In this paper, we investigate opportunistic secure multiuser scheduling in energy harvesting untrusted relay networks, where an energy-constrained amplify-and-forward (AF) relay harvests energy from the received radio frequency signal via using the power splitting protocol. To exploit the potential advantages (e.g., multiuser diversity and direct links) for secrecy improvement, we examine three opportunistic user scheduling schemes, i.e., optimal scheduling scheme, maximum scheduling scheme, and minimum scheduling scheme. Specifically, the optimal scheduling scheme performs user selection by maximizing the ratio between the signal-to-noise-ratio (SNR) at the destination and the corresponding SNR at the untrusted relay. The maximum scheduling scheme is conventional user selection that maximizes the channel gain of the direct links. For the minimum scheduling scheme, we try to reduce the overheard information at the untrusted relay by selecting the user with the lowest channel gain of the relay links. For these three schemes, we comprehensively examine the achievable secrecy performance including probability of positive secrecy rate, secrecy outage probability (SOP), asymptotic SOP, secrecy throughput (ST), as well as secure energy efficiency (SEE) to help facilitate an energy-efficient secure transmission design. Simulation results demonstrate that the maximum scheduling scheme outperforms the minimum scheduling scheme in terms of SOP at relatively low SNRs and target secrecy rates.
In this paper, we investigate opportunistic secure multiuser scheduling in energy harvesting untrusted relay networks, where an energy-constrained amplify-and-forward (AF) relay harvests energy from the received radio frequency signal via using the power splitting protocol. To exploit the potential advantages (e.g., multiuser diversity and direct links) for secrecy improvement, we examine three opportunistic user scheduling schemes, i.e., optimal scheduling scheme, maximum scheduling scheme, and minimum scheduling scheme. Specifically, the optimal scheduling scheme performs user selection by maximizing the ratio between the signal-to-noise-ratio (SNR) at the destination and the corresponding SNR at the untrusted relay. The maximum scheduling scheme is conventional user selection that maximizes the channel gain of the direct links. For the minimum scheduling scheme, we try to reduce the overheard information at the untrusted relay by selecting the user with the lowest channel gain of the relay links. For these three schemes, we comprehensively examine the achievable secrecy performance including probability of positive secrecy rate, secrecy outage probability (SOP), asymptotic SOP, secrecy throughput (ST), as well as secure energy efficiency (SEE) to help facilitate an energy-efficient secure transmission design. Simulation results demonstrate that the maximum scheduling scheme outperforms the minimum scheduling scheme in terms of SOP at relatively low SNRs and target secrecy rates.
This paper investigates secure communications of energy harvesting untrusted relay networks, where the destination assists jamming signal to prevent the untrusted relay from eavesdropping and to improve the forwarding ability of the energy constrained relay. Firstly, the source and the destination transmit the signals to the relay with maximal ratio transmission (MRT) technique or transmit antenna selection (TAS) technique. Then, the destination utilizes maximal ratio combining (MRC) technique or receive antenna selection (RAS) technique to receive the forwarded information. Therefore, four transmission and reception schemes are considered. For each scheme, the closed-form expressions of the secrecy outage probability (SOP) and the connection outage probability (COP) are derived. Besides, the effective secrecy throughput (EST) metric is analyzed to achieve a good tradeoff between security and reliability. In addition, the asymptotic performance of EST is also considered at the high signal-to-noise ratio (SNR). Finally, simulation results illustrate that: (1) the EST of the system with MRT and MRC scheme are superior to other schemes, however, in the high SNR regime, the EST of the system with MRT scheme is inferior to TAS; and (2) for the source node, there exists an optimal number of antennas to maximize the EST of the proposed schemes.
The broadcast nature of the wireless medium allows unintended users to eavesdrop on confidential information transmission. In this regard, we investigate the problem of secure communication between a source and a destination via a wireless energy harvesting untrusted node that acts as a helper to relay the information; however, the source and destination nodes wish to keep the information confidential from the relay node. To realize the positive secrecy rate, we use destination-assisted jamming. Being an energy-starved node, the untrusted relay harvests energy from the received radio-frequency (RF) signals, which include the source's information signal and the destination's jamming signal. Thus, we utilize the jamming signal efficiently by leveraging it as a useful energy source. At the relay, to enable energy harvesting and information processing, we adopt power splitting (PS) and time switching (TS) policies. To evaluate the secrecy performance of this proposed scenario, we derive analytical expressions for two important metrics, viz., the secrecy outage probability and the ergodic secrecy rate. The numerical analysis reveals design insights into the effects of different system parameters such as PS ratio, energy harvesting time, target secrecy rate, transmit signal-to-noise ratio (SNR), relay location, and energy conversion efficiency factor, on secrecy performance. Specifically, the PS policy achieves better optimal secrecy outage probability and optimal ergodic secrecy rate than that of the TS policy at higher target secrecy rate and transmit SNR, respectively.
