Transcript Enabling the transition of satellite navigation solutions

-The GALILEO & GPS Software Receiver Company
Software Receiver Technology
30-September-2004
Tampere University of Technology
Glenn MacGougan
[email protected]
+46 703113880
Copyright © 2004 NordNav Technologies AB
NordNav Technologies AB
• Unique Competence
GPS & GALILEO
 Real-time Software Receiver
Technology
• Headquarter in Luleå, Sweden
 Luleå University of Technology
 Office in Stockholm
• Developing and licensing real-time GPS & GALILEO
software receivers
Copyright © 2004 NordNav Technologies AB
Agenda
• GNSS Receiver Technology
– Traditional GNSS Receiver Technology
– Software Radio Technology
– Software GNSS Receiver Technology
• Demonstration
– NordNav-R30 Software GPS Receiver
– New Features
• GPS and Galileo
• Conclusion
Copyright © 2004 NordNav Technologies AB
GNSS Receiver – 3 Steps
• Search phase (acquisition)
t0
Start GPS
0-2 sec
Acq
t1
Tracking
1.2-6 sec
No
TOW decoded ?
t2
No
Yes
Ephemeris decoded ?
18-30 sec
No
Yes
4 satellites ?
Yes
Pos Fix
– Satellite, Carrier Frequency, Code
phase
• Track satellites (tracking)
– Adjust local replica signal using
two coupled loops
• Code - Delay-Lock-Loop
• Carrier - Phase-Lock-Loop
– Decode Data message
• Navigation computation (navigation)
– ”Triangulate” position
• Distance to satellites known and their
precise position
– X,Y,Z, Velocity and Time
t3
Copyright © 2004 NordNav Technologies AB
Traditional GNSS Receiver Architecture
• Block diagram of a typical GNSS receiver
Antenna
Baseband ASIC
Analog RF Front End ASIC
AGC
N
2
RF
Pre Amp
(LNA)
Down
Converter
Reference
Oscillator
Frequency
Synthesizer
User
Interface
Analog IF
Low Speed Comm Link
A/D
Converter
Digital IF
Digital
Receiver
Channel 1
Power
Supply
Navigation
Processing
Acquisition
Tracking
Microprocessor
Copyright © 2004 NordNav Technologies AB
•
Software Radio
The software radio concept is built upon two basic principles
1. Move the analog-to-digital converter (ADC) as close to the antenna as
possible
2. Process the resulting samples using a programmable
processor
Antenna
Amplification
Analog
filtering
low
Programmable
element
Available Processing Rate
high
ASIC
Analog to digital
Conversion (ADC)
FPGA
Microprocessor
(Assembly
Language)
Level of Flexibility
low
Microprocessor
(High Level
Language)
Microprocessor
(Simulation
Tool)
high
Copyright © 2004 NordNav Technologies AB
Software Radio: Myths & Truths
• Current technology simply does not meet the needs for the ”ideal”
software radio
– High-end analog-to-digital converter (ADC) examples
• Maxim MAX104: 8 Bits; 1.0 Gsps; 2.2 GHz Analog Input BW
• Analog Devices:AD6645: 14 Bits; 0.105 Gsps; 0.200 GHz Analog Input BW
– High performance processor element examples
• Intel Pentium IV Processor @ 3.4 GHz clock
• Xilinx Virtex II Pro FPGA (up to four embedded PowerPC 405 processors)
• Impractical to sample wide spectrum and digitally filter, decimate,
and process bands/signals of interest
– It is possible to construct multiple front ends and use software to process the output
of each
– It is possible to have a single front end and use software to provide an efficient,
flexible, and dynamic signal processing solution
• Such an ”ideal” radio would not be cost-effective
Copyright © 2004 NordNav Technologies AB
Software GNSS Receiver:
Feasibility & Comments
• The typical GPS receiver design, with a combination of hardware and
software signal processing, is well engineered design
– The high speed signal processing deals with a samples on the order of 4-20 Msps, while the
low speed programmable processor deals with pre-processed samples on the order of 1 Ksps
• Current technology allow for the implementation of a real time GNSS
software receiver
– Flexible signal processing
•
•
Possible to use for new signals and the
Hybrid GPS/Galileo receivers
– Potenial low-cost alternative for system integrators
– Bandwidth of the signals [sampling frequency] the most important parameter
• Moore’s law can be interpreted to show processing power has and
continues to increase exponentially since the 1970’s – so tradeoff
changes perspective
Copyright © 2004 NordNav Technologies AB
A Feasible Commercial
Software GNSS Receiver Architecture
Antenna
Microprocessor/DSP
Analog RF Front End
AGC
N
2
Pre Amp
(LNA)
Down
Converter
Reference
Oscillator
Frequency
Synthesizer
Analog IF
A/D
Converter
Digital IF
Navigation
Processing
Digital
Baseband
Channel 1
Acquisition
Tracking
• Downconversion is used – ADC is situated after the IF stage - Ideally
programmable bandwidth & frequency band
• Signal processing function after IF stage are realized in software 
increased flexibility
Copyright © 2004 NordNav Technologies AB
Two product lines:
• PC-based GNSS Receiver :
NordNav-Rxx
–
–
–
–
Specialized customer applications
High end receiver
End customers in R & D
R25/R30 being shipped now!
