Hong Y.-W.P., Lan P.-C., Kuo C.-C.J. Signal Processing Approaches to Secure Physical Layer Communications in Multi-Antenna Wireless Systems

Springer, 2014. — 142 p.Physical layer secrecy has received much attention in recent years, especially in wireless communications, due to the rapidly increasing data traffic and high demand for ubiquitous connectivity. Different from conventional cryptographic approaches used to address wireless security issues, physical layer secrecy utilizes channel coding and signal processing techniques to communicate secret messages between the source and the destination while maintaining confidentiality against the eavesdropper. These studies originate from the information theory literature, where the focus is often to determine the existence of channel codes that can achieve this task or to derive the fundamental limit on the maximum code rate that can be applied reliably under the secrecy constraint (i.e., the secrecy capacity). In particular, information-theoretic results have shown that the secrecy capacity increases with the difference between the reception quality at the destination and that at the eavesdropper. Motivated by this result, signal processing approaches have been developed in both the data transmission and channel estimation phases to maximize the signal quality difference between the destination and the eavesdropper. In general, both coding and signal processing aspects of the problem must be taken into consideration in order to achieve the secrecy capacity. However, when the optimal joint design is unknown, signal processing techniques can also be used to help increase the achievable secrecy rate or reduce the complexity of the channel coding operations. These approaches are especially interesting in multiantenna wireless systems, where the spatial degrees of freedom can be exploited to further enhance secrecy.
This book provides an overview of signal processing approaches that can be used to enhance physical layer secrecy in multi-antenna wireless systems. Specifically, in the data transmission phase, we review secrecy beamforming and precoding techniques that can be used to not only strengthen the signal at the destination, but also reduce the information leakage to the eavesdropper. We also consider the use of artificial noise along with the transmission of the information signal to further degrade the reception quality at the eavesdropper. Moreover, we further extend the use of these techniques to distributed antenna or relay systems where the multiple antennas may not be located at a single terminal. The additional spatial degrees of freedom provide more design flexibility and performance gains, but may also increase the security threats due to additional transmission required for coordination among the distributed terminals and also due to the trustworthiness of system members. In terms of channel estimation, we review the so-called discriminatory channel estimation scheme which utilizes the design of artificial noise aided training signals to increase the difference between the effective signal quality at the destination and that at the eavesdropper. In this case, the desired signal quality discrepancy is enhanced even before the transmission of the confidential message and need only be done once every coherence interval (instead of every symbol period).Background on Information-Theoretic Physical Layer Secrecy.
Secrecy Precoding and Beamforming in Multi-Antenna Wireless Systems.
Distributed Secrecy Beamforming and Precoding in Multi-Antenna Wireless Relay Systems.
Secrecy-Enhancing Channel Estimation in Multi-Antenna Wireless Systems.
Enhancing Physical-Layer Secrecy in Modern Wireless Communication Systems.