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

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

Modeling the Impact of New Information on Consumer Preferences for Specialty Meat Products

As the demand for organic and natural food grows in the U.S., studies show that consumers would and do pay more for these foods than their traditional counterparts. However, the question remains as to whether consumers really understand the differences between organic and natural products versus common products. The USDA provides an official definition of organic, but there is no official definition or certification for natural products. The general lack of knowledge among consumers concerning organic and natural products can be misleading and hence, there is a need for a better understanding of how consumer pre-existing knowledge and new information regarding organic and natural products influences consumer purchasing behavior. In this study, we research the effect of providing consumers with information regarding organic and natural production processes in four separate stages on their willingness to pay (WTP) for various natural/organic meat products. Through the use of survey data collected in-person during the fall of 2007 Nevada, in which 597 surveys were completed, we examine the impact of consumer perceived knowledge of organic and natural grass-fed production processes on their WTP, whether or not new information/knowledge will modify their WTP, and the degree of modification across meat types and cuts. Meats examined vary from high-end to low-end cuts and across various meat types, such as pork and beef. The modeling will include a multinomial probit model to measure WTP and also consider the modeling issues that arise when updated preferences are included. The results of this study will be important for researchers looking to model updated consumer preferences. The purpose of our research is twofold. First, we wish to observe whether or not advertising and other promotional methods truly influence consumer demand and willingness to pay for these specialty meat products. These results will likely be important to the role of marketing and the way in which information is provided to consumers on organic and natural production methods and the potential positive effects of those methods. Additionally, the paper will show how consumers purchasing experiences and pre-existing knowledge might influence their reaction to the same information.Marketing,

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

Variations on Kaluza-Klein Cosmology

We investigate the cosmological consequences of having quantum fields living in a space with compactified dimensions. We will show that the equation of state is not modified by topological effects and so the dynamics of the universe remains as it is in the infinite volume limit. On the contrary the thermal history of the universe depends on terms that are associated with having non-trivial topology. In the conclusions we discuss some issues about the relationship between the $c=1$ non-critical string-inspired cosmology and the result obtained with matter given by a hot massless field in S^{1}\times \mbox{\bf R}.Comment: 22 pages, 7 figures in a uuencoded file (using uufiles), LaTeX, FTUAM-93/13 (LaTeX errors corrected

Recounting Dyons in N=4 String Theory

A recently discovered relation between 4D and 5D black holes is used to derive weighted BPS black hole degeneracies for 4D N=4 string theory from the well-known 5D degeneracies. They are found to be given by the Fourier coefficients of the unique weight 10 automorphic form of the modular group Sp(2,Z). This result agrees exactly with a conjecture made some years ago by Dijkgraaf, Verlinde and Verlinde.Comment: 5 page