A Survey on Cooperative Jamming Applied to Physical Layer Security
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paper_title: Security, privacy, and accountability in wireless access networks

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The presence of ubiquitous connectivity provided by wireless communications and mobile computing has changed the way humans interact with information. At the same time, it has made communication security and privacy a hot-button issue. In this article we address the security and privacy concerns in wireless access networks. We first discuss the general cryptographic means to design privacy-preserving security protocols, where the dilemma of attaining both security and privacy goals, especially user accountability vs. user privacy, is highlighted. We then present a novel authentication framework that integrates a new key management scheme based on the principle of separation of powers and an adapted construction of Boneh and Shacham's group signature scheme, as an enhanced resort to simultaneously achieve security, privacy, and accountability in wireless access networks.
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paper_title: Physical-Layer Security: From Information Theory to Security Engineering

paper_content:

This complete guide to physical-layer security presents the theoretical foundations, practical implementation, challenges and benefits of a groundbreaking new model for secure communication. Using a bottom-up approach from the link level all the way to end-to-end architectures, it provides essential practical tools that enable graduate students, industry professionals and researchers to build more secure systems by exploiting the noise inherent to communications channels. The book begins with a self-contained explanation of the information-theoretic limits of secure communications at the physical layer. It then goes on to develop practical coding schemes, building on the theoretical insights and enabling readers to understand the challenges and opportunities related to the design of physical layer security schemes. Finally, applications to multi-user communications and network coding are also included.
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paper_title: On the Jamming Power Allocation for Secure Amplify-and-Forward Relaying via Cooperative Jamming

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In this paper, we investigate secure communications in two-hop wireless relaying networks with one eavesdropper. To prevent the eavesdropper from intercepting the source message, the destination sends an intended jamming noise to the relay, which is referred to as cooperative jamming. This jamming noise helps protecting the source message from being captured reliably at the eavesdropper, while the destination cancels its self-intended noise. According to the channel information available at the destination, we derive three jamming power allocation strategies to minimize the outage probability of the secrecy rate. In addition, we derive analytic results quantifying the jamming power consumption of the proposed allocation methods.
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paper_title: Cryptographic design vulnerabilities

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Strong cryptography is very powerful when it is done right, but it is not a panacea. Focusing on cryptographic algorithms while ignoring other aspects of security is like defending your house not by building a fence around it, but by putting an immense stake in the ground and hoping that your adversary runs right into it. Counterpane Systems has spent years designing, analyzing, and breaking cryptographic systems. While they do research on published algorithms and protocols, most of their work examines actual products. They've designed and analyzed systems that protect privacy, ensure confidentiality, provide fairness, and facilitate commerce. They've worked with software, stand-alone hardware, and everything in between. They've broken their share of algorithms, but they can almost always find attacks that bypass the algorithms altogether. Counterpane Systems don't have to try every possible key or even find flaws in the algorithms. They exploit errors in design, errors in implementation, and errors in installation. Sometimes they invent a new trick to break a system, but most of the time they exploit the same old mistakes that designers make over and over again. The article conveys some of the lessons this company has learned.
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paper_title: Guaranteeing Secrecy using Artificial Noise

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The broadcast nature of the wireless medium makes the communication over this medium vulnerable to eavesdropping. This paper considers the problem of secret communication between two nodes, over a fading wireless medium, in the presence of a passive eavesdropper. The assumption used is that the transmitter and its helpers (amplifying relays) have more antennas than the eavesdropper. The transmitter ensures secrecy of communication by utilizing some of the available power to produce 'artificial noise', such that only the eavesdropper's channel is degraded. Two scenarios are considered, one where the transmitter has multiple transmit antennas, and the other where amplifying relays simulate the effect of multiple antennas. The channel state information (CSI) is assumed to be publicly known, and hence, the secrecy of communication is independent of the secrecy of CSI.
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paper_title: Signal Processing Approaches to Secure Physical Layer Communications in Multi-Antenna Wireless Systems

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This book introduces various signal processing approaches to enhance physical layer secrecy in multi-antenna wireless systems. Wireless physical layer secrecy has attracted much attention in recent years due to the broadcast nature of the wireless medium and its inherent vulnerability to eavesdropping. While most articles on physical layer secrecy focus on the information-theoretic aspect, we focus specifically on the signal processing aspects, including beamforming and precoding techniques for data transmission and discriminatory training schemes for channel estimation. The discussions will cover cases with collocated and with distributed antennas, i.e., relays. The topics covered will be of interest to researchers in the signal processing community as well to practitioners and engineers working in this area. This book will also review recent works that apply these signal processing approaches to more advanced wireless systems, such as OFDM systems, multicell systems, cognitive radio, multihop networks etc. This will draw interest from researchers that wish to pursue the topic further in these new directions. This book is divided into three parts: (i) data transmission, (ii) channel estimation and (iii) advanced applications. Even though many works exist in the literature on these topics, the approaches and perspectives taken were largely diverse. This book provides a more organized and systematic view of these designs and to lay a solid foundation for future work in these areas. Moreover, by presenting the work from a signal processing perspective, this book will also trigger more research interest from the signal processing community and further advance the field of physical layer secrecy along the described directions. This book allows readers to gain basic understanding of works on physical layer secrecy, knowledge of how signal processing techniques can be applied to this area, and the application of these techniques in advanced wireless applications.
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paper_title: Physical layer security in wireless networks: a tutorial

paper_content:

Wireless networking plays an extremely important role in civil and military applications. However, security of information transfer via wireless networks remains a challenging issue. It is critical to ensure that confidential data are accessible only to the intended users rather than intruders. Jamming and eavesdropping are two primary attacks at the physical layer of a wireless network. This article offers a tutorial on several prevalent methods to enhance security at the physical layer in wireless networks. We classify these methods based on their characteristic features into five categories, each of which is discussed in terms of two metrics. First, we compare their secret channel capacities, and then we show their computational complexities in exhaustive key search. Finally, we illustrate their security requirements via some examples with respect to these two metrics.
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paper_title: Relay and jammer selection schemes for improving physical layer security in two-way cooperative networks

