Overlay Networks with Jamming and Energy Harvesting: Security Analysis

In cognitive radio networks, direct communications between a primary sender–recipient pair may be blocked due to uncertainties such as deep fading. Therefore, this paper studies overlay networks where the message of the primary sender is relayed by the secondary transmitter who also transmits its privacy message to support this communications. However, messages of the secondary transmitter may also be overheard by eavesdroppers. To secure these messages, jammers are exploited to restrict overhearing. Moreover, in order to improve energy efficiency, the secondary transmitter and all jammers only use energy harvested from primary signals for their transmission. To evaluate the security capability of both primary and secondary networks without exhaustive simulations, exact closed-form expressions of primary/secondary secrecy outage probabilities are first proposed. Then, multiple theoretical/simulated results show the validity of the proposed expressions and security improvement with increasing the number of jammers. Finally, exhaustive search based on the proposed expressions can find optimum design parameters, which perfectly serve as design instructions.