PPP-RTK: Precise Point Positioning Using State-Space Representation in RTK Networks

Gerhard Wabbena, Martin Schmitz and Andreas Bagge

Abstract:	The concept of precise point positioning (PPP) is currently associated with global networks. Precise orbit and clock solutions are used to enable absolute positioning of a single receiver. However, it is restricted in ambiguity resolution, in convergence time and in accuracy. Precise point positioning based on RTK networks (PPP-RTK) as presented overcomes these limitations and gives centimeter-accuracy in a few seconds. The primary task in RTK networks using the Geo++ GNSMART software is the precise monitoring and representation of all individual GNSS error components using state-space modeling. The advantages of state-space modeling are well known for PPP applications. It is much closer to the physical error sources and can thus better represent the error characteristics. It allows to better separate the various error sources to improve performance and can lead to much less bandwidth for transmission. With RTK networks based on GNSMART it is possible to apply the PPP concept with high accuracy. Ambiguity resolution within the RTK network is mandatory and allows the precise modeling of the system state. Since the integer nature of the carrier phase ambiguities is maintained, all error components can be consistently modeled and give full accuracy in an ambiguity fixing GNSS application. For today's realtime applications, observations of a reference station together with network derived parameters to describe distance dependent errors or a virtual reference station are transmitted to GNSS users in the field using the RTCM standards. This can be termed as representation in observation space (Observation Space Representation: OSR). In contrast to this, also the actual state-space data can be used for the representation of the complete GNSS state (State Space Representation: SSR). Hence, precise absolute positioning based on a RTK network (PPP-RTK) using state-space data is a practicable concept. In principle, the concept can be applied to small, regional and global networks. A reference station separation of several 100 km to achieve ambiguity resolution and therefore the key-issue to PPP-RTK is already possible with GNSMART. The complete transition from observation-space to state- space requires the definition of adequate formats and standardized models to provide the state-space data for GNSS application. A single receiver then can position itself with centimeter-accuracy within a few seconds in post-processing and realtime applications. In between, state-space data can still be used to generate data in observation-space, e.g. RTCM or RINEX format, through a conversion algorithm. The state-space concept and pre-requisites are discussed. The benefits of state space representation of GNSS errors and their applications are pointed out.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	2584 - 2594
Cite this article:	Wabbena, Gerhard, Schmitz, Martin, Bagge, Andreas, "PPP-RTK: Precise Point Positioning Using State-Space Representation in RTK Networks," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 2584-2594.
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