Physical layer security in wireless-powered networks with untrusted relays

This paper investigates the integration of relay-assisted Internet of Things (IoT) systems, focusing on the use of multiple relays to enhance the system performance. The central metric of interest in this study is system outage probability, evaluated in terms of latency. Our research provides a comprehensive analysis of system outage probability, considering different relay selection criteria to optimize the system’s transmission performance. Three relay selection strategies are employed to enhance the system transmission performance. Specifically, the first strategy, optimal relay selection, aims to identify the relay that minimizes the latency and maximizes the data transmission reliability. The second approach, partial relay selection, focuses on selecting a subset of relays strategically to balance the system resources and achieve the latency reduction. The third strategy, random relay selection, explores the potential of opportunistic relay selection without prior knowledge. Through a rigorous investigation, our paper evaluates the impact of these relay selection criteria on the performance of relay-assisted edge computing systems. By assessing the system outage probability in relation to latency, we provide valuable insights into the trade-offs and advantages associated with each selection strategy. Our findings contribute to the design and optimization of reliable and efficient edge computing systems, with implications for various applications, including the IoT and intelligent data processing.

Considering the problems of network lifetime and energy replenishment in wireless sensor network (WSN), a Power Beacon (PB) assisted energy harvesting Simultaneous wireless information and power transfer (SWIPT) multi-relay system model is proposed. Under the condition that the relay node has the characteristics of capturing the energy of the source node and PB signal, the system throughput of the target node using the maximum ratio combining technology is derived. Then, the problem model is established under multiple constraints to ensure the communication quality of service, and a relay selection strategy based on the adaptive chaotic particle swarm optimization (ACPSO) algorithm is proposed to optimize the system throughput. Simulation and numerical results show that PB transmission power, time switching (TS) factor, power splitting (PS) factor, and other parameters have a significant impact on throughput performance. Compared with the random relay selection (RS) strategy, the proposed strategy can achieve greater throughput gain, and it is proved that the ACPSO algorithm can quickly and effectively optimize network throughput.

In this chapter, we consider a wireless network consisting of a source and a destination with the aid of multiple relay nodes, where an eavesdropper is assumed with an intention to tap the confidential transmission from the source to destination. Considering multiple relays available, we present a relay selection scheme to protect the source-destination transmission against eavesdropping, where only the single “best” relay is selected to help the source transmit the signal to the destination. For comparison purposes, we also consider the conventional direct transmission and random relay selection as benchmark schemes. As the name implies, the direct transmission allows the source to directly transmit its signal to the destination without relying on the relays. By contrast, in the random relay selection, a relay is randomly selected to assist the source-destination transmission. Closed-form intercept probability expressions are derived for the conventional direct transmission and random relay selection as well as the proposed relay selection schemes over Rayleigh fading channels. We also present the secrecy diversity analysis of these there schemes and show that the proposed relay selection obtains the full secrecy diversity, whereas the direct transmission and random relay selection methods achieve the secrecy diversity order of only one. Numerical results demonstrate that the proposed relay selection performs better than both the direct transmission and random relay selection in terms of the intercept probability. Finally, as the number of relays increases, the intercept performance of the proposed relay selection improves significantly, showing the security benefits of exploiting the relay selection to defend against eavesdropping.

In this study, the authors investigate the energy‐efficient (EE) relay selection (RS) and power allocation (PA) in a cooperative secured system. Their scenario includes a multiple‐antenna source, a multiple‐antenna destination and multiple amplify‐and‐forward untrusted relay nodes, where the relay nodes only have the channel‐amplitude information. To prevent the untrusted relays from intercepting the source message and to achieve positive secrecy rate, the destination‐based cooperative jamming technique is used. By maintaining a minimum required secrecy rate, three optimal joint RS and power minimisation schemes are studied. The first objective is minimising the total transmit power consumption, and therefore obtaining the corresponding EE‐RS and PA schemes. Second, they focus on relay power minimisation, and third sum power minimisation of the relay and one mobile node by considering a weighted factor are investigated. Closed‐form solutions are presented for three practical optimised networks. Finally, some numerical results are provided to show the merits of the proposed scheme. They also give some insights to system design.

This paper investigates the impact of relay selection (RS) on the performance of cooperative non-orthogonal multiple access (NOMA), where relays are capable of working in either full-duplex (FD) or half-duplex (HD) mode. A number of relays (i.e., K relays) are uniformly distributed within the disc. A pair of RS schemes are considered insightfully: 1) single-stage RS (SRS) scheme; and 2) two-stage RS (TRS) scheme. In order to characterize the performance of these two RS schemes, new closed-form expressions for both exact and asymptotic outage probabilities are derived. Based on analytical results, the diversity orders achieved by the pair of RS schemes for FD/HD cooperative NOMA are obtained. Our analytical results reveal that: 1) the FD-based RS schemes obtain a zero diversity order, which is due to the influence of loop interference at the relay; and 2) the HD-based RS schemes are capable of achieving a diversity order of K , which is equal to the number of relays. Finally, simulation results demonstrate that: 1) the FD-based RS schemes have better outage performance than HD-based RS schemes in the low signal-to-noise ratio (SNR) region; 2) as the number of relays increases, the pair of RS schemes considered are capable of achieving the lower outage probability; and 3) the outage behaviors of FD/HD-based NOMA SRS/TRS schemes are superior to that of random RS and orthogonal multiple access based RS schemes.

