Physical layer security (PHY-security) takes the advantages of channel randomness nature of transmission media to achieve communication confidentiality and authentication. Wiretap coding and signal processing technologies are expected to play vital roles in this new security mechanism. PHY-security has attracted a lot of attention due to its unique features and the fact that our daily life relies heavily on wireless communications for sensitive and private information transmissions. Compared to conventional cryptography that works to ensure all involved entities to load proper and authenticated cryptographic information, PHY-security technologies perform security functions without considering about how those security protocols are executed. In other words, it does not require to implement any extra security schemes or algorithms on other layers above the physical layer. This survey introduces the fundamental theories of PHY-security, covering confidentiality and authentication, and provides an overview on the state-of-the-art works on PHY-security technologies that can provide secure communications in wireless systems, along with the discussions on challenges and their proposed solutions. Furthermore, at the end of this paper, the open issues are identified as our future research directions.

Physical Layer Security for Next Generation Wireless Networks: Theories, Technologies, and Challenges

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.

Classifications and Applications of Physical Layer Security Techniques for Confidentiality: A Comprehensive Survey

As a complement to high-layer encryption techniques, physical layer security has been widely recognized as a promising way to enhance wireless security by exploiting the characteristics of wireless channels, including fading, noise, and interference. In order to enhance the received signal power at legitimate receivers and impair the received signal quality at eavesdroppers simultaneously, multiple-antenna techniques have been proposed for physical layer security to improve secrecy performance via exploiting spatial degrees of freedom. This paper provides a comprehensive survey on various multiple-antenna techniques in physical layer security, with an emphasis on transmit beamforming designs for multiple-antenna nodes. Specifically, we provide a detailed investigation on multiple-antenna techniques for guaranteeing secure communications in point-to-point systems, dual-hop relaying systems, multiuser systems, and heterogeneous networks. Finally, future research directions and challenges are identified.

A Survey on Multiple-Antenna Techniques for Physical Layer Security

This tutorial paper addresses the physical layer security concerns and resiliency of Orthogonal Frequency Division Multiplexing (OFDM) communications; the de facto air-interface of most modern wireless broadband standards including 3GPP Long Term Evolution (LTE) and WiMAX. The paper starts with a brief introduction to the OFDM waveform and then reviews the robustness of the existing OFDM waveform in the presence of noise, multipath fading, and interference. The paper then moves on to build comprehensive adversarial models against OFDM waveforms. Robustness of OFDM is first investigated under AWGN noise and noise-like jamming attack scenarios, then under uncorrelated yet colored interferences from modulated sources (both intentional and unintentional). Finally, the paper explores some of the more recent developments in the field of energy efficient correlated jamming attacks that can disrupt communication severely by exploiting the knowledge of the target waveform structure. Potential countermeasures against such jamming attacks are presented, in an attempt to make a robust and resilient OFDM waveform.

PHY-Layer Resiliency in OFDM Communications: A Tutorial

Since the 1G of mobile technology, mobile wireless communication systems have continued to evolve, bringing into the network architecture new interfaces and protocols, as well as unified services, high data capacity of data transmission, and packet-based transmission (4G). This evolution has also introduced new vulnerabilities and threats, which can be used to launch attacks on different network components, such as the access network and the core network. These drawbacks stand as a major concern for the security and the performance of mobile networks, since various types of attacks can take down the whole network and cause a denial of service, or perform malicious activities. In this survey, we review the main security issues in the access and core network (vulnerabilities and threats) and provide a classification and categorization of attacks in mobile network. In addition, we analyze major attacks on 4G mobile networks and corresponding countermeasures and current mitigation solutions, discuss limits of current solutions, and highlight open research areas.

Survey on Threats and Attacks on Mobile Networks

Orthogonal Frequency Division Multiplexing (OFDM) is used in many modern communications systems Timing and frequency synchronization in an OFDM system are critical to performance and must be carried out early and often Current synchronization methods, such as those developed by Schmidl and Cox [1], were not designed to be robust to adversarial signals A series of attacks against the preamble synchronization stage have been developed and demonstrated to debilitate OFDM receivers Multiple attacks against the symbol timing estimation stage are discussed, and some possible improvements to OFDM synchronization algorithms are suggested

Jamming attacks against OFDM timing synchronization and signal acquisition

Orthogonal Frequency Division Multiplexing (OFDM) is used in many modern communications systems. Timing and frequency synchronization in an OFDM system are critical to performance and must be carried out early and often. Current synchronization methods, such as those developed by Schmidl and Cox [1], were not designed to be robust to adversarial signals. A series of attacks against the preamble synchronization stage have been developed and demonstrated to debilitate OFDM receivers. Multiple attacks against the frequency offset error estimation stage are discussed, and some possible improvements to OFDM synchronization algorithms are suggested.

Phase warping and differential scrambling attacks against OFDM frequency synchronization

Orthogonal Frequency Division Multiplexing (OFDM) has become an integral physical layer feature of 4G systems, and will continue to be utilized in future communications standards. In systems that utilize OFDM, synchronization between the transmitter and the receiver is paramount. However, many current acquisition algorithms and implementations are susceptible to corruption by adversarial communications systems. This paper outlines two improvements to OFDM timing and frequency offset estimation; sync-amble randomization and Cross Ambiguity Function (CAF) acquisition. Both analysis and simulation results are provided which suggest that both of these strategies offer improvements in physical layer security to OFDM synchronization in the presence of attacking communication systems, with minimal impact on overall performance.

Protecting physical layer synchronization: mitigating attacks against OFDM acquisition

Orthogonal frequency-division multiplexing OFDM has become the manifest modulation choice for 4G standards. Timing acquisition and carrier frequency offset synchronization are prerequisite to OFDM demodulation and must be performed often. Most of the OFDM methods for synchronization were not designed with security in mind. In particular, we analyze the performance of a maximum likelihood synchronization estimator against highly correlated jamming attacks. We present a series of attacks against OFDM timing acquisition: preamble whitening, the false preamble attack, preamble warping, and preamble nulling.The performance of OFDM synchronization turns out to be very poor against these attacks, and a number of mitigation strategies and security improvements are discussed. Copyright © 2014 John Wiley & Sons, Ltd.

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Matthew J. La Pan

Papers

PHY-Layer Resiliency in OFDM Communications: A Tutorial

Jamming attacks against OFDM timing synchronization and signal acquisition

Phase warping and differential scrambling attacks against OFDM frequency synchronization

Protecting physical layer synchronization: mitigating attacks against OFDM acquisition

Physical layer orthogonal frequency-division multiplexing acquisition and timing synchronization security