Abstract
This paper investigates the secrecy communication in an underlay cognitive radio (CR) networks with one primary user (PU) as well as multiple PUs, where the radio frequency (RF) energy-harvesting secondary user (SU) transmits the confidential information to the destination in the presence of a potential eavesdropper. We introduce a RF energy-harvesting secondary jammer (SJ) to secure the SU transmissions. The system works in time slots, where each time slot is divided into the energy transfer (ET) phase and the information transfer (IT) phase. In ET phase, the SU and SJ capture energy from the PU transmissions; in the IT phase, the SU uses the harvested energy to transmit information to the destination without causing the harmful interference to the PU transmissions, while the SJ utilizes the captured energy to generate jamming signals to the eavesdropper to secure the SU transmissions. We aim to maximize the secrecy rate for SU transmissionsby jointly optimizing the time allocation between ET phase and IT phase and the transmit power allocation at the SU and SJ. We first formulate the secrecy rate maximization as non-convex optimization problems. Then, we propose efficient nested form algorithms for the non-convex problems. In the outer layer, we obtain the optimal time allocation by the one dimension search method. In the inner layer, we obtain the optimal transmit power allocation by the DC programming, where the Lagrange duality method is employed to solve the convex approximation problem. Simulation results verify that the proposed schemes essentially improve the secrecy rate of the secondary network as compared to the benchmark schemes.
Highlights
IntroductionTo fulfill ever-increasing demands for wireless services and applications, cognitive radio (CR) technology has been emerged to lighten severe shortage of spectrum resources [1]
The differences between our work and the previous woks [28,29] are summarized as follows: (a) The authors in [28,29] consider overlay cognitive radio (CR) networks with one primary user (PU), while we focus on underlay CR
Networks with one PU as well as multiple PUs. (b) In [28,29], the secondary user (SU) transmits artificial noise (AN) to confuse the eavesdropper, while a wireless powered cooperative jammer is introduced in our work to impair the wiretap channel. (c) The authors in [29] consider the secure transmissions for the primary network and the authors in [28] investigate secure transmissions for both the primary and secondary networks, while we study the secure transmission for the secondary networks
Summary
To fulfill ever-increasing demands for wireless services and applications, cognitive radio (CR) technology has been emerged to lighten severe shortage of spectrum resources [1]. CR technology allows the secondary users (SUs) to access the spectrum licensed to the primary users (PUs), based on the premise that the quality of service (QoS) requirement of the PUs must be guaranteed [2,3]. In the CR networks, underlay and overlay are two main schemes that the SUs share the spectrum with the PUs [4,5]. The explosion of wireless services and applications has led to energy deficiency in the future wireless communications. Radio-frequency (RF) energy-harvesting technology is a good candidate solution for charging the low-power wireless devices [6–10], which can conquer the uncontrollability and intermittency of wireless devices powered by the renewable energy sources, such as wind, solar and vibrational energy. The harvest--transmit (HTT) protocol is proposed in [11] as one of the most common working mode of RF energy-harvesting technology, where the users first harvest energy from the RF energy source in the energy transfer (ET) phase and use the captured energy to transmit information to the destination in the information transfer (IT) phase
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