Radiated power scaling factor and its effect on the secrecy performance of multi-user massive MIMO system

In this paper, we investigate the effect of radiated power scaling (RPS) factors on the secrecy performance of multiuser massive multiple-input multiple-output (MIMO) system. We consider secure forward link and reverse link transmissions in the scenario which includes a base station (BS) equipped with a large number of service antennas, multiple single-antenna legitimate users and a passive multiantenna eavesdropper. Specifically, maximum ratio transmission (MRT) and maximum ratio combining (MRC) techniques are used as linear precoder and detector, respectively, on the forward and reverse links. Lower and upper bounds on the ergodic achievable rates corresponding to legitimate users and the eavesdropper are derived, respectively. Then the optimal RPS factors which minimize the upper bounds on the achievable rates of the eavesdropper while satisfying the rate constraints of legitimate users are presented. We also show that the required total radiated power decreases as the number of BS antennas grows larger. Moreover, in the limit of an infinite number of BS antennas, we prove that the optimal RPS factors converge to constant limits. Our work suggests that with proper selected RPS factors, assive MIMO is an effective and low power consuming scheme to achieve both the transmission and security performance. Simulation results corroborate the analysis and demonstrate the secrecy performance achieved with proposed RPS factors under certain rate constraints of legitimate users