Secure Cooperative AF Relaying Networks with Untrustworthy Relay Nodes

Abstract

In this paper, the security of multi-input single- output (MISO) amplify-and-forward relaying network with untrustworthy relay nodes is considered, where the untrustworthy nodes can help to forward the received signal and they may also try to decode such information, which can be regarded as potential eavesdroppers (Eves). To deal with such kind of smarter Eves, relay selection is adopted and both the maximal-ratio transmission (MRT) scheme and the zero-forcing beamforming (ZFBF) scheme are used at the multi-antenna base station (BS). To achieve a positive secrecy capacity, the destination also injects intended jamming signal to confuse the decoding of the untrustworthy nodes. Either approximation or lower bound of the secrecy outage probability is derived in closed form. It is shown that the proposed partial relay selection scheme approaches the optimal relay selection scheme. In particular, for the ZFBF scheme, when the number of antennas is large enough, increasing the number of relay nodes will increase the diversity order and thus improves the secrecy performance. Simulation results validate the effectiveness of the scheme and correctness of analysis.