Transmission of DGPS Correction Signals Using an Inmarsat-C Channel

David H. Layer

Abstract:	This paper will describe in detail the development of a communications system for the multiplexing, processing, and subsequent transmission of DGPS correction data over an Inmarsat-C satellite channel. This system represents a lower- cost and more portable service than those currently available which use the Imnarsat-A channel, in particular for users having a need for Imnarsat-C communications capabilities. In the present system configuration, DGPS reference station data from separate locations are delivered to an Inmarsat coast earth station (CES) using land-line modems or multipoint-to-point satellite connections when access to land lines is diffkult. Hardware at the CES multiplexes and processes these separate inputs into a single 600 bit/s data stream which is then coded and BPSK modulated onto an Imnarsat-C carrier. Rate-l/2 convolutional encoding is used to insure data integrity. Provisions exist at the CES for encryption of the multiplexed data, allowing for subscuiber- only access. This system utilizes the SC-104 standard correction data format however alternative formats could be easily supported. System design efforts will be presented including communications link analysis, as well as motivation behind and description of the selected frame structure and baseband processing algorithms. Computer simulation results of system performance will be presented which will correlate receiver performance in the fading Inmarsat-C channel to DGPS position accuracy, by charackxing the average update rate of SC-104 messages through the system as well as providing statistics on expected 2DRMS position error as a function of satellite EIRP, mobile (Imnarsat-C) receiver acquisition time, and the number of reference signals transmitted on the satellite carrier.
Published in:	Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992) September 16 - 18, 1992 Albuquerque, NM
Pages:	925 - 934
Cite this article:	Layer, David H., "Transmission of DGPS Correction Signals Using an Inmarsat-C Channel," Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992), Albuquerque, NM, September 1992, pp. 925-934.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In