NOMA FOR INTEGRATING SENSING AND COMMUNICATIONS TOWARD 6G: A MULTIPLE ACCESS PERSPECTIVE

This article focuses on the development of integrated sensing and communications (ISAC) from a multiple access (MA) perspective, where the idea of non-orthogonal multiple access (NOMA) is exploited for harmoniously accommodating the sensing and communication functionalities. We first reveal that the developing trend of ISAC is from orthogonality to non-orthogonality, and introduce the fundamental models of the down-link and uplink ISAC while identifying the design challenges from the MA perspective. For the downlink ISAC, we propose two novel designs, namely NOMA-empowered downlink ISAC and NOMA-inspired downlink ISAC, to effectively coordinate the inter-user interference and the sensing-to-communication interference, respectively. For the uplink ISAC, we first propose a pure-NOMA-based uplink ISAC design, where a fixed communication-to-sensing successive interference cancellation order is employed for distinguishing the mixed sensing-communication signal received over the fully shared radio resources. Then, we propose a general semi-NOMA-based uplink ISAC design, which includes the conventional orthogonal multiple access-based and pure-NOMA-based uplink ISAC as special cases, thus being capable of providing flexible resource allocation strategies between sensing and communication. Along with each proposed NOMA-ISAC design, numerical results are provided for showing the superiority over conventional ISAC designs.