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This paper is concerned with the relay and jammers selection in two-way cooperative networks to improve their physical layer security. Three different categories of selection schemes are proposed which are; selection schemes without jamming, selection schemes with conventional jamming and selection schemes with controlled jamming. The selection process is analyzed for two different network models; single eavesdropper model and multiple cooperating and non-cooperating eavesdroppers' model. The proposed schemes select three intermediate nodes during two communication phases and use the Decode-and-Forward (DF) strategy to assist the sources to deliver their data to the corresponding destinations. The performance of the proposed schemes is analyzed in terms of ergodic secrecy rate and secrecy outage probability metrics. The obtained results show that the selection schemes with jamming outperform the schemes without jamming when the intermediate nodes are distributed dispersedly between sources and eavesdropper nodes. However, when the intermediate nodes cluster gets close to one of the sources, they are not superior any more due to the strong interference on the destination nodes. Therefore, a hybrid scheme which switches between selection schemes with jamming and schemes without jamming is introduced to overcome the negative effects of interference. Finally, a comparison between relay and jammers selection schemes in both one-way and two-way cooperative networks is given in terms of both secrecy metrics. The obtained results reveal that, despite the presence of cooperating eavesdroppers, the proposed selection schemes are still able to improve both the secrecy rate and the secrecy outage probability of the two-way cooperative networks.
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paper_title: Harvest-and-jam: Improving security for wireless energy harvesting cooperative networks

paper_content:

The emerging radio signal enabled simultaneous wireless information and power transfer (SWIPT), has drawn significant attention. To achieve secrecy transmission by cooperative jamming, especially in the upcoming 5G networks with self-sustainable mobile base stations (BSs) and yet not to add extra power consumption, we propose in this paper a new relay protocol, i.e., harvest-and-jam (HJ), in a relay wiretap channel with an additional set of spare helpers. Specifically, in the first transmission phase, a single-antenna transmitter (Tx) transfers signals carrying both information and energy to a multi-antenna amplify-and-forward (AF) relay and a group of multi-antenna helpers; in the second transmission phase, the AF relay processes the information and forwards it to the receiver while each of the helpers generates an artificial noise (AN), the power of which is constrained by its previously harvested energy, to interfere with the eavesdropper. By optimizing the transmit beamforming matrix for the AF relay and the covariance matrix for the AN, we maximize the secrecy rate for the receiver subject to transmit power constraints for the AF relay and all helpers. The formulated problem is shown to be non-convex, for which we propose an iterative algorithm based on alternating optimization. Finally, the performance of the proposed scheme is evaluated by simulations as compared to other heuristic schemes.
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paper_title: Wireless Information-Theoretic Security

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This paper considers the transmission of confidential data over wireless channels. Based on an information-theoretic formulation of the problem, in which two legitimates partners communicate over a quasi-static fading channel and an eavesdropper observes their transmissions through a second independent quasi-static fading channel, the important role of fading is characterized in terms of average secure communication rates and outage probability. Based on the insights from this analysis, a practical secure communication protocol is developed, which uses a four-step procedure to ensure wireless information-theoretic security: (i) common randomness via opportunistic transmission, (ii) message reconciliation, (iii) common key generation via privacy amplification, and (iv) message protection with a secret key. A reconciliation procedure based on multilevel coding and optimized low-density parity-check (LDPC) codes is introduced, which allows to achieve communication rates close to the fundamental security limits in several relevant instances. Finally, a set of metrics for assessing average secure key generation rates is established, and it is shown that the protocol is effective in secure key renewal-even in the presence of imperfect channel state information.
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paper_title: On Cooperative and Malicious Behaviors in Multirelay Fading Channels

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Multirelay networks exploit spatial diversity by transmitting user's messages through multiple relay paths. Most works in the literature on cooperative or relay networks assume that all terminals are fully cooperative and neglect the effect of possibly existing malicious relay behaviors. In this work, we consider a multirelay network that consists of both cooperative and malicious relays, and aims to obtain an improved understanding on the optimal behaviors of these two groups of relays via information-theoretic mutual information games. By modeling the set of cooperative relays and the set of malicious relays as two players in a zero-sum game with the maximum achievable rate as the utility, the optimal transmission strategies of both types of relays are derived by identifying the Nash equilibrium of the proposed game. Our main contributions are twofold. First, a generalization to previous works is obtained by allowing malicious relays to either listen or attack in Phase 1 (source-relay transmission phase). This is in contrast to previous works that only allow the malicious relays to listen in Phase 1 and to attack in Phase 2 (relay-destination transmission phase). The latter is shown to be suboptimal in our problem. Second, the impact of CSI knowledge at the destination on the optimal attack strategy that can be adopted by the malicious relays is identified. In particular, for the more practical scenario where the interrelay CSI is unknown at the destination, the constant attack is shown to be optimal as opposed to the commonly considered Gaussian attack.
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paper_title: Secrecy Capacity Optimization via Cooperative Relaying and Jamming for WANETs

paper_content:

Cooperative wireless networking, which is promising in improving the system operation efficiency and reliability by acquiring more accurate and timely information, has attracted considerable attentions to support many services in practice. However, the problem of secure cooperative communication has not been well investigated yet. In this paper, we exploit physical layer security to provide secure cooperative communication for wireless ad hoc networks (WANETs) where involve multiple source-destination pairs and malicious eavesdroppers. By characterizing the security performance of the system by secrecy capacity, we study the secrecy capacity optimization problem in which security enhancement is achieved via cooperative relaying and cooperative jamming. Specifically, we propose a system model where a set of relay nodes can be exploited by multiple source-destination pairs to achieve physical layer security. We theoretically present a corresponding formulation for the relay assignment problem and develop an optimal algorithm to solve it in polynomial time. To further increase the system secrecy capacity, we exploit the cooperative jamming technique and propose a smart jamming algorithm to interfere the eavesdropping channels. Through extensive experiments, we validate that our proposed algorithms significantly increase the system secrecy capacity under various network settings.
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paper_title: Physical layer security in wireless networks: a tutorial

paper_content:

