Spread Spectrum Indoor Geolocation

Benjamin B. Peterson, Chris Kmiecik, Richard Hartnett, Patrick M. Thompson and Jose Mendom

Abstract:	The design and performance results of indoor geolocation using VHF spread spectrum signals and plans for future improvements will be presented. The development of the system is funded by the US DOD 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. 5.5 ms of data is collected and averaged to a vector length of a single PRN sequence. The cross correlation of this vector average and the PRN sequence is calculated using m techniques. We then fit the leading edge of a template cross correlation obtained in the absence of multipath to the reading edge of the envelope of the measured cross correlation, in order to extract the time of arrival of the signal. Even in a modern office building with a corrugated steel roof where 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 are able to get horizontal accuracy within 3 meters of ground truth in 90% of the fixes. Time of Arrival (TOA) information is passed to a central computer for processing fixes in real time with 1.7 sec update rate via a Wireless LAN. In the future, we plan to implement the PRN generator in a programmable ASIC that will allow for chipping rates of up to 100 MHz. This higher chipping rate will allow us to better isolate direct and indirect paths and improve accuracy.
Published in:	Proceedings of the 1998 National Technical Meeting of The Institute of Navigation January 21 - 23, 1998 Westin Long Beach Hotel Long Beach, CA
Pages:	495 - 499
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In