A New Pseudolite-Based Positioning Technology For High Precision Indoor and Outdoor Positioning

A real-time positioning technology that can operate indoors and outside anywhere in the world, with sub-cm accuracy, and at low cost, is the ultimate goal for many researchers. GPS can achieve cmlevel kinematic positioning accuracy, but with some major constraints. First and foremost the use of GPS signals for indoor positioning poses very difficult challenges, due to the very weak signal levels. Indoor positioning using high sensitivity GPS receivers cannot be guaranteed in all situations, and accuracies are typically of the order of tens to hundreds of metres at best. Of course GPS is widely used outdoors for real-time cm-level positioning in numerous applications. In these situations the realtime kinematic (RTK) GPS technique is used, where a base station transmits data to a rover unit via a radio modem. In situations where GPS satellite geometry is poor or the signal availability is limited, ground-based transmitters of GPS-like signals (called “pseudolites”) can be used to augment GPS. They therefore have the potential to be used for both outdoor and indoor positioning. With enough pseudolites it is theoretically possible to replace GPS entirely, though in practice this has been difficult to achieve. Typically pseudolites use inexpensive crystal oscillators and operate independently (in the so-calle

Chris is a Fellow of the Australian Institute of Navigation,

of Philosophy in satellite geodesy from the University of Newcastle upon Tyne, UK. Joel has assisted in the development of a Locata (the mobile positioning device) and testing of the “Locata technology”. Other current research interests include pseudolites, GPS receiver firmware customization and high precision kinematic GPS positioning. Chris Rizos is a graduate of the School of Surveying, Th

BIOGRAPHY

Joel Barnes is a senior researcher within the Satellit

Structural deformation . . .

GPS has proven to be a useful tool for precision deformation monitoring applications, in both physical geodesy, and more recently for structural engineering. For continuous structural deformation monitoring (on an epoch-by-epoch basis) it is desirable for the measurement system to deliver equal precision in all position components, all of the time. However, the quality of GPS position solutions are heavily dependent on the number and geometric distribution of the available satellites. Therefore, the positioning precision is not the same in all three components, and during a 24-hour period the positioning precision varies significantly. This situation becomes worse when the line-of-sight to GPS satellites is obstructed due to trees or buildings in urban environments, reducing the number of visible satellites (often to less than 4). Locata is a new positioning technology that uses a network of ground based transceivers which cover a specific area with strong signals. This paper discusses the Locata technology and assesses its suitability for use in structural deformation monitoring applications, through an experimental trial at the Parsley Bay suspension footbridge in Sydney, Australia

Chris is a Fellow of the Australian Institute of Navigation,

Newcastle upon Tyne, UK. Joel has assisted in the development of the Locata receiver and testing of the Locata technology. Other current research interests include pseudolites, GPS receiver firmware customisation and high precision kinematic GPS positioning. Chris Rizos is a graduate of the School of Surveying, Th