This paper provides a comprehensive review of the domain of physical layer security in multiuser wireless networks. The essential premise of physical layer security is to enable the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers, without relying on higher-layer encryption. This can be achieved primarily in two ways: without the need for a secret key by intelligently designing transmit coding strategies, or by exploiting the wireless communication medium to develop secret keys over public channels. The survey begins with an overview of the foundations dating back to the pioneering work of Shannon and Wyner on information-theoretic security. We then describe the evolution of secure transmission strategies from point-to-point channels to multiple-antenna systems, followed by generalizations to multiuser broadcast, multiple-access, interference, and relay networks. Secret-key generation and establishment protocols based on physical layer mechanisms are subsequently covered. Approaches for secrecy based on channel coding design are then examined, along with a description of inter-disciplinary approaches based on game theory and stochastic geometry. The associated problem of physical layer message authentication is also briefly introduced. The survey concludes with observations on potential research directions in this area.

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Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey

This paper provides a comprehensive review of the domain of physical layer security in multiuser wireless networks. The essential premise of physical-layer security is to enable the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers without relying on higher-layer encryption. This can be achieved primarily in two ways: without the need for a secret key by intelligently designing transmit coding strategies, or by exploiting the wireless communication medium to develop secret keys over public channels. The survey begins with an overview of the foundations dating back to the pioneering work of Shannon and Wyner on information-theoretic security. We then describe the evolution of secure transmission strategies from point-to-point channels to multiple-antenna systems, followed by generalizations to multiuser broadcast, multiple-access, interference, and relay networks. Secret-key generation and establishment protocols based on physical layer mechanisms are subsequently covered. Approaches for secrecy based on channel coding design are then examined, along with a description of inter-disciplinary approaches based on game theory and stochastic geometry. The associated problem of physical-layer message authentication is also introduced briefly. The survey concludes with observations on potential research directions in this area.

/pdf/principles-of-physical-layer-security-in-multiuser-wireless-4usqynlhdb.pdf

We propose and analyze transmit antenna selection (TAS) to enhance physical layer security in a wiretap channel with NA antennas at the transmitter, NB antennas at the receiver, and NE antennas at the eavesdropper. We focus on the practical scenario where the transmitter does not have any channel state information (CSI) of the eavesdropper's channel. The transmitter selects a single antenna that maximizes the instantaneous signal-to-noise ratio (SNR) at the receiver. The receiver and the eavesdropper employ either maximal-ratio combining (MRC) or selection combining (SC) to combine the received signals. For the proposed protocols, we derive new closed-form expressions for the probability of non-zero secrecy capacity. We consider Nakagami-m fading with non-identical fading parameters of the main channel, mB, and of the eavesdropper's channel, mE. Next, we derive new closed-form expressions for the exact secrecy outage probability, based on which the e-outage secrecy capacity is characterized. Based on the exact expressions, we derive the asymptotic secrecy outage probability which accurately reveals the secrecy diversity order and the secrecy array gain. We confirm that the proposed protocols achieve identical secrecy diversity orders of NANBmB. An interesting conclusion is reached that this diversity order is independent of NE and mE. Furthermore, we prove that under the proposed protocols, the secrecy outage probability and the e-outage secrecy capacity improve with increasing NA.

Transmit Antenna Selection for Security Enhancement in MIMO Wiretap Channels

We analyze the physical layer (PHY) security of a communication scheme consisting of a multiple antenna transmitter with a single radio frequency (RF) chain using transmit antenna selection (TAS) and a single antenna receiver, in the presence of a sophisticated multiple antenna eavesdropper. We develop closed-form expressions for the analysis of the secrecy outage probability, and we show that the PHY security can be considerably enhanced when multiple antennas are available at the legitimate transmitter. Moreover, a single RF chain multiple antenna transmitter reduces cost, complexity, size and power consumption at the expense of a slight loss in performance with respect to a multiple RF chain transmitter.

Performance of Transmit Antenna Selection Physical Layer Security Schemes

We analyze the impact of antenna correlation on secrecy performance of multiple-input multiple-output wiretap channels where transmitter employs transmit antenna selection while receiver and eavesdropper perform maximal-ratio combining with arbitrary correlation. New closed-form expressions are derived for the exact and asymptotic (high signal-to-noise ratio in transmitter-receiver channel) secrecy outage probability.

