Security Tradeoffs in Rate Splitting Multiple Access: Optimal Signal Splitting vs Revealing

This paper considers the secrecy performance of rate splitting (RS) scheme in multi-user multiple-input single-output (MU-MISO) systems. The split of the users' messages into common and private parts can enhance the sum-rate of the communication systems. However, this split of the messages reveals part of the users' messages making them prone to eavesdropping. Thus, to consider the tradeoff between the sum-rate and the secrecy of RS, new analytical expressions for the ergodic sum-rate and ergodic secrecy rate are derived. Then, based on the analytical expressions of the ergodic rates, novel power allocation strategy that maximizes the sum-rate subject to a target secrecy rate is proposed and investigated. Our Monte Carlo simulations show a close match with our theoretical derivations. They also reveal that, by tuning the portion of the split signals, our power allocation approach provides a scalable tradeoff between sum-rate benefits and secrecy.