Foot-to-Foot Range Measurement as an Aid to Personal Navigation

T.J. Brand, R.E. Phillips

Abstract:	Ultimately there will be times when all enhancements to GPS signal reception fail. In these situations a number of approaches to GPS denied navigation have been proposed. These often make use of supplemental radio frequency signals, some of which actually require setting up a local RF infrastructure. The personal navigation aid proposed here, although utilizing a radio frequency signal, is intended to be self contained and of low power. It consists of a micromechanical IMU on each boot combined with a series of foot-to-foot range measurements. A frequency generator at the waist sends a signal down one leg to a transmitting antenna on one boot. The RF signal is received on the other boot and sent to the waist pack thereby closing the loop. A detector at the waist measures phase change and thus measures the changing distance between the two feet. Our analysis shows that this scalar distance change measurement used in conjunction with micro-mechanical inertial instruments on each foot and combined with "zero-velocity updates" at each (or most) foot falls enables quite accurate personal navigation. The performance of an unaided inertial navigation system based on modest quality micromechanical instruments is truly poor. Our analysis shows a 2.5 km error in each horizontal direction after walking in a straight line for 10 minutes (2900 ft). The addition of zero velocity updates reduces this error to 60 m predominantly in the cross range axis. The addition of the foot-to-foot range change measurement reduces this value by another two orders of magnitude, to 0.6 m This measurement concept is a big step toward an accu-rate self-contained personal navigation system It is not dependent on external signals or ambient light. The RF could be very low power (it only has to extend over the foot-to-foot distance). As such it should be relatively covert compared to a Doppler radar or acoustic Doppler device. There is a price to pay in terms of body mounted hardware, but this could be mitigated by the push toward instrumented clothing.
Published in:	Proceedings of the 59th Annual Meeting of The Institute of Navigation and CIGTF 22nd Guidance Test Symposium (2003) June 23 - 25, 2003 Hyatt Regency Hotel Albuquerque, NM
Pages:	113 - 121
Cite this article:	Brand, T.J., Phillips, R.E., "Foot-to-Foot Range Measurement as an Aid to Personal Navigation," Proceedings of the 59th Annual Meeting of The Institute of Navigation and CIGTF 22nd Guidance Test Symposium (2003), Albuquerque, NM, June 2003, pp. 113-121.
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