Backscatter-Enabled RIS-Assisted NOMA ISAC

In this paper, we investigate the performance of a backscatter-enabled hybrid reconfigurable intelligent surface (RIS)-assisted non-orthogonal multiple access (NOMA) network for integrated sensing and communication (ISAC). We formulate a sum rate and sensing power maximization problem that jointly optimizes the transmit beamformer at the base station and the phase shifts at the RIS under a strict power budget, quality of service constraints at each receiving node, and unit modulus phase shift at each element of the RIS. Due to the coupling of variables and the non-convex nature of the constraints, we propose an alternate optimization (AO) based iterative algorithm that solves the problem using the successive convex approximation (SCA) method and the CVX tool. The simulation results validate the convergence and efficacy of the proposed algorithm. Finally, we demonstrate the impact of key system parameters such as the number of elements at the RIS and the maximum power budget.