Physical layer security (PLS) aims to protect end users who are equipped with low-complexity receivers for which implementing cryptographic algorithms for security purposes is not practical. This article presents a different approach to PLS and suggests natural and simple ways to achieve security in wireless networks. A practical assumption on the availability of channel state information (CSI) is considered for eavesdroppers (EVs) at the transmitter. Moreover, there is no restriction on EVs' placement, and as such EVs could be in better channel conditions when they are closer to the transmitter. The article describes how the interference channels can be exploited to simultaneously reduce the interference for the users' received signals and amplify the interference at the EV's received signal. It is also shown that when considering communication with energy- constrained nodes, the heterogeneous nature of the transmitted signals is an asset and can be exploited to confuse the eavesdropper. This is because information and energy signals are transmitted over different fractions of a time slot, and the EV can be confused since it does not know the time-fraction when information signal or energy signal is transmitted. Finally, the article also suggests how we can achieve secure information transmission under poor scattering environments, such as unmanned-aerial-vehicle-enabled communications.
Physical layer security (PLS) aims to protect end users who are equipped with low-complexity receivers for which implementing cryptographic algorithms for security purposes is not practical. This article presents a different approach to PLS and suggests natural and simple ways to achieve security in wireless networks. A practical assumption on the availability of channel state information (CSI) is considered for eavesdroppers (EVs) at the transmitter. Moreover, there is no restriction on EVs' placement, and as such EVs could be in better channel conditions when they are closer to the transmitter. The article describes how the interference channels can be exploited to simultaneously reduce the interference for the users' received signals and amplify the interference at the EV's received signal. It is also shown that when considering communication with energy- constrained nodes, the heterogeneous nature of the transmitted signals is an asset and can be exploited to confuse the eavesdropper. This is because information and energy signals are transmitted over different fractions of a time slot, and the EV can be confused since it does not know the time-fraction when information signal or energy signal is transmitted. Finally, the article also suggests how we can achieve secure information transmission under poor scattering environments, such as unmanned-aerial-vehicle-enabled communications.
The open nature of radio propagation enables ubiquitous wireless communication. This allows for seamless data transmission. However, unauthorized users may pose a threat to the security of the data being transmitted to authorized users. This gives rise to network vulnerabilities such as hacking, eavesdropping, and jamming of the transmitted information. Physical layer security (PLS) has been identified as one of the promising security approaches to safeguard the transmission from eavesdroppers in a wireless network. It is an alternative to the computationally demanding and complex cryptographic algorithms and techniques. PLS has continually received exponential research interest owing to the possibility of exploiting the characteristics of the wireless channel. One of the main characteristics includes the random nature of the transmission channel. The aforesaid nature makes it possible for confidential and authentic signal transmission between the sender and the receiver in the physical layer. We start by introducing the basic theories of PLS, including the wiretap channel, information-theoretic security, and a brief discussion of the cryptography security technique. Furthermore, an overview of multiple-input multiple-output (MIMO) communication is provided. The main focus of our review is based on the existing key-less PLS optimization techniques, their limitations, and challenges. The paper also looks into the promising key research areas in addressing these shortfalls. Lastly, a comprehensive overview of some of the recent PLS research in 5G and 6G technologies of wireless communication networks is provided.
Physical layer security (PLS) has emerged as a new concept and powerful alternative that can complement and may even replace encryption-based approaches, which entail many hurdles and practical problems for future wireless systems. The basic idea of PLS is to exploit the characteristics of the wireless channel and its impairments including noise, fading, interference, dispersion, diversity, etc. in order to ensure the ability of the intended user to successfully perform data decoding while preventing eavesdroppers from doing so. Thus, the main design goal of PLS is to increase the performance difference between the link of the legitimate receiver and that of the eavesdropper by using well-designed transmission schemes. In this survey, we propose a conceptual, generic, and expandable framework for classifying the existing PLS techniques against wireless passive eavesdropping. In this flexible framework, the security techniques that we comprehensively review in this treatise are divided into two primary approaches: signal-to-interference-plus-noise ratio-based approach and complexity-based approach. The first approach is classified into three major categories: first, secrecy channel codes-based schemes; second, security techniques based on channel adaptation; third, schemes based on injecting interfering artificial (noise/jamming) signals along with the transmitted information signals. The second approach (complexity-based), which is associated with the mechanisms of extracting secret sequences from the shared channel, is classified into two main categories based on which layer the secret sequence obtained by channel quantization is applied on. The techniques belonging to each one of these categories are divided and classified into three main signal domains: time, frequency and space. For each one of these domains, several examples are given and illustrated along with the review of the state-of-the-art security advances in each domain. Moreover, the advantages and disadvantages of each approach alongside the lessons learned from existing research works are stated and discussed. The recent applications of PLS techniques to different emerging communication systems such as visible light communication, body area network, power line communication, Internet of Things, smart grid, mm-Wave, cognitive radio, vehicular ad-hoc network, unmanned aerial vehicle, ultra-wideband, device-to-device, radio-frequency identification, index modulation, and 5G non-orthogonal multiple access based-systems, are also reviewed and discussed. The paper is concluded with recommendations and future research directions for designing robust, efficient and strong security methods for current and future wireless systems.
