Wireless systems are becoming an increasingly important part of our daily lives. The proper operation of many crucial applications and use cases, including those in healthcare, finance, e-commerce, transportation, industrial automation, etc., depends on secure and reliable communication. Conventional cryptographic security mechanisms are widely used, but they are unable to scale with increasingly heterogeneous and decentralized networks. On the other hand, by utilizing the dynamic features of the wireless environment, physical layer security (PLS) offers a promising complementary solution to ensure the authenticity, confidentiality, integrity, and availability of legitimate communications. In this chapter, we first try to paint a picture of the next-generation networks before emphasizing the need for secure wireless transmission in future networks. Later, we highlight the limitations of cryptographic methods, and the ability of PLS to address them is provided. We conclude the chapter by briefly discussing a recently developed unified framework for PLS in future networks.

Today's fast-paced world is becoming increasingly dependent on wireless communications. Whether it is for businesses or individuals, mobility, portability, and instant access (via the internet) to unlimited information are the mantras of our day. In the past few decades, wireless communication has grown exponentially, with a bright future ahead of it. It is anticipated that this technology will have a profound impact on our lives and allow us to accomplish things we had never imagined. A key element of the success of these technologies will be the ability to communicate securely and reliably. Although cryptographic security mechanisms are widely adopted, they cannot cope with increasingly decentralized and heterogeneous networks. As a complementary solution, physical layer security (PLS) exploits the dynamic features of wireless environments to ensure that legitimate transmissions are subject to CIAA requirements. A generalized PLS framework is provided in this chapter, which not only incorporates the existing work but also allows for the development of next generation PLS methods. To reflect this, PLS fabric is divided into observation and modification planes. Furthermore, different domains of PLS are discussed under these plane concepts, allowing a vision of future PLS mechanisms.

This chapter presents the physical-layer security mechanisms in the analog domain under the name of physical layer authentication (PLA). PLA has attracted extensive research interest in recent years for the new generation of communication networks since it provides information-theory security with low complexity. In this chapter, we discuss the PLA system process and its metrics. After that, the PLA techniques that are based on the hardware devices available in the transceiver are presented according to the radio-frequency (RF) components such as an oscillator, power amplifier, device clock, and modulator/demodulator. Furthermore, due to the use of multiple-input multiple-output (MIMO) technology in 5G networks and beyond, new PLA techniques are introduced based on the beam pattern and sparsity of the MIMO channel, which is discussed deeply in this chapter. Finally, we provide some research challenges in PLA systems and future discussion.

In wireless communication, the data is conveyed through transmission over a physical signal, occupying a bounded specific space-time-frequency block in hyperspace. The building block of this signal is a distinct waveform that conveys the data symbols. A successful reception or detection of a signal requires the receiver to know the exact location of the transmitted signal in space-time-frequency hyperspace. Moreover, a successful identification requires that the receiver knows the features of the transmitted signal in order to decode the data. The goal of physical layer security (PLS) is to ensure the successful detection and identification of the information at the legitimate receiver while preventing illegitimate receivers from doing that. Initially, this chapter presents an overview of the inherent security characteristics provided by different waveforms against detection and identification. Then, it investigates how securing the control channel signals can affect the secrecy capacity of the communication system. However, inherent security and securing the control signal cannot fulfill the security requirements of all wireless applications. Therefore, in order to provide the required level of security, PLS comes into play, where it includes designing different processes that affect the signal based on the parameters extracted from the observation plane to modify the transmissions to ensure secure communication as highlighted in Chapter 3 (Modification plan).

According to the framework presented in Chapter 3, the network domain represents the various physical nodes present in the propagation environment and how their transmissions can be modified or adapted to enable physical layer security (PLS).. Specifically, these nodes may include relays, transmission points (TPs), and reconfigurable intelligent surfaces (RISs) in cooperative communication, coordinated multipoint (CoMP) and smart radio environment paradigms, respectively. All three of these are discussed as potential solutions against eavesdropping, jamming, and spoofing attacks.

This chapter focuses on providing physical layer security (PLS) to the joint radar and communication (JRC) systems. The integration of sensing and communication via shared spectral, hardware, and signal processing framework provides energy and cost efficiency. However, the inclusion of information into radar probing signals makes the communication susceptible to eavesdropping from the potential radar targets thereby generating a tradeoff, where the JRC transmitter needs to direct sufficient power toward the target to illuminate it while simultaneously limiting useful signal power to prevent eavesdropping. In addition to that, critical sensing information gathered via various sensing techniques including radar systems must also be protected. Therefore, in this chapter, various attacks such as exploratory, manipulation and disruption attacks on wireless sensing are discussed along with the techniques to counter them. Moreover, certain algorithms and PLS techniques are described for the realization of secure joint radar and communication systems.

Fifth-generation (5G) networks and beyond are anticipated to support a vast number of connections and services. Due to the enormous amount of confidential data shared between devices in these networks, the risk of security vulnerabilities escalates proportionally. Cognitive radio networks (CRNs) are no exception since they are vulnerable to a variety of physical-layer threats; hence, a physical-layer approach is necessary to safeguard these networks. Consequently, physical-layer security (PLS) has recently been applied for examining and strengthening the security of wireless networks, including CRNs. In light of this, this chapter examines a brief overview of CRNs, as well as the main physical layer attacks and their respective primary countermeasures. In addition, the employment of energy harvesting (EH) techniques to improve CRNs security is discussed. The security threats on cognitive unmanned aerial vehicles (UAVs) and their primary defense mechanisms are presented. In addition, the consideration of cascaded fading channels and their effect on the security of CRNs are explored. Finally, this chapter includes conclusions and potential future directions.

Applications of quantum technologies are rapidly progressing in communications systems implementations. In particular, quantum key distribution (QKD) and quantum random number generation have become key applications for cryptography and physical layer security. Unlike classical cryptography and network security, in QKD, security is ensured by the laws of physics and is, in principle, unbreachable by an interceptor. In particular, peculiar properties and postulates of quantum physics, such as superposition, entanglement, and quantum measurement uncertainty, are exploited to achieve system security. Quantum random number generator (QRNG) is also an important component in the implementation of QKD protocols. Likewise, in QRNG, true randomness (unpredictability using past data and uniformity of statistical distribution) is guaranteed by the laws of quantum physics. In this study, we review prominent aspects of QKD and QRNG, related standards, protocols, and hardware components. Moreover, a comprehensive review of the current QKD protocols and quantum random number generation methods is also presented.