Cooperative Jamming for Secure Communications in MIMO Relay Networks

Abstract

Secure communications can be impeded by eavesdroppers in conventional relay\nsystems. This paper proposes cooperative jamming strategies for two-hop relay\nnetworks where the eavesdropper can wiretap the relay channels in both hops. In\nthese approaches, the normally inactive nodes in the relay network can be used\nas cooperative jamming sources to confuse the eavesdropper. Linear precoding\nschemes are investigated for two scenarios where single or multiple data\nstreams are transmitted via a decode-and-forward (DF) relay, under the\nassumption that global channel state information (CSI) is available. For the\ncase of single data stream transmission, we derive closed-form jamming\nbeamformers and the corresponding optimal power allocation. Generalized\nsingular value decomposition (GSVD)-based secure relaying schemes are proposed\nfor the transmission of multiple data streams. The optimal power allocation is\nfound for the GSVD relaying scheme via geometric programming. Based on this\nresult, a GSVD-based cooperative jamming scheme is proposed that shows\nsignificant improvement in terms of secrecy rate compared to the approach\nwithout jamming. Furthermore, the case involving an eavesdropper with unknown\nCSI is also investigated in this paper. Simulation results show that the\nsecrecy rate is dramatically increased when inactive nodes in the relay network\nparticipate in cooperative jamming.\n