Hiroshi Inamura

A hybrid frequency assignment for femtocells and coverage area analysis for co-channel operation

Successful deployment of femtocells requires intelligent cell planning and introduces some unique challenges. In this letter, an efficient frequency assignment technique is proposed for femtocells considering practical issues such as hand-off, coverage, and interference. Moreover, interference-limited coverage area (ILCA) of a co-channel femtocell base station is calculated based on parameters such as the distance to the macrocell BS, path loss exponents, and transmission power levels.

NLOS identification and weighted least-squares localization for UWB systems using multipath channel statistics

Non-line-of-sight (NLOS) identification and mitigation carry significant importance in wireless localization systems. In this paper, we propose a novel NLOS identification technique based on the multipath channel statistics such as the kurtosis, the mean excess delay spread, and the root-mean-square delay spread. In particular, the IEEE 802.15.4a ultrawideband channel models are used as examples and the above statistics are found to be well modeled by log-normal random variables. Subsequently, a joint likelihood ratio test is developed for line-of-sight (LOS) or NLOS identification. Three different weighted least-squares (WLSs) localization techniques that exploit the statistics of multipath components (MPCs) are analyzed. The basic idea behind the proposed WLS approaches is that smaller weights are given to the measurements which are likely to be biased (based on the MPC information), as opposed to variance-based WLS techniques in the literature. Accuracy gains with respect to the conventional least-squares algorithm are demonstrated via Monte-Carlo simulations and verified by theoretical derivations.

Dynamic test input generation for web applications

Web applications routinely handle sensitive data, and many people rely on them to support various daily activities, so errors can have severe and broad-reaching consequences. Unlike most desktop applications, many web applications are written in scripting languages, such as PHP. The dynamic features commonly supported by these languages significantly inhibit static analysis and existing static analysis of these languages can fail to produce meaningful results on realworld web applications. Automated test input generation using the concolic testing framework has proven useful for finding bugs and improving test coverage on C and Java programs, which generally emphasize numeric values and pointer-based data structures. However, scripting languages, such as PHP, promote a style of programming for developing web applications that emphasizes string values, objects, and arrays. In this paper, we propose an automated input test generation algorithm that uses runtime values to analyze dynamic code, models the semantics of string operations, and handles operations whose argument and return values may not share a common type. As in the standard concolic testing framework, our algorithm gathers constraints during symbolic execution. Our algorithm resolves constraints over multiple types by considering each variable instance individually, so that it only needs to invert each operation. By recording constraints selectively, our implementation successfully finds bugs in real-world web applications which state-of-the-art static analysis tools fail to analyze.

Potential of UWB Technology for the Next Generation Wireless Communications

This paper discusses the potential deployment of ultra-wideband (UWB) radio technology for next generation wireless communications. Firstly, the state-of-art in UWB technology is reviewed. Then, the current status of worldwide regulatory efforts and industrial standardization activities is discussed. Various technical challenges that remain to be solved prior to the successful deployment of UWB systems as well as the possible technical approaches are also reported. Specifically, we envisioned the potential of location awareness capabilities to provide new applications and usage models for future mobile terminals. An overview of the existing ranging and localization techniques is presented and some technical aspects as well as design trade-offs in terms of device complexity and ranging accuracy are highlighted. Finally, since UWB systems operate as overlay systems, issues of coexistence and interference with existing narrowband systems are presented

Enhancements to Linear Least Squares Localization Through Reference Selection and ML Estimation

Linear least squares (LLS) estimation is a low complexity but sub-optimum method for estimating the location of a mobile terminal (MT) from some distance measurements. It requires selecting one of the fixed terminals (FTs) as a reference FT for obtaining a linear set of expressions. However, selection of the reference FT is commonly performed arbitrarily in the literature. In this paper, a method for selection of the reference FT is proposed, which improves the location accuracy compared to a fixed selection of the reference FT. Moreover, a covariance- matrix based LLS estimator is proposed in line of sight (LOS) and non-LOS (NLOS) environments which further improves accuracy since the correlations between the observations are exploited. Simulation results prove the effectiveness of the proposed techniques.

