Secure Cooperative Communication With Nondedicated Relays

Abstract

The security issue is considered for a cooperative communication system with multiple nondedicated relays, which have their own information to transmit. Distributed spatial modulation (DSM) is a promising technique for nondedicated relay networks. However, any receiver in the relays’ coverage can decode the source information by examining the status of the relays in conventional DSM systems. To prevent the eavesdropper from intercepting the source information and, at the same time, guarantee the transmissions of the relays, a secure distributed spatial modulation (SDSM) scheme is proposed in this paper. In the broadcasting phase, the relays that can successfully decode the source signal form a decoding set. In the relaying phase, only a certain number of the relays in the decoding set carry the source information via their indices, while all the relays in the decoding set transmit their own information simultaneously. By designing a precoder for these relays’ signals, the destination can extract the source information in the spatial domain, but the eavesdropper is confused by the concurrent transmissions of the relays. The secrecy rate analysis shows that the mutual information from the source to the eavesdropper is zero. Simulation results validate the superiority of the proposed SDSM scheme when compared with the competing candidates.