On the Secrecy Analysis of Dual-Hop SWIPT-Based Multi-Source Underlay Cognitive Radio Networks

This paper investigates the intercept probability (IP) performance for a dual-hop multi-secondary user (SU) underlay cognitive-radio networks. Whereby, the relay R is self-powered by harvesting energy from secondary sources using the time switching variant (TS) of simultaneous wireless information and power transfer (SWIPT) protocol. Single-antenna SUs are transmitting data to multi-antennas end-user D, performing maximal-ratio combining (MRC) diversity technique, through R in presence of (i) a primary network composed of a primary transmitter (PUt) and receiver (PUr) pair, and (ii) a passive eavesdropper at each hop (i.e., E(1 )and E-2), attempting to overhear the communication. Moreover, we suppose that the second eavesdropper has multiple antennas and employs the MRC technique, that the relay employs the Decode-and-Forward relaying protocol, that the two hops are subject to the Rayleigh fading model, and that the channel state information is fully known at both D and E-2. Because of the underlying strategy, the SUs are constantly modifying their transmit powers to prevent interference with primary users. A closed-form expression of the IP is obtained by taking into consideration the correlation between the secrecy capacities for both hops. The impact of other essential factors on IP, such as the transmit power of sources, the fading severity parameter, and the maximum tolerable interference power (MTIP), is also investigated. Specifically, we want to know if the energy harvester (i.e., relay) might improve the security of such a system even more for low MTIP or transmit power of SUs. Monte Carlo simulations verify all of the obtained results, and valuable insights into the secrecy of the considered system are achieved.