  This paper considers secure communication in buffer-aided cooperative
wireless networks in the presence of one eavesdropper, which can intercept the
data transmission from both the source and relay nodes. A new max-ratio
relaying protocol is proposed, in which different relays are chosen for
reception and transmission according to the ratio of the legitimate channels to
the eavesdropper channels, so that the relay selected for reception and the
relay selected for transmission can receive and transmit at the same time. It
is worth noting that the relay employs a randomize-and-forward (RF) strategy
such that the eavesdropper can only decode the signals received in the two hops
independently. Theoretical analysis of the secrecy throughput of the proposed
scheme is provided and the approximate closed-form expressions are derived,
which are verified by simulations. Through numerical results, it is shown that
the proposed scheme achieves a significant improvement in secrecy throughput
compared with existing relay selection policies.