/pdf/physical-layer-security-of-tas-mrc-with-antenna-correlation-46qart917k.pdf

Physical Layer Security of TAS/MRC With Antenna Correlation

In this paper, we present a method of utilizing channel diversity to increase secrecy capacity in wireless communication. With the presence of channel diversity, an intended receiver can achieve a relatively high secrecy capacity even at low SNRs. We present a theoretical analysis on the outage probability at a normalized target secrecy capacity in Rayleigh fading environment. Our numerical results strongly support our conclusion that maximal ratio combining of channel diversity can enhance the security of the wireless communication system in normal operating scenarios.

Maximal Ratio Diversity Combining Enhanced Security

Secure wireless communications is a challenging problem due to the shared nature of the wireless medium. Most existing security mechanisms focus on traditional cryptographic schemes. In recent years, features of the multi-path channel (such as randomness and reciprocity), have driven researchers to exploit its potential to enhance the security of wireless networks. As OFDM occupies wide bandwidth, it will experience a prolific source of multi-path components. In this paper, we comprehensively exploit the inherent physical parameters of the multi-path fading channel to achieve continuous two way authentication between wireless terminals. In our scheme, pilot information is randomly spread in a wideband channel, leading to low probability of detection (LPD). Unlike other channel-based approaches, the information of both amplitude and phase in the channel signature is fully utilized to enhance the security of the OFDM communication network. More specially, the receiver will detect the channel response continuously according to the randomly inserted pilots and identify the valid user based on the statistical channel signature information. Simulation results indicate the high efficiency of the proposed method.

EPSON: Enhanced Physical Security in OFDM Networks

The broadcast nature of the wireless medium poses a serious challenge to the security of wireless communications and networks. Traditional computational security strategies always fail to prevent the eavesdropper from overhearing the communications. Recently, the unique characteristics of wireless channel fingerprints, e.g. randomness and reciprocity, have been successfully used to enhance the security of the wireless network. We expand our previous work on exploring particular physical parameters of fingerprints, and focus on a new scheme in which we use the RAKE receiver to differentiate users under low transmission power. RAKE receiver may capture and estimate fingerprints through poor autocorrelation of the spreading coding. As the fingerprint is incomputable and unpredictable, and may only be detected by the pair of transmitter and receiver, it may be fully utilized to design an efficient authentication method. Simulation results strongly verify the efficiency of our proposed method, especially in the case of low SNR.

REAM: RAKE receiver enhanced authentication method

Automatic modulation recognition (AMR) of communication signals is a critical and challenging task in cognitive radio systems. In this work, classifications of four digital modulation types, including BPSK, QPSK, GMSK and 2FSK, are investigated. From the received radio signal, a set of cyclic spectrum features are first calculated, and a principal component analysis (PCA) is applied to extract the most discriminant feature vector for classification. A novel max-multiple layer perceptron (MaxMLP) neural network is introduced for classification of modulation feature vectors through supervised learning. In the experiments, real radio signals with different modulation types were generated from an Agilent vector signal generator, and sampled by an Agilent digital signal analyzer. The proposed AMR method is tested at various channel SNR levels. Experimental results indicate that the performance of this method is highly competitive, and the computational cost is relatively low.

Principal component analysis of cyclic spectrum features in automatic modulation recognition

In this paper, we introduce a learning based cognitive radio receiver to automatically demodulate several types of modulated signals without sophisticated digital signal pre-processing. Our embedded learning engine can automatically learn the signal features and then achieve signal demodulation through feature-based classification. The proposed demodulator consists of a neural network (NN) structure with one sub-NN for each possible demodulation bit pattern. To capture the temporal behaviors of different modulation types, the sampling features in two consecutive time slots are collected for each decision. The final classification result is jointly decided by ensemble learning. To validate our proposed method, three classical modulation signal (i.e. BPSK, QPSK and GMSK) are investigated with SNR varying from 0 dB to 9 dB. The simulation results indicate that the performance of our proposed method is highly competitive and the system provide much more flexibilities than the traditional demodulation method.

Fangming He

Papers

Maximal Ratio Diversity Combining Enhanced Security

EPSON: Enhanced Physical Security in OFDM Networks

REAM: RAKE receiver enhanced authentication method

Principal component analysis of cyclic spectrum features in automatic modulation recognition

A learning based cognitive radio receiver