Title: Ionospheric delays compensation for on-the-fly integer ambiguity resolution in long baseline LEO formations

Authors: Urbano Tancredi; Alfredo Renga; Michele Grassi

Addresses: Department of Engineering, University of Naples Parthenope, Centro Direzionale C4, Napoli, 80143, Italy ' Department of Industrial Engineering, University of Naples Federico II, Piazzale Tecchio 80, Napoli, 80125, Italy ' Department of Industrial Engineering, University of Naples Federico II, Piazzale Tecchio 80, Napoli, 80125, Italy

Abstract: This paper deals with the real-time onboard accurate relative positioning by carrier-phase differential GPS (CDGPS) of LEO formations with baselines of hundreds of kilometres. On long baselines, high accuracy can be achieved only using dual-frequency measurements and exploiting the integer nature of double difference (DD) carrier-phase ambiguities. However, large differential ionospheric delays and broadcast ephemeris errors complicate the integer resolution task. This paper is concerned with analysing possible approaches to DD ionospheric delays compensation in such applications. The first formulation models differential ionospheric delays as a function of the vertical electron content above the receivers, whereas the second one is based on combining DD measurements for removing ionospheric delays from the observation model. The effectiveness of the developed solutions is assessed by comparing the relative positioning accuracy that can be obtained on flight data. Results show that modelling the delays is advantageous for relative positioning only in mild ionospheric conditions.

Keywords: low earth orbit; LEO formations; LEO satellites; satellite formations; precise relative positioning; long baselines; carrier-phase differential GPS; CDGPS; global positioning systems; on-the-fly integer ambiguity resolution; ionospheric delays; delay compensation; delay modelling.

DOI: 10.1504/IJSPACESE.2014.060107

International Journal of Space Science and Engineering, 2014 Vol.2 No.1, pp.63 - 80

Received: 12 Aug 2013
Accepted: 18 Sep 2013
Published online: 13 May 2014 *

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