Wireless networking plays an extremely important role in civil and military applications. However, security of information transfer via wireless networks remains a challenging issue. It is critical to ensure that confidential data are accessible only to the intended users rather than intruders. Jamming and eavesdropping are two primary attacks at the physical layer of a wireless network. This article offers a tutorial on several prevalent methods to enhance security at the physical layer in wireless networks. We classify these methods based on their characteristic features into five categories, each of which is discussed in terms of two metrics. First, we compare their secret channel capacities, and then we show their computational complexities in exhaustive key search. Finally, we illustrate their security requirements via some examples with respect to these two metrics.
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paper_title: Wireless Secrecy in Cellular Systems With Infrastructure-Aided Cooperation

paper_content:

In cellular systems, confidentiality of uplink transmission with respect to eavesdropping terminals can be ensured by creating intentional interference via scheduling of concurrent downlink transmissions. In this paper, this basic idea is explored from an information-theoretic standpoint by focusing on a two-cell scenario where the involved base stations (BSs) are connected via a finite-capacity backbone link. A number of transmission strategies are considered that aim at improving uplink confidentiality under constraints on the downlink rate that acts as an interfering signal. The strategies differ mainly in the way the backbone link is exploited by the cooperating downlink to the uplink-operated BSs. Achievable rates are derived for both the Gaussian (unfaded) and the fading cases, under different assumptions on the channel state information available at different nodes. Numerical results are also provided to corroborate the analysis. Extensions to scenarios with more than two cells are briefly discussed as well. Overall, the analysis reveals that a combination of scheduling and base-station cooperation is a promising means to improve transmission confidentiality in cellular systems.
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paper_title: Cooperative Jamming and Power Allocation for Wireless Relay Networks in Presence of Eavesdropper

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Relying on physical layer security is an attractive alternative of utilizing cryptographic algorithms at upper layers of protocol stack for secure communications. In this paper, we consider a two-hop wireless relay network in the presence of an eavesdropper. Our scenario of interest spans over a four-node network model including a source, a destination, a trusted relay, and an untrusted eavesdropper in which the relay forwards the source message in a decode-and-forward (DF) fashion. The source and relay are allowed to use some of their available power to transmit jamming signals in order to create interference at the eavesdropper. The relay and destination are assumed to have the knowledge of the jamming signals. An important question is how to allocate the transmission power of the message signal and that of the jamming signal. First, we propose an optimal power allocation solution in which the knowledge of global channel state information (CSI) is required. To facilitate practical system design, two simple yet sub-optimal power allocation solutions are proposed which do not rely on eavesdropper's channels. For the purpose of performance comparisons, power allocation problems for two benchmark schemes without jamming are also analyzed.
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paper_title: Cooperative jamming via spectrum leasing

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Secure communication rates can be facilitated or enhanced via deployment of cooperative jammers in a multi-terminal environment. Such an approach typically assumes dedicated and/or altruistic jamming nodes, investing their resources for the good of the whole system. In this paper, we demonstrate that jammers can be recruited to provide significant improvements of secrecy rates even when this assumption is alleviated. A game-theoretic framework is proposed where a source node, towards the maximization of its secrecy rate, utilizes the jamming services from a set of non-altruistic nodes, compensating them with a fraction of its bandwidth for transmission of their user data. With the goal of maximizing their user-data transmission rate priced by the invested power, potential cooperative jammers will provide the jamming/transmitting power that is generally proportional to the amount of leased bandwidth. Elaborating initially on a single-jammer scenario, interaction between the source and a cooperative jammer is modeled as the Stackelberg leader-follower game. The scheme is further extended to involve multiple potential jammers, applying competition mechanisms such as the auctioning and power control game, while maintaining the Stackelberg framework.
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paper_title: Recruiting multi-antenna transmitters as cooperative jammers: An auction-theoretic approach

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This paper proposes and investigates a distributed mechanism that motivates otherwise non-cooperative terminals to participate as cooperative jammers assisting a source-destination pair that communicates over a wireless medium, in the presence of an eavesdropper from whom the communicated messages need to be kept secret. The cooperation incentive is provided by an opportunity for potential jammers, possibly equipped with multiple antennas, to utilize the spectrum belonging to the ongoing secure transmission for their own data traffic. A fully decentralized framework is put forth through a competition of potential cooperative jammers for spectrum access by trying to make the jamming offer that most improves the secrecy rate of the source-destination pair. Effective arbitration of cooperative jamming is performed using auction theory, with the source in the role of the auctioneer, and the jammers acting as bidders. The proposed scheme can be alternatively seen as a practical basis for the implementation of cognitive radio networks operating according to the property-rights model, i.e., spectrum leasing.
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paper_title: Deaf Cooperation and Relay Selection Strategies for Secure Communication in Multiple Relay Networks

