvent this issue, we formulate an approximate probability density function (PDF) of the received signals including phase noise, which enables us to jointly perform MUD and phase noise compensation; this makes it possible to compute reliable LLRs to be input to the channel decoder, without phase noise enhancement. Numerical results demonstrate the efficacy of the proposed method in terms of the bit error rate (BER) performance in coded mmWave MIMO systems.