A Prototype Loran Augmented GPS

Jan Andersen and Charles Sweet

Abstract:	The proposed LAGPS (Loran Augmented GPS), based on the Eurofix [l] concept uses a balanced, modulated Loran- C communications channel to transmit Differential GPS (DGPS) corrections. With the addition of inexpensive modulators and DGPS reference stations, the existing Loran-C infrastructure offers a communications channel with high availability, reliability and a coverage area including the entire CONUS and Western Europe. GPS with Loran can improve the reliability and accuracy of the navigation solution over either method used separately. The asynchronous DGPS format proposed by Delft University of Technology, data compression methods and a very robust modulation scheme ensure performance within the FRP-92 requirements for harbor and non- precision approaches as well as resource exploration. Simulations and analytical models of the LAGPS system were used to resolve the tradeoffs between channel capacity and data integrity. Experimental results were obtained using an on-air LAGPS system consisting of a DGPS base station sending RTCM SC 104 type 1 messages via telephone to an RTCM-to-LAGPS encoder and Loran transmitter which broadcasts the LAGPS messages to a mobile Loran sampling receiver. The receiver transfers data to an LAGPS-to-RTCM decoder which provides the DGPS receiver with RTCM SC104 type 1 corrections. To gather preliminary results with this prototype system, position errors were measured at several locations at distances up to 850 km from the transmitter during the day and night. These preliminary test results support theoretical models which predict that FRP-92 requirements can be met even under worst case channel capacity. Since the experimental setup is intentionally subject to much higher cross-rate interference levels than a system using the strongest modulated station of a chain, the communications channel would be even more robust if implemented throughout CONUS or Western Europe. Not only is the LAGPS system an elegant integration of two proven navigation systems, it can be implemented using low cost hardlimited Loran demodulation and standard GPS receivers, that are prepared for RTCM SC 104. The LAGPS system offers a wide range of options to the navigation world.
Published in:	Proceedings of the 1995 National Technical Meeting of The Institute of Navigation January 18 - 20, 1995 Disneyland Hotel Anaheim, CA
Pages:	453 - 462
Cite this article:	Andersen, Jan, Sweet, Charles, "A Prototype Loran Augmented GPS," Proceedings of the 1995 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 1995, pp. 453-462.
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