As wireless networking has a wide range of applications, its security is an issue of concern. Encryption is traditionally the main route to secure communications. Nevertheless, this security solution may be difficult to implement in some modern wireless networks, e.g., ad hoc and radio-frequency identification (RFID) networks which require large-scale organization and low computational complexity, respectively. An alternative approach is physical-layer security, which leverages the physical properties of radio channels to achieve reliable data transmission without the need of secret keys. Since this kind of security emerged from the information theoretical characterization of secrecy, there has been great interest in secrecy capacity of various wireless channels. This paper provides an overview of such capacity for a single user.
As wireless networking has a wide range of applications, its security is an issue of concern. Encryption is traditionally the main route to secure communications. Nevertheless, this security solution may be difficult to implement in some modern wireless networks, e.g., ad hoc and radio-frequency identification (RFID) networks which require large-scale organization and low computational complexity, respectively. An alternative approach is physical-layer security, which leverages the physical properties of radio channels to achieve reliable data transmission without the need of secret keys. Since this kind of security emerged from the information theoretical characterization of secrecy, there has been great interest in secrecy capacity of various wireless channels. This paper provides an overview of such capacity for a single user.
Security in wireless networks has traditionally been considered to be an issue to be addressed separately from the physical radio transmission aspects of wireless systems. However, with the emergence of new networking architectures that are not amenable to traditional methods of secure communication such as data encryption, there has been an increase in interest in the potential of the physical properties of the radio channel itself to provide communications security. Information theory provides a natural framework for the study of this issue, and there has been considerable recent research devoted to using this framework to develop a greater understanding of the fundamental ability of the so-called physical layer to provide security in wireless networks. Moreover, this approach is also suggestive in many cases of coding techniques that can approach fundamental limits in practice and of techniques for other security tasks such as authentication. This paper provides an overview of these developments.
Recent years have been marked by an enormous growth of wireless communication networks and an extensive use of wireless applications. In return, this phenomenal expansion is inducing more concerns about the privacy and the security of the users. For many years, the security challenge has been mainly addressed at the application layer using cryptographic techniques. However, with the emergence of ad-hoc and decentralised networks and the deployment of 5G and beyond wireless communication systems, the need for less complex securing techniques had become a necessity. It is mainly for this reason that wireless physical layer security has gained much attention from the research community. What distinguishes information-theoretic security compared to other high-layer cryptographic techniques is that it exploits the randomness and the fluctuations of the wireless channel to achieve security at a remarkably reduced computational complexity. However, these technical virtues rely heavily on perhaps idealistic channel state information assumptions. In this chapter, we look at the physical layer security paradigm from the channel uncertainty perspective. In particular, we discuss the ergodic secrecy capacity of wiretap channels when the transmitter is hampered by the imperfect knowledge of the channel state information (CSI).
Wireless networking has kept evolving with additional features and increasing capacity. Meanwhile, inherent characteristics of wireless networking make it more vulnerable than wired networks. In this thesis we present an extensive and comprehensive review of physical layer security in wireless networking. Different from cryptography, physical layer security, emerging from the information theoretic assessment of secrecy, could leverage the properties of wireless channel for security purpose, by either enabling secret communication without the need of keys, or facilitating the key agreement process. Hence we categorize existing literature into two main branches, namely keyless security and key-based security. We elaborate the evolution of this area from the early theoretic works on the wiretap channel, to its generalizations to more complicated scenarios including multiple-user, multiple-access and multiple-antenna systems, and introduce not only theoretical results but practical implementations. We critically and systematically examine the existing knowledge by analyzing the fundamental mechanics for each approach. Hence we are able to highlight advantages and limitations of proposed techniques, as well their interrelations, and bring insights into future developments of this area.
Electromagnetic induction, the earliest form of wireless energy transfer, was demonstrated by Michael Faraday in 1831, happening to be the infancy of radio communication. Since then, this technique in various scales was used for communications, eventually converging to a democratic name "Radio" in the early 1900s as we know it today. Radio frequency or RF communications are collectively and broadly referred to the communication of wireless nature using electromagnetic waves with a frequency of roughly a few kHz to several THz. RF communications are used for several applications ranging from leisure, meteorology, public broadcast, commercial, domestic and defense communications, and so forth. However, when information is communicated, often there is a need to distinguish among the intended receivers and eavesdroppers, for reasons of secrecy, confidentiality, and integrity, like for requirements from personal privacy, till national security. At present, wireless communications are mostly secured in the top level through mathematic encryption - the Advanced Encryption Standard (AES) and the Rivest-Shamir-Adleman (RSA) methods are some examples of this, and in smaller levels by techniques like range limiting, frequency diversity and similar. Anyhow the prominent mode of security is mathematic-based software encryption.Now it is apparent that researchers (ethical or unethical) are working hard like the research community in software encryption to find techniques to crack into the information transmitted. Very often a scenario is encountered such that a transmitted spectrum is recorded and is then cracked over time using several reverse engineering and computational approaches. After all, software encryption is nothing but a complicated mathematical function that, in principle, is always solvable, provided enough time and computational effort is applied to the challenge. This is like eavesdropping an unknown language speaker, recording the conversation, and then transliterating it later with the help of a proficient translator.The current advances in computing and artificial intelligence, like the advent of quantum computing makes this plot worse as computation power and competence is evolving day by day [1-4].An added fortress to wireless communication in the shadow of such an impending vulnerability is hardware security, which is interchangeably called physical layer network security. This is synonymous to adding an extra padlock alongside a combination lock that extends the security over time and effort. Thus, physical layer wireless security is a set of hardware control approaches which makes sure that an effective reception of transmitted data constellation (often software encrypted) could be received in the right format only along pre-defined secure directions or locations. The transmission along all other directions or locations is either scrambled or prevented. This is a relevant concern and is backed by the fact that in a conventional antenna-based transmission, even though the directional gain of the antenna can be controlled, the constellation pattern of transmitted data is distributed in free space almost omnidirectionally around it. Thus, a receiver of adequate sensitivity would be able to record the transmitted data even though it is encrypted mathematically.In this chapter, we broadly classify this concept, discuss several types of reported technologies for physical layer wireless security, and outline their comparisons. Finally, a future perspective of the same is drawn for readers who are interested in this promising research topic.
The issues of privacy and security in wireless communication networks have taken on an increasingly important role as these networks continue to flourish worldwide. Traditionally, security is viewed as an independent feature addressed above the physical-layer and all widely used cryptographic protocols are designed and implemented assuming the physical-layer has already been established and provides an error free link. However, with the emergence of ad-hoc and decentralized networks, higher-layer techniques, such as encryption, are complex and hard to be implemented. Therefore, there has been a recent attention on studying the fundamental ability of the physical-layer to provide secure wireless communications. In this contribution, we discuss the challenges ahead in implementing wireless physical-layer security.
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.