The achievable secrecy rate of multi-antenna AF relaying using joint transmit and receive beamforming

Physical layer security has attracted a great deal of attentions in recent years. This is achieved through using the physical layer characteristics to help sender to transfer data reliably with perfect secrecy. Using multiple-antenna relay node can improve the secrecy capacity of such channel. In this paper, we study the cooperative wiretap channel in which secure data transmission is achieved with the help of a MIMO Amplify and Forward (AF) relay. In such network, it is assumed multiple eavesdroppers attempt to listen to the relay transmitted signal and try to decode the source message. We assume the relay makes use of separated transmit/receive beamforming vectors, dubbed rank-one beamforming matrix. The beamforming vectors are computed such that the achievable secrecy rate is maximized, assuming the relay is subject to a maximum transmit power constraint. Accordingly, it is shown that the problem of finding proper receive beamforming vector can be translated into a scalar optimization problem, where using that the transmit beamforming vector can be obtained through solving a Semi-Definite Programming (SDP) problem.