On the optimum secrecy capacity of multiple relay networks

We consider a confidential communication system in which a source sends a confidential information to the destination in the presence of an eavesdropper. Multiple relays are used to provide cooperative diversity to the destination. The destination and the eavesdropper are equipped with multiple antennas while each relay and source are equipped with single antenna. We are interested to protect the transmitted information from eavesdropping and to find the effect of receive diversity on the secrecy capacity of the proposed model. We consider the maximal ratio combining (MRC) technique at the destination and derive the expression of combiner output signal-to-noise ratio (SNR) using optimum weighting vector so that the eavesdropper is unable to decode a single bit from the original massage. Finally, we derive the expression of optimum secrecy capacity in terms of the number of relays and the number of antennas at the destination. Our results show that the optimization of weighting vector at the receiver enhances secrecy capacity of a wiretap channel.