Maintaining security in wireless systems has been a challenge due to the broadcast nature of wireless communication channels. Many methods have been proposed as countermeasures to eavesdropping attacks, which stand as one of the most important secrecy attack types that use the vulnerabilities of wireless channels. The majority of these methods come with the cost of additional power consumption for maintaining secrecy. In order to provide a framework that can enable a tradeoff between energy efficiency and secrecy, we provide a flexible adaptive physical layer security approach that enables tunable security levels for distinct bit streams of a single user. Our main motivation stems from the fact that not all data bits within a single bit steam require the same amount of security. The proposed adaptive power optimization framework allows the assignment of different secrecy rate constraints for distinct data streams. Via simulations, we show that the proposed approach can increase the power efficiency compared to the non-adaptive physical layer security solution, while satisfying the required secrecy constraints.
Maintaining security in wireless systems has been a challenge due to the broadcast nature of wireless communication channels. Many methods have been proposed as countermeasures to eavesdropping attacks, which stand as one of the most important secrecy attack types that use the vulnerabilities of wireless channels. The majority of these methods come with the cost of additional power consumption for maintaining secrecy. In order to provide a framework that can enable a tradeoff between energy efficiency and secrecy, we provide a flexible adaptive physical layer security approach that enables tunable security levels for distinct bit streams of a single user. Our main motivation stems from the fact that not all data bits within a single bit steam require the same amount of security. The proposed adaptive power optimization framework allows the assignment of different secrecy rate constraints for distinct data streams. Via simulations, we show that the proposed approach can increase the power efficiency compared to the non-adaptive physical layer security solution, while satisfying the required secrecy constraints.
Information security has been a very important issue in wireless networks. With the ever-increasing amount of data being exchanged over wireless networks, the confidentiality of information needs to be protected from unauthorized users called eavesdropper. Due to the broadcast nature of the wireless medium, the transmissions between legitimate users maybe overheard and intercepted by the unauthorized parties, which makes wireless transmission vulnerable to potential eavesdropping attacks. The security of wireless communications plays an increasingly important role in the cybercrime defense against unauthorized activities. We consider the wireless physical layer security which has been explored for the sake of enhancing the protection of wireless communications against eavesdroppers. We consider the problem of secret communication through Rayleigh fading channel in the presence of an eavesdropper in which the transmitter knows the channel state information of both the main and eavesdropper channel. Then, we analyze the average capacity of the main channel and eavesdropper channel from which an expression of secrecy capacity is derived based on the cumulative distribution function and probability density function of the signal to noise ratio. We also analyze an expression for the symbol error rate of the main channel, and the outage probability is obtained for the main transmission. Finally, we perform the numerical results in MATLAB.
Due to their broadcast nature, wireless systems are vulnerable in the physical layer. While many physical layer security techniques are being developed, current security solutions are based on encryption techniques. This paper analyzes the relation between encryption techniques and physical layer security approaches and proposes a new encryption-aware multilayer security framework. The proposed framework optimizes transmit power by taking the adopted encryption technique into account, while guaranteeing both a quality of service (QoS) level for the legitimate receiver and a secrecy constraint against the eavesdropper. Numerical results are given for two most widely used symmetric encryption techniques, the data encryption (DES) and the advanced encryption (AES) standards. Numerical results show that the proposed encryption-aware physical layer security system achieves a better power efficiency when compared to the classical physical layer security approaches.
In this dissertation, we present novel physical (PHY) and cross-layer design guidelines and resource adaptation algorithms to improve the security and user experience in the future wireless networks. Physical and cross-layer wireless security measures can provide stronger overall security with high efficiency and can also provide better flexibility in response to the typically time-varying wireless environment. To better utilize limited wireless resources, we present approaches and techniques based on new performance criteria for wireless system optimization by thoroughly exploiting user information including its Quality of Service (QoS) requests and channel state information (CSI) to improve network throughput and security.
In recent years, there has been a growing research interest in wireless system security from PHY layer perspective. In a wiretap channel model introduced in the seminal work by Wyner, a sender “Alice” wishes to transmit a secret message to the intended receiver “Bob” in presence of a passive eavesdropper “Eve”. Existing works have characterized maximum achievable secrecy rate or secrecy capacity for single- and multiple-antenna systems by applying Gaussian signaling and secrecy code. Despite the impracticality of Gaussian input, its compact closed-form expression of mutual information motivated the wide use of Gaussian input assumption in theoretical analysis. In contrast to the Gaussian codebook, practical wiretap codes must consist of finite-alphabet symbols. Because of this constraint, the achievable secrecy rate for a finite-alphabet input scenario would differ from the secrecy rate achievable by a Gaussian codebook. In this thesis, we quantify the effect of finite discrete-constellation on instantaneous and ergodic secrecy rate of multiple-antenna wire-tap channels. Our results demonstrate substantial performance difference between systems involving finite-alphabet inputs and systems with Gaussian inputs. In addition, we investigate the secrecy performance of multi-terminal wiretap systems when a codebook based transmission beamforming is implemented. We characterize the secrecy outage probability of a communication link under eavesdropping. We consider a limited feedback scenario where the transmitter uses a pre-defined codebook known to both the transmitter and the receiver for beamforming, and analyze the secrecy outage probability of the link when it being eavesdropped.
