Yaoqing Lamar Yang

Impact of Interference on Secrecy Capacity in a Cognitive Radio Network

In this paper, we investigate secrecy capacity of a cognitive radio network based on stochastic geometry distributions. We consider the Poisson process of both the secondary users and the eavesdroppers, and analyze how the stochastic interference from the secondary users can influence the secrecy capacity of the primary users. First, we describe a network model with primary users, secondary users and eavesdroppers in a cognitive radio communication network environment, and obtain the expression of secrecy capacity in an additive white Gaussian noise channel. Then, we study the outage probability of secrecy capacity of a primary node from a secure communication graph point of view. Furthermore, we present numerical results of the cumulative distribution function (c.d.f.) of the secrecy capacity between a primary transmitter and a primary receiver. Our analysis brings the insights on secure communications in terms of spatially Poisson distributions of primary users, secondary users and eavesdroppers.

Impact of channel estimation errors on effectiveness of Eigenvector-based jamming for physical layer security in wireless networks

In this paper, we present our study of an Eigenvector-based artificial noise-based jamming technique developed to provide increased wireless physical layer security in transmit-receive diversity systems and analyze the impact of channel estimation errors on system performance. Our simulation results showed that with knowledge of perfect channel state information, the technique provided secrecy capacity of approximately 7 bits/s/Hz for a normalized transmit power of 25 dB for a variety of transmit, receive, and eavesdropper configurations. We also describe a novel method to simulate generalized channel state information estimation errors. While other publications neglect the impact of these estimation errors, our simulations show that the secrecy capacity decreased rapidly as the channel estimation errors increased. For instance, at 25% error the secrecy capacity of the jamming technique was only slightly better than the non-jamming case. Our paper also outlines upcoming research efforts to further explore error sensitivity and channel state temporal stability through experimentation.

Energy harvesting for wireless sensor networks: applications and challenges in smart grid

The electric power grid is experiencing a transformation to the smart grid. One crucial step for this evolution is to establish a nationwide digital communication system which enables pervasive control and real-time monitoring of the power grid. Considering the large geographically spread characteristics of the power grid, a wireless sensor network is an ideal candidate for distributed monitoring and control. However, battery-powered sensors have a limited lifetime and the maintenance is expensive due to battery replacement. Thus, energy harvesting from different sources offers an alternative solution. This paper provides a detailed survey of recent energy harvesting technologies in wireless sensor networks. Various energy sources and their harvesting methods are reviewed. This paper also addresses the applications and challenges caused by energy harvesting in the smart grid environment. Our study shows that electromagnetic field-based harvesting approaches and other ambient energy are potential solutions to powering the sensors in smart grid.

Steganography attack based on Discrete Spring Transform and image geometrization

In order to prevent harmful secret information sharing by steganography, a new active-warden countermeasure approach against steganography is proposed in this paper. Differently from the other countermeasure approaches presented in current literature which need to have some knowledge of the steganographic algorithms to be attacked, our proposed method is a generic method which is independent of any particular steganography methods being utilized. In other words, our approach blindly attacks the steganography without any prior knowledge of the used algorithms or their existence. In general, the hidden information is embedded in a carrier by adjusting the coefficients of the audio or image. In our method, by exploiting the large margin between the numerical value and visual perception of the images, large amounts of visually non-detectable distortions are incurred in the image. As a result, the hidden message is destroyed by this method while the perceptual quality of the image is maintained. Inspired by the print-scan process in which most of the steganographic methods cannot survive, a transform called Discrete Spring Transform (DST) is proposed in this paper as the foundation of our attack algorithm. An image geometrization method is also developed to reconstruct the image in this paper. The simulation results have demonstrated that the PSNR of the attacked image is above 30dB with a high perceptive quality while the BER of the hidden steganographic message in the attacked image is above 0.5.

