Global Navigation Satellite Systems
Research efforts in Luleå
Staffan Backén, LTU
Dr. Dennis M. Akos, LTU
Presentation Outline
 Crash Course in GNSS (GPS, Galileo)
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Constellation
Signal Structure
Signal Processing
Positioning – Accuracy - Augmentations
GNSS in Space
 Research efforts in Luleå
 Thesis - Phased Array Antenna
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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
L1
GPS bands
Galileo SAR downlink
87
15
15
.4
75
15
15
4
15 4
45
15
59
15
63
00
13
.7
78
12
60
12
37
Galileo bands
E1
Fr 91
e
(M q u e
H nc
z) y
E2
2
SAR
5
E6
12
12
8?
11
.4
76
11
64
11
L2
07
.1
12 4
1214
15
12
27
.6
E5b
5
E5a/L5
CDMA – All three systems (Glonass with a twist)
Modulation
GPS
Glonass
Galileo
BPSK (QPSK)
BPSK
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/m2 → 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
Satellite 2 position
xs2=(xs2, ys2, zs2)
Four satellites required for 3D position + time
Accuracy ≈ 7m RMS
Satellite 1 position
x =(x , y , z )
Error sources
Range r
s1
Multipath
Ionospheric, tropospheric delay
Ephemeris inaccuracies
s1
s1
s1
WAAS (America)
EGNOS (Europe)
MSAS (Asia)
DGPS, AGPS etc
2
Range r3
Range r1
Augmentation systems
SBAS
Satellite 3 position
xs3=(xs3, ys3, zs3)
Satellite 4 position
xs4=(xs4, ys4, zs4)
User location
xu=(xu, yu, zu)
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. Akos
Software Receivers
Bi-static Radar
Staffan Backén
Ph.D. student
Antenna Arrays
Quantization
GNSS course
Tore Lindgren
Research Engineer
VRS Algorithms
Student Projects
Ex: GPS/INS
Rapid Acq.
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
16.3676MHz
Rubidium oscillator
8 • 2 bits
16.3676MHz
USB2 board
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 …