Benjamin B. Peterson, Chris Kmiecik, Richard Hartnett, Patrick M. Thompson, Jose Mendoza, and Hung Nguyen

Peer Reviewed

Abstract: The design and performance results of indoor geolocation using very high frequency (VHF) spread spectrum signals and plans for future improvements are presented. The development of the system is funded by the U.S. Department of Defense to support small unit operations in urban environments. In the present system, direct-sequence spread spectrum signals at 258.5 MHz carrier frequency and 23.5 MHz chipping rate are generated and transmitted by a small hand-held, battery-operated transmitter inside the building. The signal is received by four or more receivers located external to the building. The signals are downconverted and digitized at 8 bits and 94 MHz. The cross- correlation envelope is calculated using fast Fourier transform (FFT) techniques. The leading edge of the cross-correlation envelope is fit to a template cross- correlation obtained in the absence of multipath to extract the time of arrival (TOA) of the signal. Even in a modern office building with a corrugated steel roof where the indirect path is orders of magnitude greater than the direct path, we are able to reliably track the leading edge of the direct path. In data collected thus far, we have been able to obtain horizontal accuracy within 3 m of ground truth in 90 percent of the fixes. TOA information is passed to a central computer via a wireless network for processing and plotting fixes in real time with a 1.7 s update rate.
Published in: NAVIGATION: Journal of the Institute of Navigation, Volume 45, Number 2
Pages: 97 - 102
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