Potential Benefits and Risks of Co-Locating DGPS With Loran-C

C. A. Treib, M. W. Parsons, E. Shofner and M. E. McKaughan

Abstract:	The U. S. Coast Guard is part of the U. S. Department of Transportation’s team to expand the maritime Differential Global Positioning System (DGPS) service into a national transportation safety system. The U. S. Coast Guard's role is to implement a Nationwide DGPS (N/DGPS) expansion effort to more than double the existing number of broadcast sites. The N/DGPS system is designed to meet all surface transportation navigation requirements in the United States and will provide double terrestrial DGPS coverage across the continental United States. The DGPS system operates in the Medium Frequency (MF) band where efficient antenna systems are large and costly to build. The N/DGPS project team is researching the possibility of co-locating N/DGPS sites at U.S. Coast Guard maintained Long Range Navigation (LORAN) stations, as a cost saving measure. Previous Radio Frequency Working Group (RF WG) studies showed that the signals might be generated from the same transmitter. However, the filtering techniques required are cost prohibitive and difficult to support and maintain. The RF WG transitioned from diplexing methods to co-location methods—sharing geographic location and resources while transmitting two independent signals. Co-location minimizes most of the risks encountered with diplexing, but risks are still present and must be accounted for when designing a solution. The most significant risks co-locating DGPS with LORAN are destructive signal interference, insufficient power sources, radiation safety, and single point of failure issues. Any one of these risks could make co-location undesirable by altering the existing LORAN signal and support. By transmitting two radio navigation signals at one geographical location, the USCG will operate both systems more economically. Savings will be realized through reduced installation costs, maintenance, and energy. Installation savings are currently projected at approximately $500,000 per site while maintenance and energy savings prove to be substantial, but will vary from site to site. The solution to co-locating DGPS signals with LORAN has been discussed at several RF WG meetings. Through free communication of knowledge, creativity, and the spirit of improving existing engineering solutions, the RF WG has developed several solutions that minimize the associated risks.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	1746 - 1751
Cite this article:	Treib, C. A., Parsons, M. W., Shofner, E., McKaughan, M. E., "Potential Benefits and Risks of Co-Locating DGPS With Loran-C," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 1746-1751.
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