Distributed Antennas Aided Secure Communication in MU-Massive-MIMO with QoS Guarantee

We consider in this paper the physical layer security in multi-user massive multiple-input multiple-output (MU-Massive-MIMO) system, where an eavesdropper (Eve) is assumed to be able to intercept the information intended to any of the users. Distributed antenna sets, commonly known as remote radio heads (RRHs), are deployed at the base station, which enables autonomous power allocation between the information signal and artificial noise (AN) at each antenna set. Assuming a large number of antennas at each RRH and cooperative downlink maximum-ratio transmission beamforming, we first derive the closed-form deterministic equivalents of post-processing signal to interference-plus-noise ratio (SINR) of users and Eve in both the centralized and autonomous full transmission schemes. Then, we maximize the minimum user SINR over the signal and AN powers subject to the sum power and Eve SINR constraints. The optimization in the former scheme leads to a linear programming problem, while the latter results in a complementary geometric programming (GP), which has to be transformed into an ordinary GP problem in order to be solved efficiently. Numerical results demonstrate the significance of deploying the RRHs as well as autonomous power allocation to improve the user SINR along with the secure communication with QoS guarantee in MU-Massive-MIMO.