Performance Analysis of a Single-Frequency, Low-Cost GPS Surveying System

Chris Rizos, Shaowei Han and Xiujiao Han

Abstract:	Over the last decade GPS "surveying" (or carrier phase-based) technology has undergone tremendous improvement and can now routinely deliver centimetre accuracy, though a not inconsiderable cost. Each GPS receiver typically costs between US$10,000 and $25,000. Furthermore, two of them are needed to perform baseline surveys. Top-of-the- line RTK ("real-time-kinematic") systems are even more expensive. Must there always be a high price to pay for high performance GPS survey technology? Single-frequency GPS receiver "boards" are now available that cost significantly less than US$1,000. (Dual-frequency GPS receiver "boards" are significantly more expensive, around US$10,000 each, and are therefore not considered here.) Baseline processing software is also now available less than US$5,000 a licence. However, real gains in efficiency, and hence significant reductions in operating costs, will require the development of new operational pro-cedures. One strategy is to use data from GPS reference stations operated by government agencies or private com-panies. The user need only purchase one GPS unit, and the requirement for user ownership and operation of a refer-ence station receiver is removed. A serious impediment in many countries is therefore the lack of a public GPS refer-ence station network at sufficient density to support sur-veyors. The "GPS traversing" technique developed by the authors a few years ago overcomes such a constraint and a reference receiver located many tens of kilometres away can be used. In this paper, a carrier phase-based GPS positioning system based on a low-cost hardware configuration is described. Several innovative data processing algorithms have re-cently been developed, such as the aforementioned "GPS traverse surveying" mode, and these have been incorpo-rated within the system design. Testing of the three main functional positioning modes has commenced: (1) Rapid static positioning, (2)GPS kinematic positioning, and (3) the GPS traverse surveying mode. Preliminary results indicate that the occupation time for each baseline in the rapid static positioning mode, to ensure quick ambiguity resolution, is of the order of 10 min-utes, although it varies for different antenna environments. GPS kinematic positioning with centimetre accuracy using "on-the-fly" ambiguity resolution is not reliable enough, though the system is capable of delivering 1 to 2 decimetre accuracy. (Kinematic positioning after initial static ambi-guity resolution is, however, accurate to the few centimetre level.) The "GPS traverse surveying" mode is a very at-tractive technique for surveying across areas where lock on the GPS satellite signals can be easily maintained, and hence is a feasible alternative to the "stop & go" technique. It can then be used for rapid static positioning (with very short observation periods of 1-2 minutes) and for kinematic positioning with centimetre accuracy. A low-cost GPS surveying system such as this can be used for a variety of applications, including low order geodetic control surveys, detail surveys, profile and engineering surveys, large-scale mapping, cadastral surveys, and so on. However, new base station-user receiver configurations that do not mimic current state-of-the-art GPS surveying systems may have to be developed in order to truly unlock the potential of such a "no-frills" system as is proposed here. One promising option is to use a multi-reference sta-tion network. A network of 3 or 4 reference receivers could "service" an entire metropolitan area. Accuracy and speed of survey using low-cost GPS receivers could be considerably enhanced, and new services such as Internet-based data processing introduced.
Published in:	Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998) September 15 - 18, 1998 Nashville, TN
Pages:	427 - 435
Cite this article:	Rizos, Chris, Han, Shaowei, Han, Xiujiao, "Performance Analysis of a Single-Frequency, Low-Cost GPS Surveying System," Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 427-435.
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