Global Navigation Satellite Systems Research efforts in Luleå Staffan Backén, LTU Dr. Dennis M. Akos, LTU

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?

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

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× W/m 2 → Received signal below thermal noise floor

GNSS CC - Signal Processing  Acquisition  Find a specific satellite signal buried in noise  Code tracking  Decode time stamp  Carrier tracking  Decode data bits

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

GNSS in Space - Considerations  Software altitude/speed limit – commercial low cost receiver  To counteract missile development … 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

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

Antenna Array Principle – Nulling Example

GNSS Antenna Arrays – why #1?

GNSS Antenna Arrays – why #2?

Example of Beam Forming

IF Data Recording Setup Front end 1 Front end 8 USB2 board MHz Rubidium oscillator 8 2 bits MHz 33MB/s

Antenna Array Layout  Groundplane  Aluminum  1m diameter  Antenna elements  Commercial GPS patch antennas  Spacing  λ/2 ( ≈ 9,5 cm)

Typical Front End Design

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 …