INI and ICI in Mixed-Numerology MIMO-OFDM Systems in Spatially Correlated Time-Varying Wideband Channels: Analysis and Mitigation

5G new radio (NR) is based on the mixed-numerology multiple-input multiple-out (MIMO) orthogonal frequency division multiplexing (OFDM) physical layer. Unlike conventional single-numerology systems, subcarriers of different numerologies interfere with each other. The larger Doppler spreads and phase noise that occur at higher speeds and carrier frequencies make the channel vary with time, which affects inter-numerology interference (INI) and exacerbates inter-carrier interference (ICI). We derive novel insightful expressions for the INI and ICI covariances for a mixed-numerology, multi-user MIMO-OFDM system in a wideband spatially correlated time-varying channel with phase noise. On the other hand, the literature has only studied simpler single-input single-out systems or MIMO channels with several limitations. With this analytical foundation, we propose a first-of-its-kind joint INI and ICI mitigation technique that is based on statistical information and incorporates fairness. We derive the precoder for each user that achieves the single-user ergodic capacity. We also determine a novel power allocation that maximizes the weighted sum rate. We solve this using an iterative algorithm based on the difference of convex programming framework. The proposed approach achieves a higher weighted sum rate than several benchmarks. Our results highlight the joint impact of INI and ICI and the influence of various system parameters.