Sanghyun Son

Implementation of a precision time protocol over low rate wireless personal area networks

Time synchronization is essential for a number of network applications. As the era of ubiquitous computing is ushered in, high precision time synchronization of nodes in wireless networks is required. High precision time synchronization can enable a variety of extensions of applications. This paper includes the design and implementation of the precision time protocol over low rate wireless personal area networks (LR-WPANpsilas). To achieve high precision in LR-WPANpsilas, we analyze the factors of latency and jitter in wireless environments, and we aim to minimize these factors. In addition, this paper presents experiments and the performance evaluation of the precision time protocol in LR-WPANpsilas. The result is that we established for nodes in a network to maintain their clocks to within a 50 nanosecond offset from the reference clock.

Real Time Locating System for Wireless Networks using IEEE 802.15.4 Radio

Real time locating systems (RTLS) determine and track the location of assets and person using active tags. Two or more readers can estimate the tags range from each reader and determine its location. In order to determine tags location, there are several methods. This paper presents a real time locating system which is based on time difference of arrival(TDOA) of a signal, for wireless networks using IEEE 802.15.4 radio. In order to measure the time that a signal arrives at, exact time measurement is crucial. This paper proposes a multi-phase radio method to provide exact time measurement. In addition, to calculate the time difference, readers in the network should be synchronized with themselves. We also present a precision time synchronization protocol. This paper includes the performance evaluation. The performance shows that our RTLS has accuracy of within 3 meters.

Precise location tracking system based on time difference of arrival over LR-WPAN

As the era of ubiquitous computing approaches, there is a growing need for a reliable, efficient positioning and tracking system. Localization involves continuous determination and tracking of the location of assets and personnel. Localization using time difference of arrival (TDOA) involves determining the location of a tag by calculating the time difference of arrival of the signal received from the tag. In order to calculate the time difference of the signal, TDOA-based methods require precision time synchronization of within a few nanoseconds. This paper presents a location tracking system(LTS), which consists of readers, tags, and an engine, based on TDOA in IEEE 802.15.4. In addition, we propose a precise time measurement method and a precision time synchronization protocol which provides a common clock with an accuracy of within a few nanoseconds. The proposed precision time synchronization protocol results in accurate locating services. The performance shows that readers achieve precision time synchronization of within 5 nanoseconds from a reference clock, and the location tracking system has a location error of within 2 meters.

Design and Implementation of a Real Time Locating Systems over IEEE 802.15.4a Radio for Port Logistics

Real time locating systems (RTLS) are required to provide high quality service for port logistics. When such locating systems are applied to port logistics, however, they encounter the problem of unreachable signals. The environments of port logistics have radio-shaded areas (RSA), which often cause failures in measurement or positioning errors. This paper addresses the design and implementation of a real time locating system over IEEE 802.15.4a radio for application to port logistics. The proposed RTLS include methods that employ assistant tags and a directional-antenna-based reader. In addition, this paper describes experiments and records their performance in order to solve the problem associated with RSAs in the port logistics environment. The results show that the measurement success rate is increased by up to 38%, with a locating accuracy that has a circular error probability (CEP) of 1.13 m.

Multi-step Location System using Mobile Reader and Trajectory Information in Container Port Environments

In this paper, we propose an asset tracking system for applying a container port environment. If we attempt to apply this common locating system to a port environment for logistics automation, the system performance is degraded because there are many steel obstacles that cause interference in the RF communication and measurement. We divided readers into two types - fixed and mobile readers; hence, the location method operates in two steps for efficient wireless communication and precise measurement. In addition, the system estimates the location with trajectory information of assets when the small number of measurement is gathered. We implemented all the system components and installed these at a real port for evaluation. The success rate of communication and estimation is much better than that of the existing general locating system, and the location precision is substantially increased.

