Takaaki Umedu

Middleware providing dynamic group communication facility for cellular phone applications

In this paper, we propose a middleware library for efficiently developing distributed cooperative applications consisting of a large number of cellular phone users. Our middleware provides: (1) a dynamic group formation mechanism depending on users locations and preferred subjects; and (2) a group communication mechanism called multiway synchronization for multicasting, synchronization and mutual exclusion. Most of Java executors on cellular phones do not support direct communication among user programs. Usable resources are also restricted. Therefore, in our middleware, most of user programs are executed on their servers as agents. Group communication is implemented as inter-process communication on the server, and only the user-interface parts are executed on the cellular phones.

An analysis model of queue length fluctuation at signals using vehicle trajectories

Floating car systems have attracted much attention. In particular, trajectory information of vehicles, which cannot be obtained in legacy traffic monitoring systems, would be significant for more detailed and precise traffic prediction. In this paper, we focus on vehicle queues formed in front of intersections and present a model that analyzes the dynamics of their length using vehicle trajectory information. In general, a queue grows in a red phase of the traffic signal cycle and shrinks in a green phase. We assume that vehicles arrive at a signal with a Poisson process, and estimate the queue length for each signal cycle. Our method was evaluated using a traffic simulator where the real field data were injected. Evaluation results have shown that the queue length could be estimated and the mean error was about 5 vehicles, which is acceptable compared with the whole queue sizes.

Cooperative positioning method using on-board LED communication and distance measurement devices

A new kind of LED communication device, by which the receiver can measure the distance and angle to the sender, is proposed. In this article, we propose a cooperative positioning method using such LED communication devices to estimate vehicle positions with high accuracy. In the method, we assume that signals which can transmit own position information are deployed and the vehicles equip headlights and taillights that have a function of LED communication transmitter, and hold image sensors for reception of LED communication. The results of estimation will propagated to the surrounding vehicles and they estimate their positions by using the information.

Mitigating location and speed errors in floating car data using context-based accuracy estimation

Although the floating car data contains detailed behavior of vehicles, most researches utilizing the floating car data mainly focus on providing link-level, large-scale traffic estimation because raw floating car data usually contains location and speed errors due to the characteristics of on-board sensors such as GPS and tachometers. Such errors are usually vehicle-dependent and considered hard to be eliminated. To tackle the challenge, in this paper, we propose a method to mitigate location and speed error in raw floating car data. The method takes two different information sources from GPS and tachometers respectively, and relies more on “more dependable” source. The dependability is assessed based on the locations and situations where the data are observed (e.g. in urban canyons the accuracy of GPS decreases and tachometers are more reliable). By analyzing and modeling such characteristics, we eliminate errors contained in those information sources to obtain more accurate traces and behavior of vehicles. We have evaluated our method using the real floating car data obtained over 7 days from 4777 vehicles that have installed commercial on-board navigation systems. We have shown that the relative distance errors have been reduced from 3.84% to 2.86% in 81.6% of vehicles.