Design and Implementation of Practical Asset Tracking System in Container Terminals

摘要

A container terminal plays an important logistical role in handling transshipping containers. Therefore, location information regarding vehicles that carry containers in a port is critical to cost- and time- efficient management for harbor automation. In terms of scalability, cost, and energy efficiency, an active radio-frequency-identification (RFID) based real-time locating system (RTLS) is an appropriate technology for obtaining location information. In general, an RTLS estimates locations using the transmission time of wireless signals. Accurate distance measurement depends on not only time measurement but also guaranteed line-of-sight (LOS) communication. However, in a container terminal environment, the performance of existing system can be seriously degraded because of densely deployed obstacles, e.g., containers and vehicles. Furthermore, places that readers can be installed in a terminal are limited, and thus a sufficient number of readers cannot be installed to provide reliable communication. To overcome these problems, this paper presents a novel and practical approach to overcoming non-line-of-sight (NLOS) RF propagation problems in asset tracking systems for container terminals. In proposed system, we have considered practicable methods from unit experimentsin real world as well as theoretical methods: the system tries to reducerange estimates obtained under NLOS conditions, and estimate the tag locations using vehicles' range estimates and route information. For evaluation, the proposed method has been implemented at a real container terminal in South Korea, and experimental tests demonstrated its validity.