Secure Transmission in Spectrum Sharing Relaying Networks With Multiple Antennas

In this letter, we design a novel secure transmission scheme for dual-hop multiantenna spectrum sharing relaying systems over Rayleigh fading channels. To exploit the benefit of available multiple antennas, maximum ratio combining/zeroforcing beamforming (MRC/ZFB) scheme at the relay is proposed to enhance the secrecy performance. In doing so, we derive a novel exact closed-form expression of the secrecy outage probability, which enables us to evaluate the impact of system parameters on the secrecy performance. Moreover, we look into the high signal-to-noise ratio (SNR) regime, and present simple secrecy outage approximation for the proposed scheme, which reveals that the secrecy diversity order is NR- NP- NE, where NR, NP, and NE are the number of antennas at relay, primary receiver, and eavesdropper, respectively.