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In this paper, we investigate the roles of cooperative jamming (CJ) and noise forwarding (NF) in improving the achievable secrecy rates of a Gaussian wiretap channel (GWT). In particular, we study the role of a deaf helper in confusing the eavesdropper in a GWT channel by either transmitting white Gaussian noise (cooperative jamming) or by transmitting a dummy codeword of no context yet drawn from a codebook known to both the destination and the eavesdropper (noise forwarding). We first derive the conditions under which each mode of deaf cooperation improves over the secrecy capacity of the original wiretap channel and show that a helping node can be either a useful cooperative jammer or a useful noise forwarder but not both at the same time. Secondly, we derive the optimal power allocation for both the source and the helping node to be used in each of the two modes of deaf helping. Thirdly, we consider the deaf helper selection problem where there are N relays present in the system and it is required to select the best K deaf helpers, K ≥ 1, that yield the maximum possible achievable secrecy rate. For the case of K=1, we give the optimal selection strategy with optimal power allocation. The computational complexity of the optimal selection strategy when K > 1 is relatively large, especially for large values of K and N. Thus, we propose a suboptimal strategy for the selection problem when K > 1. We derive the complexity of the proposed selection strategies and show that, for K > 1, our suboptimal strategy, which works in a greedy fashion, enjoys a significantly less computational complexity than the optimal strategy. Nevertheless, as demonstrated by numerical examples, our suboptimal strategy gives rise to reasonable performance gains in terms of the achievable secrecy rate with respect to the case of K=1.
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paper_title: Cooperative jamming and power allocation in three-phase two-way relaying wiretap systems

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The security of the three-phase two-way relaying system with an eavesdropper is investigated in this paper. A cooperative jamming and power allocation scheme is proposed to enhance the system secrecy capacity. When a source node transmits user signals to the relay node, the other source node interferes the relay node with pre-defined jamming signals simultaneously. Optimum power allocation between the user and jamming signals at each source node is analyzed. Our analytical results suggest that the proposed cooperative jamming scheme improves on the system secrecy capacity, especially when the channel gains of the two source-relay links are of large difference. Simulation results in close agreement with analytical results clearly demonstrate the advantage of the proposed cooperative jamming scheme.
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paper_title: Physical layer security from inter-session interference in large wireless networks

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Physical layer secrecy in wireless networks in the presence of eavesdroppers of unknown location is considered. In contrast to prior schemes, which have expended energy in the form of cooperative jamming to enable secrecy, we develop schemes where multiple transmitters send their signals in a cooperative fashion to confuse the eavesdroppers. Hence, power is not expended on “artificial noise”; rather, the signal of a given transmitter is protected by the aggregate interference produced by the other transmitters. We introduce a two-hop strategy for the case of equal path-loss between all pairs of nodes, and then consider its embedding within a multi-hop approach for the general case of an extended network. In each case, we derive an achievable number of eavesdroppers that can be present in the region while secure communication between all sources and intended destinations is ensured.
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paper_title: Distributed Coalition Formation of Relay and Friendly Jammers for Secure Cooperative Networks

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In this paper, we investigate cooperation of conventional relays and friendly jammers subject to secrecy constraints for cooperative networks consisting of one source node, one corresponding destination node, one malicious eavesdropper node, and several intermediate nodes. In order to obtain a higher secrecy rate, the source selects one conventional relay and several friendly jammers from the intermediate nodes to assist message transmission, and in return, it needs to make a payment. Each intermediate node here has two possible identities to choose, i.e., to be a conventional relay or a friendly jammer, which results in a direct impact on the final utility of the intermediate node. After the intermediate nodes determine their identities, they seek to find optimal partners forming coalitions, which improves their chances to be selected by the source and thus to obtain the payoffs in the end. We formulate this cooperation as a coalitional game with transferable utility and also study its properties. Furthermore, we define a Max-Pareto order for comparison of the coalition value, based on which we employ the merge-and-split rules. We also construct a distributed merge-and-split coalition formation algorithm for the defined coalition formation game. The simulation results verify the efficiency of the proposed coalition formation algorithm.
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paper_title: Strongly Secure Communications Over the Two-Way Wiretap Channel

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We consider the problem of secure communications over the two-way wiretap channel under a strong secrecy criterion. We improve existing results by developing an achievable region based on strategies that exploit both the interference at the eavesdropper's terminal and cooperation between legitimate users. We leverage the notion of channel resolvability for the multiple-access channel to analyze cooperative jamming and we show that the artificial noise created by cooperative jamming induces a source of common randomness that can be used for secret-key agreement. We illustrate the gain provided by this coding technique in the case of the Gaussian two-way wiretap channel, and we show significant improvements for some channel configurations.
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paper_title: Cooperative jamming and power allocation with untrusty two-way relay nodes

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This study investigates the security of the two-way relaying system with untrusty relay nodes. Cooperative jamming schemes are considered for bi-directional secrecy communications. The transmit power of each source node is divided into two parts corresponding to the user and jamming signals, respectively. Two different assumptions of the jamming signals are considered. When the jamming signals are a priori known at the two source nodes, closed-form power allocation expressions at two source nodes are derived. Under the assumption of unknown jamming signals, it is proven that the cooperative jamming is useless for the system secrecy capacity, because that all the power should be allocated to the user signals at each source node. Relay selection is also investigated based on the analysis of cooperative jamming. Simulation results are presented to compare the system secrecy capacities under the two jamming signal assumptions.
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paper_title: CSI-Secured Orthogonal Jamming Method for Wireless Physical Layer Security

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In this paper, we propose a new cooperative jamming (CJ) method to prevent eavesdroppers from using beam-formers to suppress the jamming signals. In this method, the broadcasting of system-node channel state information (CSI) is first averted. The transmitting and jamming signals are then aligned in two separate single dimensions in complex space. The decode-and-forward relaying protocol is employed.The proposed method is more effective than current CJ techniques.
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paper_title: On Secrecy Capacity of Gaussian Wiretap Channel Aided by A Cooperative Jammer

