Pseudolite Implementation for Social Infrastructure and Seamless Indoor/Outdoor Positioning

I. Petrovski, K. Okano, M. Ishii, H. Torimoto, Y. Konishi, R. Shibasaki

Abstract:	In 2001 the GPS Division of DX Antenna (now GNSS Technologies Inc.) initiated a consortium named a Precise Positioning Social Infrastructure Research Forum for pseudolite related researches and applications in Japan. The consortium consists of leading companies and research institutes. As a result of consortium activity, we are now participating in the development of prototypes for two ITS (Intelligent Transportation Systems). These prototypes have been accepted by Japan Public Works Research Institute for evaluation, together with four alternate proposals out of more than one hundred applicants. This paper presents current results and status of these projects. Proposed two ITS, namely ITS for pedestrians (PITS) and highway ITS (HITS), although aim slightly different application areas, share the same approach and basic components. The systems were accepted as a basis for a development of corresponded test systems at evaluation stage. Both systems implement pseudolites as main augmentation system to GPS to allow continuous and uninterrupted positioning on highways, in tunnels, parking lots and urban canyons. Indeed, pseudolites allow user to continue to use GPS-based equipment in places with limited GPS satellites visibility or even without GPS satellites at all. Pseudolites also have an advantage that their error budget (as compared with satellite signals) is free from atmospheric and orbital errors. Pseudolites however contribute extra clock terms and therefore require some synchronization technique. Pseudolite signals also have larger multipath errors than are typical in satellite applications. Main problem for pseudolite implementation outdoor is in-band interference with GPS. Different types of pseudolites can induce different interference. There are also different ways to cope with it. We have conducted number of tests to ensure the absence of interference on non-participant receivers from different manufactures. We tested how such factors as power attenuation, frequency shift, pulsing scheme with variable duty cycle and few pseudolites with overlap zone will affect interference. Procedures that had been implemented during licensing of our outdoor tests in Japan can be proposed as a basis for a standard test. To provide seamless positioning in places, where GPS satellites are inaccessible, an inexpensive pseudolite system had been developed and tested. We considered a variety of system designs and concepts including pseudolite combined with DGPS, pseudolite monitored by master station, single-site installation vs. network installation, GPS synchronization vs. external clock synchronization, etc. The developed prototype was tested with GSS single-channel simulators and off the shelf IntegriNautics Pseudolites. Two types of GPS receiver had been used in combination with proprietary software, which was implemented in post-processing mode and in real time in attached PC. Now we are putting the algorithms into the receiver firmware to make the system more portable. The developed pseudolite system allows code-based indoor positioning with just two pseudolites. A re-translation of GPS signals into the premises allows us to compensated receiver clock error. A user altitude and coordinates of an outdoor antenna are transmitted as a part of special correction message. The developed pseudolite based system has been tested both indoor and outdoor in a real city environment in Tsukuba and downtown Tokyo for two weeks (one week during a preparation and one week during an official test). The paper presents results of these tests, which demonstrate possibility and great potential for pseudolite implementation in social infrastructure.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	69 - 76
Cite this article:	Petrovski, I., Okano, K., Ishii, M., Torimoto, H., Konishi, Y., Shibasaki, R., "Pseudolite Implementation for Social Infrastructure and Seamless Indoor/Outdoor Positioning," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 69-76.
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