Secrecy Performance of Incremental Relaying With Outdated CSI

Secrecy performance is investigated for relay networks with multiple antennas N-t at the transmitter. As K relays are available, we propose an incremental threshold relaying scheme with low complexity, where both transmit antenna selection (TAS) and relay selection are deployed without eavesdropper channel state information (CSI). Both the exact and approximate secrecy outage probability (SOP) of proposed scheme are derived with outdated CSI under the cases of maximal ratio combining (MRC) scheme at the legitimate receiver. In the high signal-to-noise ratio(SNR) regime, due to outdated CSI, the secrecy diversity order of MRC decreases to N-t + 1 for relay selection and K + 1 for antenna selection. Finally, simulation results validate our analysis, and show that the proposed scheme alleviates the effect of the transmitter and relay links on SOP.