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We study the secrecy capacity of Gaussian wiretap channel aided by an external jammer/helper. Both the transmitter and the intended receiver are equipped with a single antenna, while the eavesdropper and the jammer are equipped with M and N antennas, respectively. Generally, an analytical form of the secrecy capacity in this scenario is difficult to obtain. Instead, we consider a null-space jamming scheme which totally nulls out the jamming signal at the legitimate receiver, and derive lower and upper bounds on its maximal achievable secrecy rate R<sub>N</sub>. The relationship between the average secrecy capacity C̅<sub>N</sub> of Gaussian wiretap channel and the average secrecy rate R̅<sub>N</sub> achieved by the null-space jamming scheme is investigated, and we prove that R̅<sub>N</sub> ≤ C̅<sub>N</sub> ≤ R̅<sub>N+1</sub>. Based on this inequality and the derived lower and upper bounds on R<sub>N</sub>, the upper and lower bounds on the average secrecy capacity of Gaussian wiretap channel aided by an external jammer can be obtained, where our result shows that when N > M, the average secrecy capacity increases linearly with the total transmit power; while when N ≤ M - 1, there exists a performance ceiling on it.
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paper_title: Joint Cooperative Beamforming and Jamming to Secure AF Relay Systems With Individual Power Constraint and No Eavesdropper's CSI

paper_content:

Cooperative beamforming and jamming are two efficient schemes to improve the physical-layer security of a wireless relay system in the presence of passive eavesdroppers. However, in most works these two techniques are adopted separately. In this letter, we propose a joint cooperative beamforming and jamming scheme to enhance the security of a cooperative relay network, where a part of intermediate nodes adopt distributed beamforming while others jam the eavesdropper, simultaneously. Since the instantaneous channel state information (CSI) of the eavesdropper may not be known, we propose a cooperative artificial noise transmission based secrecy strategy, subjected to the individual power constraint of each node. The beamformer weights and power allocation can be obtained by solving a second-order convex cone programming (SOCP) together with a linear programming problem. Simulations show the joint scheme greatly improves the security.
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paper_title: Harvest-and-jam: Improving security for wireless energy harvesting cooperative networks

paper_content:

The emerging radio signal enabled simultaneous wireless information and power transfer (SWIPT), has drawn significant attention. To achieve secrecy transmission by cooperative jamming, especially in the upcoming 5G networks with self-sustainable mobile base stations (BSs) and yet not to add extra power consumption, we propose in this paper a new relay protocol, i.e., harvest-and-jam (HJ), in a relay wiretap channel with an additional set of spare helpers. Specifically, in the first transmission phase, a single-antenna transmitter (Tx) transfers signals carrying both information and energy to a multi-antenna amplify-and-forward (AF) relay and a group of multi-antenna helpers; in the second transmission phase, the AF relay processes the information and forwards it to the receiver while each of the helpers generates an artificial noise (AN), the power of which is constrained by its previously harvested energy, to interfere with the eavesdropper. By optimizing the transmit beamforming matrix for the AF relay and the covariance matrix for the AN, we maximize the secrecy rate for the receiver subject to transmit power constraints for the AF relay and all helpers. The formulated problem is shown to be non-convex, for which we propose an iterative algorithm based on alternating optimization. Finally, the performance of the proposed scheme is evaluated by simulations as compared to other heuristic schemes.
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paper_title: Secure Transmission with Optimal Power Allocation in Untrusted Relay Networks

paper_content:

We consider the problem of secure transmission in two-hop amplify-and-forward untrusted relay networks. We analyze the ergodic secrecy capacity (ESC) and present compact expressions for the ESC in the high signal-to-noise ratio regime. We also examine the impact of large scale antenna arrays at either the source or the destination. For large antenna arrays at the source, we confirm that the ESC is solely determined by the channel between the relay and the destination. For very large antenna arrays at the destination, we confirm that the ESC is solely determined by the channel between the source and the relay.
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paper_title: Secrecy Capacity Optimization via Cooperative Relaying and Jamming for WANETs

paper_content:

Cooperative wireless networking, which is promising in improving the system operation efficiency and reliability by acquiring more accurate and timely information, has attracted considerable attentions to support many services in practice. However, the problem of secure cooperative communication has not been well investigated yet. In this paper, we exploit physical layer security to provide secure cooperative communication for wireless ad hoc networks (WANETs) where involve multiple source-destination pairs and malicious eavesdroppers. By characterizing the security performance of the system by secrecy capacity, we study the secrecy capacity optimization problem in which security enhancement is achieved via cooperative relaying and cooperative jamming. Specifically, we propose a system model where a set of relay nodes can be exploited by multiple source-destination pairs to achieve physical layer security. We theoretically present a corresponding formulation for the relay assignment problem and develop an optimal algorithm to solve it in polynomial time. To further increase the system secrecy capacity, we exploit the cooperative jamming technique and propose a smart jamming algorithm to interfere the eavesdropping channels. Through extensive experiments, we validate that our proposed algorithms significantly increase the system secrecy capacity under various network settings.
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paper_title: Hybrid Cooperative Beamforming and Jamming for Physical-Layer Security of Two-Way Relay Networks

paper_content:

In this paper, we propose a hybrid cooperative beamforming and jamming scheme to enhance the physical-layer security of a single-antenna-equipped two-way relay network in the presence of an eavesdropper. The basic idea is that in both cooperative transmission phases, some intermediate nodes help to relay signals to the legitimate destination adopting distributed beamforming, while the remaining nodes jam the eavesdropper, simultaneously, which takes the data transmissions in both phases under protection. Two different schemes are proposed, with and without the instantaneous channel state information of the eavesdropper, respectively, and both are subjected to the more practical individual power constraint of each cooperative node. Under the general channel model, it is shown that both problems can be transformed into a semi-definite programming (SDP) problem with an additional rank-1 constraint. A current state of the art technique for handling such a problem is the semi-definite relaxation (SDR) and randomization techniques. In this paper, however, we propose a penalty function method incorporating the rank-1 constraint into the objective function. Although the so-obtained problem is not convex, we develop an efficient iterative algorithm to solve it. Each iteration is a convex SDP problem, thus it can be efficiently solved using the interior point method. When the channels are reciprocal such as in TDD mode, we show that the problems become second-order convex cone programming ones. Numerical evaluation results are provided and analyzed to show the properties and efficiency of the proposed hybrid security scheme, and also demonstrate that our optimization algorithms outperform the SDR technique.
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paper_title: Optimal Cooperative Jamming for Multiuser Broadcast Channel with Multiple Eavesdroppers

paper_content:

