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Global Navigation Satellite Systems Research efforts in Luleå Staffan Backén, LTU Dr. Dennis M. Akos, LTU
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Presentation Outline Crash Course in GNSS (GPS, Galileo) Constellation Signal Structure Signal Processing Positioning – Accuracy - Augmentations GNSS in Space Research efforts in Luleå Thesis - Phased Array Antenna How? Why 1 & 2 & example Hardware Design – Dataset Recording Research Status Questions?
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GNSS CC - GPS Constellation Minimum 24 satellites Period of 11 hours 58 minutes Six circular orbits, 20200km above the earth - MEO Inclination angle of 55° relative to the equator Passive system Virtual stars
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GNSS CC – Signal Structure CDMA – All three systems (Glonass with a twist) Modulation GPS BPSK (QPSK) Glonass BPSK Galileo Boc(1,1), Boc(10,5), AltBoc(15,10) – not finalized GPS transmitted and received power at L1: Satellite antenna input ≈ 27W Received power ≈ 5×10 -14 W/m 2 → Received signal below thermal noise floor
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GNSS CC - Signal Processing Acquisition Find a specific satellite signal buried in noise Code tracking Decode time stamp Carrier tracking Decode data bits
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Positioning Four satellites required for 3D position + time Accuracy ≈ 7m RMS Error sources Multipath Ionospheric, tropospheric delay Ephemeris inaccuracies Augmentation systems SBAS WAAS (America) EGNOS (Europe) MSAS (Asia) DGPS, AGPS etc
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GNSS in Space - Considerations Software altitude/speed limit – commercial low cost receiver To counteract missile development … 18000 m, 515 m/s Roll issue Antenna direction not fixed relative to the earth Higher doppler More extensive acquisition when traveling very fast GNSS satellite antenna pattern Directed towards earth Predictable motion Kalman filter
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GNSS Research Efforts in Luleå Dr. Dennis M. Akos Software Receivers Bi-static Radar GNSS course Student Projects Ex: GPS/INS Rapid Acq. Staffan Backén Ph.D. student Antenna Arrays Quantization Tore Lindgren Research Engineer VRS Algorithms
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Antenna Array Principle – Nulling Example
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GNSS Antenna Arrays – why #1?
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GNSS Antenna Arrays – why #2?
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Example of Beam Forming
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IF Data Recording Setup Front end 1 Front end 8 USB2 board 16.3676MHz Rubidium oscillator 8 2 bits 16.3676MHz 33MB/s
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Antenna Array Layout Groundplane Aluminum 1m diameter Antenna elements Commercial GPS patch antennas Spacing λ/2 ( ≈ 9,5 cm)
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Typical Front End Design
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Research Status Completed Hardware design and implementation Antenna array USB2 transfer – hardware, firmware and host program Dataset recording Several dataset during a day In progress Verifying dataset Antenna phase center determination Coming up Algorithm development Adaptive algorithms, pre and/or post correlation beam forming Future work Interference mitigation New hardware platform required …
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