Secure Switch-and-Stay Combining with Multiple Antennas in Cognitive Radio Relay Networks

— Eavesdropping is a major concern in Cognitive Radio relay systems, due to the broadcast nature of these systems. Physical Layer Security (PLS) has been seen as a good alternative to enhance the secrecy performance of these networks. Based on the concept of perfect secrecy, PLS uses an information-theoretic approach to prevent secondary transmissions from malicious attacks. In this paper, the Secure Switch-and-Stay Combining (SSSC) protocol is extended to a multiple antenna scenario, namely Secure Switch-and-Stay Combining with Multiple Antennas (SSSC-MA) protocol. To choose the best out of two relays, the SSSC-MA is adopted, and the whole transmission process is subject to a multiple antenna eavesdropper attack. Using a Transmit Antenna Selection/Maximal Ratio Combining scheme within the SSSC-MA, the secrecy performance of the extended protocol is compared to three relaying protocols, the single relay Selective Decode-and Forward, the two relay Opportunistic Relaying and the original SSSC. Results show that the proposed SSSC-MA outperforms the other protocols, achieving satisfying secrecy performance even when the eavesdropper has more antennas than the relays.