RISAC: Rate-splitting Multiple Access Enabled Integrated Sensing and Communication Systems

Integrated sensing and communication (ISAC) is considered to be a promising paradigm for future wireless evolution and emerging services. In such a framework, the spectrum efficiency and hardware utilization are significantly enhanced, since the radar detection and data transmission share the same spectrum and hardware. This paper studies a rate-splitting multiple access enabled ISAC (RISAC), wherein the multi-antenna RISAC transmitter simultaneously senses a single target with the help of a multi-antenna radar receiver, and communicates with a group of users with single-antenna for data transmission based on RSMA. We focus on optimizing the sensing performance in terms of Cramer-Rao lower bound (CRLB), while achieving acceptable data transmission performance in terms of data rate. To this end, we aim to minimize the CRLB of the sensing response matrix at the radar receiver, by adequately designing the RSMA structure and the associated parameters, with constraints of data rate requirement and transmit power budget. To tackle the non-convex CRLB minimization problem, we split the original problem into outer and inner subproblems, which can be efficiently solved by particle swarm optimization algorithm and semidefinite relaxation method, respectively. Numerical results confirm that RISAC outperforms the space division multiple access based strategy in terms of CRLB.