Multi-hop based collection utilizing ZigBee networks for a large-scale active RFID deployment

RFID (Radio Frequency Identification) is an automatic identification technology where information is carried by radio waves. The active type of RFID focuses on a long communication range while the passive type focuses on a low cost for a number of dense deployments. Nevertheless, the active type cannot be applied to a large-scale area due to its limited radio communication. This paper proposes a multi-hop based collection utilizing ZigBee networks for a large-scale active RFID deployment. The proposed method uses a collection agent on ZigBee networks to extend the coverage of the RFID reader and collect RFID tags outside its communication range. This paper also includes an experiment and a performance evaluation. To evaluate the performance of the proposed method, we implemented an RFID system, which complies with a standard of 433MHz active RFIDs based on ISO/IEC 18000-71.

RF-Based Indoor Locating System for NLOS Environment

RTLS (Real-time locating systems) are used for tracking the location of people or assets in real time. In general, these systems use the radio frequency (RF) for wireless communication within a local coverage area. However, when we attempt to apply this system to an indoor environment, the non-line-of-sight (NLOS) problem is critical to the system performance because of the obstacles in the room. In this paper, we suggest a new location estimation method for an indoor NLOS environment using a reader-selection strategy. We have implemented all components of the locating system and carried out experiments in a testbed.

Time Synchronization of Distributed Readers for a Large-Scale Active RFID Network

Radio frequency identification (RFID) is an emerging automatic identification technology that uses radio waves to transmit information. However, it is difficult to apply in large-scale or in dense environments because of its limited radio communication range and obstacles such as water and steel infrastructure. To overcome these problems, distributed and multiple deployment of RFIDs is needed. The distributed deployment of RFID readers can reduce the labor and cost involved in data collection and various applications. In a distributed RFID environment, time synchronization is essential for efficient collection of RFIDs and to allow readers to communicate with each other. This paper proposes a method to provide time to distributed RFID readers and synchronize their time with a reference clock. The proposed time synchronization method reduces traffic needed for synchronization and provides an accurate time by correcting the drift at a lower level. Our results show that the performance of the proposed method is 2.6 times better than that of the conventional time synchronization protocol.

Hierarchical asset tracking system using IEEE 802.15.4a radio in container terminals

Due to the increase in the volume of international trading, throughput of logistics terminals has emerged as an important issue. It is important to ship and unload container cargo rapidly to improve throughput. The real-time location tracking of various vehicle assets is a major factor for efficient port terminal processing. In this paper, we will describe a system that we designed for asset tracking using IEEE 802.15.4a-based wireless communications for the efficient management of vehicles in the logistics terminals, and we will provide data from performance evaluations obtained from a real terminal environment. We applied a hierarchical-based tracking technique to overcome a non-line of sight (NLOS) problem. We improved the tracking estimation accuracy of yard tractors between container stacks by measuring a transfer cranes precise location using communication between the light towers readers and cranes mobile readers. We improved the tracking estimation accuracy of yard tractors between container stacks using a transfer cranes precision location. For measuring the cranes precision location, a mobile reader was attached to the crane. The mobile reader communicates with readers attached to light towers so that line of sight (LOS) is guaranteed. The proposed tracking system was installed at Gwangyang International Terminal, where we carried out an asset tracking performance evaluation. The results of the evaluation in a real logistics terminal confirmed that the tracking system has an estimated tracking error of approximately 6.53 m.

Design and implementation of camera network platform for information exchange using dual wireless interface

Exchange of image information is one of the main features of a camera network. In order to exchange a large amount of information, a platform with good communication speed is needed. In this study, we designed and implemented a specialized camera network platform using Wi-Fi Direct devices. This platform can provide various services to other devices within the same network. We designed the platform in 3 parts: a network, image processing and an embedded database. We modified the operation model of Wi-Fi Direct for adjustment. We designed a method to form a camera network using Wi-Fi Direct. In addition, we proposed two methods for minimizing delay in network formation. The performance of the proposed methods was evaluated using simulation. The feasibility of the proposed platform was also evaluated with experiments. Our results show that the proposed group formation methods outperformed the conventional method.