GETA Sandals : Walk Away with Localization

The GETA sandals are Japanese wooden sandals embedded with location tracking devices. By wearing them, the GETA sandals can track anywhere a user walks to. The GETA sandals work both in the indoor and outdoor environments. The motivation for the GETA sandals is to create a location system that needs minimum infrastructural setup and support in the environment, making it easy for deployment in everyday environments. This is in contrast to most of the current indoor location systems based on WiFi or ultrasound, which need to setup access points, fixed transmitters and receivers in the environment. The GETA sandals track a user’s location using a footprint-based method. The footprintbased method uses location sensors installed underneath the GETA sandals to continuously measure the displacement vectors formed between the left and right sandals along a trail of advancing footprints. By progressively adding up these displacement vectors, the GETA sandals can calculate the user's current location anytime anywhere. INTRODUCTION Physical locations of people and objects have been one of the most widely used context information in context-aware applications. To enable such location-aware applications 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], RADAR [4], and Ekahau [6]. However, we have seen very limited market success of these indoor location systems outside of academic and industrial research labs. The main obstacle that prevents their widespread adoption is that they require certain level of system infrastructural support (including hardware, installation, calibration, maintenance, etc.) inside the deployed environments. For examples, Active Badge [1], Active Bat [2], and Cricket location systems [3] require the installation 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 [4] and Ekahau [6] require an existing WiFi network in the deployed environment. 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 measurements of WiFi signal strength at various points in the environment. This forms another barrier for users. Significantly reducing the needed system infrastructure serves as our main motivation to design and prototype a new footprint location system on traditional Japanese GETA (pronounced “gueta”) sandals. Figure 1. Add up displacement vector to compute current location in the footprint method. FOOTPRINT LOCATION SYSTEM This footprint location system computes 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. The basic idea of the footprint location system can be described by looking at a person walking from location A to location B on a beach shown in Figure 1. 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. The footprint location system has been prototyped using the following four sensor components shown in Figure 2: (1) pressure sensors, (2) ultrasonic transmitter/receivers, (3) orientation sensor, and (4) RFID tags and readers. Two pressure sensors, installed at the bottom of both sandals, are used to detect when both feet are on the ground, forming a full step. At that time, the ultrasonic transmitter at the right sandal transmits a beacon toward the two ultrasonic receivers at the left sandal. Using time-of-flight information and triangulation method, the footprint location system can compute the displacement vector between left and right sandals. The reading from the orientation sensor is used to vdi Starting point vdi Current location Displacement vector Displacement vector Σ displacement