Bandwidth Efficient ATSC TDOA Positioning in GPS-Denied Environments

Kaylene L. Carter, Rohan Ramlall, Murali Tummala, John McEachen

Abstract:	It is widely known that GPS is unreliable in indoor environments due to its low signal strength and high frequency [1], and thus some type of system complementary to GPS is required for navigation in indoor environments. In contrast with GPS, certain radio frequency (RF) signals of opportunity (SoOP) provide high powered, low frequency signals. SoOP are signals that can be used for positioning, navigation, and timing (PNT) even though their design intent is for applications other than PNT [2]. The Advanced Television Systems Committee (ATSC) signal is designed for digital television transmission, yet the exploitation of its recurring training sequences and known transmitter locations allows positioning estimates to be made. The objective of this research is to use ATSC signals to produce two-dimensional indoor positioning solutions. The recurring pseudo-random noise (PN) sequence embedded in the signal may be used in cross-correlation to produce time of arrival (ToA) information. A reference station (known position) and mobile station (unknown position) each measure the time of arrival of DTV signals from three or more TV towers. The clocks of both stations are synchronized, and the reference only shares its ToA measurements with the mobile; unlike conventional time difference of arrival (TDoA) where the reference shares the entire received signal with the mobile [3]. A least squares algorithm is then implemented to compute a TDoA-based position estimate. With thousands of DTV towers across the North American continent, the proposed scheme could be applied anywhere there is reception from at least three TV towers. An advantage of DTV positioning is that it does not require any changes to the existing DTV infrastructure. The only additions required are the monitor receiver, a user receiver, and a communications link between the two. This paper presents actual experimental results of the aforementioned TDoA positioning scheme using the ATSC signal in San Diego, CA. Dynamic indoor and stationary open-sky test results are presented representing worst and best case scenarios [4]. The hardware platform used is the Universal Software Radio Peripheral (USRP) N210. A review of current literature on the use of the USRP did not turn up any results on its use for positioning using the ATSC signal. The experimental results demonstrate that the positioning scheme is capable of producing meter level (order of magnitude) positioning accuracy in outdoor environments and tens of meters (order of magnitude) positioning accuracy in indoor environments. The effects that factors such as TV tower elevation, power transmission, and TV tower geometry have on the accuracy of the estimated ranges, and thus on overall positioning accuracy, are also discussed.
Published in:	Proceedings of the 2013 International Technical Meeting of The Institute of Navigation January 29 - 27, 2013 Catamaran Resort Hotel San Diego, California
Pages:	717 - 725
Cite this article:	Carter, Kaylene L., Ramlall, Rohan, Tummala, Murali, McEachen, John, "Bandwidth Efficient ATSC TDOA Positioning in GPS-Denied Environments," Proceedings of the 2013 International Technical Meeting of The Institute of Navigation, San Diego, California, January 2013, pp. 717-725.
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