Cooperative jamming for multiuser multiple input multiple output (MIMO) broadcast channel is studied to enhance the physical layer security with the help of a friendly jammer. We assume the base station transmits multiple independent data streams to multiple legitimate users. During the transmission, however, there are multiple eavesdroppers with multiple antennas that have interests in the streams from the base station. In order to wiretap the desired streams, the eavesdroppers may collude or not, and maximize the signal-to-interference-plus-noise ratio (SINR) of the desired streams using receive beamforming. The optimal cooperative jammer is designed to keep the achieved SINR at eavesdroppers below a threshold to guarantee that the transmission from the base station to legitimate users is confidential. One main advantage of the proposed cooperative jamming scheme is that no modification is needed for the existing precoding schemes at the base station and decoding schemes at legitimate users. Thus, any existing practical precoding/decoding schemes for multiuser MIMO broadcast channel can be applied directly with the help of a friendly jammer using the proposed cooperative jamming.
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paper_title: MIMO decode-and-forward relay beamforming for secrecy with cooperative jamming

paper_content:

In this paper, we consider decode-and-forward (DF) relay beamforming for secrecy with cooperative jamming (CJ) in the presence of multiple eavesdroppers. The communication between a source-destination pair is aided by a multiple-input multiple-output (MIMO) relay. The source has one transmit antenna and the destination and eavesdroppers have one receive antenna each. The source and the MIMO relay are constrained with powers P S and P R , respectively. We relax the rank-1 constraint on the signal beamforming matrix and transform the secrecy rate max-min optimization problem to a single maximization problem, which is solved by semidefinite programming techniques. We obtain the optimum source power, signal relay weights, and jamming covariance matrix. We show that the solution of the rank-relaxed optimization problem has rank-1. Numerical results show that CJ can improve the secrecy rate.
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paper_title: On the Jamming Power Allocation for Secure Amplify-and-Forward Relaying via Cooperative Jamming

paper_content:

In this paper, we investigate secure communications in two-hop wireless relaying networks with one eavesdropper. To prevent the eavesdropper from intercepting the source message, the destination sends an intended jamming noise to the relay, which is referred to as cooperative jamming. This jamming noise helps protecting the source message from being captured reliably at the eavesdropper, while the destination cancels its self-intended noise. According to the channel information available at the destination, we derive three jamming power allocation strategies to minimize the outage probability of the secrecy rate. In addition, we derive analytic results quantifying the jamming power consumption of the proposed allocation methods.
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paper_title: Secrecy Transmission With a Helper: To Relay or to Jam

paper_content:

In this paper, we consider the problem of secure communications for a four-node system consisting of one source, one destination, one eavesdropper, and one helper. We investigate the question of which role should the helper act to improve the secrecy, to jam, or to relay. Two transmission schemes are investigated: 1) direct transmission scheme (DTS) with jamming and 2) relay transmission scheme (RTS). We consider both the path-loss and fading-in channel models and define a notion of distance normalized signal-to-noise-ratio (DN-SNR) to account for propagation. The ergodic secrecy rate (ESR) is adopted as the performance metric and semi-closed-form expressions of ESR for the two schemes are derived. Additionally, optimal power allocations in both low and high DN-SNR regimes are characterized analytically. We give the performance comparison of the two schemes from the perspective of energy efficiency in the low DN-SNR regime, and characterize the secrecy degree of freedom in the high DN-SNR regime. In the high DN-SNR regime, DTS provides higher secrecy rate compared with RTS, while in the low DN-SNR regime, RTS outperforms DTS. Furthermore, we show that eavesdropper’s position impacts greatly on security.
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paper_title: Joint relay selection and artificial jamming power allocation for secure DF relay networks

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This paper studies cooperative transmission for securing a decode-and-forward (DF) two-hop network where massive cooperative nodes coexist with a potential single eavesdropper. With only the statistical channel state information (CSIs) of the eavesdroppers, we propose an opportunistic relaying with artificial jamming secrecy scheme, where a “best” cooperative node is chosen to forward the confidential signal and the others act as jammers to send the jamming signals to confuse the eavesdropper. Utilizing the limiting distribution technique of extreme order statistics, we optimize the power allocation between the confidential information and jamming signal based on the statistical CSIs of the legitimate nodes for ergodic secrecy rate (ESR) maximization. Although the optimization problems are non-convex, we propose a sequential parametric convex approximation (SPCA) algorithm to locate the KKT solutions. Then, we derive an analytical closed-form expression of the achievable ESR, which reduces the complexity of the system analysis and design.
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paper_title: Cooperative jamming and power allocation with untrusty two-way relay nodes

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This study investigates the security of the two-way relaying system with untrusty relay nodes. Cooperative jamming schemes are considered for bi-directional secrecy communications. The transmit power of each source node is divided into two parts corresponding to the user and jamming signals, respectively. Two different assumptions of the jamming signals are considered. When the jamming signals are a priori known at the two source nodes, closed-form power allocation expressions at two source nodes are derived. Under the assumption of unknown jamming signals, it is proven that the cooperative jamming is useless for the system secrecy capacity, because that all the power should be allocated to the user signals at each source node. Relay selection is also investigated based on the analysis of cooperative jamming. Simulation results are presented to compare the system secrecy capacities under the two jamming signal assumptions.
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paper_title: Joint Design of Optimal Cooperative Jamming and Power Allocation for Linear Precoding