Traditional cryptographic encryption techniques at higher layers require a certain form of information sharing between the transmitter and the legitimate user to achieve security. Besides, it also assumes that the eavesdropper has an insufficient computational capability to decrypt the ciphertext without the shared information. However, traditional cryptographic encryption techniques may be insufficient or even not suit- able in wireless communication systems. Physical layer security (PLS) can enhance the security of wireless communications by leveraging the physical nature of wireless transmission. Thus, in this thesis, we study the PLS performance in emerging wireless transmission systems. The thesis consists of two main parts. We first consider the PLS design and analysis for ground-based networks em- ploying random unitary beamforming (RUB) scheme at the transmitter. With RUB technique, the transmitter serves multiple users with pre-designed beamforming vectors, selected using limited channel state information (CSI). We study multiple-input single-output single-eavesdropper (MISOSE) transmission system, multi-user multiple-input multiple-output single-eavesdropper (MU-MIMOSE) transmission system, and massive multiple-input multiple-output multiple-eavesdropper (massive MI- MOME) transmission system. The closed-form expressions of ergodic secrecy rate and the secrecy outage probability (SOP) for these transmission scenarios are derived. Besides, the effect of artificial noise (AN) on secrecy performance of RUB-based transmission is also investigated. Numerical results are presented to illustrate the trade-off between performance and complexity of the resulting PLS design. We then investigate the PLS design and analysis for unmanned aerial vehicle (UAV)-based networks. We first study the secrecy performance of UAV-assisted relaying transmission systems in the presence of a single ground eavesdropper. We derive the closed-form expressions of ergodic secrecy rate and intercept probability. When multiple aerial and ground eavesdroppers are located in the UAV-assisted relaying transmission system, directional beamforming technique is applied to enhance the secrecy performance. Assuming the most general κ-μ shadowed fading channel, the SOP performance is obtained in the closed-form expression. Exploiting the derived expressions, we investigate the impact of different parameters on secrecy performance. Besides, we utilize a deep learning approach in UAV-based network analysis. Numerical results show that our proposed deep learning approach can predict secrecy performance with high accuracy and short running time.
Under both long (infinite) and short (finite) blocklength transmissions, this paper considers physical layer security for a wireless interference network of multiple transmitter-user pairs, which is overheard by multiple eavesdroppers (EVs). The EVs are assumed to have better channel conditions than the legitimate users (UEs), making the conventional transmission unsecured. The paper develops a novel time-fraction based transmission, under which the information is transmitted to the UEs within a fraction of the time slot and artificial noise (AN) is transmitted within the remaining fraction to counter the strong EVs' channels. Based on channel distribution information of UEs and EVs, the joint design of transmit beamforming, time fractions and AN power allocation to maximize the worst users' secrecy rate is formulated in terms of nonconvex problems. Path-following algorithms of low complexity and rapid convergence are proposed for their solution. Simulations are provided to demonstrate the viability of the proposed methodology.
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.
This article concerns the physical layer security (PLS) problem in distributed antenna systems (DASs), where eavesdroppers are equipped with multiple antennas. If both legitimate transmitter (Alice) and receiver (Bob) broadcast wireless signals via a DAS, the channel state information (CSI) between Alice and Bob may be exposed to an eavesdropper (Eve) due to the broadcast nature of wireless signals. Based on the exposed CSI, Eve can use multiple antennas to improve the eavesdropping capability on the confidential message transmitted from Alice. The prior PLS approaches to defend against the eavesdropping attack have two limitations. The first limitation is to assume that the CSI of Bob is available to Alice. The second limitation is to assume that there is no error in the feedback CSIs. In this article, we propose a new PLS scheme of a DAS by using one-bit feedback information. The basic idea of our approach is to generate a null transmission vector from the distributed transmitters of Alice to Bob while using different artificial noise components to protect the exposure problem of CSI between Alice and Bob. The proposed scheme has the following advantages: improved secrecy rate, rapid convergence, and good performance under a time-varying channel. We implemented our scheme and conducted extensive performance comparisons through simulations. Our experimental results show that the proposed scheme improves the secrecy rate with 1.20 b/s/Hz as compared to prior approaches. At last, we present some interesting future works for the PLS problem in a DAS.