Road to seamless positioning: Hybrid positioning system combining GPS and television signals.

摘要

A new type of positioning system that combines the Global Positioning System (GPS) and a television positioning system (TPS) is introduced. GPS is a satellite-based positioning system and has been widely used in navigation systems since its introduction in the 1970s. TPS is a relatively new system introduced in the 2000s which utilizes ground-based broadcast television stations as ranging sources.;In this dissertation, these two positioning systems, GPS and TPS, are combined to achieve seamless positioning service. Seamless coverage includes open spaces and obstructed spaces, urban and rural areas, outdoors, and indoors. GPS provides a global service, good for outdoor activities, but suffers in dense urban and indoor areas. In contrast, although TPS is successful in metropolitan areas, TPS has weaker coverage in rural areas. Because GPS and TPS are complementary in their coverage, an integrated hybrid GPS and TPS positioning system is expected to provide enhanced positioning coverage over the individual systems.;The development and demonstration of the hybrid positioning system is conducted through a comparison of pseudorange formats, a fault detection and exclusion algorithm implementation, a hybrid system implementation, and field tests. First, pseudorange formats, time of arrival (TOA) and a time difference of arrival (TDOA), are compared. Pseudoranges (range measurements with a clock bias) can be represented either in a TOA format or in a TDOA format. TOA is used in GPS while TDOA is used in TPS. Although it is known that there is no difference in positioning accuracy between TOA and TDOA, TOA-based position estimation is shown to provide more robust results under inaccurate measurement statistics and suboptimal system implementation. Thus, TOA is used for both GPS and TPS.;Second, a fault detection and exclusion algorithm is developed. Due to multipath effects in urban canyons and indoors and clock drifts in television transmitters, there exist a large number of outliers, in particular, in TPS pseudoranges. To detect and exclude these outliers, a multi-fault tolerant receiver autonomous integrity monitoring (RAIM) algorithm is proposed. The proposed RAIM combines and implements iterative steps of the multi-hypothesis solution separation (MHSS) test for fault detection and the maximum likelihood test for fault exclusion which are, respectively, based on the algorithms by Pervan and Sturza.;Third, a hybrid positioning system which combines GPS and TPS is constructed. The hybrid system is composed of a GPS receiver, a TPS receiver, and Matlab-based position estimation software. Based on pseudorange measurements from the GPS and TPS receivers, the hybrid positioning software estimates a user position and executes the multi-fault tolerant RAIM for outlier removal.;Lastly, the hybrid system is tested through an extensive field test campaign. Thirty nine sites are selected from the San Francisco Bay Area which include outdoors, indoors, urban, suburban, residential, and rural areas. At each location, one hour of stationary data is collected and processed by the hybrid positioning system.;The field test results of the hybrid system (after exclusion of two zero availability urban indoor sites) show substantially improved availability compared to the individual GPS or TPS results. While the GPS availability is fifty-one percent and the TPS availability eighty-two percent, the hybrid system is available ninety percent of the time at the tested locations. Also, after further improvement by time domain filtering and local optimization of RAIM parameters, this availability reaches over ninety-nine percent outdoors and ninety-five percent indoors. The high availability illustrates the potential of the hybrid GPS and TV positioning system as a "road to seamless positioning service." However, the low accuracy in a few harsh environments and the existence of two zero availability sites (out of thirty nine sites) reveal the challenge in urban and indoor areas. These remain as future work.