—In wireless communications, security issues have become difficult due to unchangeable and unpredictable nature of the wireless medium. There are many traditional cryptographic techniques which were used previously. The physical layer security used for ensuring secure wireless communications apart from the cryptographic techniques, which is achieved after proper understanding of the nature wireless channels. Classical information theoretic secrecy is one of the metrics followed, in which, we assume that there is no(zero) leaked information at the eavesdropper which means the information decoding probability at the eavesdropper is '0'. But, practically achieving classical information theoretic secrecy is not possible. So, this project deals with partial secrecy. The partial secrecy of a system is measured in terms of equivocation, which gives the information of the level at which the eavesdropper (active) is confused. It means that in partial secrecy, there is information leakage but the eavesdropper cannot exactly decode the original message. The new secrecy metrics used GSOP (generalized secrecy outage probability), AFE (average fractional equivocation) and AILR (average information leakage rate) altogether provides more comprehensive and in-depth understanding of the secrecy performance over the fading channels.
—In wireless communications, security issues have become difficult due to unchangeable and unpredictable nature of the wireless medium. There are many traditional cryptographic techniques which were used previously. The physical layer security used for ensuring secure wireless communications apart from the cryptographic techniques, which is achieved after proper understanding of the nature wireless channels. Classical information theoretic secrecy is one of the metrics followed, in which, we assume that there is no(zero) leaked information at the eavesdropper which means the information decoding probability at the eavesdropper is '0'. But, practically achieving classical information theoretic secrecy is not possible. So, this project deals with partial secrecy. The partial secrecy of a system is measured in terms of equivocation, which gives the information of the level at which the eavesdropper (active) is confused. It means that in partial secrecy, there is information leakage but the eavesdropper cannot exactly decode the original message. The new secrecy metrics used GSOP (generalized secrecy outage probability), AFE (average fractional equivocation) and AILR (average information leakage rate) altogether provides more comprehensive and in-depth understanding of the secrecy performance over the fading channels.
Securing information in future mobile networks is particularly challenging for devices with limited computational resources. In such contexts, physical layer security (PLS) offers a promising alternative by exploiting the inherent randomness of wireless channels. When full secrecy cannot be guaranteed, the partial secrecy regime provides a realistic and effective approach to system design. This study investigates the partial secrecy performance of wireless systems operating over the recently introduced generalized multicluster fluctuating two-ray (MFTR) fading model. This model is highly regarded for its adaptability in representing a broad range of propagation environments and includes various classical fading models as exceptional cases. We consider a secure communication setup involving a transmitter (A), an intended receiver (B), and an eavesdropper (E). Inspired by previous work showing the benefits and simplicity of diversity schemes for improving PLS, we assume that both B and E are equipped with antenna arrays and apply maximal ratio combining (MRC). The model also considers independently but not identically distributed (i.n.i.d.) fading conditions on the A → B and A → E links. We derive exact and closed-form approximate expressions for three central metrics in partial secrecy theory: generalized secrecy outage probability (GSOP), average fractional equivocation (AFE), and average information leakage rate (AILR). Unlike previous approaches based on simpler fading models, the proposed expressions maintain a constant computational complexity, irrespective of the number of diversity branches, and are compatible with standard mathematical tools. Validation via Monte Carlo simulations confirms the accuracy of the derived expressions and highlights the impact of key system parameters on secrecy performance. The flexible MFTR framework enables assessment across varied fading conditions. In particular, increasing the number of MRC branches at B improves the GSOP diversity order and alters PLS behavior based on the fading characteristics of the A → E link.
Growing need for secure wireless communication in networks like Internet of Things (IoT), 5G, and future 6G has raised concerns about efficient ways to ensure security. Cryptography techniques are considered to be efficient from the standpoint of providing security; however, they are also limited in computational complexity, energy consumption, and key management. In order to overcome the above-mentioned issue, it is possible to employ Physical Layer Security (PLS). Using unique characteristics of wireless communication channel, it is possible to enhance the confidentiality of the process. The current research paper analyzes the PLS approach for investigation of partial secrecy in case wireless channel operates under such fading distributions as Rayleigh, Rician, and Nakagami-m. The diversity-based approach for enhancing physical layer security is employed through use of such diversity types as Selection Combining (SC), Maximal Ratio Combining (MRC), and Cooperative Diversity. Analysis of performance of such a system is performed with the help of MATLAB simulations using the following parameters: Secrecy Capacity, Generalized Secrecy Outage Probability (GSOP), Average Information Leakage Rate (AILR), Average Fractional Equivocation (AFE), and Secrecy Throughput. The results of simulations demonstrate the advantage of diversity approach with respect to ensuring secure wireless communications at different SNR values. Among all kinds of diversity, MRC performs better than others due to its efficient signal combining capability.
Theoretical studies on physical layer security often adopt the secrecy outage probability as the performance metric for wireless communications over quasi-static fading channels. The secrecy outage probability has two limitations from a practical point of view: 1) it does not give any insight into the eavesdropper's decodability of confidential messages and 2) it cannot characterize the amount of information leakage to the eavesdropper when an outage occurs. Motivated by the limitations of the secrecy outage probability, we propose three new secrecy metrics for secure transmissions over quasi-static fading channels. The first metric establishes a link between the concept of secrecy outage and the decodability of messages at the eavesdropper. The second metric provides an error-probability-based secrecy metric which is typically used for the practical implementation of secure wireless systems. The third metric characterizes how much or how fast the confidential information is leaked to the eavesdropper. We show that the proposed secrecy metrics collectively give a more comprehensive understanding of physical layer security over fading channels and enable one to appropriately design secure communication systems with different views on how secrecy is measured.
