Author: Wang, Ning
Title: An alternative DGPS algorithm for GPS mobile phone
Degree: M.Sc.
Year: 2009
Subject: Hong Kong Polytechnic University -- Dissertations.
Global Positioning System.
Telecommunication systems.
Cellular telephones.
Department: Department of Land Surveying and Geo-Informatics
Pages: ix, 74 leaves : ill. (some col.) ; 30 cm.
Language: English
Abstract: Besides handheld GPS receivers, GPS has been gradually integrated with many other devices and mobile phone is a typical example. The accuracy of GPS built in mobile phone is also paid great attention by users, telecommunication service provider, chip vendors as well as mobile phone manufactures. Several opinions have been conceived to improve the positioning accuracy of GPS mobile phone and these opinions are considered in different point of views such as chipset, navigation software and telecommunication network. Ntrip (Networked Transport of RTCM via Internet Protocol) provides a convenient way to easily transmit any kind of GNSS data via Internet including DGPS corrections. Ntrip has been applied in surveying engineering since its birth on the year of 2004, but little research has been made on using DGPS data coming from Ntrip to correct single point positioning of mobile phone. This dissertation attempts to verify the feasibility of the opinion with the existing knowledge, experience and tools. Experiments are also designed and carried out for verifying the effect of corrections data applied for improving the positioning accuracy of GPS mobile phone. Single point positioning of GPS mobile phone tells users latitude, longitude and altitude. At the same time RTCM DGPS data are obtained via Ntrip service. After decoding, pseudo-range correction could be acquired. Pseudo-range difference can not be applied directly here because currently most existing mobile phones embedded with GPS chips can not output raw pseudo-range measurement. But positional difference is applicable here. That is through a series of mathematical operations, pseudo-range corrections can be converted to coordinates' corrections multiplied by the direction cosines of the unit vector pointing from the approximate user position to each satellite. Finally approximate positions are subtracted by coordinates' corrections directly and a new pair of coordinates is obtained for every point. Practically, for better precision, this computation is iterative until a satisfying accuracy appears. That is, the newly obtained coordinates should be taken as the approximate position again, and the all computations should be based on this new positional value, including the distance between satellites and users. Experiments result shows that the opinion and working flow are feasible. And the calculation results reveal that the improvement of positional difference applied in mobile phone positioning is obvious.

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