Integrated Sensing and Communications (ISAC) surpasses the conventional frequency-division sensing and communications (FDSAC) in terms of spectrum, energy, and hardware efficiency, with potential for greater enhancement through integration of non-orthogonal multiple access (NOMA). Leveraging these advantages, a multiple-input multiple-output NOMA-ISAC framework is proposed in this paper, in which the technique of signal alignment is adopted. The performance of the proposed framework for both downlink and uplink is analyzed. 1) The downlink ISAC is investigated under three different precoding designs: a sensing-centric (S-C) design, a communications-centric (C-C) design, and a Pareto optimal design. 2) For the uplink case, two scenarios are investigated: a S-C design and a C-C design, which vary based on the order of interference cancellation between the communication and sensing signals. In each of these scenarios, key performance metrics including sensing rate (SR), communication rate (CR), and outage probability are investigated. For a deeper understanding, the asymptotic performance of the system in the high signal-to-noise ratio (SNR) region is also explored, with a focus on the high-SNR slope and diversity order. Finally, the SR-CR rate regions achieved by ISAC and FDSAC are studied. Numerical results reveal that in both downlink and uplink cases, ISAC outperforms FDSAC in terms of sensing and communications performance and is capable of achieving a broader rate region, clearly showcasing its superiority.

翻译：集成感知与通信（ISAC）在频谱、能量和硬件效率方面超越了传统的频分感知与通信（FDSAC），而与非正交多址接入（NOMA）技术的结合有望带来进一步的性能提升。基于这些优势，本文提出了一种采用信号对齐技术的多输入多输出NOMA-ISAC框架，并分析了该框架在下行与上行链路的性能。1）在下行ISAC中，研究了三种不同的预编码设计方案：以感知为中心的设计、以通信为中心的设计以及帕累托最优设计。2）对于上行链路，研究了两种场景：以感知为中心的设计和以通信为中心的设计，其差异取决于通信信号与感知信号之间的干扰消除顺序。在每种场景中，均对关键性能指标进行了分析，包括感知速率、通信速率和中断概率。为深入理解系统特性，还探究了高信噪比区域的渐近性能，重点关注高信噪比斜率和分集阶数。最后，对比研究了ISAC与FDSAC所能实现的感知速率-通信速率区域。数值结果表明，在下行与上行链路中，ISAC在感知与通信性能方面均优于FDSAC，且能够实现更宽广的速率区域，充分体现了其优越性。