Kurt Partridge

On the Anonymity of Home/Work Location Pairs

Many applications benefit from user location data, but location data raises privacy concerns. Anonymization can protect privacy, but identities can sometimes be inferred from supposedly anonymous data. This paper studies a new attack on the anonymity of location data. We show that if the approximate locations of an individuals home and workplace can both be deduced from a location trace, then the median size of the individuals anonymity set in the U.S. working population is 1, 21 and 34,980, for locations known at the granularity of a census block, census track and county respectively. The location data of people who live and work in different regions can be re-identified even more easily. Our results show that the threat of re-identification for location data is much greater when the individuals home and work locations can both be deduced from the data. To preserve anonymity, we offer guidance for obfuscating location traces before they are disclosed.

Activity-based serendipitous recommendations with the Magitti mobile leisure guide

This paper presents a context-aware mobile recommender system, codenamed Magitti. Magitti is unique in that it infers user activity from context and patterns of user behavior and, without its user having to issue a query, automatically generates recommendations for content matching. Extensive field studies of leisure time practices in an urban setting (Tokyo) motivated the idea, shaped the details of its design and provided data describing typical behavior patterns. The paper describes the fieldwork, user interface, system components and functionality, and an evaluation of the Magitti prototype.

TiltType: accelerometer-supported text entry for very small devices

TiltType is a novel text entry technique for mobile devices. To enter a character, the user tilts the device and presses one or more buttons. The character chosen depends on the button pressed, the direction of tilt, and the angle of tilt. TiltType consumes minimal power and requires little board space, making it appropriate for wristwatch-sized devices. But because controlled tilting of ones forearm is fatiguing, a wristwatch using this technique must be easily removable from its wriststrap. Applications include two-way paging, text entry for watch computers, web browsing, numeric entry for calculator watches, and existing applications for PDAs.

Escape: a target selection technique using visually-cued gestures

Many mobile devices have touch-sensitive screens that people interact with using fingers or thumbs. However, such interaction is difficult because targets become occluded, and because fingers and thumbs have low input resolution. Recent research has addressed occlusion through visual techniques. However, the poor resolution of finger and thumb selection still limits selection speed. In this paper, we address the selection speed problem through a new target selection technique called Escape. In Escape, targets are selected by gestures cued by icon position and appearance. A user study shows that for targets six to twelve pixels wide, Escape performs at a similar error rate and at least 30% faster than Shift, an alternative technique, on a similar task. We evaluate Escapes performance in different circumstances, including different icon sizes, icon overlap, use of color, and gesture direction. We also describe an algorithm that assigns icons to targets, thereby improving Escapes performance.

Empirical measurements of intrabody communication performance under varied physical configurations

Intrabody communication (IBC) is a wireless communications technology that uses a persons body as the transmission medium for imperceptible electrical signals. Because communication is limited to the vicinity of a persons body, ambiguities arising from communication between personal devices and environmental devices when multiple people are present can, in theory, be solved simply. Intrabody communication also potentially allows data to be transferred when a person touches an IBC-enabled device. We have designed and constructed an intrabody communication system, modeled after Zimmermans original design, and extended it to operate up to 38.4Kbps and to calculate signal strength. In this paper, we present quantitative measurements of data error rates and signal strength while varying hand distance to transceiver plate, electrode location on the body, touch plate size and shape, and several other factors. We find that plate size and shape have only minor effects, but that the distance to plate and the coupling mechanism significantly effect signal strength. We also find that portable devices, with poor ground coupling, suffer more significant signal attenuation. Our goal is to promote design guidelines for this technology and identify the best contexts for its effective deployment.

Which Way Am I Facing: Inferring Horizontal Device Orientation from an Accelerometer Signal

We present a method to infer the orientation of mobile device carried in a pocket from the acceleration signal acquired when the user is walking. Whereas previous work has shown how to determine the the orientation in the vertical plane (angle towards earth gravity), we demonstrate how to compute the orientation within the horizontal plane. To validate our method we compare the output of our method with GPS heading information when walking in a straight line. On a total of 16 different orientations and traces we have a mean difference of 5 degrees with 2.5 degrees standard deviation.

ipChinook: an integrated IP-based design framework for distributed embedded systems

IPCHINOOK is a design tool for distributed embedded systems. It gains leverage from the use of a carefully chosen set of design abstractions that raise the level of designer interaction during the specification, synthesis, and simulation of the design. IPCHINOOK focuses on a component-based approach to system building that enhances the ability to reuse existing-software modules. This is accomplished through a new model for constructing components that enables composition of control-flow as well as data-flow. The designer then maps the elements of the specification to a target architecture: a set of processing elements and communication channels. IPCHINOOK synthesizes all of the detailed communication and synchronization instructions. Designers get feedback via a cosimulation engine that permits rapid evaluation. By shortening the design cycle, designers are able to more completely explore the design space of possible architectures and/or improve time-to-market. IPCHINOOK is embodied in a system development environment that supports the design methodology by integrating a user interface for system specification, simulation, and synthesis tools. By raising the level of abstraction of specifications above the low-level target specific implementation, and by automating the generation of these difficult and error-prone details, IPCHINOOK lets designers focus on global architectural and functionality decisions.

On using existing time-use study data for ubiquitous computing applications

Governments and commercial institutions have conducted detailed time-use studies for several decades. In these studies, participants give a detailed record of their activities, locations, and other data over a day, week, or longer period. These studies are particularly valuable for the ubicomp community because of the large number of participants (often the tens of thousands), and because of their public availability. In this paper, we show how to use the data from these studies to provide validated and cheap (although noisy) classifiers, baseline metrics, and other benefits for activity inference applications.

Integrated safety analysis of requirements specifications

This paper describes an integrated approach to safety analysis of software requirements and demonstrates the feasibility and utility of applying the individual techniques and the integrated approach on the requirements specification of a guidance system for a high-speed civil transport being developed at NASA Ames. Each analysis found different types of errors in the specification; thus together the techniques provided a more comprehensive safety analysis than any individual technique. We also discovered that the more the analyst knew about the application and the model, the more successful they were in finding errors. Our findings imply that the most effective safety-analysis tools will assist rather than replace the analyst.

Collaborative Filtering Is Not Enough? Experiments with a Mixed-Model Recommender for Leisure Activities

Collaborative filtering (CF) is at the heart of most successful recommender systems nowadays. While this technique often provides useful recommendations, conventional systems also ignore data that could potentially be used to refine and adjust recommendations based on a users context and preferences. The problem is particularly acute with mobile systems where information delivery often needs to be contextualized. Past research has also shown that combining CF with other techniques often improves the quality of recommendations. In this paper, we present results from an experiment assessing user satisfaction with recommendations for leisure activities that are obtained from different combinations of these techniques. We show that the most effective mix is highly dependent on a users familiarity with a geographical area and discuss the implications of our findings for future research.