OTFS-NOMA System for MIMO Communication Networks with Spatial Diversity

TL;DR

This paper proposes a MIMO communication system combining OTFS and NOMA to efficiently serve users with diverse mobility profiles, enhancing spectral efficiency and robustness in high-mobility scenarios.

Contribution

It introduces a novel OTFS-NOMA MIMO framework with clustering, precoding, and interference management tailored for heterogeneous mobility users.

Findings

Performance improves with more LM users and clusters.

Optimal power allocation enhances detection SNRs.

Closed-form SNR expressions facilitate system analysis.

Abstract

In this work, we study the use of non-orthogonal multiple access (NOMA) and orthogonal time frequency space (OTFS) modulation in a multiple-input multiple-output (MIMO) communication network where mobile users (MUs) with different mobility profiles are grouped into clusters. We consider a downlink scenario where a base station (BS) communicates with multiple users that have diverse mobility profiles. High-mobility (HM) users' signals are placed in the delay-Doppler (DD) domain using OTFS modulation in order to transform their time-varying channel into a sparse static channel, while low-mobility (LM) users signals are placed in the time-frequency (TF) domain. Precoding is adopted at the BS to direct focused beams towards each cluster of users. Moreover, NOMA spectrum sharing is used in each cluster to allow the coexistence of a single HM user and multiple LM users within the same resource block. LM users access disjoint subchannels to ensure their orthogonality. All users within the same cluster first detect the HM user's signal. Afterward, LM users suppress the interference from the HM user and detect their own signals. Closed-form expressions of the detection signal-to-noise ratios (SNRs) are derived. The numerical results showed that the performance of the proposed system highly depends on the number of LM users, the number of clusters and the power allocation factors between HM and LM users.