Inter-Numerology Interference Analysis and Cancellation for Massive MIMO-OFDM Downlink Systems

The extremely diverse service requirements is an important challenge for the upcoming fifth-generation (5G) wireless communication technologies. Orthogonal frequency division multiplexing (OFDM)-based massive multiple-input multiple-output (MIMO) and mixed numerologies transmission are proposed as solutions. This paper investigates the use of spatial multiplexing of users, sharing the same bandwidth, whose associated numerologies are different. We first introduce a precoding design that aims to manage the mixed numerologies spectrum sharing (SS) transmission. Then, we analyse the inter-numerology interference (INI) and derive the theoretical expressions of its radiation pattern in massive MIMO-OFDM downlink systems. We demonstrate that by using the proposed precoding scheme and considering two groups of users using two different numerologies, INI appears only in frequency selective channels. Besides, the transmission of users using numerology with large subcarrier spacing (SCS) is always with the best quality, only users using the numerology with small SCS suffer from INI. In that case, INI increases due to the difference in SCS, channel selectivity and power allocation. Based on the derived INI, in closed-form expressions, the precoding scheme is improved and a new INI cancellation scheme is introduced. Our analysis demonstrates that the INI theoretical model matches the simulation results, and the introduced INI cancellation based precoder efficiently mitigates the INI and enhances the performance of massive MIMO-OFDM downlink systems.