Global Navigation Satellite Systems Research efforts in Luleå
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Transcript Global Navigation Satellite Systems Research efforts in Luleå
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
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 …