Two-way amplify-and-forward (AF) relaying networks have been widely studied because of its simplicity and high spectral efficiency. In this paper, we investigate the relay selection problem and the diversity-multiplexing tradeoff (DMT) for two-way AF relaying systems over independent flat Rayleigh fading channels. We first derive the closed-form expression of the minimum total transmit power under the predefined data rate requirements. Based on the minimum total transmit power, we propose a simple relay selection which only requires user-relay channel state information (CSI). We proved that the proposed relay selection scheme can achieve the same DMT performance as obtained by the popular outage-optimal two-way opportunistic relaying scheme. Simulation results demonstrate that the proposed scheme can significantly decrease the power consumption compared with random relay selection and other schemes.

In this paper, we study the end-to-end performance of multi-hop wireless powered relaying networks cognitively operating with primary networks over Nakagami-m fading channels. Our analysis considers multi-hop wireless powered relaying systems in which all communication nodes harvest energy from a multiple antennas power beacon (PB) to transmit data to multiple destinations in the presence of a multiple antennas primary receiver (PR). Aiming at improving end-to-end system performance, we propose two relay selection schemes, namely data channel based relay selection (DbRS) and interference channel based relay selection (IbRS), under cognitive radio approach. By taking into account the harvested energy and the interference power constraint, we derive the exact closed-form expression for the outage probability (OP) of the proposed schemes, which is then verified by Monte Carlo simulations over Nakagami-m fading channels. The tractable asymptotic OP of each scheme is also provided unveiling several important insights on system characteristics and performance trends. Moreover, we develop the asymptotic upper bounds for the ergodic capacity and bit error rate (BER) of the considered multi-hop relaying network. Numerical results in terms of system OP, ergodic capacity, and average BER performance are provided to demonstrate that DbRS scheme outperforms IbRS one, which by its turn outperforms random relay selection scheme. Finally, the influences of the number of antennas at PB and PR, number of relays in each cluster, number of hops, the PB and PR placements, and time switching ratio on the overall system performance are examined and discussed comprehensively.

This paper studies on the relaying selective matter in amplify-and-forward (AF) cooperation communication with full-duplex (FD) activity. Various relay choice models supposing the present of different instant information are investigated. We examine a maximal relaying choice that optimizes the instant FD channel capacity and asks for global channel state information (CSI) as well as partial CSI learning. To make comparison easy, accurate outage probability clauses and asymptote form of these strategies that give a diversity rank are extracted. From that, we can see clearly that the number of relays, noise factor, the transmittance coefficient as well as the information transfer power had impacted on their performance. Besides, the optimal relay selection (ORS) model can promote than that of the partial relay selection (PRS) model.

In this paper, we investigate the performance of asymmetric radio frequency (RF) and free space optical (FSO) dual-hop cooperative relay network along with a direct RF link between source and destination. The FSO link experiences double generalized Gamma turbulence in the presence of the generalized non-zero boresight pointing errors, and RF links experience non-identically distributed Nakagami-m fading. Moreover, considering both cognitive radio and non-cognitive scenarios, a partial relay selection (PRS) strategy has been employed. Furthermore, both relay selection and underlay power restriction are governed with the outdated channel state information (CSI). We also assume both heterodyne and intensity modulation/direct detection methods in the FSO receiver. Under the assumption of amplify-and-forward relaying and PRS, we derive closed-form expressions for outage probability (OP) of both scenarios, while bit-error probability and ergodic capacity of the non-cognitive scenario are also obtained. The asymptotic expressions of OP and diversity order of this network are derived for both perfect CSI and outdated CSI cases. It is demonstrated that the diversity order is a function of the fading severity of the RF links, turbulence parameters of the FSO link, and pointing error, regardless of interference channel parameter of the primary user.

In this paper, we compare the performance in terms of symbol error probability, data rate and power consumption of the use of fixed transmit power (FTP) and adaptive transmit power (ATP) in underlay cognitive radio networks. The use of FTP alleviates the signaling requirements of underlay cognitive radio networks compared to the ATP. Nevertheless, the use of FTP influences the performances of the underlay cognitive radio networks. To study this influence, we consider three relay selection schemes using FTP: opportunistic decode and forward with FTP (O-DF with FTP), opportunistic amplify and forward with FTP (O-AF with FTP) and partial relay selection with FTP (PR with FTP). We compare the performances of these schemes in terms of symbol error probability, data rate and power consumption with three relay selection schemes using ATP: opportunistic decode and forward with ATP (O-DF with ATP), opportunistic amplify and forward with ATP (O-AF with ATP) and partial relay selection with ATP (PR with ATP). We provide exact and/or lower bound expressions of the symbol error probabilities of O-DF, O-AF and PR with FTP. The analytical study for the data rate and the power consumption is also provided. Our comparison study shows that FTP has a positive impact on the data rate and power consumption performance while it deteriorates the symbol error probability performance.

