Secure Communication for Multi-user Massive MIMO System With Finite Alphabet Inputs

This paper investigates the secure transmission for multi-user massive MIMO system with finite alphabet inputs, where a multi-antenna eavesdropper attempts to wiretap the confidential data to legitimate users. Specifically, by exploiting the null-space artificial noise (AN) generation for security enhancement, the closed-form expression of an approximated ergodic secrecy rate is derived with respect to key system parameters including the number of the antennas and users, transmit power, finite alphabet set, etc. Considering the large antenna regime, the behavior of the asymptotic ergodic secrecy rate is also analyzed. Based on the asymptotical results, a low complexity power allocation optimization problem for maximizing the achievable secrecy rate is then presented. Numerical results demonstrate the accuracy of the analytical expressions, as well as the effectiveness of the proposed power control algorithm.