CSI-Based NOMA With EM Algorithm for ISAC

Channel state information (CSI)-based sensing can interfere with communication signals in existing wireless networks. To address this and achieve integrated sensing and communication (ISAC) with higher spectral efficiency, in this letter, we propose a novel expectation maximization (EM) algorithm-aided non-orthogonal multiple access (NOMA) scheme that enables a communication user and a sensing user to share same time and frequency resources, and extend it to multi-input multi-output (MIMO) scenarios. By using the EM algorithm, communication CSI, sensing CSI, and data symbols are iteratively estimated. Moreover, we introduce a new sensing pattern for highly accurate initial estimation of the communication channel, such that enhanced sensing channel estimation subsequently refines communication channel estimation. The initial sensing channel estimation performance is theoretically analyzed. Simulation results demonstrate the superiority of our approach for both phase shift keying (PSK) and quadrature amplitude modulation (QAM) signals over the benchmark scheme.