Pirazzi GabrieleIntecs S.p.A
Bruxelles, 10/04/2008
““Study of an SDR GNSS receiver”Study of an SDR GNSS receiver”
Chapter of Rome
M.Sc. In Advanced Communication and
Navigation Satellite Systems
AFCEA’s Student Conference 2008
Slide 2 of 20
Agenda
• SDR Definitions• SDR Applications• GNSS receiver• Acquisition Phase
• GPS• Giove-A(Galileo)• SBAS
• Tracking Phase• GPS• Giove-A(Galileo)• SBAS
• Space Software Receiver
Slide 3 of 20
Definitions
• Software Radio:the digitization is at the antenna and all of the processing required is performed for the radio by software.
• Software Defined Radio:the digitization is performed at some stage downstream from the antenna, typically after wideband filtering, low noise amplification, and down conversion to a lower frequency in subsequent stages.
Slide 4 of 20
SDR purpose
• The purpose of the Software Radio:• Move the ADC (analog-to-digital) as close as possible to
the antenna. • Elaborate the samples obtained through a
reprogrammable processor.
• Advantages:• Removing analog components with non-linear
characteristics, depending on the temperature and age. • Single antenna for multi-constellation, multiband and
multi-modes systems . • High flexibility in the implementation of new algorithms:
update software without replace hardware. • Reducing costs and maintaining
Slide 5 of 20
Applications (1)
SDRSDR
One Terminal, multiple Applications.
Slide 6 of 20
Applications (2)
User Terminal
Hardware Layer
Software Layer(management, control
and configuration)
Application Layer
Installing, upgrading
software module
GPS Galileo
UAV
Radar
SatCom
Control Center
Slide 7 of 20
GNSS Receiver Structure
Channel n SoftwareCorrelatorCanale 2
SoftwareCorrelator
Downconversion
Frequency synthesize
r
Reference oscillator
A/Dconverter
AGC
Channel 1 SoftwareCorrelatorIF
AnalogueRF
Acquisition
Tracking
IF Digital
Navigationprocessing
Hardware Software
Slide 8 of 20
• RF Carrier:
• Single IF conversion:
• Bandwidth (-3dB):
• 2 bit ADC (sign and mag)
• Sampling frequency:
• AGC• TCXO
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
x 10-3
-3
-2
-1
0
1
2
3Segnale uscita ADC (IF)
Tempo [ms]
Am
pie
zza
0 1 2 3 4 5 6 7 8
-20
-15
-10
-5
0
5
Frequenza [MHz]
Ma
gn
itud
e [d
B/H
z]
Stima spettro di Densita di Potenza (Welch)
-4 -3 -2 -1 0 1 2 3 40
1
2
3
4
5
x 104 Istogramma
Campioni
Nu
me
ro d
i ca
mp
ion
iFront-end
MHzfL 42.15751
MHzf IF 1304.4
MHzBWIF 2.2
MHzfCamp 3676.16
Slide 9 of 20
Acquisition phase
• Acquisition scope:
• Determinate the number of visible satellites.
• Coarse estimate of the beginning C/A code .
• Coarse estimate of the carrier included Doppler.
Slide 10 of 20
GPS, Giove-A real data acquisition
PRN CodePhase Doppler [Hz] Amplitude2 6612 -500 7803731,65 10134 -500 125892056 4419 2000 193867257 15860 2000 121419409 14228 -3500 7486397
12 13644 -1500 1063796624 14005 3500 6385256,130 5942 500 1869288031 14096 3500 5739081,8
Slide 11 of 20
Incoherent Integration SBAS
Slide 12 of 20
Unexpected Signal: GAGAN!
