Security-Reliability Tradeoff in RSMA-Based Communications Against Eavesdropper Collusion

This letter exploits secure beamforming for achieving security-reliability tradeoff in rate splitting multiple access (RSMA)-based communications against eavesdropper collusion. Considering user fairness, we maximize the minimum secrecy rate (MSR) among all legitimate users subject to the quality of service (QoS) constraints and transmit power constraint. A feasibility check problem is first presented to avoid infeasible cases. Then, a successive convex approximation-based algorithm is proposed to iteratively optimize the beamforming design. Numerical results show that the proposed RSMA-based design outperforms the baseline design in terms of MSR within certain QoS requirement ranges to trade security for reliability by balancing the power allocated to the common stream and private streams. And the performance advantage enlarges as the number of collusive eavesdroppers increases.