We consider the K-user cellular network coexisting with a single helper node (HN) (or cooperative jammer) whose objective is to enhance the secrecy of the confidential data transmission. Due to the broadcast nature of the wireless medium, the information leakage to the undesired users is unavoidable when the base station (BS) transmits the private information to the intended mobile user (MU). In this paper, the unintended users are regarded as the potential eavesdroppers and called as the internal eavesdroppers. In [1], the proposed optimal transmission strategy for the helper maximizes the secrecy capacity of the intended user. However, its computational complexity geometrically increases as the number of the legitimate users or the network size grows. This property is inappropriate to the cellular network where dozens of users generally exist. To resolve such practical issue, we design the low complexity transmission strategies of the helper which are insensitive to the network size. In addition, as a part of an effort to develop the usability, we classify the helper's cooperation according to whether the helper possesses the channel state information (CSI) about the downlink channel BS → MUkfor k ∈ K = {1, 2, …, K} or not. We analyze the computational complexity of the proposed schemes and verify that their complexity dramatically decreases compared to the optimal transmission strategy in [1]. Also, through the simulation results, it is observed that the proposed transmission strategies provide the comparable secrecy rates to that of the optimal transmission.
We consider the K-user cellular network coexisting with a single helper node (HN) (or cooperative jammer) whose objective is to enhance the secrecy of the confidential data transmission. Due to the broadcast nature of the wireless medium, the information leakage to the undesired users is unavoidable when the base station (BS) transmits the private information to the intended mobile user (MU). In this paper, the unintended users are regarded as the potential eavesdroppers and called as the internal eavesdroppers. In [1], the proposed optimal transmission strategy for the helper maximizes the secrecy capacity of the intended user. However, its computational complexity geometrically increases as the number of the legitimate users or the network size grows. This property is inappropriate to the cellular network where dozens of users generally exist. To resolve such practical issue, we design the low complexity transmission strategies of the helper which are insensitive to the network size. In addition, as a part of an effort to develop the usability, we classify the helper's cooperation according to whether the helper possesses the channel state information (CSI) about the downlink channel BS → MUkfor k ∈ K = {1, 2, …, K} or not. We analyze the computational complexity of the proposed schemes and verify that their complexity dramatically decreases compared to the optimal transmission strategy in [1]. Also, through the simulation results, it is observed that the proposed transmission strategies provide the comparable secrecy rates to that of the optimal transmission.
In this paper, we consider a cooperative jammer to improve secrecy of the wireless transmission in a cellular downlink network. The private message intended for a single user should be kept from the remainder of the users who are regarded as internal eavesdroppers. To improve the secrecy of the intended user, we propose an employment of a helper with multiple antennas and design its optimal transmit beamforming vector. Specifically, the helper node generates the artificial interference to the internal eavesdroppers and so enhances the security by increasing the ambiguity at the eavesdroppers. Based on a framework of power gain region in [1], we optimize the transmission strategy for the helper which maximizes the secrecy capacity of the intended user. The analytical and simulation results show that the proposed scheme enhances the secrecy capacity. In addition, all users whose secrecy rates are zero with no helper's cooperation can achieve the positive secrecy rate by the proposed scheme.
In this paper, a novel transmission scheme is proposed to improve the security of downlink cellular network. The confidential message intended to one of K mobile users (MUs) should be securely kept from the undesired recipients. In this work, the K-1 remaining users are regarded as potential eavesdroppers and called as internal eavesdroppers. For the security enhancement, we propose an adaptation of a single cooperative jammer (CJ) to increase the ambiguity at all malicious users by distracting them with artificial interference. With the help of CJ, we derive the optimal joint transmission scheme by beamforming solution to maximize the secrecy rate of the intended user. Numerical results show the performance improvement of the proposed scheme.
