Enhancing Secrecy with Multi-Antenna Transmission in Wireless Ad Hoc Networks

We study physical-layer security in wireless ad hoc networks and investigate two types of multi-antenna transmission schemes for providing secrecy enhancements. To establish secure transmission against malicious eavesdroppers, we consider the generation of artificial noise with either sectoring or beamforming. For both approaches, we provide a statistical characterization and tradeoff analysis of the outage performance of the legitimate communication and the eavesdropping links. We then investigate the networkwide secrecy throughput performance of both schemes in terms of the secrecy transmission capacity, and study the optimal power allocation between the information signal and the artificial noise. Our analysis indicates that, under transmit power optimization, the beamforming scheme outperforms the sectoring scheme, except for the case where the number of transmit antennas are sufficiently large. Our study also reveals some interesting differences between the optimal power allocation for the sectoring and beamforming schemes.Comment: to appear in IEEE Transactions on Information Forensics and Securit

Source, Evolution, and Properties of Non-Parker-spiral IMF and Its Role on Geomagnetic Activity.

The most important driver of geomagnetic activity has been shown to be out of ecliptic or non-Parker-spiral interplanetary magnetic field (IMF), especially large-amplitude and long-duration (LALD) southward IMF. However, neither current solar/heliospheric models provide accurate forecasts of IMF Bz component, nor they provide them at all. This thesis combines in situ observations of magnetic field, plasma, and ion composition with remote sensing measurements of solar features as well as predictive modeling of the solar wind and IMF to understand the source, evolution and properties of IMF Bz. We find that the integrated duration and number of Bs-events follow the sunspot number when Bz 3 hrs) do not always induce large storms. We also point out that MC, ejecta, and SIR drive storms in different ways, and that while Alfvenic Bs-events are relatively weak in triggering geomagnetic storms, they are possible drivers for large-scale ULF wave oscillations in the Earth's magnetosphere. We also show that the probabilistic forecasting technique provides a tool for predicting the occurrence rate of geomagnetic activity based on a combination of solar wind quantities, obtainable from either measurements or models. We finally propose that the evolution of the active region adjacent to the LLCH, and the geometric parameters of the LLCH are important to determine the intensity of the IMF Bs intervals observed at 1 AU, which could be used to improve the current space weather forecasting.PhDAtmospheric, Oceanic and Space SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111596/1/zhangxy_1.pd

On the Design of Artificial-Noise-Aided Secure Multi-Antenna Transmission in Slow Fading Channels

In this paper, we investigate the design of artificial-noise-aided secure multi-antenna transmission in slow fading channels. The primary design concerns include the transmit power allocation and the rate parameters of the wiretap code. We consider two scenarios with different complexity levels: i) the design parameters are chosen to be fixed for all transmissions, ii) they are adaptively adjusted based on the instantaneous channel feedback from the intended receiver. In both scenarios, we provide explicit design solutions for achieving the maximal throughput subject to a secrecy constraint, given by a maximum allowable secrecy outage probability. We then derive accurate approximations for the maximal throughput in both scenarios in the high signal-to-noise ratio region, and give new insights into the additional power cost for achieving a higher security level, whilst maintaining a specified target throughput. In the end, the throughput gain of adaptive transmission over non-adaptive transmission is also quantified and analyzed.Comment: to appear in IEEE Transactions on Vehicular Technolog

A Semiblind Two-Way Training Method for Discriminatory Channel Estimation in MIMO Systems

Discriminatory channel estimation (DCE) is a recently developed strategy to enlarge the performance difference between a legitimate receiver (LR) and an unauthorized receiver (UR) in a multiple-input multiple-output (MIMO) wireless system. Specifically, it makes use of properly designed training signals to degrade channel estimation at the UR which in turn limits the UR's eavesdropping capability during data transmission. In this paper, we propose a new two-way training scheme for DCE through exploiting a whitening-rotation (WR) based semiblind method. To characterize the performance of DCE, a closed-form expression of the normalized mean squared error (NMSE) of the channel estimation is derived for both the LR and the UR. Furthermore, the developed analytical results on NMSE are utilized to perform optimal power allocation between the training signal and artificial noise (AN). The advantages of our proposed DCE scheme are two folds: 1) compared to the existing DCE scheme based on the linear minimum mean square error (LMMSE) channel estimator, the proposed scheme adopts a semiblind approach and achieves better DCE performance; 2) the proposed scheme is robust against active eavesdropping with the pilot contamination attack, whereas the existing scheme fails under such an attack.Comment: accepted for publication in IEEE Transactions on Communication