Automotive
General DSP or
Microprocessor
• Embedded Receiver :
NordNav-Exx Family
– Single point fixes/continuous tracking
– Designed for a DSP/Embedded processors
– Extremely cost effective
(re-use existing processing power in mobile
terminal)
Mobile Terminals
Exx
SW
NordNav Soft GPS
Copyright © 2004 NordNav Technologies AB
NordNav-RXX characteristics
• Complete receivers targeted towards R&D and Test & Verification
market segments
– Desktop research
– Desktop verification
• Specialized customer applications
• Designed to run on an PC platform
• Multiple sensor integration (GPS/INS/dead reckoning),
interference investigations, antenna arrays/beamforming etc.
• Record raw IF samples & replay samples
Copyright © 2004 NordNav Technologies AB
NordNav-RXX Architecture
Microprocessor
GPS Antenna
USBv2
Data
Acqusition
Interface IF Samples
Engine
RF
Multibit L1
Front End
Correlator
Engine
Acqusition &
Tracking
Hard
drive
User
App.
API
Navigation
SampleStreamer GUI
Receiver GUI
Copyright © 2004 NordNav Technologies AB
NordNav-R30 Demonstration
• Receiver will be run on Pentium 1.7 GHz Notebook PC
– Replay a recorded datafile from Stockholm
• Unique features briefly demonstrated
–
–
–
–
–
24 channels (typically 14-16 realtime depending on configuration)
Configurable parameters
Add multiple correlators – New feature!
Tracking loop framework – Updated framework
Signal Injection – example study interference effects
Copyright © 2004 NordNav Technologies AB
Baseband Configuration
Copyright © 2004 NordNav Technologies AB
Receiver GUI Examples
Horizontal scatter plot
Monitor AGC
level
Monitor the antenna frequency spectrum
Copyright © 2004 NordNav Technologies AB
Real-Time GUI Correlator Plot
• Add multiple
correlator pairs
• Each channel can
be individually
configured
• User can set the
tracking pairs &
spacing
Copyright © 2004 NordNav Technologies AB
Impact of Tracking Loop Parameters
10 Hz PLL
20 Hz PLL
Copyright © 2004 NordNav Technologies AB
External Tracking Loop Framework 1(2)
• The user can
implement its own
discriminators for code
& carrier
• Implement its own
code and carrier
tracking loop
• Excellent for
”aiding” of tracking
loops by for example
IMU
NordNav
R30 GUI
NordNav R30 API
NordNav
R30
Receiver
Visual C Framework
• User implemented code - dll
• Example implementation included
CloseLoops API
CloseLoops.dll
Copyright © 2004 NordNav Technologies AB
External Tracking Loop Framework 2(2)
Updated and added functionality
• Updated values every navigation update rate
(not every ms as the accumulators):
– Satellite positions
– Receiver position & velocity
• Indicator to tell the receiver to NOT try and
extract data
– For low C/No studies
Copyright © 2004 NordNav Technologies AB
Signal Combiner 1(4)
• Allows to inject a simulated signal into real GPS
samples prior receiver processing
• Possibility to study the effect interference signals and
jamming scenarios
• The user can implement any signal structure, even
GPS signals which the receiver can track
– Simulated file : each sample stored as signed char (byte)
Copyright © 2004 NordNav Technologies AB
Signal Combiner 2(4)
GPS Signal
Stored GPS
samples
Sample
Streamer
Antenna
Front end
Stored external
signal samples
Example :
Simulated CW, Noise
A/D
Multiplication
factor
R30 Software
Receiver
Signal Combiner
Copyright © 2004 NordNav Technologies AB
Signal Combiner 3(4)
>> cw_gen(5e5, 1e6, 0.05, 'cw_500kHz.sim')
Included
example
signal
generation
scripts
CW tone
noise