In this paper, a secure energy harvesting relay communication system with partial relay selection over Nakagami-m fading channels is proposed. A power beacon can provide wireless energy for the source and relay. A time-switching-based (TS) radio frequency energy harvesting technique is deployed at the power beacon. An eavesdropper is able to wiretap to the signal transmitted from the source and the relays. The exact closed-form expression of secrecy outage probability is derived. The results show that with increasing number of relays the system performs better in terms of secrecy outage probability (SOP). In addition, the energy harvesting duration has a significant effect on the secrecy outage probability. There exist an optimal energy harvesting duration that can achieve the lowest SOP and therefore this parameter should be carefully designed.

We investigate the physical-layer security of a wireless sensor network comprised of a source-destination pair, multiple decode-and-forward (DF) relays, and an eavesdropper. When the relays forward the source signal to the destination, they should dissipate certain power for driving their physical circuits (e.g., amplifiers and filters), in addition to the transmit power required for emitting radio signals. However, no existing work considers the circuit power when exploiting relays for enhancing the wireless security against eavesdropping. We thus propose the relay-selection based cooperative beamforming framework, where partial relays are selected to forward the source signal in a beamforming manner. We present two relay-selection strategies, namely, the exponential-complexity exhaustive search and linear-complexity relay ordering. For comparison purposes, we also evaluate the conventional all-relay based and best-relay based beamforming schemes, where all relays or only the best one is selected to assist the source-destination transmission. It is shown that the proposed beamforming schemes significantly outperform the conventional all-relay and best-relay based beamforming schemes in terms of secrecy capacity. Additionally, the relay-ordering based beamforming scheme almost achieves the same secrecy capacity as the exhaustive-search method, but with a reduced computational complexity.

A novel cross-layer joint relay selection and power allocation (CL-JRSPA) scheme over physical layer and data-link layer is proposed for cooperative relaying system in this paper. Our goal is finding the optimal relay selection and power allocation scheme to maximize system achievable rate when satisfying total transmit power constraint in physical layer and statistical delay quality-of-service (QoS) demand in data-link layer. Using the concept of effective capacity (EC), our goal can be formulated into an optimal joint relay selection and power allocation (JRSPA) problem to maximize the EC when satisfying total transmit power limitation. We first solving optimal power allocation (PA) problem with Lagrange multiplier approach, and then solving optimal relay selection (RS) problem. Simulation results demonstrate that CL-JRSPA scheme gets larger EC than other schemes when satisfying delay QoS demand. In addition, the proposed CL-JRSPA scheme achieves the maximal EC when relay located approximately halfway between source and destination, and EC becomes smaller when the QoS exponent becomes larger.

Physical-layer network coding (PNC) promises a significant gain In overall network throughput for multi-user cooperative communications. In a multi-unicast scenario, one drawback associated with PNC is an additional noise term, coined as network coding (NC) noise, which severely degrades the system data rate. In this paper, our contribution to address this challenging problem is source and relay power control with the objective of maximization of the minimum average achievable rate among all the source-destination pairs subject to a given total power constraint. We further develop a joint power allocation and relay selection scheme, which only rely on long-term channel statistics, to extend our results to general network topologies. We show that the joint optimization problem can be divided into two problems: optimal power allocation and optimal relay selection where the former is scalable and leads to a power assignment algorithm that exhibits the same optimization complexity for any number of sources in the network and the latter can be performed in a decentralized manner. By means of simulations, we validate our theoretical developments and verify the efficiency of our algorithm in improving the average achievable rate compared to a multi-unicast system with no power control or relay selection. We conclude that the proposed algorithm largely combats the adverse effects of NC noise while achieving near optimal fairness.

Opportunistic relaying scheme is a single cooperative relay selection method based on Channel State Information. However, the failure probability of the best relay selection may become unacceptable when the number of relays increases. Although most of the existing solutions can reduce the failure probability of relay selection, they ignore the fairness of the relay selection. In order to improve the fairness of the relay selection without affecting the failure probability of the best relay selection, we propose a modified practical best relay selection scheme in this paper, and by introducing proportional fair algorithm, the relay timer will be given a smaller correlation coefficient. The proposed method makes the probability of selection be improved. In the light of defined fairness factor, the relay fairness is represented. Simulation results show that the new algorithm can improve the fairness of the relay selection on the basis of maintaining the original failure probability of relay selection. DOI : http://dx.doi.org/10.11591/telkomnika.v12i1.3910