In this paper, we consider secure transmissions of millimeter wave (mmWave) Simultaneous Wireless Information and Power Transfer (SWIPT) unmanned aerial vehicle (UAV) relay networks, where a source transmits confidential information to an energy-constrained destination on the ground with the help of a UAV-based relay in the presence of multiple independent homogeneous Poisson point process (HPPP) eavesdroppers. First, we derive closed-form expression of the lower bound of average secrecy rate using 3D antenna gain model. Then, we study the secrecy rate lower bound maximization problem by optimizing the source/UAV transmit power, power splitting ratio and UAV’s location. To solve this non-convex problem, we propose an alternate optimization algorithm by solving three sub-problems iteratively. Simulation results show that the proposed algorithm can greatly improve the average secrecy rate.

This paper investigates the secrecy outage performance of buffer-aided multirelay multiple-input multiple-output cooperative systems in the presence of a passive eavesdropper. Due to the unavailability of the channel state information of eavesdropper's channel, a buffer-aided joint transmit antenna and relay selection scheme based on the main channel is proposed to enhance the secrecy performance. Specifically, we model the evolution of the relay buffers as a Markov chain and derive new exact and asymptotic closed-form expressions for the secrecy outage probability, which provides an efficient way to assess the effect of system parameters on the secrecy outage probability. Moreover, simple asymptotic results are further exploited under two special scenarios, i.e., L → ∞ and L → ∞ (where L denotes the size of the relay buffers), for characterizing the achievable secrecy diversity gain, the secrecy coding gain, and the secrecy diversity-multiplexing tradeoff. Our results reveal that: 1) a secrecy diversity gain of N _R Mmin(N _S , N _D ) is achieved when L → ∞, however, when L → ∞, the secrecy diversity gain increases to NRM(N _S + N _D ), where N _S , N _R , and ND represent the number of antennas at the source, each of M relays and the destination, respectively. 2) The eavesdropper's channel does not affect the secrecy diversity gain but only the secrecy coding gain in both the two scenarios.

In this paper, we investigate the secrecy performance of energy-constrained wireless powered networks with considering the passive eavesdropping scenario, where the simultaneous wireless information and power transfer based full-duplex selfjamming (SWIPT-FDSJ) scheme is developed. The maximal ratio transmission (MRT) protocol is applied at the multi-antenna source such that the wireless signals are designated to the destination directly. Besides, the energy harvesting and fullduplex (FD) self-jamming operations are adopted at the energyconstrained destination to prolong its lifetime as well as to confuse the eavesdropper. Specifically, the exact and asymptotic closedform expressions of the connection outage probability (COP), the secrecy outage probability (SOP), and the secrecy throughput of the proposed system are obtained, based on which we optimize the time-switching ratio to maximize the secrecy throughput. We also degenerate the proposed SWIPT-FDSJ scheme to the reduced half-duplex with no self-jamming (HDNSJ) scheme. The finds suggest that in the HDNSJ scheme, adding the antenna number of the source only benefits the COP performance, but has no impact on the SOP performance. By contrast, it will promote the COP and SOP performance at the same time in the SWIPT-FDSJ scheme, which eventually results in the great improvement of secrecy throughput. In addition, we present the practical application condition of the SWIPT-FDSJ scheme. It is demonstrated that the secrecy throughput performance of the SWIPT-FDSJ scheme is much superior to the HDNSJ scheme on condition that the application condition is satisfied.

In this paper, the secrecy performance of the two-user simultaneous wireless information and power transfer (SWIPT) sensor networks is studied and a novel secure transmission scheme of cooperative zero-forcing (ZF) jamming is proposed. The two sensors opportunistically conduct the SWIPT and cooperative ZF jamming, respectively, where the energy required for jamming the eavesdropper is provided by the SWIPT operation so as to keep the energy balance at the sensors in the long run. By deriving the exact closed-form expressions of the secrecy outage probability and the secrecy throughout, we provide an effective approach to precisely assess the impacts of key parameters on the secrecy performance of the system. It has been shown that the secrecy outage probability is a monotonically increasing function of the growth of secrecy rate ( $R_s$ ), and a monotonically decreasing function of the increase of the transmit signal-to-noise ratio ( ${\gamma }_S$ ), and energy conversion efficiency ( $\eta$ ). Furthermore, the secrecy throughput could be enhanced when $\eta$ increases, which becomes especially obvious when a large ${\gamma }_S$ is provided. Moreover, the existence of an optimum $R_s$ maximizing the secrecy throughput is depicted, which also grows with the increase of ${\gamma }_S$ . Simulations are provided for the validation of the analysis.

This paper studies a multiple unmanned aerial vehicle (UAV) relaying communication system, where multiple UAV relays assist the blocked communication between a group of ground users (GUs) and a base station (BS). Since the UAVs only have limited-energy in practice, our design aims to maximize the energy efficiency (EE) through jointly designing the communication scheduling, the transmit power allocation, as well as UAV trajectory under the buffer constraint over a given flight period. Actually, the formulated fractional optimization problem is difficult to be solved in general because of non-convexity. To resolve this difficulty, an efficient iterative algorithm is proposed based on the block coordinate descent (BCD) and successive convex approximation (SCA) techniques, as well as the Dinkel-bach's algorithm. Specifically, the optimization variables of the formulated problem are divided into three blocks and we alternately optimize each block of the variables over iteration. Numerical results verify the convergence of the proposed iterative algorithm and show that the proposed designs achieve significant EE gain, which outperform other benchmark schemes.