Copyright © 2004 NordNav Technologies AB
Signal Combiner 3(4)
Example of GPS L1 frequency spectrum with a injected 20
dB CW tone (sinusoid) at 500 KHz off L1 frequency
Copyright © 2004 NordNav Technologies AB
New features in this software release
•
•
•
•
•
•
•
Fault Detection and isolation
Improved Dynamic performance
Velocity output
Troposphere (same as WAAS model)
2-D navigation (height fixing)
Almanac
Configuration per channel basis
– Correlators (spacing and numbers)
– Tracking loop parameters
– Acquisition parameters
• External Tracking Loop Framework updated
Copyright © 2004 NordNav Technologies AB
Fault Detection Example
(severe multipath reflection)
Normal Processing – R30
With
Reference
Fault Detection
Receiver Processing
Processing – R30
Copyright © 2004 NordNav Technologies AB
Next Major Software Release
• SBAS
– Support for WAAS/EGNOS
• Scheduled IF recording
• Improved Sensitivity
• External Position API
• Next Next Major Software release
– Galileo L1 (software IF signal generator & processing)
Copyright © 2004 NordNav Technologies AB
Galileo
• Galileo – European ”GPS”. Designed to be independent
but compatible with GPS
– Same frequency band as GPS
– Different signal structure
• Operational 2008 [2010]
– Civil system Great asset for all users with hybrid GPS/Galileo
receivers!
• Increase service availability drastically!
• Five different service categories
– Open Service (OS) - Free of charge!
– Safety of Life (SoL), Commercial services (CS), Search and Rescue
(SAR), Public Regulated Service (PRS)
Copyright © 2004 NordNav Technologies AB
GNSS Frequency Spectrum
Modernized GPS and Glonass signals not included
Copyright © 2004 NordNav Technologies AB
GPS Signals
Carrier at 1575.42 MHz (L1)
1227.60 MHz (L2)
19 cm (L1)
Code at 1.023 Mcps (C/A)
10.23 Mcps (P(Y))
300 m (CA)
Navigation Data at 50 bps
6000 km
Copyright © 2004 NordNav Technologies AB
Galileo – Open Service Signal
L1 Band, BOC(n,m)
PRN Signal
1
t
-1
1
Square Wave
t
-1
1
Resulting BOC(m,m) Signal
t
-1
Copyright © 2004 NordNav Technologies AB
Normalized Magnitude
GPS C/A and GALILEO BOC(1,1) spectrum
GPS
and
Galileo
Sharing
L1
GPS C/A
1
GALILEO BOC(1,1)
0.8 Spectrum : C/A and BOC(1,1)
GPS C/A 0.6
Galileo BOC(1,1) (data bearing signal)
• Code length 1023 chips
0.4
• 1.023 MHz chipping rate (1 ms period time)
• 50 Hz data 0.2
rate (20 code periods per data bit)
• ~90 % of signal power within ~2 MHz bandwidth
• Code length 8184 chips
• 1.023 Mhz base frequency (8 ms period time)
• 125 Hz data rate (1 code period per data bit)
• ~85 % of signal power within ~4 Mhz bandwidth
0
0 BW
~4 MHz
Normalized PSD (dB)
GPS C/A and GALILEO BOC(1,1) Power Spectral Density
0
-5
-10
-15
-20
-25
-30
-35
-6000
GPS C/A
GALILEO BOC(1,1)
-4000
-2000
0
2000
Frequency Offset (kHz)
4000
6000
Copyright © 2004 NordNav Technologies AB
Conclusion
• ”Ideal Software Receiver” is still a dream
– Current technology do not allow for such designs
• However for bandlimited signals, such as GPS/GNSS,
software receiver are commercially feasible
– Downconversion front end used
– Process digital IF samples in software
• Software receivers are receiving market acceptance
– Technology not only for research in a laboratory
• Although fantastic for this purpose!
– More and more feasible as alternative to traditional Rx
– Multi-channnel receivers exists today
• Important technology for Galileo
– Hybrid GPS/Galileo L1 receiver for mass market
Copyright © 2004 NordNav Technologies AB