Theoretical studies on physical layer security often adopt the secrecy outage probability as the performance metric for wireless communications over quasi-static fading channels. The secrecy outage probability has two limitations from a practical point of view: 1) it does not give any insight into the eavesdropper's decodability of confidential messages and 2) it cannot characterize the amount of information leakage to the eavesdropper when an outage occurs. Motivated by the limitations of the secrecy outage probability, we propose three new secrecy metrics for secure transmissions over quasi-static fading channels. The first metric establishes a link between the concept of secrecy outage and the decodability of messages at the eavesdropper. The second metric provides an error-probability-based secrecy metric which is typically used for the practical implementation of secure wireless systems. The third metric characterizes how much or how fast the confidential information is leaked to the eavesdropper. We show that the proposed secrecy metrics collectively give a more comprehensive understanding of physical layer security over fading channels and enable one to appropriately design secure communication systems with different views on how secrecy is measured.
For secure communications over wireless fading channels, the secrecy outage probability is widely used as the performance measure. However, the current secrecy outage formulation has two major limitations in evaluating the secrecy performance: a) the amount of information leakage to the eavesdropper cannot be characterized when an outage occurs, b) the current formulation does not give insights into the eavesdropper's decodability of confidential messages. To overcome such limitations and obtain in-depth understanding of secrecy performance over wireless fading channels, this paper proposes three new secrecy measures for different practical aims, namely, 1) generalized secrecy outage probability, 2) asymptotic lower bound on eavesdropper's decoding error probability, and 3) average information leakage rate. A specific example of wireless transmissions with a fixed-rate wiretap code is given to illustrate the use of the proposed secrecy measures.
Intrigued by the rapid growth and expand of wireless devices, data security is increasingly playing a significant role in our daily transactions and interactions with different entities. Possible examples, including e-healthcare information and online shopping, are becoming vulnerable due to the intrinsic nature of wireless transmission medium and the widespread open access of wireless links. Traditionally, the communication security is mainly regarded as the tasks at the upper layers of layered protocol stack, security techniques, including personal access control, password protection, and end-to-end encryption, have been widely studied in the open literature. More recently, plenty of research interests have been drawn to the physical layer forms of secrecy. As a new but appealing paradigm at physical layer, physical layer security is based on two pioneering works: (i) Shannon’s information-theoretic formulation and (ii) Wyner’s wiretap formulation. \n \nOn account of the fundamental of physical layer security and the different nature of various wireless network, this dissertation is supposed to further fill the lacking of the existing research outcomes. To be specific, the contributions of this dissertation can be summarized as three-fold:(i) exploration of secrecy metrics to more general fading channels; (ii) characterization a new fading channel model and its reliability and security analysis in digital communication systems; and (iii) investigation of physical layer security over the random multiple-input multiple-output (MIMO) α −μ fading channels. \n \nTaking into account the classic Alice-Bob-Eve wiretap model, the first contribution can be divided into four aspects: (i) we have investigated the secrecy performance over single-input single-output (SISO) α −μ fading channels. The probability of non-zero (PNZ) secrecy capacity and the lower bound of secrecy outage probability (SOP) are derived for the special case when the main channel and wiretap channel undergo the same non-linearity fading parameter, i.e., α. Later on, for the purpose of filling the gap of lacking closed-form expression of SOP in the open literature and extending the obtained results in chapter 2 to the single-input multiple-output (SIMO) α − μ wiretap fading channels, utilizing the fact that the received signal-tonoise ratios (SNRs) at the legitimate receiver and eavesdropper can be approximated as new α −μ distributed random variables (RVs), the SOP metric is therefore derived, and given in terms of the bivariate Fox’s H-function; (ii) the secrecy performance over the Fisher-Snedecor F wiretap fading channels is initially considered. The SOP, PNZ, and ASC are finalized in terms of Meijer’s G-function; (iii) in order to generalize the obtained results over α −μ and Fisher-Snedecor F wiretap fading channels, a more flexible and general fading channel, i.e., Fox’s H-function fading model, are taken into consideration. Both the exact and asymptotic analysis of SOP, PNZ, and average secrecy capacity (ASC), are developed with closed-form expressions; and (iv) finally, motivated by the fact that the mixture gamma (MG) distribution is an appealing tool, which can be used to model the received instantaneous SNRs over wireless fading channels, the secrecy metrics over wiretap fading channels are derived based on the MG approach. \n \nDue to the limited transmission power and communication range, cooperative relays or multi-hop wireless networks are usually regarded as two promising means to address these concerns. Inspired by the obtained results in Chapters 2 and 3, the second main contribution is to propose a novel but simple fading channel model, namely, the cascaded α −μ. This new distribution is advantageous since it encompasses the existing cascaded Rayleigh, cascaded Nakagami-m, and cascaded Weibull with ease. Based on this, both the reliability and secrecy performance of a digital system over cascaded α −μ fading channels are further evaluated. Closed-form expressions of reliability metrics (including amount of fading (AF), outage probability, average channel capacity, and average symbol error probability (ABEP).) and secrecy metrics (including SOP, PNZ, and ASC) are respectively provided. Besides, their asymptotic behaviors are also performed and compared with the exact results. \n \nConsidering the impacts of users’ densities, spatial distribution, and the path-loss exponent on secrecy issue, the third aspect of this thesis is detailed in Chapter 8 as the secrecy investigation of stochastic MIMO system over α −μ wiretap fading channels. Both the stochastic geometry and conventional space-time transmission (STT) scheme are used in the system configuration. The secrecy issue is mathematically evaluated by three metrics, i.e., connection outage, the probability of non-zero secrecy capacity and the ergodic secrecy capacity. Those three metrics are later on derived regarding two ordering scheme, and further compared with Monte-Carlo simulations.