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In a port terminal, containers are stored and transshipped by yard tractors and cranes. Information on the location of these vehicles is an essential factor for efficient operation of the terminal. However, most port terminals try to estimate the location of these assets using indirect methods such as event locating of shipping or unshipping containers. Because these kinds of events do not occur often, the location of the event triggered includes serious location error, as it is different from the real location of the vehicle. In this paper, we propose a real-time asset locating system that accurately and reliably obtains the location of terminal assets. The proposed system overcomes location estimation errors caused by container stacks disrupting wireless communication. In order to mitigate uncertainty and increase the accuracy of the location estimate, we designed hardware and a multi-step locating system to resolve additional problems. We implemented the system components, and installed the system at a port environment for evaluation. Our results indicate that our proposed system has a locating error level of approximately 5.87 m and that it is superior to existing systems.

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.

Real time locating systems (RTLS) determine and track the location of assets and person using active tags. Two or more readers can estimate the tag's range from each reader and determine its location. In order to determine tag's 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.