Telecommunications networks are subject to an incessant enhancement process that enriches its features and capabilities, but also comes with its own set of challenges and boundaries. Besides the serious energy efficiency issues, the growth in telecommunication devices resulted in major privacy threats. This problem is even more critical for wireless networks due to their use of a channel that is easily reachable by eavesdroppers [1]. Spectrum scarcity is yet another challenge to overcome for researches in wireless communication. Indeed, the available spectrum in these systems is a very limited resource due the increasing demand. Emerging cooperative communication techniques and cognitive radio networks offer a great way to overcome the spectrum insufficiency challenge on one hand, but also increase the signal secrecy issue as the signal would now be shared not only between the source and the destination, but also with a set of relays that might or not be trusted. In this paper, we present a study of the existing methods that attempt to overcome the security problem in wireless networks and propose a new approach to achieve secrecy in a more general way considering multiple relays and multiple eavesdroppers as well as a system design for secrecy rate maximization.
Telecommunications networks are subject to an incessant enhancement process that enriches its features and capabilities, but also comes with its own set of challenges and boundaries. Besides the serious energy efficiency issues, the growth in telecommunication devices resulted in major privacy threats. This problem is even more critical for wireless networks due to their use of a channel that is easily reachable by eavesdroppers [1]. Spectrum scarcity is yet another challenge to overcome for researches in wireless communication. Indeed, the available spectrum in these systems is a very limited resource due the increasing demand. Emerging cooperative communication techniques and cognitive radio networks offer a great way to overcome the spectrum insufficiency challenge on one hand, but also increase the signal secrecy issue as the signal would now be shared not only between the source and the destination, but also with a set of relays that might or not be trusted. In this paper, we present a study of the existing methods that attempt to overcome the security problem in wireless networks and propose a new approach to achieve secrecy in a more general way considering multiple relays and multiple eavesdroppers as well as a system design for secrecy rate maximization.
Physical (PHY) layer security approaches for wireless communications can prevent eavesdropping without upper layer data encryption. However, they are hampered by wireless channel conditions: absent feedback, they are typically feasible only when the source-destination channel is better than the source-eavesdropper channel. Node cooperation is a means to overcome this challenge and improve the performance of secure wireless communications. This paper addresses secure communications of one source-destination pair with the help of multiple cooperating relays in the presence of one or more eavesdroppers. Three cooperative schemes are considered: decode-and-forward (DF), amplify-and-forward (AF), and cooperative jamming (CJ). For these schemes, the relays transmit a weighted version of a reencoded noise-free message signal (for DF), a received noisy source signal (for AF), or a common jamming signal (for CJ). Novel system designs are proposed, consisting of the determination of relay weights and the allocation of transmit power, that maximize the achievable secrecy rate subject to a transmit power constraint, or, minimize the transmit power subject to a secrecy rate constraint. For DF in the presence of one eavesdropper, closed-form optimal solutions are derived for the relay weights. For other problems, since the optimal relay weights are difficult to obtain, several criteria are considered leading to suboptimal but simple solutions, i.e., the complete nulling of the message signals at all eavesdroppers (for DF and AF), or the complete nulling of jamming signal at the destination (for CJ). Based on the designed relay weights, for DF in the presence of multiple eavesdroppers, and for CJ in the presence of one eavesdropper, the optimal power allocation is obtained in closed-form; in all other cases the optimal power allocation is obtained via iterative algorithms. Numerical evaluation of the obtained secrecy rate and transmit power results show that the proposed design can significantly improve the performance of secure wireless communications.
Privacy and security have an increasingly important role in wireless networks. A secure communication enables a legitimate destination to successfully retrieve information sent by a source, while it disables the eavesdropper (illegitimate destination) to interpret the intercepted information. Physical (PHY) layer security approaches for wireless communications can prevent eavesdropping without encryption. It exploits the physical characteristics of the wireless channel in order to transmit messages securely. They are typically feasible when the source-destination channel is better than the source-eavesdropper channel. Cooperative schemes are a means to improve the performance of secure wireless communications. We propose an improved relay selection scheme, based on source-eavesdropper channel SNR restriction, that will guarantee the best secrecy rate at the destination under QoS condition. Performance has been studied in terms of secrecy rate, outage probability and average error probability. Simulations shows that the proposed scheme outperforms in terms of the secrecy rate at the destination when compared to techniques in the literature.
