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).
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).
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 induced more concerns about the privacy and the security of the users. Physical layer security is one of the most promising solutions that were proposed to enhance the security of next generation wireless systems. The fundamental idea behind this technique is to exploit the randomness and the fluctuations of the wireless channel to achieve security without conditional assumptions on the computational capabilities of the eavesdropper. In fact, while these elements have traditionally been associated with signal deterioration, physical layer security uses them to ensure the confidentiality of the users. Nevertheless, these technical virtues rely heavily on perhaps idealistic channel state information assumptions. In that regard, the aim of this thesis is to look at the physical layer security paradigm from the channel uncertainty perspective. In particular, we discuss the ergodic secrecy capacity of different wiretap channels when the transmitter is hampered by the imperfect knowledge of the channel state information (CSI). We consider two prevalent causes of uncertainty for the CSI at transmitter (CSIT); either an error of estimation occurs at the transmitter and he can only base his coding and the transmission strategies on a noisy version of the CSI, or the CSI feedback link has a limited capacity and the legitimate receivers can only inform the transmitter about the quantized CSI. We investigate both the single-user multiple-input multiple-output (MIMO) wiretap channel and the multi-user broadcast wiretap channel. In the latter scenario, we distinguish between two situations: multiple messages transmission and common message transmission. We also discuss the broadcast channel with confidential messages (BCCM) where the transmitter has one common message to be transmitted to two users and one secret message intended to only one of them. In all cases, we show that by appropriately designing the coding and the transmission schemes, a secure communication can still be achieved even with an imperfect knowledge of the CSIT.
Physical layer security is an emerging technique to improve the wireless communication security, which is widely regarded as a complement to cryptographic technologies. To design physical layer security techniques under practical scenarios, the uncertainty and imperfections in the channel knowledge need to be taken into consideration. This paper provides a survey of recent research and development in physical layer security considering the imperfect channel state information (CSI) at communication nodes. We first present an overview of the main information-theoretic measures of the secrecy performance with imperfect CSI. Then, we describe several signal processing enhancements in secure transmission designs, such as secure on-off transmission, beamforming with artificial noise, and secure communication assisted by relay nodes or in cognitive radio systems. The recent studies of physical layer security in large-scale decentralized wireless networks are also summarized. Finally, the open problems for the on-going and future research are discussed.
The concept of physical layer security builds on the pivotal idea of turning the channel's imperfections, such as noise and fading, into a source of security. This is established through appropriately designed coding techniques and signal processing strategies. In this vein, it has been shown that fading channels can enhance the transmission of confidential information and that a secure communication can be achieved even when the channel to the eavesdropper is better than the main channel. However, to fully benefit from what fading has to offer, the knowledge of the channel state information at the transmitter (CSIT) is of primordial importance. In practical wireless communication systems, CSIT is usually obtained, prior to data transmission, through CSI feedback sent by the receivers. The channel links over which this feedback information is sent can be either noisy, rate-limited, or delayed, leading to CSIT uncertainty. In this paper, we present a comprehensive review of recent and ongoing research works on physical layer security with CSIT uncertainty. We focus on both information theoretic and signal processing approaches to the topic when the uncertainty concerns the channel to the wiretapper or the channel to the legitimate receiver. Moreover, we present a classification of the research works based on the considered channel uncertainty. Mainly, we distinguish between the cases when the uncertainty comes from an estimation error of the CSIT, from a CSI feedback link with limited capacity, or from an outdated CSI.
Physical layer security is an emerging technique to improve the wireless communication security, which is widely regarded as a complement to cryptographic technologies. To design physical layer security techniques under practical scenarios, the uncertainty and imperfections in the channel knowledge need to be taken into consideration. This paper provides a survey of recent research and development in physical layer security considering the imperfect channel state information (CSI) at communication nodes. We first present an overview of the main information-theoretic measures of the secrecy performance with imperfect CSI. Then, we describe several signal processing enhancements in secure transmission designs, such as secure on-off transmission, beamforming with artificial noise, and secure communication assisted by relay nodes or in cognitive radio systems. The recent studies of physical layer security in large-scale decentralized wireless networks are also summarized. Finally, the open problems for the on-going and future research are discussed.
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.
Physical-layer security offers an alternative to cryptology, where instead of using the secrecy keys, randomness of the wireless channel is utilized to conceal information. In this chapter, we give an overview of different state-of-the-art multi-terminal information theoretic models to secure information with varying quality of channel state information at the transmitter. We first introduce the essential elements of information theoretic security, and later on discuss its application from a degrees of freedom viewpoint. In particular, we focus our attention on the models in which the topology of the network is known at the transmitter. Introduction Wireless communication has completely revolutionized the lives of common users. Modern communication systems provide high data rates, which allow users to perform different day-to-day tasks wirelessly. For example, users can access their bank account details and monitor their home security remotely. However, due to the broadcast nature of the medium, the information exchange between these communication nodes can be overheard by unintended users in the network. The leakage of information to unintended users may have serious consequences. In this chapter, we intend to answer this fundamental question of how to secure wireless communication. State of the Art and Preliminaries In conventional systems, cryptographic encryption is used to conceal information from adversaries. Figure 7.1 shows a simple example which sheds light on the problem of secret key sharing studied in cryptology. The source message at Alice is converted to ciphertext with the help of a secret key which is shared between Alice and the legitimate receiver, Bob. The ciphertext is then communicated over the wireless channel and is received by both Bob and Eve. Upon getting the ciphertext and having access to the secret key, Bob can easily recover Alice's message [1]. It is assumed that Eve, the eavesdropper, is of limited computational complexity or has limited resources. Thus, it is unable to generate all combinations of secret key, and consequently cannot recover Alice's message. In this framework, secrecy relies on the difficulty level of some hard mathematical problem which the eavesdropper is unable to solve due to limited computational resources.