On the Secrecy Rate Achievability in Dual-Hop Amplify-and-Forward Relay Networks

The achievable secrecy rate of a dual-hop amplify-and-forward relaying system, in the presence of an eavesdropper, is investigated based on the different values of the wireless links´ signal-to-noise ratios (SNRs). It is shown that when the direct link to the eavesdropper is in a better condition than the direct link to the destination, but the relaying link for the destination is better than the relaying link for the eavesdropper, under specific conditions for the links SNRs, it is possible to achieve the secrecy rate for a limited range of the relay power. On the other hand, when the direct link to the destination is better than the direct link to the eavesdropper, under certain conditions for the links´ SNRs, it is not always beneficial to employ the relay, since there exists a limited range of relaying power for which secrecy rate is not achievable. Finally, it is shown that the source transmit power has no impact on the secrecy rate achievability. Simulation results confirm the theoretical analysis carried out in this letter.