From Divergence to Convergence, GNSS Assistance in Network Carrier Independent Format

Kimmo Alanen and Jari Syrjarinne

Abstract:	In the cellular business, the location based services are nowadays getting more focus from the emergency call positioning. The assisted Global Positioning System (GPS) positioning is currently seen as the best means of positioning. Even though the GPS has currently the status of being the only truly usable satellite constellation, there are several other Global Navigation Satellite Systems (GNSS) to come. The European Union is deploying the GALILEO system, Russia has GLONASS and they are already executing their plans for the moderated GLONASS, and Japan is constructing a GPS augmentation system called the Quasi-Zenith Satellite System (QZSS). Above this, there are also ongoing activities towards a modernized version of the GPS. All of these new constellations will introduce several new positioning signals for open service use. As a matter of fact, the number of usable signals for open service will most likely triple in the next decade. Of course, all of the satellite based positioning methods benefit from the assistance data similarly as assisted GPS. With assistance, improvements in sensitivity and faster time to first fix can be obtained. The benefits to the end user from using more than one satellite constellation in a hybrid solution are of course undisputable as shown in many studies. The improvement in coverage due to the increased number of satellites in the constellation is already reason enough to implement such hybrid capability into the cellular terminals. The assistance data itself is delivered to the terminal using several different protocols. Each cellular network has its own protocol of delivering this information; actually each cellular network has more than one way of delivering this information to the terminal. However, the assistance data itself, in highly categorized structures, consists of only four different information elements that are actually needed in terminal based positioning: navigation model (ephemeris), reference time, reference location, and ionosphere model. Even though this is the case, the information elements for the current GPS assistance for these parts are already slightly different in each different protocol. The differences in information elements create design and implementation challenges and especially many interoperability testing issues with multi-mode phones supporting more than one cellular system. This present paper will list the differences between these major cellular systems from the GNSS assistance point-of- view. The paper will describe in more detail the consequences of this divergence. It will also compare other aspects of the assistance, such as bandwidth limitations of the data channel, power consumption, suitability for broadcasted data delivery and suitability for global data delivery. The paper will then describe a solution to convergence from all of these diverged standards without any compromises in performance. In closing, a short glance is given to the current A-GNSS standardization status in 3GPP work groups.
Published in:	Proceedings of the 2007 National Technical Meeting of The Institute of Navigation January 22 - 24, 2007 The Catamaran Resort Hotel San Diego, CA
Pages:	85 - 90
Cite this article:	Alanen, Kimmo, Syrjarinne, Jari, "From Divergence to Convergence, GNSS Assistance in Network Carrier Independent Format," Proceedings of the 2007 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2007, pp. 85-90.
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