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Suggested Citation:"ACCQPOINT." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
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APPENDIX C 175 John E. Chance & Associates, Inc. (A member of the Fugro Group of Companies) John E. Chance & Associates, Inc, now affiliated with the Dutch Fugro Group, provides DGPS services to North America and much of the rest of the world with a system known as Starfix II.62 Starfix II systems operate throughout the world by sending differential corrections from each of the reference sites to a central network control center using leased telephone lines, communications satellites, or both. Differential corrections are broadcast to users via L-Band and C-Band geostationary communications satellites and are received by user equipment that consists of a small (3.8 cm high, 7.6 cm diameter) omnidirectional antenna and a signal downconverter (5.0 x 7.6 x 25.4 cm in size).63 John E. Chance advertises real-time positioning accuracies of 53 centimeters (2 drms). John E. Chance also provides continuous DGPS coverage to all of the continental United States and most of North America using the OMNISTAR system. The OMNISTAR system is essentially the same as Starfix II, except that differential corrections are broadcast to OMNISTAR users in RTCM SC-104 format, and an ionospheric model that takes the user's location into consideration is utilized in determining the corrections .64 This approach is a convenient mechanism for providing differential corrections to users with a variety of GPS receivers. ACCQPOINT John E. Chance will also provide DGPS correction data via satellite to ACCQPOINT, an FM subcarrier- based DGPS service based on an alliance between Lecia of Torrance, California, and CUE Network based in Irvine, California. ACCQPOINT plans to eventually install receivers for the John E. Chance data at all 500 radio stations that currently are part of CUE's North American paging network. The pseudorange corrections received at the stations will then be broadcast to users within a reception range of 35 to 85 miles (56 to 136 kilometers) using mobile broadcast service (MBS) technology originally developed in Europe. MBS technology allows conventional FM radio broadcasts to carry digital data, such as differential corrections, by modulating the data on an inaudible subcarrier frequency of 57 KHz at approximately 1100 bits per second. The FM subcarrier signal is received by equipment that is only slightly larger than a standard pager and provides users with an advertised accuracy of approximately 1.5 meters. 62 The original Starfix service provided non-GPS positioning accuracy of approximately 5 meters to the Gulf of Mexico and the mid-western United States. 63 C-band user equipment is larger, but is used only for special applications. 64 The RTCM SC-104 format also is the standard that has been chosen for the U.S. Coast Guard DGPS network.

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The Global Positioning System: A Shared National Asset Get This Book
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The Global Positioning System (GPS) is a satellite-based navigation system that was originally designed for the U.S. military. However, the number of civilian GPS users now exceeds the military users, and many commercial markets have emerged. This book identifies technical improvements that would enhance military, civilian, and commercial use of the GPS. Several technical improvements are recommended that could be made to enhance the overall system performance.

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