Implementation of Differential GPS Using Dissimilar Commercial Off-The-Shelf Receivers

David Pearson, Roger K. Wells, and Alan T. Massey

Abstract:	The need exists for navigation system integrators to implement differential GPS using available commercial GPS receivers. A number of current users had been effectively utilizing GPS based navigation systems prior to the implementation of S/A and require a cost effective means of upgrading their systems to differential GPS. Additionally, the requirements of new applications dictate utilization of mobile and reference site equipment which varies in quality and in cost. This paper reports the results of algorithm development, experimental data collection, communication requirements and testing of a differential GPS system conceived, developed and implemented to deal with the problems encountered in using different manufacturer’s GPS receiver equipment. Specifically the equipment coniguration included the use of an eight channel Motorola Eagle 8 receiver as a reference station along with a two channel Magnavox MX 1107/GPS receiver as a mobile, marine receiver. All differential computations were performed on a PC/AT level laptop computer for use in real time positioning of marine platforms. Various data link requirements were studied and resulted in the implementation of two systems, one in the low VHF range for inshore use (e.g. up to 50 miles) and another in the HF band for offshore applications (e.g. up to 200 miles). The difficulty encountered in the interpretation of clock model, ephemeris and pseudorange data from differing receivers is discussed. The assumption of commonality and the correct utilization of this data at both the reference station and at the mobile station is presented. Particular attention is given to the problems of computation of clock bias and use of ephemeris data in the presence of S/A. Finally, the results of stationary and mobile marine testing will be reviewed and recommendations concerning equipment and algorithm selections will be addressed.
Published in:	Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990) September 19 - 21, 1990 The Broadmoor Hotel Colorado Spring, CO
Pages:	367 - 375
Cite this article:	Pearson, David, Wells, Roger K., Massey, Alan T., "Implementation of Differential GPS Using Dissimilar Commercial Off-The-Shelf Receivers," Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990), Colorado Spring, CO, September 1990, pp. 367-375.
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