Positioning in environments where GPS fails

SUMMARY The applications of GPS can be found across almost all of a nation's economic, scientific and social activities. The major shortcoming of GNSS is that it is usable everywhere where there is clear sky, and hence fails to operate where it's impossible or difficult to receive the satellite signals. In some difficult signal environments – principally where the satellite signals are weak (<-142 dBm) and multipath is severe – " high sensitivity " GPS/GNSS and/or assisted-GPS/GNSS can be used to improve positioning, navigation and timing availability. Other sensors can also be integrated with GPS/GNSS to improve positioning. In environments where GPS/GNSS completely fails alternative positioning technologies based on WiFi signals or ultrasound etc. could be used. In this paper, some of the research carried out in the School of Surveying and Spatial Information Systems, University of New South Wales, into positioning in environments where standard GPS fails is described.