The H

This paper discusses the state feedback H∞ control problem for a class of bilinear stochastic systems driven by both Brownian motion and Poisson jumps. By completing square method, we obtain the H∞ control by solutions of the corresponding Hamilton-Jacobi equations (HJE). By the tensor power series method, we also shift such HJEs into a kind of Riccati equations, and the H∞ control is represented with the form of tensor power series

Artificial-Noise-Aided Secure Multi-Antenna Transmission with Limited Feedback

We present an optimized secure multi-antenna transmission approach based on artificial-noise-aided beamforming, with limited feedback from a desired single-antenna receiver. To deal with beamformer quantization errors as well as unknown eavesdropper channel characteristics, our approach is aimed at maximizing throughput under dual performance constraints - a connection outage constraint on the desired communication channel and a secrecy outage constraint to guard against eavesdropping. We propose an adaptive transmission strategy that judiciously selects the wiretap coding parameters, as well as the power allocation between the artificial noise and the information signal. This optimized solution reveals several important differences with respect to solutions designed previously under the assumption of perfect feedback. We also investigate the problem of how to most efficiently utilize the feedback bits. The simulation results indicate that a good design strategy is to use approximately 20% of these bits to quantize the channel gain information, with the remainder to quantize the channel direction, and this allocation is largely insensitive to the secrecy outage constraint imposed. In addition, we find that 8 feedback bits per transmit antenna is sufficient to achieve approximately 90% of the throughput attainable with perfect feedback.Comment: to appear in IEEE Transactions on Wireless Communication

Enhancing secrecy with multi-antenna transmission in wireless ad hoc networks

We study physical-layer security in wireless ad hoc networks and investigate two types of multi-antenna transmission schemes for providing secrecy enhancements. To establish secure transmission against malicious eavesdroppers, we consider the generation of artificial noise with either sectoring or beamforming. For both approaches, we provide a statistical characterization and tradeoff analysis of the outage performance of the legitimate communication and the eavesdropping links. We then investigate the network-wide secrecy throughput performance of both schemes in terms of the secrecy transmission capacity, and study the optimal power allocation between the information signal and the artificial noise. Our analysis indicates that, under transmit power optimization, the beamforming scheme outperforms the sectoring scheme, except for the case where the number of transmit antennas are sufficiently large. Our study also reveals some interesting differences between the optimal power allocation for the sectoring and beamforming schemes.The work of X. Zhang andM. R.McKay was supported by the Hong Kong Research Grants Council under Grant 616312. The work of X. Zhou was supported by the Australian Research Council's Discovery Projects funding scheme under Project DP11010254

Enhancing secrecy with sectorized transmission in decentralized wireless networks

In this paper, we combine sectorized transmission with artificial noise to establish secrecy in decentralized wireless networks. The locations of the legitimate nodes and the eavesdroppers are both modeled by homogeneous Poisson point processes. Using sectorized antennas, each legitimate transmitter sends an information signal in the sector which contains its intended receiver, while simultaneously emitting artificial noise in other sectors, in order to provide secrecy against the eavesdroppers. We first separately characterize the reliability performance of the legitimate link and the secrecy performance against malicious eavesdropping. Then, we derive the secrecy transmission capacity to measure the networkwide secrecy throughput. To facilitate the practical system design, we provide a sufficient condition, in terms of the system parameters and constraints, under which a positive secrecy transmission capacity is achievable. The optimal transmit power allocation between the information signal and the artificial noise for achieving the maximal secrecy transmission capacity is also investigated. Our analysis indicates that sectorized transmission provides significant secrecy enhancements in decentralized wireless networks.The work of X. Zhang and M. R. McKay was supported by the Hong Kong Research Grants Council (Grant No. 616312). The work of X. Zhou was supported by the Australian Research Council's Discovery Projects funding scheme (Project No. DP110102548)