Shihao Yan

Transmit Antenna Selection with Alamouti Coding and Power Allocation in MIMO Wiretap Channels

In this work, we propose a new transmit antenna selection (TAS) scheme which examines the trade-off between feedback overhead and secrecy performance in multiple-input multiple-output wiretap channels. Our new scheme is carried out in two steps. First, the transmitter selects the first two strongest antennas to maximize the instantaneous signal-to-noise ratio (SNR) of the transmitter-receiver channel. Second, Alamouti coding is employed at the selected antennas in order to perform secure data transmission. When equal power is applied to the selected antennas, we refer to our new scheme as TAS-Alamouti. To provide valuable insights into TAS-Alamouti, we derive new closed-form expressions for the secrecy performance metrics. In terms of these metrics, we show how in a Rayleigh fading channel that our TAS-Alamouti scheme outperforms the traditional single TAS scheme conditioned on the SNR of the transmitter-receiver channel being larger than a specific value. We show how in some antenna configurations no additional feedback, relative to single TAS, is required in order to realize such performance enhancements. Furthermore, we show how optimal power allocation (OPA) across the selected antennas at the transmitter leads to a new scheme, which we refer to as TAS-Alamouti-OPA, that outperforms single TAS unconditionally. Relative to TAS-Alamouti, TAS-Alamouti-OPA requires only one additional feedback bit.

Artificial Noise: Transmission Optimization in Multi-Input Single-Output Wiretap Channels

We analyze and optimize the secrecy performance of artificial noise (AN) in multi-input single-output wiretap channels with multiple antennas at the transmitter and a single antenna at the receiver and the eavesdropper. We consider two transmission schemes: 1) an on-off transmission scheme with a constant secrecy rate for all transmission periods, and 2) an adaptive transmission scheme with a varying secrecy rate during each transmission period. For the on-off transmission scheme, an easy-to-compute expression is derived for the hybrid outage probability, which allows us to evaluate the transmission outage probability and the secrecy outage probability. For the adaptive transmission scheme where transmission outage does not occur, we derive a closed-form expression for the secrecy outage probability. Using these expressions, we determine the optimal power allocation between the information signal and the AN signal and also determine the optimal secrecy rate such that the effective secrecy throughput is maximized for both transmission schemes. We show that the maximum effective secrecy throughput requires more power to be allocated to the AN signal when the quality of the transmitter-receiver channel or the transmitter-eavesdropper channel improves. We also show that both transmission schemes achieve a higher maximum effective secrecy throughput while incurring a lower secrecy outage probability than existing schemes.

Optimal Information-Theoretic Wireless Location Verification

We develop a new location verification system (LVS) focused on network-based intelligent transport systems (ITSs) and vehicular ad hoc networks (VANETs). The system that we develop is based on an information-theoretic framework in which the mutual information between the systems input and output data is maximized. Our system takes as inputs a users claimed location and base station (BS) received signal strength (RSS) measurements to form an optimal decision rule on the legitimacy of the claimed location. The scenario that we consider is where a noncolluding malicious user alters his transmit power in an attempt to fool the LVS. We develop a practical threat model for this attack scenario and investigate the performance of the LVS in terms of its input/output mutual information. We show how our LVS decision rule can be straightforwardly implemented with a performance that delivers near optimality under realistic threat conditions. The practical advantages that our new information-theoretic scheme delivers, relative to more traditional Bayesian verification frameworks, are discussed.

Optimization of Code Rates in SISOME Wiretap Channels

We propose a new framework for determining the wiretap code rates of single-input-single-output multiantenna eavesdropper wiretap channels when the capacity of the eavesdroppers channel is not available at the transmitter. In our framework, we introduce the effective secrecy throughput (EST) as a new performance metric that explicitly captures the two key features of wiretap channels, namely, reliability and secrecy. Notably, the EST measures the average rate of the confidential information transmitted from the transmitter to the intended receiver without being eavesdropped on. We provide easy-to-implement methods to determine the wiretap code rates for two transmission schemes: 1) adaptive transmission scheme in which the capacity of the main channel is available at the transmitter and 2) fixed-rate transmission scheme in which the capacity of the main channel is not available at the transmitter. Such determinations are further extended into an absolute-passive eavesdropping scenario where even the average signal-to-noise ratio of the eavesdroppers channel is not available at the transmitter. Notably, our solutions for the wiretap code rates do not require us to set reliability or secrecy constraints for the transmission within wiretap channels.

