Signal Model and Linear Combining Design for Multi-Numerology Massive MIMO Systems

In order to provide flexible radio access technologies, the fifth generation (5G) New Radio (NR) employs various choices of orthogonal frequency division multiplexing (OFDM) numerologies. Nevertheless, a comprehensive signal model of massive multiple-input multiple-output (MIMO) uplink (UL) systems with multiple numerologies remains unclear. Most previous studies have solely considered the signals of two numerologies within only one least common multiplier (LCM) symbol duration, which is the time duration for synchronizing distinct numerologies, and aimed to address inter-numerology interference (inter-NI). However, the inter-NI from OFDM symbols in the previous LCM symbol duration should also be considered in UL systems. Accordingly, this paper provides a generalized baseband signal model with an arbitrary number of numerologies that encompasses all the inter-NI. In addition, we conduct an analysis of signal power and derive a tractable form of the signal-to-interference-plus-noise ratio (SINR) expression. Based on the analysis, we propose linear combining designs with respect to the zero-forcing (ZF) and minimum mean square error (MMSE) criteria for multi-numerology systems. Simulation results verify the superiority of the proposed linear combiners. In particular, we demonstrate that the proposed ZF combiner is able to perfectly eliminate all the inter-NI. Furthermore, the simulation results verify that the derived lower bound of the achievable rate with the proposed ZF combiner is very tight.