In this paper, we study a secure communication scheme assisted by multiple distributed friendly users over fading channels. To defeat a malicious user, friendly users transmit artificial noise continuously regardless of whether the transmitter is sending signals or not. The idle nodes in wireless networks can be selected as friendly users to assist in achieving secure communications. Due to the different positions of friendly users relative to the malicious user and receiver, the assisting abilities of friendly users in secure communications are different. To explore the potential of friendly users, a metric factor is proposed in this paper to evaluate the assisting abilities of friendly users. Based on the evaluating results, an optimum user selection and power allocation scheme is designed to maximize the secure throughput under the power limit and secure constraint. Compared with the benchmark scheme, the proposed secure communication scheme is easy to implement. Moreover, according to the numerical results, the proposed scheme can improve the secure throughput by more than 16% compared with the benchmark scheme when the secure constraint is larger than 0.5.
In this paper, we study a secure communication scheme assisted by multiple distributed friendly users over fading channels. To defeat a malicious user, friendly users transmit artificial noise continuously regardless of whether the transmitter is sending signals or not. The idle nodes in wireless networks can be selected as friendly users to assist in achieving secure communications. Due to the different positions of friendly users relative to the malicious user and receiver, the assisting abilities of friendly users in secure communications are different. To explore the potential of friendly users, a metric factor is proposed in this paper to evaluate the assisting abilities of friendly users. Based on the evaluating results, an optimum user selection and power allocation scheme is designed to maximize the secure throughput under the power limit and secure constraint. Compared with the benchmark scheme, the proposed secure communication scheme is easy to implement. Moreover, according to the numerical results, the proposed scheme can improve the secure throughput by more than 16% compared with the benchmark scheme when the secure constraint is larger than 0.5.
In this paper, we explore the physical-layer security in a wireless network consisting of multiple user pairs in the face of multiple eavesdroppers, which are deployed by an adversary for tapping the confidential transmissions of the user pairs deliberately. We propose a friendly jammer-assisted user-pair selection (FJaUPS) scheme to improve the security-reliability tradeoff (SRT). Conventionally, a friendly jammer is used to transmit the artificial noise that is specially designed onto the null space of the main channel (spanning from the source to legitimate destination) for the sake of not interfering with the destination. However, due to the presence of the channel state information estimation error, it is impossible to guarantee that the artificial noise perfectly lies in the null space of the main channel, resulting in a certain interference received at the legitimate destination caused by the friendly jammer. Hence, the impacts of the friendly jammer on the legitimate user transmissions and eavesdroppers are taken into account for evaluating the wireless SRT performance, which are quantified by the so-called self-interfering factor and jamming factor, respectively. Moreover, we derive the SRT of the proposed FJaUPS, as well as the traditional round-robin schemes over Rayleigh fading channels. For comparison purposes, we also provide the SRT result of the conventional pure user-pair selection (PUPS) in computer simulations. In addition, it is shown that the proposed FJaUPS schemes outperform both the traditional round-robin and PUPS methods in terms of their SRT.
In this paper, we examine the physical layer security for cooperative wireless networks with multiple intermediate nodes, where the decode-and-forward protocol is considered. We propose a new joint relay and jammer selection (JRJS) scheme for protecting wireless communications against eavesdropping, where an intermediate node is selected as the relay for the sake of forwarding the source signal to the destination and meanwhile, the remaining intermediate nodes are employed to act as friendly jammers, which broadcast the artificial noise for disturbing the eavesdropper. We further investigate the power allocation among the source, relay and friendly jammers for maximizing the secrecy rate of proposed JRJS scheme, and derive a closed-form sub-optimal solution. Specifically, all the intermediate nodes, which successfully decode the source signal, are considered as relay candidates. For each candidate, we derive the sub-optimal closed-form power allocation solution and obtain the secrecy rate result of the corresponding JRJS scheme. Then, the candidate, which is capable of achieving the highest secrecy rate, is selected as the relay. Two assumptions about the channel state information (CSI), namely the full CSI (FCSI) and partial CSI (PCSI), are considered. Simulation results show that the proposed JRJS scheme outperforms the conventional pure relay selection, pure jamming, and generalized singular-value-decomposition-based beamforming schemes in terms of secrecy rate. Additionally, the proposed FCSI-based power allocation and PCSI-based power allocation schemes both achieve higher secrecy rates than the equal power allocation scheme.
In this paper, we examine the physical layer security for cooperative wireless networks with multiple intermediate nodes, where the decode-and-forward (DF) protocol is considered. We propose a new joint cooperative beamforming and jamming (JCBJ) scheme to protect wireless communication against eavesdropping, where the intermediate nodes which successfully decode the source signal are selected as the relays for simultaneously forwarding the source signal by employing a weight vector, and meanwhile, the others are used to act as the friendly jammers for broadcasting artificial noise to disturb the eavesdropper. We further investigate the optimal power allocation among the source, relays and friendly jammers for maximizing the secrecy rate of the proposed JCBJ scheme and derive a closed-form sub-optimal solution. Simulation results show that the proposed JCBJ scheme achieves obviously higher secrecy rate than the conventional generalized singular-value-decomposition (GSVD) based beamforming and pure jamming schemes. Additionally, the proposed optimal power allocation scheme performs much better than the equal power allocation scheme in terms of secrecy rate.
Abstract This paper addresses the power allocation problem in a network where joint information-theoretic secrecy and covert communication are required. In this network, a single transmitter (Alice) sends information to two legitimate users (Bob and Carol). There is also an untrusted user who attempts to detect the content of Bob’s message and a warden (Willie) who wants to detect the existence of communication between Alice and the two users. Thus, Carol requires covert transmission, and Bob requires secure and covert communication. The network utilizes a friendly jammer to address these demands and overcome the low transmission rate of covert communication. To achieve covert communication, Alice sends both users’ data simultaneously in selected time slots to hide it from Willie, while the jammer continuously transmits signals in all time slots. The objective is to maximize the average transmission rate over the allocated powers of Bob, Carol, and the jammer while meeting the two users’ requirements. A novel iterative algorithm is proposed to obtain an effective solution. Simulation results indicate that the proposed method can enhance the network’s average rate while satisfying the users’ demands.
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 article, we investigate the physical layer security for a wireless communication system consisting of a base station (BS) and a user (U) in the face of an eavesdropper (E). A friendly jammer is opportunistically selected from multiple jammers to create intentional interference upon E. However, the legitimate user U is not aware of the information transmitted by the jammer and thus cannot remove the interfering signal. In this context, we propose interference-limited opportunistic jammer selection (IL-OJS) scheme and interference-canceled opportunistic jammer selection (IC-OJS) scheme to reduce the damage of interference to U for improving physical layer security. Specifically, in the IL-OJS scheme, the selected jammer sets an interference threshold. When the interference to U is less than the threshold value, the selected jammer will work (i.e., emit artificial noise), and vice versa, it will stop jamming. By contrast, IC-OJS scheme utilizes a specially designed signal to eliminate interference received by U from the selected jammer. For comparison, we also present the conventional non-jammer (NJ) scheme as a benchmark. Exact and asymptotic closed-form secrecy outage probability expressions for NJ, IL-OJS, and IC-OJS schemes are derived over Nakagami-mfading channels. Numerical results show that the secrecy performance of proposed IL-OJS and IC-OJS schemes is better than that of NJ scheme. Additionally, the secrecy outage probability performance of IL-OJS and IC-OJS schemes can be improved by increasing the number of jammers.