Fast Acquisition Correlators for GPS

Robert Van Wechel

Abstract:	Parallel correlators for fast acquisition of GPS and other direct sequence spread spectrum signals have been built for a number of years to shorten the acquisition time of the signals. The objective of this paper is to review the background of these correlators, present performance analysis methods, and describe correlators that have been built and tested. Early cot-relator development efforts were directed toward the use of charge-coupled devices. Problems with the fabrication of these devices and the advance of digital technology led to the development of digital devices, otherwise known as digital matched filters. Using current technology, we are currently supplying to various programs a small GPS receiver with a 2046 tap, 1 bit/sample C/A code correlator. For fast acquisition of the GPS C/A code, the entire code is searched in parallel. This device will also function as a direct P code fast acquisition correlator with 1023 taps and 2 bits/sample, which provides acquisition in high jamming. Development of these correlators is on-going, with larger devices planned as the semiconductor technology will allow, which will provide even faster acquisition and in greater interference. A spreadsheet program has been developed which allows the analysis and tradeoffs of GPS acquisition systems, and provides performance estimates in terms of acquisition time, given the position, velocity and time uncertainties, a given interference condition, and the correlator parameters. Theoretical bounds are presented which can be used as a guide to the feasibility of meeting acquisition time goals as technology progresses. These bounds assume that both delay and Doppler can be searched in parallel, and technology does not limit performance.
Published in:	Proceedings of the 52nd Annual Meeting of The Institute of Navigation (1996) June 19 - 21, 1996 Royal Sonesta Hotel Cambridge, MA
Pages:	255 - 262
Cite this article:	Van Wechel, Robert, "Fast Acquisition Correlators for GPS," Proceedings of the 52nd Annual Meeting of The Institute of Navigation (1996), Cambridge, MA, June 1996, pp. 255-262.
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