Artus - A Second Generation Galileo/GPS Receiver

Thorsten Lueck, Jon Winkel, Michael Bondenbach, Eckart Gohler, Nico Falk, Angelo Consoli, Francesco Piazza, Danilo Gerna, Robin Granger, Peter Readman, Steve Simpson, and Hans-Juergen Euler

Abstract:	The present paper describes the development of a second generation GNSS receiver. It is being developed in the frame of a GJU 50% funded project named Artus (Advanced Receiver Terminal for User Services) un- der the contract GJU/05/2414/CTR/ARTUS. The consortium members involved in the Artus receiver development are IFEN (overall system design and base-band processing), NemeriX (analog RF-front-end), Roke Manor Research (Antenna and RF-splitter), Leica Geosystems and inPosition (RTK software). IFEN coordinates the consortium. In essence the Artus design is based on previous receiver developments carried out by IFEN in the frame of the German Galileo Test Bed (GATE). The Artus receiver is a fully-fledged, all-in-view, all-frequencies Galileo/GPS receiver. It also supports AltBOC tracking of the Galileo E5 frequency in a bandwidth of 72 MHz. The individual sub-systems are described in the following: Antenna : Regarding the antenna, the geodetic requirement for a highly stable phase centre is examined from a basic theoretical viewpoint. To do this the relationships between beam pattern and antenna aperture distribution is examined and it is explained how these theoretical parameters relate to the mechanical layout of the antenna’s radiating structure. It is reasoned that the antenna’s phase centre is only an apparent phenomenon, as the radiation actually emanates from the whole antenna surface and not just from one point. By doing this much physical insight into why some antenna technologies can be expected to perform better than others is gained. The requirement for truewide band performance coupled with high phase centre stability results in a very demanding requirement, satisfied by only a few antenna technologies. A real world constraint is that the antenna must play its part in multi-path rejection and control. It is also necessary however that these technologies satisfy sensible size and weight constraints and can be produced at reasonable cost. RF-Front-End Founded in 2002, NemeriX developed the world’s lowest power RF front-end for GPS L1 receivers. The front-end developed in the Artus project is based on the previously developed RF ASICs NJ1007. The NJ1007 was limited to a signal bandwidth of 24MHz, which is insufficient for Galileo. In order to accommodate the higher bandwidth for the Galileo E5ab signal, NemeriX started in 2005 the development of a new RF down-converter (NJ1008). The main new features of NJ1008, which is accommodated within the RF-Front-End section of the ARTUS receiver, are the additional IF output with a much higher signal bandwidth of up to 72 MHz as well as a fully integrated VCO. Digital base band processing Based on extensive experience made within the German Galileo Test Environment (GATE), the base-band processor is based on a highly flexible FPGA design. Providing 30 channels in the basic configuration and up to 120 channels when fully equipped, each of these channels can be configured to track any signal at the L1, L2, E5 (E5a/L5 and E5b) and E6 frequency band. The analog IF signal from the four different RF-Front-Ends is digitized at a sample rate of 300 MHz with 8-bit sample resolution. The following digital signal conditioning – also realized in a single FPGA for all four input bands – ends up with four digital I-Q data stream at 100 MHz sample rate. These digital IQ data of all four frequency bands is streamed to every base-band processor. With the correlators being realized in fast baseband FPGAs of the most modern Xilinx Virtex5-type and the correlator steering in terms of signal acquisition, loop closure and tracking performed through several Microcontrollers realized by soft-cores within dedicated controller-FPGAs, maximum flexibility is achieved and allows easy adoption of new technologies and algorithms. An additional hardcore CPU within a master Virtex5-FPGA collects the measurements and navigation data from all independent channels and performs a rudimentary PVT solution to allow a flexible channel management and fast (re-) acquisition. All measurements can be made available for the user through a USB or LAN interface for further processing. Navigation solution The navigation software is the last of important key elements for use of GNSS in positioning. For maximum flexibility it has been decided in the ARTUS project to have the navigation software component on a separate computer board. The positioning itself is designed to perform the traditional navigation solution in parallel to differential positioning solutions. The paper will highlight the novel design of the navigation software component. Furthermore it will summarize positioning results based on Galileo only and in combination with GPS observations. Based on these four core technology issues, the ARTUS professional receiver for Galileo and GPS has been realized. This paper presents in detail the key elements of this modern GNSS professional receiver and characterizes their single performance as well as the overall receiver performance based on signals simulated using a constellation simulator like IFEN’s NavX-NCS and signal in space simulated within the German Galileo Test Environment (GATE)[5].
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	1008 - 1016
Cite this article:	Lueck, Thorsten, Winkel, Jon, Bondenbach, Michael, Gohler, Eckart, Falk, Nico, Consoli, Angelo, Piazza, Francesco, Gerna, Danilo, Granger, Robin, Readman, Peter, Simpson, Steve, Euler, Hans-Juergen, "Artus - A Second Generation Galileo/GPS Receiver," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 1008-1016.
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