Improving the Security and Spectrum Efficiency in Overlay Cognitive Full-Duplex Wireless Networks.

In this paper, we design a new collaboration interference (CI) transmission scheme for overlay cognitive full-duplex wireless wiretap networks, where a full-duplex secondary user utilizes the licensed spectrum to transmit the secondary information and uses the secondary signal as a special noise to help and protect the secure transmission of primary information in the presence of multiple passive eavesdroppers, simultaneously. Specifically, the full-duplex secondary user firstly uses the joint transmit antenna selection/maximal ratio combining (TAS/MRC) scheme to transmit the secondary information and receive the primary information at the same time. Then, the full-duplex secondary user utilizes a new interactive zero forcing beamforming (IZFB) algorithm to transmit the primary and secondary information without mutual interference simultaneously. For comprehensively analyzing the secure performance of the primary transmission, two eavesdropping modes, i.e., non-colluding eavesdropping (NCE) and colluding eavesdropping (CE) are considered. Based on the two modes, we derived the exact and asymptotic closed-form expressions for secrecy outage probability (SOP) of the primary transmission. Furthermore, the effective throughput of secondary transmission is also derived. The results demonstrate that the proposed CI-based transmission scheme can simultaneously improve the secrecy performance of primary transmission and throughput of secondary transmission, and can further achieve better spectrum-and-energy efficiency than traditional overlay transmission.