Rate-splitting multiple access-assisted ISAC design in NAFD cell-free mMIMO systems

Integrated Sensing And Communication (ISAC) is regarded as a promising technology for facilitating the rapid advancement of Sixth-Generation (6G) due to its concurrent transmission of information and environmental sensing capabilities. Rate-Splitting Multiple Access (RSMA), through the utilization of Successive Interference Cancellation (SIC) and Rate-Splitting (RS) at the transceiver, can fulfill the sensing requirement and supersede individual radar sequence to mitigate the interference between communication and sensing. This paper investigates the transceiver design of the RSMA-assisted ISAC in a Network-Assisted Full-Duplex (NAFD) cell-free Massive Multiple-Input Multiple-Output (mMIMO) system. We first derive the expressions of the communication achievable data rate and radar sensing Signal to Interference plus Noise Ratio (SINR). Subsequently, an optimization problem is formulated to maximize the communication achievable data rate, subject to both radar sensing constraints and fronthaul constraints, an effective algorithm based on sparse beamforming scheme and Semi-Definite Relaxation (SDR) is then proposed to acquire the near-optimal transceiver. Numerical results demonstrate that the application of RSMA technology in ISAC systems can significantly enhance system performance, and reveal that Dual-Functionalities Radar-Communication (DFRC) scheme can achieve higher data rate than the traditional scheme.