• Geostationary satellite acquired, tracked and decoded:
AOR-E Artemis IOR-W Gagan
Constellation Name PRN Orbital
Position
EgnosInmarsat-3-F2
(AOR-E)120 15.5°W
Egnos Artemis 124 21.5°E
EgnosInmarsat-3-F5
(IOR-W)126 25°E
WAAS Anik F1R 138 107.3°W
WAAS Galaxy 15 135 133°W
MSAS MTSAT-1R 129 140°E
MSAS MTSAT-2 137 145°E
Gagan Inmarsat-4-F1 127 64°E
First signal transmitted at the end of December 2007
Analisis of Message 18
(Ionosperic Grid Points
Mask, IGP) and Message 9
(Geo Navigation Message)
confirm it’s Gagan!
EGNOS GAGAN
Slide 13 of 20
Tracking
• Tracking scope: Tracking over time the carrier and the GPS code.
• Implemented Tracking closed loop: PLL (Phase Lock Loops) Costas 2° order. DLL (Delay Lock Loops) incoherent 2° order. FLL (Frequency Lock Loops) del 1° order.
Slide 14 of 20
Tracking Giove-A E1B
Slide 15 of 20
Tracking GPS real data
0 100 200 300 400 500 600 700 800 900 10000
0.5
1
1.5
2
2.5
3x 10
7
Tempo [msec]
Co
rre
lazi
on
e
SV 6 Componente in Fase (pull-in)
IPrompt2
ILate2
IEarly2
0 100 200 300 400 500 600 700 800 900 10000
0.5
1
1.5
2
2.5
3x 10
7
Tempo [msec]
Co
rre
lazi
on
e
SV 6 Componente in Quadratura (pull-in)
QPrompt2
QLate2
QEarly2
0 100 200 300 400 500 600 700 800 900 10001500
1600
1700
1800
1900
2000
Tempo [msec]
Fre
qu
en
za [H
z]
SV 6 Inseguimento in Frequenza (pull-in)
0 100 200 300 400 500 600 700 800 900 1000-6000
-4000
-2000
0
2000
4000
6000
Tempo [msec]
Am
pie
zza
SV 6 Dati di Navigazione (pull-in)
0 100 200 300 400 500 600 700 800 900 1000
-50
0
50
Tempo [msec]
Err
ore
su
lla fa
se [°
]
SV 6 PLL discriminatore errore (pull-in)
0 100 200 300 400 500 600 700 800 900 1000-1
-0.5
0
0.5
1
Tempo [msec]
Err
ore
su
l co
dic
e [c
hip
s]
SV 6 DLL discriminatore errore (pull-in)
Slide 16 of 20
Giove-A Message Decoded (Viterbi)
Packets 5-8
First Frame
Packets 1-4
Packets 1-4
Packets 5-8
Carrier Status Nav. Data Health
Slide 17 of 20
MIOSat mission
MIssione Ottica su microSATellite
Slide 18 of 20
SSR Requirements
Function Value
Dimensions 100x100x90mm
Weight <0.7 Kg
Antenna weight <50g (cable excluded)
Power 5 V
Power consumption <12W
Antenna gain > 5 dBi at Zenith
Noise figure < 2.5 dB
Operative frequency L1 GPS e GALILEO
GNSS systems GPS (GALILEO HW-ready)
Receiver linearity TBD
ADC quantization bits 1
AGC Embedded in the receiver
Sampling frequency 16.8 MHz (TBC)
Oscillator stability TCXO typical
Electric interface RS 422
Launch vibrations compliance TBD (reference VEGA launcher suggested)
Mission lifetime 6 months ground, 2.5 years in flight
Operating temperature -20°/+50°
Radiation tolerance >10 Krad
Slide 19 of 20
SSR Scheme
• Satellite or System on Chip (SoC).• Less volume and mass.• Reduced power consumption.• Fewer interconnects, solder joints e
bound wires.• Soft-core CPU: Leon3
Slide 20 of 20
Pirazzi GabrieleIntecs S.p.A.
Bruxelles, 10/04/08
““Study of an SDR GNSS receiver”Study of an SDR GNSS receiver”
Q & A
SESSION
Thank you for your attention