In this paper, we investigate secure communication in a hybrid relay (HR)-assisted wireless powered cooperative communication network (WPCCN), where an eavesdropper tries to intercept the data transmitted by a source user and the HR simultaneously. The HR has the ability to wireless powered the energy-constrained multiple users in the downlink and to relay the received confidential information in the uplink. In particular, the full-duplex destination-based jamming (FD-DBJ) strategy is exploited to improve the secrecy performance. Moreover, in order to conduct effective secure communications, we design two multiuser scheduling schemes, i.e., random user selection (RUS), and best user selection (BUS) based on the main channel quality. In order to evaluate the secrecy performance, we analytically derive the energy outage probability (EOP), the secrecy outage probability (SOP), and the hybrid outage probability (HOP), respectively. As such, we formulate the secrecy throughput (ST) maximization problem to optimize the predetermined transmission rate. Our analysis and numerical results reveal that: 1) The BUS scheme has better security performance. 2) Both of the energy conversion efficiency and the number of users have a positive effect on secrecy performance. 3) The FD-DBJ scheme is an effective method to achieve secure communications. 4) The time-switching factor and predetermined transmission rate have a crucial influence on the secrecy performance, which should be considered carefully in system design.
In this paper, we investigate secure communication for a dual-hop multiuser relay network, where a source communication with N ( N ≥ 1 ) destinations via an untrusted variable gains relay. To exploit multiuser diversity while protecting source’s confidential message, we first propose a joint destination-based jamming and opportunistic scheduling (DJOS) scheme. Then, we derive closed-form approximated and asymptotic expressions of the secrecy outage probability (SOP) for the considered system with DJOS. Furthermore, we determine an asymptotical optimal power allocation (OPA), which minimizes the asymptotic SOP, to further improve the secrecy performance. Our analytical results show that the achievable secrecy diversity order in terms of SOP with fixed power allocation is min ( 1 , N 2 ) , whereas, with OPA, the achievable secrecy diversity order can be improved up to min ( 1 , 2 N N + 2 ) . This interesting result reveals that OPA can improve the secrecy diversity order of the single-user network. This is intuitive since full diversity order of 1 cannot be achieved when N = 1 , thus leaving some space for OPA to improve the diversity order. Nevertheless, for N ≥ 2 , the effect of OPA is to increase the secrecy array gain rather than the secrecy diversity order since full diversity order 1 has been achieved by the OS scheme. Finally, simulation results are presented to validate our analysis.
To improve the physical-layer security performance in the multiuser untrusted relay networks,we propose an opportunistic scheduling combined with cooperative jamming(OSCJ)scheme.We derive the analytical expression of the ergodic secrecy capacity(ESC)lower bound for the OSCJ scheme and the closed-form expression of the lower bound of the secrecy outage probability(SOP).Furthermore,we conduct an asymptotic analysis for ESC.The numerical simulations validate the accuracy of our analysis and show that the proposed OSCJ scheme outperforms the random scheduling and jamming scheme in terms of both ESC and SOP performance.
In this paper, the radio frequency energy harvesting (EH) and security issues in Internet of Things (IoT) sensor networks with multiple untrusted relays are considered. In particular, the communication protocol is divided into two phases. The first phase is used for EH, in which the IoT sensor nodes (SNs) and relays harvest energy from multiple power transfer stations. The second phase is used for information transmission in two steps: 1) the selected SN uses the harvested energy to broadcast information to the controller and the relays, and 2) the selected relay forwards information to the controller by applying the amplify-and-forward protocol to improve the quality of the communication between the SN and the controller. During information transmission, the controller is at risk of losing information because the relay may act as an eavesdropper (namely, an untrusted relay). Thus, to improve the secrecy performance of the considered system, we propose an optimal scheme, namely, best-sensor-best-untrusted-relay (BSBR) and compare this scheme with random-sensor-random-untrusted-relay and a threshold-based scheme. The closed-form expressions for the secrecy outage probability (SOP) and secrecy throughput (ST) are obtained and verified through Monte Carlo simulations to confirm the superior performance of our approach. EH time optimization and the target secrecy rate optimization algorithms are also proposed. In addition, the impacts of the EH time, the EH efficiency coefficient, the numbers of SNs and untrusted relays, and the target secrecy rate on the SOP and the ST are investigated. The results indicate that the BSBR generally outperforms the two baseline schemes in terms of the SOP and ST.