The growth of wireless networks has been considerable over the last decades. Due to the broadcast nature of these networks, security issues have taken a critical role in today’s communications. A promising direction towards achieving secure communications is information theoretic secrecy, which is an approach exploiting the randomness of the channels to ensure secrecy. Based on this approach, there has been a recent surge of interest in a potential cooperation between users to enhance the secrecy of communications. In this thesis we investigate the interaction between cooperation and secrecy. In particular the contributions of the thesis can be divided into two parts. In the first part, we study cooperative strategies for secrecy for wireless channels. Our goal is to evaluate the effect of fading and limited CSI on the eavesdropper’s channels. In that purpose we consider a scenario where a helper aims at increasing the secrecy of the communication between a source and destination in the presence of an eavesdropper. Several strategies are discussed for the helper, namely decode-and-forward, amplify-and-forward, and cooperative jamming. We introduce the secrecy outage probability, the conditional secrecy outage probability and the secure throughput as secrecy measures. For each measure, we investigate and compare the secrecy performance of cooperation. We furthermore elaborate a system optimization in terms of strategy selection, node positioning, power allocation and rate design. In the second part, we consider cooperation in the 4-node scenario against a more sophisticated adversary: an active eavesdropper, which can either passively eavesdrop, or jam the transmission. A game-theoretic perspective is a natural way to analyze the competitive interaction between the helper and the eavesdropper. Therefore we define several secrecy games, for which we find the Nash and Stackelberg equilibria as well as the corresponding secrecy rate outcomes. Another important consideration in this scenario is the interaction between the source and the helper, which we model and solve as a Stackelberg game, and we illustrate its impact on the achievable secrecy rates.
This paper investigates cooperative security in wireless networks, where a source (Alice) intends to transmit a confidential message to a legitimate destination (Bob), with the help of a cooperative jammer (Charlie), coexisting with multiple passive eavesdroppers (Eves). In particular, by assuming knowledge of Bob's perfect channel state information (CSI) but only Eves’ statistical CSIs, secrecy beamforming with artificial noise (AN) is utilized for secure transmission, and cooperative jamming (CJ) is explored to further enhance secrecy. We first derive an accurate closed-form expression for the secrecy outage probability (SOP), and establish the condition under which positive secrecy rate is achievable. Then, we provide a secure transmit design for maximizing the SOP constrained secrecy rate. Moreover, based on a strict mathematical analysis, we characterize the impact of the main channel quality and the number of Eves on transmit design and secrecy performance. Specifically, optimal power allocation ratio between the information-bearing signal and the AN signal increases as the main channel quality improves, and decreases with the number of Eves. Numerical results confirm that our design achieves performance improvement in terms of both secrecy rate and secure energy efficiency, as compared to the approach without CJ.
In this paper, we investigate the security of cellular networks using cooperative jamming with imperfect wiretap channel status information (CSI). Firstly, the CSI of the eavesdropper is considered imperfect and modeled as a sphere with a certain center and a radius which is the estimated channel of eavesdropper, and then the optimization of the worst-case secrecy rate is given. Secondly, using semidefinite relaxation (SDR) and a search method, the SDR-based scheme is proposed to maximize the secrecy rate. To reduce the complexity, a second scheme to optimize the ratio between interference to the eavesdropper and to the legitimate user, which is transmitted by jammers, is introduced. Finally, the numerical results demonstrate the excellent performance of the two strategies, and the performance of the low-complexity scheme is very close to that of the SDR-based scheme.
In this paper, we consider secure downlink transmission in two-cell networks where the one base station (Alice) provides secure wireless services to its legitimate receiver (Bob) in the presence of a passive eavesdropper (Eve). For multi-cell networks, the inter-cell interference to Bob and Eve has a great impact on the security performance. In order to improve the confidentiality of information transfer from Alice to Bob, it is crucial to properly design the transmit strategies. With the results of conventional cooperative jamming (CJ) scheme, we propose a modified CJ scheme for cooperative base station (CBS) to further degrade the quality of signal reception at Eve, and therefore the secrecy rate can be increased. Both theoretical analysis and numerical results show that the modified CJ scheme outperforms the conventional CJ scheme by achieving a higher secrecy rate. Additionally, by taking the energy efficiency into account, we formulate an adaptive cooperation, in which the CBS is allowed to provide services to its desired receiver. We design a cooperative beamforming for CBS to satisfy the rate requirement while maximizing the secrecy rate of legitimate channel. Numerical results validate the effectiveness of the proposed cooperation scheme.