Abstract: Aiming at the problems of low spectrum utilization, short lifetime and the physical layer security caused by the openness of the wireless channel of energy-constrained cooperative relay network, a new two hop cognitive cooperative relay network with distributed relay nodes is constructed by combining power beacon assisted RF energy collection technology, cognitive radio technology and cooperative relay network. Then, a single eavesdropping node is introduced to eavesdrop the second hop transmission, and the optimal relay selection and the sub optimal relay selection are proposed in combination with the active and passive eavesdropping modes respectively, and the closed-form secrecy outage probability expressions of secondary network under two relay selection modes is deduced. It is shown in simulations that the secrecy outage performance of secondary network is significantly affected by the number of primary receiver nodes and relays, the location of relays and the eavesdropping node, the ratio of energy harvesting, the efficiency of energy conversion, and the thresholds of channel capacity and secrecy capacity. The secrecy outage performance of the secondary network under the optimal relay selection scheme is obviously better than that of the suboptimal relay selection scheme. The secrecy outage probability of secondary network is reduced and tends to be saturated by increasing interference constraint or power beacon signals' power.

Key words: energy harvesting, cognitive relay network, relay selection scheme, secrecy outage probability