In a wireless system, transmitted electromagnetic waves can propagate in all directions and can be received by other users in the system. The signals received by unintended receivers pose two problems; increased interference causing lower system throughput or successful decoding of the information which removes secrecy of the communication. Radio frequency spectrum is a scarce resource and it is allocated by technologies already in use. As a result, many communication systems use the spectrum opportunistically whenever it is available in cognitive radio setting or use unlicensed bands. Hence, efficient use of spectrum by sharing users is crucial to increase maximize system throughput. In addition, secrecy of a wireless communication system is traditionally provided by computational complexity of cryptography techniques employed. However, cryptography systems depend on either a random secret key generation mechanism or a trusted key distribution system. Recent developments in the wireless communication area provided a solution to both key generation and distribution problem via exploiting randomness of the wireless channel unconditional to the computational complexity. In this dissertation, we propose solutions to the problems discussed. For spectrum sharing, we present a detailed analysis of challenges of efficient spectrum sharing without a central enforcing mechanism, provide insight to already existing power control algorithms and propose a novel non-greedy power allocation algorithm. Numerical simulations show that the proposed algorithm increases system throughput more than greedy algorithms and can use available spectrum to the fullest, yet it is robust to the presence of greedy users. For secrecy, we propose a practical and fast system for random secret key generation and reconciliation. We extend the proposed system to multiple-input-multiple-output systems and increase security via role reversal of the nodes while making it quicker by pre-encoding procedure. Information theory calculation and numerical simulations demonstrates that the proposed system provides a secure channel for legitimate users in the presence of a passive eavesdropper.
Abstract Cooperative communication has emerged as a pivotal innovation in wireless networks, allowing multiple sites with single antennas to collaborate in signal transmission, thereby improving power efficiency, enhancing spatial diversity, and increasing the reliability of signal reception. This paper introduces a cooperative communication system comprising two communicating nodes, multiple relays, and an eavesdropper. The eavesdropper attempts to intercept the signals transmitted between the two nodes. To mitigate this threat, a jamming signal is employed as artificial interference, degrading the quality of the wiretap channel and preventing the eavesdropper from successfully acquiring the transmitted data, thereby enhancing system security. The α−μ α - μ fading distribution is utilized as a generalized model for wireless channel fading. The system model is analyzed, and closed-form expressions for secrecy outage probability are derived for single-relay and the asymptotic secrecy outage probability is derived for multiple-relay scenarios, and finally the probability of the correct computation of the secrecy packets is evaluated. Analytical results are provided to substantiate the theoretical outcomes.
This paper proposes a joint cooperative relaying and jamming scheme based on distributed beamforming to enhance the secrecy rate of a wireless channel in the presence of an eavesdropper. Specifically, we consider the scenario that a source node transmits messages to a destination with the help of multiple cooperative relays, where a relay might be compromised to become an eavesdropper as an inside attacker. Our joint relaying and jamming approach is to assign some relay nodes to act as jammers to interfere the eavesdropper, while the remaining ones continue relaying information to the destination. We propose a protocol to implement the joint cooperative relaying and jamming. Our protocol further considers the particular challenge brought by the inside attacker: it may know the jamming signal and can use it to remove the interference from the jammers. The issue of phase and frequency synchronization in the distributed beamforming is also taken into account. A mixed integer programming problem is formulated to maximize the secrecy rate with the proposed joint relaying and jamming, by which the optimal role assignment to a relay and the associated optimal power assignment can be solved. Numerical results are presented to demonstrate the efficiency of the proposed joint relaying and jamming in improving the secrecy rate, with comparison to existing approaches.
Cooperative jamming is an approach that has been recently proposed for improving physical layer based security for wireless networks in the presence of an eavesdropper. While the source transmits its message to its destination, a relay node transmits a jamming signal to create interference at the eavesdropper. In this paper, a scenario in which the relay is equipped with multiple antennas is considered. A novel system design is proposed for determining the antenna weights and transmit power of source and relay, so that the system secrecy rate is maximized subject to a total transmit power constraint, or, the transmit power is minimized subject to a secrecy rate constraint. Since the optimal solutions to these problems are difficult to obtain, suboptimal closed-form solutions are proposed that introduce an additional constraint, i.e., the complete nulling of jamming signal at the destination.