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Global Navigation Satellite SystemsResearch 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 satellitesPeriod of 11 hours 58 minutesSix circular orbits,
20200km above the earth - MEOInclination 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 BPSKGalileo Boc(1,1), Boc(10,5), AltBoc(15,10) – not finalized
GPS transmitted and received power at L1:Satellite antenna input ≈ 27WReceived power ≈ 5×10-14 W/m2 → Received signal below thermal noise floor
E5a/L5 E5b L2 E6 SAR
1164
1176
.45
118?
1207
.14
121412
1512
27.6
1237
1260
1278
.75
1300
1544
1545
1559
1563
1575
.42
1587
1591
Frequen
cy
(MHz)
E2 L1 E1
Galileo bands GPS bands Galileo SAR downlink
GNSS CC - Signal Processing
AcquisitionFind a specific satellite signal buried in noise
Code trackingDecode time stamp
Carrier trackingDecode data bits
PositioningFour satellites required for 3D position + timeAccuracy ≈ 7m RMSError sources
MultipathIonospheric, tropospheric delay Ephemeris inaccuracies
Augmentation systemsSBAS
WAAS (America)EGNOS (Europe)MSAS (Asia)
DGPS, AGPS etc
User location xu=(xu, yu, zu)
Satellite 1 position xs1=(xs1, ys1, zs1)
Range r1
Satellite 2 position xs2=(xs2, ys2, zs2)
Satellite 3 position xs3=(xs3, ys3, zs3)
Satellite 4 position xs4=(xs4, ys4, zs4)
Range r2
Range r3
Range r4
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
GNSS Research Efforts in Luleå
Dr. Dennis M. AkosSoftware Receivers
Bi-static Radar
Dr. Dennis M. AkosSoftware Receivers
Bi-static Radar
GNSS courseGNSS courseStudent Projects
Ex: GPS/INSRapid Acq.
Student ProjectsEx: GPS/INS
Rapid Acq.
Staffan BackénPh.D. student
Antenna ArraysQuantization
Staffan BackénPh.D. student
Antenna ArraysQuantization
Tore LindgrenResearch Engineer
VRS Algorithms
Tore LindgrenResearch 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
16.3676MHz Rubidium oscillator
8 • 2 bits 16.3676MHz
33MB/s
•
••
Antenna Array Layout
GroundplaneAluminum1m diameter
Antenna elementsCommercial GPS patch antennas
Spacingλ/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 …