Location-Based Beamforming for Enhancing Secrecy in Rician Wiretap Channels

We propose a new optimal location-based beamforming (LBB) scheme for the wiretap channel, where both the main channel and the eavesdroppers channel are subject to Rician fading. In our LBB scheme, the two key inputs are the location of the legitimate receiver and the location of the potential eavesdropper. Notably, our scheme does not require any channel state information of the main channel or the eavesdroppers channel being available at the transmitter. This makes our scheme easy to deploy in a host of application settings in which the location inputs are known. Our beamforming solution assumes a multiple-antenna transmitter and a multiple-antenna eavesdropper, and its aim is to maximize the physical layer security of the channel. To obtain our solution, we first derive the secrecy outage probability of the LBB scheme in an easy-to-evaluate expression that is valid for arbitrary real values of the Rician K-factors of the main channel and the eavesdroppers channel. Using this expression, we then determine the location-based beamformer solution that minimizes the secrecy outage probability. To assess the usefulness of our new scheme, and to quantify the value of the location information to physical layer security, we compare our scheme to other schemes, some of which do not utilize any location information. Our new beamformer solution provides optimal physical layer security for a wide range of location-based applications.

Artificial-Noise-Aided Secure Transmission in Wiretap Channels With Transmitter-Side Correlation

This paper, for the first time, examines the impact of transmitter-side correlation on the artificial-noise (AN)-aided secure transmission, based on which a new power allocation strategy for AN is devised for physical layer security enhancement. Specifically, we design a correlation-based power allocation (CPA) for AN, of which the optimality in terms of achieving the minimum secrecy outage probability is analytically proved in the large system regime with the number of transmit antennas approaching infinity. In order to fully reveal the benefits of the CPA, we derive easy-to-evaluate expressions for the secrecy outage probability achieved by the CPA. Our study demonstrates that the CPA is nearly optimal and significantly outperforms the widely used uniform power allocation (UPA) even for a moderately small number of correlated transmit antennas. Furthermore, our numerical results reveal a fundamental difference between the CPA and UPA. That is when the number of correlated transmit antennas increases, the secrecy outage probability of the CPA always reduces while the secrecy outage probability of the UPA suffers from a saturation point.

On the target secrecy rate for SISOME wiretap channels

We propose a new framework for optimizing the target secrecy rate for SISOME wiretap channels when the instantaneous capacity of the eavesdroppers channel is not available at the transmitter. In our framework we introduce the effective secrecy throughput, a new optimization metric that implicitly captures the two key features of wiretap channels, namely, reliability and secrecy. We derive target secrecy rates which maximize the effective secrecy throughput for two different schemes, an on-off transmission scheme and an adaptive transmission scheme. Our analysis demonstrates that the adaptive transmission scheme outperforms the on-off transmission scheme and that the difference in the effective secrecy throughput between the two schemes increases with the SNR of the main channel. The work reported here solves the important problem of how to optimally set the target secrecy rate of wiretap codes for an important class of channels. Notably, our solution for the target secrecy rate does not require us to set a priori any reliability or secrecy constraint for the channel.

An information theoretic Location Verification System for wireless networks

As location-based applications become ubiquitous in emerging wireless networks, a reliable Location Verification System (LVS) will be of growing importance. In this paper we propose, for the first time, a rigorous information-theoretic framework for an LVS. The theoretical framework we develop illustrates how the threshold used in the detection of a spoofed location can be optimized in terms of the mutual information between the input and output data of the LVS. In order to verify the legitimacy of our analytical framework we have carried out detailed numerical simulations. Our simulations mimic the practical scenario where a system deployed using our framework must make a binary Yes/No “malicious decision” to each snapshot of the signal strength values obtained by base stations. The comparison between simulation and analysis shows excellent agreement. Our optimized LVS framework provides a defence against location spoofing attacks in emerging wireless networks such as those envisioned for Intelligent Transport Systems, where verification of location information is of paramount importance.

On Covert Communication With Noise Uncertainty

Prior studies on covert communication with noise uncertainty adopted a worst-case approach from the warden’s perspective. That is, the worst-case detection performance of the warden is used to assess covertness, which is overly optimistic. Instead of simply considering the worst limit, we take the distribution of noise uncertainty into account to evaluate the overall covertness in a statistical sense. Specifically, we define new metrics for measuring the covertness, which are then adopted to analyze the maximum achievable rate for a given covertness requirement under both bounded and unbounded noise uncertainty models.

Antenna switching for security enhancement in full-duplex wiretap channels

We propose an antenna switching scheme in the full-duplex wiretap channel where the legitimate receiver, equipped with two antennas, operates in a full-duplex mode. We focus on a practical eavesdropping scenario where the instantaneous channel state information of the eavesdroppers channel is not available at the transmitter and the receiver. In our proposed scheme, the receiver selects the antenna that maximizes the main channel gain as the receive antenna and uses the remaining antenna to transmit jamming signals. We derive an exact expression for the secrecy outage probability to evaluate the secrecy performance of our new scheme. This expression allows us to quantify the secrecy performance gain of our proposed scheme relative to a standard antenna predetermination scheme where the receive and transmit antennas at the receiver are predetermined. We demonstrate that our scheme achieves a lower secrecy outage probability than the antenna predetermination scheme. We also show that our scheme achieves the full secrecy diversity order whereas the antenna predetermination scheme does not.