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Linear precoding and cooperative jamming for multiuser broadcast channel is studied to enhance the physical layer security. We consider the system where multiple independent data streams are transmitted from the base station to multiple legitimate users with the help of a friendly jammer. It is assumed that a normalized linear precoding matrix is given at the base station, whereas the power allocated to each user is to be determined. The problem is to jointly design the power allocation across different users for linear precoding and the cooperative jamming at the friendly jammer. The goal is to maximize a lower bound of the secrecy rate, provided that a minimum communication rate to the users is guaranteed. The optimal solution is obtained when the number of antennas at the friendly jammer is no less than the total number of antennas at the users and eavesdropper. Moreover, a suboptimal algorithm is proposed, which can be applied for all the scenarios. Numerical results demonstrate that the proposed schemes are effective for secure communications.
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paper_title: Hybrid Opportunistic Relaying and Jamming With Power Allocation for Secure Cooperative Networks

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This paper studies the cooperative transmission for securing a decode-and-forward (DF) two-hop network where multiple cooperative nodes coexist with a potential eavesdropper. Under the more practical assumption that only the channel distribution information (CDI) of the eavesdropper is known, we propose an opportunistic relaying with artificial jamming secrecy scheme, where a “best” cooperative node is chosen among a collection of $N$ possible candidates to forward the confidential signal and the others send jamming signals to confuse the eavesdroppers. We first investigate the ergodic secrecy rate (ESR) maximization problem by optimizing the power allocation between the confidential signal and jamming signals. In particular, we exploit the limiting distribution technique of extreme order statistics to build an asymptotic closed-form expression of the achievable ESR and the power allocation is optimized to maximize the ESR lower bound. Although the optimization problems are non-convex, we propose a sequential parametric convex approximation (SPCA) algorithm to locate the Karush-Kuhn-Tucker (KKT) solutions. Furthermore, taking the time variance of the legitimate links' CSIs into consideration, we address the impacts of the outdated CSIs to the proposed secrecy scheme, and derive an asymptotic ESR. Finally, we generalize the analysis to the scenario with multiple eavesdroppers, and give the asymptotic analytical results of the achievable ESR. Simulation results confirm our analytical results.
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paper_title: Competing for Secrecy in the MISO Interference Channel

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A secure communication game is considered for the two-user MISO Gaussian interference channel with confidential messages, where each transmitter aims to maximize the difference between its secrecy rate and the secrecy rate of the other transmitter. In this novel problem, the weaker link tries to minimize the extra secret information obtained by its adversary, while the stronger link attempts to maximize it. We provide an information theoretic formulation for this non-cooperative zero-sum game scenario and determine that, under the assumption of Gaussian signaling at the transmitters, there exists a unique Nash equilibrium solution for the proposed problem. Moreover, we obtain in closed-form the optimal strategies (beamformers) at the transmitters that result in the Nash equilibrium. While the NE strategies are achievable in one shot when full channel state information is available at the transmitters (CSIT), we also propose an iterative step-by-step algorithm that converges to the NE point, but only requires limited CSIT. Numerical results are presented to illustrate the analytical findings and to study the role of different channel parameters on the NE strategies.
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paper_title: On the Jamming Power Allocation for Secure Amplify-and-Forward Relaying via Cooperative Jamming

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In this paper, we investigate secure communications in two-hop wireless relaying networks with one eavesdropper. To prevent the eavesdropper from intercepting the source message, the destination sends an intended jamming noise to the relay, which is referred to as cooperative jamming. This jamming noise helps protecting the source message from being captured reliably at the eavesdropper, while the destination cancels its self-intended noise. According to the channel information available at the destination, we derive three jamming power allocation strategies to minimize the outage probability of the secrecy rate. In addition, we derive analytic results quantifying the jamming power consumption of the proposed allocation methods.
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paper_title: An Effective Secure Transmission Scheme for AF Relay Networks with Two-Hop Information Leakage

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In this letter, we propose a novel scheme to improve physical layer security for amplify-and-forward (AF) relay networks with two-hop information leakage. Unlike traditional joint cooperative beamforming (CB) and cooperative jamming (CJ) design, where mere artificial noise (AN) is exploited by the jammers to degrade eavesdroppers' channels, in our proposed scheme, the jammers send AN along with the confidential signal to simultaneously confuse the eavesdroppers and enhance the quality of received signals at the destination. In particular, the CB vectors and AN covariance matrix are jointly optimized for the relays and jammers under individual power constraints. By decoupling this resultant design problem, suboptimal solutions are obtained using the semidefinite relaxation technique. Simulation results are also provided to demonstrate that the proposed scheme has an obvious advantage in enhancing the secrecy rate.
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paper_title: Relay Selection for Security Enhancement in Cognitive Relay Networks

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This letter proposes several relay selection policies for secure communication in cognitive decode-and-forward relay networks, where a pair of cognitive relays is opportunistically selected for security protection against eavesdropping. The first relay transmits the secrecy information to the destination, and the second relay, as a friendly jammer, transmits the jamming signal to confound the eavesdropper. We present new exact closed-form expressions for the secrecy outage probability. Our analysis and simulation results strongly support our conclusion that the proposed relay selection policies can enhance the performance of secure cognitive radio. We also confirm that the error floor phenomenon is created in the absence of jamming.
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paper_title: Destination Assisted Cooperative Jamming for Wireless Physical-Layer Security

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A wireless network with one source, one destination, one eavesdropper, and multiple decode-and-forward relays is considered. A two-slot cooperative relaying scheme is proposed that targets at maximizing the secrecy rate. In the first slot, the source transmits the information bearing signal, and at the same time, it cooperates with the destination in jamming the eavesdropper without creating interference at the relay. In the second slot, one optimally selected relay retransmits the decoded source signal, and at the same time, that particular relay cooperates with the source to jam the eavesdropper without creating interference at the destination. Optimal relay selection and also optimal power allocation among the first/second slot data signal and jamming noise are proposed. It is shown that the secrecy rate of the proposed scheme scales with the total system power P0 and the number of available relays K according to 1/2log2(1 + P0 /8logK) - 1.6 bits/channel use . Although the proposed power allocation and relay selection assume global CSI available, the performance under imperfect relay CSI is also investigated. Also, the performance under distributed relay selection with limited feedback is demonstrated.
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paper_title: On Cooperative and Malicious Behaviors in Multirelay Fading Channels

