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The GETA Sandals - A Footprint Location Tracking System

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1The GETA Sandals: A Footprint Location Tracking System Shun-yuan Yeh, Chon-in Wu, Keng-hao Chang, Hao-hua Chu, Jane Yung-jen Hsu Department of Computer Science and Information Engineering Graduate Institute of Networking and Multimedia National Taiwan University #1 Roosevelt Road, Section 4, Taipei, Taiwan 106 {r93124, r92079, r93018, hchu, yjhsu}@csie.ntu.edu.tw Abstract. This paper presents the design, implementation, and evaluation of a footprint-based indoor location system on traditional Japanese GETA sandals. Our foot-print location system can significantly reduce the amount of infrastructure re-quired in the deployed environment. In its simplest form, a user simply has to put on the GETA sandals to track his/her locations without any setup or calibra-tion efforts. This makes our footprint method easy for everywhere deployment. The footprint location system is based on the dead-reckoning method. It works by measuring and tracking the displacement vectors along a trial of footprints (each displacement vector is formed by drawing a line between each pair of footprints). The position of a user can be calculated by summing up the current and all previous displacement vectors. Additional benefits of the footprint based method are that it does not have problems found in existing indoor loca-tion systems, such as obstacles, multi-path effects, signal noises, signal inter-ferences, and dead spots. However, the footprint based method has two prob-lems (limitations): (1) accumulative error over distance traveled, and (2) stair climbing and jumping motions. To address the first issue, it is combined with a light RFID infrastructure to correct its positioning error over some long dis-tance traveled. Furthermore, it incorporates an accelerometer-based method to work under stair climbing and jumping motions. 1 Introduction Physical locations of people and objects have been one of the most widely used con-text information in context-aware applications. To enable such location-aware appli-cations in the indoor environment, many indoor location systems have been proposed in the past decade, such as Active Badge [1], Active Bat [2], Cricket [3], smart floor [4], RADAR [5], and Ekahau [6]. However, we have seen very limited market suc-cess of these indoor location systems outside of academic and industrial research labs.2We believe that the main obstacle that prevents their widespread adoption is that they require certain level of system infrastructural support (including hardware, installa-tion, calibration, maintenance, etc.) inside the deployed environments. For example, Active Badge [1], Active Bat [2], and Cricket location systems [3] require the instal-lation of infrared/ultrasonic transmitters (or receivers) at fixed locations (e.g., ceilings or high walls) in the environments. In order to attain high location accuracy and good coverage, the system infrastructure requires large number of transmitters (or receivers) installed in the deployed environments. This is beyond the reach of ordinary people to afford, operate, and maintain the infrastructure. WiFi based location systems such as RADAR [5] and Ekahau [6] require an existing WiFi network in the deployed envi-ronment. For example, the Ekahau location system recommends a WiFi client to be able to receive signals from 3~4 WiFi access points in order to attain the specified location accuracy of 3 meters. This high density of access points is unlikely in our everyday home and small office environments. In addition, most WiFi based location systems require users’ calibration efforts to construct a radio map by taking meas-urements of WiFi signal strength at various points in the environment. This forms another barrier for users. Furthermore, the instability caused by dynamic environ-mental factors can also reduce the positioning accuracy and stability in the WiFi loca-tion systems [7]. Smart floor [4] can track the location of a user by using pressure or presence sensors underneath the floor tiles to detect the user’s gait. This infrastructure cost is expensive because it requires custom-made floor tiles and flooring re-construction. Significantly reducing the needed system infrastructure serves as our main motiva-tion to design and prototype a new footprint location system on traditional Japanese GETA (pronounced “gue-ta”) sandals. This footprint location system can compute a user’s physical location solely by using sensors installed on the GETA sandals. To enable location tracking, a user simply has to wear the GETA sandals with no extra user setup & calibration effort. This system works by attaching location sensors, including two ultrasonic-infrared-combo receivers and one ultrasonic-infrared-combo transmitter, on the GETA sandals. The basic idea can be described by looking at a person walking from location A to location B on a beach. He/she will leave a trial of footprints. To track a person’s physical location, the system continuously measures a displacement vector formed between two advancing footprints (advancing in the temporal sense). To track a user’s current location relative to a starting point, the system simply sums up all previous footprint displacement vectors leading to his/her current footprint location. This idea is similar to the so-called (deduced) dead-reckoning navigation dated back to the medieval time when the sailor/navigator lo-cated himself/herself by measuring the course and distance sailed from a starting point. In our system, this dead reckoning idea is adapted in tracking human footprints. We believe that having a wearable location tracker is an important advantage in our footprint location system over infrastructure-based indoor location systems. Users simply need to wear our GETA-like shoes, and our location system can work any-where they want to go. In addition to the benefit of low infrastructure cost, the footprint location system does not have problems commonly found in existing indoor location systems. For example, existing wireless based solutions (e.g., using radio, ultrasonic, or infrared)3can experience poor position accuracy when encountering obstacles between trans-mitters and receivers, multi-path effects, signal noises, signal interferences, and dead spots. On the other hand, our footprint location system avoids almost all of these problems. The reason is that the location sensors (ultrasonic-infrared transmitters and receivers) in our footprint method only need to cover


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