Optimal Power Allocation in Multipair Full-duplex Relaying Massive MIMO Networks in Presence of Eavesdropper

In this paper, we investigate the physical layer secrecy of a multipair cooperative network in presence of an eavesdropper. Simultaneous ccommunication between the transmitter and receiver pairs is established through a massive antenna array equipped full-duplex relay station, while the passive eavesdropper overhears communication between one pair. We consider that the relay uses zero-forcing, maximum mixing ratio, and maximum transmission ratio linear processing techniques. In the first part of the paper, we study the secrecy rate of the adopted linear processing techniques. We derive closed-form expressions for the average secrecy rate as a functions of the system parameters, such as number of pairs, the number of relay’s transmit and receive antennas, and the channel estimation coefficients. In the second part of the paper, in order to improve the system’s secrecy, an optimal power allocation scheme is presented at the relay station and source nodes. The formulated problem is a complex non-convex problem that is solved by recasting as a geometric programming problem. The simulation results show that the proposed power allocation scheme significantly improves the system's secrecy rate.