Next, we consider the security of wireless multi-hop networks. Certainly, network security is an overarching issue that transcends all layers of communication protocol stack. Therefore, we tackle the problem of network security by proper user scheduling, routing, and resource management. Our approach of secrecy is complementary to the traditional cryptography based techniques. Together, they can provide stronger overall security and flexibility in selecting the desired solution and can reduce bandwidth and energy overhead as much as possible. Multi-hop wireless networks frequently employ the traditional routing and resource allocation strategies. Such strategies often fail to take into account the additional need for protection against security vulnerabilities due to the wireless medium. Thus, to address security concerns, we investigate the problem of eavesdropping control by proposing security-aware power allocation strategies and routing algorithms for multi-hop networks.
The future wireless infrastructure will consists of a plethora of heterogeneous collections of applications and services. A differentiated service structure would therefore be an essential part of the future wireless infrastructure. In addition to the security consideration of wireless network, we focus on the heterogeneous structure of the network. We study the problem of cross-layer resource allocation and admission control in a multiuser heterogeneous OFDMA network providing both QoS-constrained user servicesand best-effort services. Such heterogeneous networks provide service to both High-Priority (HP) users and Best-Effort (BE) users. By clustering subcarriers, efficient algorithms for cluster and power allocation have been proposed. Our strategy maximizes the total network utility of the BE users while satisfying the QoS request for maximum number of HP users. The feasibility of the resource allocation problem depends on the number of HP users in the network. Since a large number of demanding HP users would render the resource allocation problem infeasible, a joint admission control and resource allocation scheme could be an efficient way of tackling both problems with less overhead. By incorporating admission control, we propose an efficient and optimal joint admission control and resource allocation algorithm.
The applications of Wireless Sensor Networks (WSNs) are widespread in areas such as environmental monitoring, industrial automation, healthcare and smart infrastructures, where secure and reliable wireless communication is essential. The nature of a wireless channel, however, lends itself to the problem of eavesdropper-directed wireless sensor networking, interception and unauthorized access. This paper presents a secure physical layer communication system featuring the combination of channel estimator, physical layer key generator, artificial noise generator and adaptive power allocator to increase the confidentiality of physical layer communications and simultaneously achieve energy efficiency. A hybrid security mechanism is used, which takes advantage of the channel characteristics to create secret keys and to make the eavesdropper's signal reception worse by introducing controlled artificial noise. Key performance parameters considered for simulation-based evaluation are secrecy capacity, BER, PDR, Throughput, Energy consumption and Network lifetime. Results show that the secrecy capacity is 6.3 bps/Hz, the packet delivery ratio is 98.7%, the bit error rate is 10⁻⁶, and the network lifetime is 1675 rounds. The proposed framework is much more effective in terms of both communication security and energy efficiency than the traditional WSNs security schemes.
Nowadays, security in wireless communication is in high demand. The communication of messages or data should be secure, and various security technologies are used to achieve this. Although there are many advanced cryptographic approaches for securing confidential information, they have one disadvantage: high complexity and computational requirements. To address this drawback, physical layer security has been introduced into wireless networks. This paper provides a brief analysis of various approaches to security (physical security). Two main factors are identified: secrecy rate and security design through optimization. Security design depends on the selection of antennas and nodes, beamforming, and the distance between the source and destination. Based on these factors, optimization approaches for security design are discussed. Four main types of optimization problems are identified: Maximizing the secrecy rate, Minimizing secrecy outage probability, Reducing power consumption, Maximizing secure energy efficiency. The best method to maximize the secrecy rate is cooperative schemes. In the cooperative approach, a relay node is used to enhance security between the source and destination by introducing a noise signal.
Wireless communications offer data transmission services anywhere and anytime, but with the inevitable cost of introducing major security vulnerabilities. Indeed, an eavesdropper can overhear a message conveyed over the open insecure wireless media putting at risk the confidentiality of the wireless users. Currently, the way to partially prevent eavesdropping attacks is by ciphering the information between the authorised parties through complex cryptographic algorithms. Cryptography operates in the upper layers of the communication model, bit it does not address the security problem where the attack is suffered: at the transmission level. In this context, physical layer security has emerged as a promising framework to prevent eavesdropping attacks at the transmission level. Physical layer security is based on information-theoretic concepts and exploits the randomness and the uniqueness of the wireless channel. In this context, this thesis presents signal processing techniques to secure wireless networks at the physical layer by optimising the use of multiple-antennas. A masked transmission strategy is used to steer the confidential information towards the intended receiver, and, at the same time, broadcast an interfering signal to confuse unknown eavesdroppers. This thesis considers practical issues in multiple-antenna networks such as limited transmission resources and the lack of accurate information between the authorised transmission parties. The worst-case for the security, that occurs when a powerful eavesdropper takes advantage of any opportunity to put at risk the transmission confidentiality, is addressed. The techniques introduced improve the security by offering efficient and innovative transmission solutions to lock the communication at the physical layer. Notably, these transmission mechanisms strike a balance between confidentiality and quality to satisfy the practical requirements of modern wireless networks.