Max-Min Fairness of Cooperative RSMA for Aggregated VLC/RF Systems

The aggregated visible light communication (VLC) and radio frequency (RF) system, which can be regarded as a heterogeneous multiple-input multiple-output system, has been studied to operate with novel multiple access technologies for effectively expanding spectrum resources. In this letter, we propose a novel cooperative rate splitting multiple access (RSMA)-based aggregated VLC/RF system that forwards part of common stream via device-to-device (D2D) RF sidelinks to tackle the problem of fairness among users. Meanwhile, with the objective of maximizing the minimum achievable rate, we jointly optimize the precoder, rate allocation of common stream, and power allocation of RF sidelinks under the constraint of limited total system power. Since the formulated optimization problem is non-convex, semidefinite relaxation (SDR) and successive convex approximation (SCA) methods are applied to solve it. Numerical results show that the proposed scheme significantly outperforms other baseline schemes in terms of user fairness, i.e., the minimum achievable rate in different scenarios and demonstrates robustness against blockages.