Generalized Signal Phase Inversion-Based NOMA Technique for 6G Integrated Sensing and Communication Systems

In this paper, we propose a novel uplink signal phase inversion-based non-orthogonal multiple access (SPIN-NOMA) technique to effectively suppress mutual interference in integrated sensing and communication (ISAC) systems. Specifically, we consider an ISAC system where a base station (BS) operates as a monostatic radar to sense targets while simultaneously receiving communication signals from multiple user equipments (UEs). We identify limitations in the conventional SPIN-NOMA approach and introduce technical advancements to support high-order modulation schemes and an arbitrary number of UEs. Additionally, we theoretically derive the generalized bit-error rate (BER) performance as a function of modulation order and the number of UEs, employing linear zero-forcing beamforming. Extensive simulations confirm that the proposed SPIN-NOMA technique significantly outperforms the conventional approach in terms of both sensing and communication performance. Furthermore, the simulation results align closely with the derived theoretical BER expressions, confirming their accuracy.