GPS and eLoran Integrated Navigation for Marine Applications Using Augmented Measurement Equation Based on Range Domain
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ISSN:1598-6446 eISSN:2005-4092 http://www.springer.com/12555
GPS and eLoran Integrated Navigation for Marine Applications Using Augmented Measurement Equation Based on Range Domain Tae Hyun Fang*, Youngki Kim, Sul Gee Park, Kiyeol Seo, and Sang Hyun Park Abstract: Vulnerability to the interference of GPS (Global Positioning Systems) is one of the main obstacles to performing safe marine navigation. As eLoran (Enhanced Long Range Navigation), considered as the backup navigation system of GPS, has been developed specifically in several countries, the need for GPS / eLoran integrated navigation has emerged. This study represents the integrated algorithm for GPS and eLoran to overcome the vulnerability of GPS. The main research contents are as follows: a) Formula for integrated positioning of GPS / eLoran based on range domain is suggested. b) Essential ASF (Additional Secondary Factor) estimation filter to implement positioning by eLoran is presented in terms of real-time processing instead of employing ASF grid map, which should be pre-made at a local area and be distributed to marine users. c) Procedures for determining HPL (Horizontal Protection Level) are represented so that the reliability of the integrated navigation can be investigated. d) The marine test results are presented to validate the suggested methods based on the Loran-C signal. Test results show the integrated GPS and eLoran by the suggested methods can complement each other in terms of accuracy and reliability. Keywords: eLoran, GPS, integrated navigation, range domain.
1.
INTRODUCTION
In the first marine navigation field, there was a demand for how to conveniently obtain navigation information. This demand has been primarily satisfied by Global Navigation Satellite Systems (GNSS) [1], one of which is GPS (Global Positioning Systems). GPS provides navigation data to users around the world with high accuracy, but the signal from the satellite is low and is vulnerable to radio interference. Therefore, a backup radio-navigation system has been required to withstand radio interference for maritime safety [2–4]. Enhanced Loran, also known as eLoran (Enhanced Long Range Navigation), is an internationally-standardized positioning, navigation, and timing service for use in many applications [2,3,5,6]. It is the latest in Long-Range Navigation (Loran) systems, which is a hyperbolic radionavigation system developed in the United States. Unlike the conventional Loran using hyperbolic positioning, eLoran determines the position by measuring the range between the transmitting station and the receiver. The radio waves of eLoran propagate from the transmitting station on the ground. eLoran operates wholly indepen-
dently of GPS or any other GNSS and has at least 10, 000 times stronger signal than GPS in terms of radio interference [7] because it uses high-power transmitters and low-frequency (100kHz) signals. eLoran has been evaluated as a backup radio-navigation system that can reduce its reliance on GPS. The United States modified conventional Loran into an
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