GPS for Tracking 100g Dynamic Vehicles

Anthony R. Pratt

Abstract:	Vehicles demonstrating acceleration levels in excess of 100g may be tracked using translator type GPS receivers. In these equipments, GPS signals are received in a common antenna on board the host vehicle and the composite signal is processed only by a frequency change prior to retransmission to a ground based processing station. In some versions of translators, the composite received GPS signal is digitized prior to retransmission. The system architectures for either of these systems requires significant bandwidth to support the vehicle to ground station datalink. For CA code receivers, the analogue bandwidth is of the order of 2.5 MHz with a pilot tone or 5MHz without a pilot. The digital equivalent requires at least 5 Mbit/sec. The ground station is able to close code and possibly carrier tracking loops in order to derive the host vehicle position. An alternative receiver structure is possible, however, in which the code loops may be closed in the host vehicle. The paper demonstrates simulations of a suitable architecture which show that signal acquisition is possible in external conditions where clear LOS visibility to each satellite can be guaranteed. The limit for signal acquisition appears to be at dynamic levels of approximately 100g at present GPS signal levels. Carrier tracking appears to be possible in ground based stations by transmission of suitable signal measurements over a host vehicle to ground data-link. One major advantage of this approach appears to be the significant reduction in data-link bandwidth required to support ground based carrier phase tracking. The system architecture suggests that data-link requirements may be as low as 100kbits/sec of up to 8 satellites tracked. The paper describes the architecture of this type of receiver. Photographs are shown for a miniature version of a suitable receiver with 96 tracking channels. These endow the receiver with a time to first fix of approximately 3 seconds, even at 100g LOS acceleration. The paper demonstrates the feasibility of this approach through a series of simulation results, which demonstrate the acquisition and tracking process of this architecture at levels up to 100g. It is clear that there is trade-off of signal to noise ratio for acquisition during such dynamics. Plans to perform real life tests both on a centrifuge and in alternative ‚straight line™ trajectories are currently in progress with results expected by early 2001.
Published in:	Proceedings of the 2001 National Technical Meeting of The Institute of Navigation January 22 - 24, 2001 Westin Long Beach Hotel Long Beach, CA
Pages:	415 - 425
Cite this article:	Pratt, Anthony R., "GPS for Tracking 100g Dynamic Vehicles," Proceedings of the 2001 National Technical Meeting of The Institute of Navigation, Long Beach, CA, January 2001, pp. 415-425.
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