NOMA-Assisted Full Space STAR-RIS-ISAC

Abstract

A novel non-orthogonal multiple access (NOMA) assisted full space integrated sensing and communication (ISAC) framework is proposed to elevate the radio sensing performance. Exploiting the simultaneously transmitting and reflecting RIS (STAR-RIS) to extend the half-space into full-space ISAC coverage intensifies the competition for wireless resources. To alleviate this fierce competition as well as ensure ISAC performance, the cluster-based NOMA (CB-NOMA) technique is employed to save the joint communication and sensing (C&S) beams. Furthermore, the dedicated sensing beam accompanied by the joint C&S beams supports the radio sensing functionality. A minimum beampattern gain maximization problem is formulated to jointly optimize the power allocation, active and passive beamformer (BF) design, subject to communication requirements. To solve this non-convex problem, a block coordinate descent (BCD) based integral matrix algorithm is proposed to reach a suboptimal solution. For the joint power allocation and active BF block, the semidefinite relaxation and successive convex approximation are employed to optimize the coupled variables. For the passive BF block, the penalty-based method is invoked. To further reduce the complexity of the passive BF design, a BCD-based element-wise algorithm is proposed, where the joint phase shift and amplitude coefficients of each STAR-RIS element are optimized one by one. Simulation results verified that our proposed algorithms achieve higher beampattern gain towards the intended targets than the benchmark schemes accompanying less mismatch error.