A game theoretic approach for energy-efficient communications in multi-hop cognitive radio networks

In multi-hop cognitive radio networks, it is a challenge to improve the energy efficiency of the radio nodes. To address this challenge, in this paper, we propose a two-level Stackelberg game model, where the primary users and the secondary users act as the leaders and the followers, respectively. Based on the game model, our proposed scheme not only considers the power allocation problem for secondary users but also takes into account the price of spectrum. First, we give the cognitive radio network model, and show how to set up the game theoretic model in multi-hop cognitive radio networks. We then analyze this problem and show the existence and uniqueness of the Nash equilibrium point for the game. We also study the impact of the spectrum price of the primary users in the cognitive radio network and study how to select the best price for the primary users to maximize their own profit. Finally, we implement simulations to show the performance of our schemes. Our work gives an insight on how to improve the energy efficiency and allocate spectrum resources in multi-hop cognitive radio networks. Copyright

Distributed beamforming with imperfect phase synchronization for cognitive radio networks

In this paper, we present the analysis and simulation evaluation of a cognitive radio network employing a distributed beamforming technique with imperfect phase synchronization in the presence of a primary receiver. Our system model consists of a group of cognitive transmitters, each with an ideal isotropic antenna and equal transmit power, communicating with a secondary receiver in the far-field. The objective of the network of cognitive transmitters is to optimize its beampattern in the direction of the secondary receiver while minimizing the beampattern in the direction of the primary receiver to a certain threshold. The phases of the transmitted signals determine the beampattern, and we demonstrate that an optimization problem can be formulated to determine the phases of the transmitters that satisfy the constraints. We then evaluate the beampattern under imperfect phase synchronization and present how the phase error can impact the performance of beamforming and cause protection to the primary receiver to suffer. The results bring some interesting insights to distributed beamforming with imperfect phase synchronization for cognitive radio networks.

Delay Spread Characteristics of Wideband MIMO Channels Based on Outdoor Non-Line-of-Sight Measurements

This paper presents the delay spread characteristics based on the measurements of the wideband multiple-input multiple-output radio channels in outdoor environments. Measurement data were collected by a channel testbed which consists of four transmitters and eight receivers, and operates at a carrier frequency of 1.8 GHz with a bandwidth of 2.5 MHz. The four transmitting antennas and eight receiving antennas can work simultaneously. The experiments were originally conducted within the J. J. Pickle Research Campus, University of Texas at Austin. Based on the measurement data in the non-line-of-sight environments, the channel features such as multipath intensity profiles, root-mean-square delay spreads and their distributions were examined. It was found that the empirical probability density function of the rms delay spread in the non-line-of-sight MIMO channels roughly follows Gaussian distribution.

Xing-zone bridge construction for multi-hop cognitive radio networks with channel bonding

Cognitive radio is an efficient technique to relieve the tense of wireless spectrum scarcity by allowing unlicensed secondary users (SUs) to access the licensed band opportunistically without causing interference to primary users (PUs). Although Federal Communications Commission (FCC) recently ruled that the data of PU activity schedule is accessible to SUs 24 hours ahead, which relieves SUs from heavy sensing or interruption by sudden PU activity, however, multi-hop wireless cognitive radio networks (MWCRN) suffers a unique problem caused by the fact that the spectrum resources are not unified in different areas affected by different PUs. In other words, an SU origin-destination (OD) pair transmission would meet the bottleneck in bandwidth when crossing areas with different available spectrum resources. To solve this problem, we formulate an optimization problem to maximize the number of connection bridges to cross different areas. Moreover, we introduce channel bonding technique into the MWCRN for network performance improvement. We also propose a distributed algorithm for practical application. Simulation results verifies the better performance of our proposed scheme.

Securing wireless communications in transmit-beamforming systems by precoding jamming noise signals

Information transmission in wireless communication systems is traditionally protected by cryptographic techniques at the higher layers. Recently, a method of physical layer security has attracted much attention because it can potentially provide lower probability of interception of the signals at the eavesdroppers and hence augment the link security in addition to the conventional encryptions. In this paper, we propose a novel approach to securing transmit-beamforming systems by using uniquely designed jamming noise signal, which can significantly degrade the signal quality at the eavesdropper but not at the intended receiver. The jamming noise signal is generated from the null space of the channel matrix. An eigenvector-based implementation of this theoretical method is also provided. Unlike previous physical layer security methods, the proposed approach can provide secure communications over systems with arbitrary antenna configurations. Our proposed method offers more degrees of freedom to generate the jamming noise signal, resulting in the eavesdropper being unable to decode the information signals. Moreover, the eavesdropper cannot influence the system secrecy capacity by employing more antennas or by moving close to the transmitter. Simulation results show that the secrecy capacity increases significantly, by about 7 bits/s/Hz for a 4 × 4 antenna configuration, under typical transmit power constraints. Copyright