Integrated Sensing and Communication: NOMA vs Cooperative NOMA

This paper examines the integrated sensing and communication technology (ISAC) in the downlink scenario where a base station exploits cooperative non-orthogonal multiple access (CNOMA) to jointly offer communication functions to users and sensing functions to targets. CNOMA allows the user with good channel conditions to assist another user with a weak channel using the decode and forward strategy in full duplex mode while forming a beam-pattern that is capable of sensing the targets. The main objective in this work is to maximize the sum rate of the users by jointly optimizing the communication beamformers and the power allocation of the near user subject to the quality of service requirements for sensing and communication functions. The formulated problem is non-convex and hard to solve using traditional solvers. For that reason, a penalty-based approach is adopted to provide an efficient solution. Numerical results demonstrated the advantage of C-NOMA in ISAC, showing gains reaching up to 38% compared to the traditional NOMA, and 65% compared to the spatial division multiple access (SDMA).