JavaScript Instrumentation in Practice

JavaScript has been exploited to launch various browser-based attacks. Our previous work proposed a theoretical framework applying policy-based code instrumentation to JavaScript. This paper further reports our experience carrying out the theory in practice. Specifically, we discuss how the instrumentation is performed on various JavaScript and HTML syntactic constructs, present a new policy construction method for facilitating the creation and compilation of security policies, and document various practical difficulties arose during our prototyping. Our prototype currently works with several different web browsers, including Safari Mobile running on iPhones. We report our results based on experiments using representative real-world web applications

Design and implementation of mobile grid middleware for handsets

This paper proposes mobile grid middleware based on an adaptive QoS framework to conceal the instability and resource constraints of mobile server hosts (MSHs). In a mobile grid system, data and codes on an MSH are replicated and synchronized on a fixed grid proxy for enhanced availability. However, operation time of MSH is limited by battery consumption due to the synchronization needed to maintain the freshness of replicas and the session management needed to maintain responsiveness of the MSH. According to application QoS requests, the framework optimizes synchronization scheduling and polling intervals to maximize sustainability. It also adapts to dynamic resource changes including low residual battery and poor wireless connectivity, by decreasing the target QoS and by reducing the aggregation period for synchronization. We built a prototype of mobile grid middleware on a J2ME handset and grid proxy on PC running Globus toolkit. Experiments showed that the framework enables MSH to increase its operation time while meeting diverse application QoS requests.

Formal Specification and Analysis of Timing Properties in Software Systems

Specifying and analyzing timing properties is a critical but error-prone aspect of developing many modern software systems. In this paper, we propose a new specification language and analysis framework for expressing and analyzing timing behaviors of complex software systems. Our framework has the following significant benefits: a) it is expressive, b) it supports trace analysis and simulation of timing behaviors, c) allows for verification of properties of specification, and d) checks for common usage errors of timing constructs. The language constructs for timing were chosen to be very flexible, suitable for expressing different kinds of timing behaviors, and are inspired from timing constructs used in previous languages like SDL. We define the formal semantics of our language using a real-time rewrite theory. Since real-time rewrite theories are executable in Real-Time Maude, our framework supports trace analysis and simulation of timing behavior for specifications. Furthermore, the timed model checker for Real-Time Maude can be readily used for analyzing and verifying various real-time properties of the specifications. Finally, to prevent misuses of timing constructs that can be made possible due to their flexibility, we develop abstract interpretation based static analysis tools that check for common usage errors. We believe that our framework, with the above benefits, provides a significant step forward in facilitating the use of formal tools for specification and analysis of timing behaviors in software development.

Better abstractions for secure server-side scripting

It is notoriously difficult to program a solid web application. Besides addressing web interactions, state maintenance, and whimsical user navigation behaviors, programmers must also avoid a minefield of security vulnerabilities. The problem is twofold. First, we lack a clear understanding of the new computation model underlying web applications. Second, we lack proper abstractions for hiding common and subtle coding details that are orthogonal to the business functionalities of specific web applications. This paper addresses both issues. First, we present a language BASS for declarative server-side scripting. BASS allows programmers to work in an ideal world, using new abstractions to tackle common but problematic aspects of web programming. The meta properties of BASS provide useful security guarantees. Second, we present a language MOSS reflecting realistic web programming concepts and scenarios, thus articulating the computation model behind web programming. Finally, we present a translation from BASS to MOSS, demonstrating how the ideal programming model and security guarantees of BASS can be implemented in practice.

Optimizing user interaction for web-based mobile tasks

the small form-factor of mobile handsets and the longer, variable latency of cellular networks are major hindrances to good user experience in mobile web related activities. Existing approaches have yet to adequately address the usability concerns caused by them. This paper describes the design and prototype implementation of MIntOS (Mobile Interaction Optimization System), a system for improving mobile interaction in web-based activities. MIntOS monitors users’ interactions both for gathering interaction history and for the runtime construction of interaction context. A simple approach based on interaction burstiness is used to break interaction sequences into Trails, which approximates user tasks. Such Trails are then used to generate rules for online, context-sensitive prediction of future interaction sequences. Predicted user interaction sequences are then optimized to reduce the amount of user input and user wait time using techniques such as interaction short-cuts, automatic text copying and form-filling, as well as page pre-fetching. Such optimized interaction sequences are, at real-time, recommended to the user through UI enhancements in a non-intrusive manner. MIntOS also uses content and structure based techniques to generalize prediction rules to extend to new but similar user tasks. Several sample applications are used to demonstrate the benefits of MIntOS.