Secrecy Rate Analysis for Millimeter-Wave Lens Antenna Array Transmission

Physical layer security is vital to millimeter-wave communications enabled by large-scale arrays, particularly the energy-efficient lens antenna arrays (LAAs). However, the broad application of LAAs can be hindered by the lack of a proper understanding of the secrecy performance. This letter derives an asymptotic closed-form expression for the secrecy rate of LAA, despite the critical challenges including the coupling of unknown lens beam responses. With the new secrecy rate analysis, the optimal power assignment for the legitimate transmission is achieved, leading to the maximization of LAA secrecy. This power assignment is unprecedentedly studied in LAA due to the previous absence of an analytical secrecy rate. Simulations validate the accuracy of the analysis over wide ranges of system parameters.