Simon D. Byers

Testing for homogeneity of variance in time series: Long memory, wavelets, and the Nile River

[1] We consider the problem of testing for homogeneity of variance in a time series with long memorystructure.Wedemonstratethat atest whose nullhypothesis isdesigned tobewhite noisecan, in fact, be applied, on a scale by scale basis, to the discrete wavelet transform of long memory processes. In particular, we show that evaluating a normalized cumulative sum of squares test statistic using critical levels for the null hypothesis of white noise yields approximately the same null hypothesis rejection rates when applied to the discrete wavelet transform of samples from a fractionally differenced process. The point at which the test statistic, using a nondecimated version of the discrete wavelet transform, achieves its maximum value can be used to estimate the time of the unknown variance change. We apply our proposed test statistic on five time series derived from the historical record of Nile River yearly minimum water levels covering 622–1922 A.D., each series exhibiting various degrees of serial correlation including long memory. In the longest subseries, spanning 622–1284 A.D., the test confirms an inhomogeneity of variance at short time scales and identifies the change point around 720 A.D., which coincides closely with the construction of a new device around 715 A.D. for measuring the Nile River. The test also detects a change in variance for a record of only 36 years. INDEX TERMS: 1829 Hydrology: Groundwater hydrology; 1869 Hydrology: Stochastic processes; 3299 Mathematical Geophysics: General or miscellaneous;

802.11b access point mapping

Considering some of the practical issues encountered when finding and mapping wireless network access points.

Defending against an Internet-based attack on the physical world

We discuss the dangers that scalable Internet functionality may present to the real world, focusing upon an attack that is simple, yet can have great impact, which we believe may occur quite soon. We offer and critique various solutions to this class of attack and hope to provide a warning to the Internet community of what is currently possible. The attack is, to some degree, a consequence of the availability of private information on the Web, and the increase in the amount of personal information that users must reveal to obtain Web services.

Analysis of security vulnerabilities in the movie production and distribution process

Unauthorized copying of movies is a major concern for the motion picture industry. While unauthorized copies of movies have been distributed via portable physical media for some time, low-cost, high-bandwidth Internet connections and peer-to-peer file sharing networks provide highly efficient distribution media. Many movies are showing up on file sharing networks shortly after, and in some cases prior to, theatrical release. It has been argued that the availability of unauthorized copies directly affects theater attendance and DVD sales, and hence represents a major financial threat to the movie industry. Our research attempts to determine the source of unauthorized copies by studying the availability and characteristics of recent popular movies in file sharing networks. We developed a data set of 312 popular movies and located one or more samples of 183 of these movies on file sharing networks, for a total of 285 movie samples. 77% of these samples appear to have been leaked by industry insiders. Most of our samples appeared on file sharing networks prior to their official consumer DVD release date. Indeed, of the movies that had been released on DVD as of the time of our study, only 5% first appeared after their DVD release date on a web site that indexes file sharing networks, indicating that consumer DVD copying currently represents a relatively minor factor compared with insider leaks. We perform a brief analysis of the movie production and distribution process and identify potential security vulnerabilities that may lead to unauthorized copies becoming available to those who may wish to redistribute them. Finally, we offer recommendations for reducing security vulnerabilities in the movie production and distribution process.

Searching for privacy: design and implementation of a p3p-enabled search engine

Although the number of online privacy policies is increasing, it remains difficult for Internet users to understand them, let alone to compare policies across sites or identify sites with the best privacy practices. The World Wide Web Consortium (W3C) developed the Platform for Privacy Preferences (P3P 1.0) specification to provide a standard computer-readable format for privacy policies. This standard enables web browsers and other user agents to interpret privacy policies on behalf of their users. This paper introduces our prototype P3P-enabled Privacy Bird Search engine. Users of this search service are given visual indicators of the privacy policies at sites included in query results. Our system acts as a front end to a general search engine by evaluating the P3P policies associated with search results against a users privacy preference settings. To improve system performance we cache unexpired P3P policy information (including information about the absence of P3P policies) for thousands of the most popular sites as well as for sites that have been returned in previous search results. We discuss the system architecture and its implementation, and consider the work necessary to evolve our prototype into a fully functional and efficient service.

Information leakage caused by hidden data in published documents

This article demonstrates mining for hidden text in published data and concludes that user behavior - in combination with default program settings - creates an uncomfortable state of affairs for Microsoft Word users concerned about information security. The article also presents some countermeasures.

Inference on a collapsed margin in disease mapping.

This paper describes a method for estimating the risk from a disease over a set of contiguous geographical regions, when data on a potentially important covariate, such as race, are not available. Conditions under which the extra margin can be recovered are suggested. An application to prostate cancer mortality among the non-white population in the counties of the U.S.A. is discussed.

Ensuring Access to Emergency Services in the Presence of Long Internet Dial-Up Calls

Telephone availability is critical, particularly in emergency situations when people need immediate help. We used statistical data analysis and queueing models to identify the root cause of dial-tone unavailability in parts of the AT&T network and to develop remedies. Our solutions restored quality service, protecting the AT&T brand name and ensuring the safety of our customers. This work also gave AT&T opportunities to reduce transit charges paid to other carriers by

Can you find me now? Evaluation of network-based localization in a 4G LTE network

15 million per year. In addition, we have filed five patent requests, of which two have been granted and the rest are pending (Chaudhury et al. 2004, Kaplan and Ramaswami 2004). Furthermore, our findings have important implications for several current areas of research related to Internet and broadband technologies, call-center engineering, and network security.

Exposing digital content piracy: approaches, issues and experiences

User location is of critical importance to cellular network operators. It is often used for network capacity planning and to aid in the analysis of service and network diagnostics. However, existing localization techniques rely on user-provided information (e.g., Angle-of-Arrival), which are not available to the operator, and often require a significant effort to collect training data. Our main contribution is the design and evaluation of the Network-Based Localization (NBL) System for localizing a user in a 4G LTE network. The NBL System consists of 2 stages. In an offline stage, we develop RF coverage maps based on a large-scale crowd-sourced channel measurement campaign. Then, in an online stage, we present a localization algorithm to quickly match RF measurements (which are already collected as part of normal network operation) to coverage map locations. The system is more practical than related works, as it does not make any assumptions about user mobility, nor does it require expensive manual training measurements. Despite the realistic assumptions, our extensive evaluations in a national 4G LTE network show that the NBL System achieves a localization accuracy which is comparable to related works (i.e., a median accuracy of 5% of the cells coverage region).