Radio Positioning using the Digital Audio Broadcasting (DAB) Signal

Over the recent decades, there have been a number of trends that have driven the desire to improve the ability to position and 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 location. These limitations are mostly due to the low transmission power of GPS satellites, where navigation signals broadcast from space are comparatively weak, especially by the time they have travelled to receivers on the ground. This makes the signals particularly vulnerable to fading in difficult environments such as built-up urban areas. The low signal-to-noise ratio (SNR) also means 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, for example, terrestrial based alternatives to GNSS such as 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 often use alternative multi-carrier modulation techniques to those methods used by most GNSS services. The major challenge of using a SoOP for location purposes is that the transmitter network infrastructure has not generally been designed with positioning as a requirement. An ongoing project, at the Institute of Engineering Surveying and Space Geodesy (IESSG) of the University of Nottingham, is directed towards an investigation of the potential of the Digital Audio Broadcast (DAB) signal for positioning purposes. A prototype Software Defined Radio (SDR) DAB positioning receiver has been developed and has now been tested. This paper presents a detailed review of the structure of the DAB signals and explains how these signals can be used as the basis of a positioning system. In addition the development of the prototype SDR receiver and the initial results are presented and discussed.