Non-GNSS Radio Positioning using the Digital Audio Broadcasting (DAB) Signal

D. Palmer, T. Moore, C. Hill, M. Andreotti, D. Park

Abstract:	Over the past decades, there have been a number of trends that have driven the desire to improve the ability to navigate in all environments. While GPS has been the driving factor behind most of these trends, there are limitations to GPS that have become more evident over time as the world has increasingly come to rely on navigation. These limitations are mostly due to the low transmission power of GNSS satellites, where navigation signals broadcast from space are comparatively weak by the time they have travelled to receivers on the ground. This makes the signals particularly vulnerable to fading in difficult environments such as urban jungles and other built up areas. The low signal-to-noise ratios (SNR) also mean that the signals are susceptible to jamming, both hostile and accidental. This motivates the need for non-GPS (or, more generally, non-GNSS) navigation technologies, and terrestrial based alternatives to GNSS such as Loran-C and eLoran, but there is also significant interest in the exploitation of other non-navigation signals for positioning and navigation purposes. These so-called ´Signals of Opportunity´ (SoOP) do not generally require any alterations to existing communications transmission infrastructure and utilise alternative multi-carrier modulation techniques to Code Division Multiple Access (CDMA) used by most GNSS. The major challenge of using a SoOP for location purposes is that the transmitter network infrastructure (which is imperative to producing a robust positioning system) is not generally designed with this particular objective as a requirement. This paper presents the initial results of an ongoing project at the Institute of Engineering Surveying and Space Geodesy (IESSG), at the University of Nottingham, UK and the Geospatial Research Centre Ltd (GRC), New Zealand. A feasibility investigation was undertaken in the use of SoOPs to track where a receiver has been when there are no GNSS signals available locally, and to do this without the prerequisite for additional infrastructure. The investigation is based on a Software Defined Radio (SDR) approach, adopted to capture the recorded "raw" spectrum and store this for post-processing. The equipment in use is the Universal Software Radio Peripheral (USRP) manufactured by Ettus Research LLC, which provides the front-end capable of capturing the raw signals. The USRP was specifically designed to be used with software called GNU Radio, an open source package of signal processing blocks written in C++/Python and run in this case on the Linux (Ubuntu) platform. Following an initial review of many candidate signals, the focus of this project was directed towards an investigation of the potential of the Digital Audio Broadcast (DAB) signal for positioning purposes. The DAB Signal has a robust composition allowing it to be captured and processed by in-vehicle (i.e. dynamic) receivers. Coded Orthogonal Frequency Division Multiplexing (COFDM) provides the multi-carrier modulation technique used by DAB. This allows a large amount of data to be transmitted in parallel over slowly-modulating individual sub-carriers. These sub-carriers are then modulated by the Differential Quadrature Phase Shift Keying (DQPSK) technique. COFDM systems encompass a synchronisation channel at the start of each transmission frame to allow a receiver to identify and correct for receiver clock errors. Results presented in this paper feature a series of Matlab based computations. An initial simulation is run to predict the potential Horizontal Dilution of Precision (HDOP) possible using combinations of national, regional and local networks in the United Kingdom, and present a contour map based on these frequency block combinations. These results are based on the latest available list of DAB transmitters in the UK. Secondly, each of the SDR processing blocks from the data reading to TDoA extraction and position computation are examined in turn to describe the complete process end to end. Finally, the results of a set of positioning trials based on real-world DAB signals using these techniques are then explored and error sources discussed.
Published in:	Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009) September 22 - 25, 2009 Savannah International Convention Center Savannah, GA
Pages:	864 - 872
Cite this article:	Palmer, D., Moore, T., Hill, C., Andreotti, M., Park, D., "Non-GNSS Radio Positioning using the Digital Audio Broadcasting (DAB) Signal," Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 864-872.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In