Physical layer security for non-orthogonal multiple access toward 6G

Abstract

The sixth-generation (6G) networks are expected to support an extremely high data rate, a very large number of users, and a variety of applications and services. In order to achieve these stringent targets, one of the most fundamental issues is the design of sophisticated multiple access techniques, intending to enable a tremendous number of users/devices to be efficiently and flexibly connected with the network over the given wireless radio resources. Non-orthogonal multiple access (NOMA) provides significant benefits in supporting massive connectivity, achieving high spectrum efficiency (SE) and energy efficiency (EE), guaranteeing user fairness, being compatible with many other techniques, and thus is one of the promising candidates for 6G [1,2]. On the one hand, NOMA empowers other promising techniques for 6G, like terahertz (THz), grant-free (GF) access, orthogonal time-frequency space (OTFS) modulation, visible light communication (VLC), backscatter communication (BC), etc., which can significantly maximize the achievable rates, SE and number of connectivity to support diverse applications in 6G. On the other hand, NOMA can be empowered by the emerging 6G techniques, like reconfigurable intelligent surface (RIS), OTFS, etc., which can motivate NOMA to support flexible quality of service (QoS) requirements.Moreover, physical layer security (PLS) has drawn extensive attention in recent years. Abundant studies have been carried out for various scenarios including traditional NOMA. However, new challenges and requirements arise when NOMA is being applied in 6G. In this chapter, we first review the PLS for NOMA toward 6G. Then we take the RIS-aided NOMA as case studies to show its PLS against internal or external eavesdropping attacks.