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Multirelay networks exploit spatial diversity by transmitting user's messages through multiple relay paths. Most works in the literature on cooperative or relay networks assume that all terminals are fully cooperative and neglect the effect of possibly existing malicious relay behaviors. In this work, we consider a multirelay network that consists of both cooperative and malicious relays, and aims to obtain an improved understanding on the optimal behaviors of these two groups of relays via information-theoretic mutual information games. By modeling the set of cooperative relays and the set of malicious relays as two players in a zero-sum game with the maximum achievable rate as the utility, the optimal transmission strategies of both types of relays are derived by identifying the Nash equilibrium of the proposed game. Our main contributions are twofold. First, a generalization to previous works is obtained by allowing malicious relays to either listen or attack in Phase 1 (source-relay transmission phase). This is in contrast to previous works that only allow the malicious relays to listen in Phase 1 and to attack in Phase 2 (relay-destination transmission phase). The latter is shown to be suboptimal in our problem. Second, the impact of CSI knowledge at the destination on the optimal attack strategy that can be adopted by the malicious relays is identified. In particular, for the more practical scenario where the interrelay CSI is unknown at the destination, the constant attack is shown to be optimal as opposed to the commonly considered Gaussian attack.
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paper_title: Secure Relay and Jammer Selection for Physical Layer Security

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Secure relay and jammer selection for physical-layer security is studied in a wireless network with multiple intermediate nodes and eavesdroppers, where each intermediate node either helps to forward messages as a relay, or broadcasts noise as a jammer. We derive a closed-form expression for the secrecy outage probability (SOP), and we develop two relay and jammer selection methods for SOP minimization. In both methods a selection vector and a corresponding threshold are designed and broadcast by the destination to ensure each intermediate node knows its own role while knowledge of the relay and jammer set is kept secret from all eavesdroppers. Simulation results show the SOP of the proposed methods are very close to that obtained by an exhaustive search, and that maintaining the privacy of the selection result greatly improves the SOP performance.
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paper_title: Opportunistic Relaying for Secrecy Communications: Cooperative Jamming vs. Relay Chatting

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In this letter, we study the opportunistic use of relays for secret communications, and propose two transmission schemes that do not require the knowledge of the eavesdropper's channel state information. Both analytic and numerical results are provided.
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paper_title: Improving Secrecy Rate via Spectrum Leasing for Friendly Jamming

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Cooperative jamming paradigm in secure communications enlists network nodes to transmit noise or structured codewords, in order to impair the eavesdropper's ability to decode messages to be kept confidential from it. Such an approach can significantly help in facilitating secure communication between legitimate parties but, by definition, assumes dedicated and/or altruistic nodes willing to act as cooperative jammers. In this paper, it is demonstrated that cooperative jamming leads to meaningful secrecy rate improvements even when this assumption is removed. A distributed mechanism is developed that motivates jamming participation of otherwise non-cooperative terminals, by compensating them with an opportunity to use the fraction of legitimate parties' spectrum for their own data traffic. With the goal of maximizing their data transmission rate priced by the invested power, cooperative jammers provide the jamming/transmitting power that is generally proportional to the amount of leased bandwidth. The fully decentralized framework is facilitated through a game-theoretic model, with the legitimate parties as the spectrum owners acting as the game leader, and the set of assisting jammers constituting the follower. To facilitate the behavior of non-cooperative and competitive multiple jammers, auctioning and power control mechanisms are applied for a follower sub-game in a two-layer leader-follower game framework.
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paper_title: Power control Stackelberg game in cooperative anti-jamming communications

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As wireless networks are vulnerable to malicious attacks, security issues have aroused enormous research interest. In this paper, we focus on the anti-jamming power control of transmitters in a cooperative wireless network attacked by a smart jammer with the capability to sense the ongoing transmission power before making a jamming decision. By modeling the interaction between transmitters and a jammer as a Stackelberg game, we analyze the optimal strategies for both transmitters and the jammer and thus derive the Stackelberg equilibrium of the game. In addition, the Nash equilibrium of the anti-jamming game is also derived to compare with the Stackelberg equilibrium strategy. Finally, the impacts of the fading channel gains of the transmitters and the jammer on their utilities and the SINR are measured, respectively. Simulation results are presented to verify the performance of the proposed Stackelberg equilibrium strategy.
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Title: A Survey on Cooperative Jamming Applied to Physical Layer Security

Section 1: INTRODUCTION
Description 1: Introduce the significance of wireless communications, the associated security challenges, and the traditional vs. physical layer security solutions. Summarize the paper's contributions.

Section 2: Physical Layer Security
Description 2: Describe the generic wireless communication network model, the concept of secrecy capacity, and various methods to enhance physical layer security.

Section 3: Cooperative jamming
Description 3: Discuss the concept of cooperative jamming and how it aids in enhancing physical layer security by introducing interferers to reduce the eavesdropper's SNR.

Section 4: Artificial Jamming Signals types
Description 4: Categorize and explain the different types of artificial jamming signals used in cooperative jamming, highlighting their impact on communication security.

Section 5: Cooperative Jamming with Multiple Antennas and Beamforming
Description 5: Explore the use of multiple antennas and beamforming techniques in conjunction with cooperative jamming to enhance security.

Section 6: Cooperative jamming with Power Allocation method
Description 6: Discuss various power allocation strategies in cooperative jamming to optimize the secrecy capacity and minimize outage probability.

Section 7: Jamming Policies
Description 7: Outline different jamming policies, including relay selection and game theory approaches, to enhance secure communication.

Section 8: CONCLUSION
Description 8: Summarize the surveyed challenges and techniques in physical layer security and jamming, and conclude with considerations for future research directions.

Section 9: ACKNOWLEDGMENT
Description 9: Acknowledge the support and contributions towards the research work presented in the paper.