The Art of ARTUS–A Second-Generation Galileo/GPS Receiver
Europe’s Galileo program is seeking to accelerate receiver technology development even as the space and ground segments of the system are being implemented. A group of companies have collaborated on development of a geodetic-grade Galileo-GPS receiver: ARTUS. The engineering team in charge of the project describes their work to date, including tests that tracked signals from China’s Compass system as well as GIOVE-A and GPS.
Creation of new global navigation satellite systems and modernization of existing ones is introducing many new signals across a wide swath of RF spectrum now and in the near future. These developments are accompanied by a growing need to design new GNSS receivers that can work with new signal structures on an increasing number of frequencies.
Europe’s Galileo program has supported a number of activities intended to promote innovations in receiver design, such as prototype Galileo user equipment, reference receivers, and so on.
One such activity is a project named ARTUS (Advanced Receiver Terminal for User Services), 50 percent of which is financed by funds allocated by the Galileo Joint Undertaking (GJU). A consortium of four companies is leading the ARTUS project (see "Acknowledgments" below)
ARTUS supports the development of receiver technologies to aid the research and development activities for Galileo “professional” receivers. These efforts are designed to facilitate the availability of Galileo professional receiver prototypes and antennas at an early stage.
ARTUS provides Galileo/GPS navigation capability. All three Galileo frequencies (L1, E6 and E5a/E5b) are supported as well as the GPS L1, L2 and L5 (L5=E5a) frequencies.
The receiver supports any BPSK (GPS-C/A, Galileo E5a and E5b (sideband tracking), AltBOC (E5ab), Galileo L1-B/C (BOC(1,1)) as well as BOCc(15,2.5) (E1-A / E6-A); GIOVE-A transmits BPSK (E5a/E5b/E6) and BOC(1,1) (E1).
Although the receiver can track the modulations foreseen for the PRS, it cannot generate the corresponding codes. One can, however, do performance measurements using periodic substitute codes.
Although not initially planned, the consortium has decided to also implement the GPS L2 band for commercial reasons. The unit performs the measurements and processes the raw data to provide an RTK solution.
The Artus design will also form the basis for a breadboard development of the next generation RIMS receivers. This development will be conducted in the frame of an ESA contract lead by IFEN with NemeriX and Euro Telematik as subcontractors.
This article describes the design and operation of the second-generation ARTUS receiver with a particular focus on innovations in four key areas: antenna, RF front-end, digital baseband processing, and navigation software.
Although originally intended to focus primary on tracking Galileo and GPS signals, the flexible design of ARTUS also allows it to receive and track signals from the Russian GLONASS system and China’s Beidou.
After discussing the receiver design and operation, we will briefly describe some of the results of testing using combinations of laboratory GNSS signal simulators, signals-in-space, and simulated signals generated in the German Galileo Test Bed (GATE). . .
With the availability of up to 120 channels, the receiver is well equipped for future navigation systems; however, it can also be configured in a version with only 20 or 40 channels for tracking the currently available GPS (L1 and L2) alone.
The modular concept, applied even for the firmware of the baseband processor FPGAs, allows easy adaptation of the algorithms developed for the ARTUS receiver or fast implementation of new algorithms. And if the IP protocol is used, any user interface can easily connect — even remotely — to the receiver — whether for navigation or monitoring purposes.
The ARTUS project is now in its qualification phase. Further developments aim for the commercialization of the receiver.
(For the complete article, including figures, charts, and images, please download the PDF version at the link above.)
The consortium members involved in the ARTUS receiver development are ifEN (overall system design and baseband processing), NemeriX (analog RF-front-end), Roke Manor Research (antenna and RF splitter), Leica Geosystems and inPosition (RTK software). 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).
GATE is being developed on behalf of the DLR (German Aerospace Center, Bonn-Oberkassel) under contract number FKZ 50 NA 0604 with funding by the BMWi (German Federal Ministry of Economics and Technology). DLR kindly gave its permission to publish the preliminary test results.
ManufacturersThe RF ASIC used in ARTUS is the NJ1008 from NemeriX, Manno, Switzerland; the earlier generation RF ASIC is the NemeriX NJ1007. The simulated GNSS signals were generated by a NavX-NCS from IfEN GmbH, Poing, Germany. The ARTUS receiver integrates the TRI-G07 antenna from Roke Manor Research Ltd., Romsey, Hampshire, United Kingdom, Virtex5 FPGAs from Xilinx, San Jose, California, USA, and ADF4110 PLLs from Analog Devices, Norwood, Massachusetts, USA. The medium- and low-speed baseband processing following signal conditioning is executed on Xilinx Microblaze soft-core CPUs. Figures 8 and 9 are displayed on Google Maps by Google Inc., Mountain View, California, USA.
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