1. Software Receiver Technology
The GALILEO & GPS Software Receiver Company
Software Receiver Technology
30-September-2004
Tampere University of Technology
Glenn MacGougan

2. 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

3. Agenda GNSS Receiver Technology Demonstration GPS and Galileo
Traditional GNSS Receiver Technology
Software Radio Technology
Software GNSS Receiver Technology
Demonstration
NordNav-R30 Software GPS Receiver
New Features
GPS and Galileo
Conclusion

4. GNSS Receiver – 3 Steps Search phase (acquisition)
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 t t
Start GPS
Start GPS - - 2 2
sec
sec
Acq
Acq t t 1 1
Tracking
Tracking
1.2
1.2 - - 6 6
sec
sec No No
TOW
TOW
decoded
decoded ? ? t t 2 2 No No
Yes
Yes
Ephemeris decoded
Ephemeris decoded ? ? 18 18 - - 30 30
sec
sec
Yes
Yes No No 4 4
satellites
satellites ? ?
Yes
Yes
Pos Fix t t 3 3

5. Traditional GNSS Receiver Architecture
Block diagram of a typical GNSS receiver
Baseband ASIC
Antenna
Analog RF Front End ASIC
AGC N 2
Digital
Receiver
Channel 1 RF
Pre Amp (LNA)
Down
Converter
Analog IF
A/D
Converter
Digital IF
Reference
Oscillator
Frequency
Synthesizer
Power
Supply
Navigation
Processing
Acquisition
Tracking
User
Interface
Low Speed Comm Link
Microprocessor

6. Software Radio
The software radio concept is built upon two basic principles
Move the analog-to-digital converter (ADC) as close to the antenna as possible
Process the resulting samples using a programmable processor
Antenna
Amplification
Analog
filtering
Analog to digital
Conversion (ADC)
Programmable
element
high
Available Processing Rate
low
Microprocessor
Microprocessor
Microprocessor
ASIC
FPGA
(Assembly
(High Level
(Simulation
Language)
Language)
Tool)
low
Level of Flexibility
high

7. 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; Gsps; GHz Analog Input BW
High performance processor element examples
Intel Pentium IV 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

8. 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

9. A Feasible Commercial Software GNSS Receiver Architecture
Antenna
Microprocessor/DSP
Analog RF Front End
AGC N 2
Digital
Baseband
Channel 1
Pre Amp (LNA)
Down
Converter
Analog IF
A/D
Converter
Digital IF
Reference
Oscillator
Frequency
Synthesizer
Navigation
Processing
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

10. 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!
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)
Automotive
General DSP or Microprocessor
Mobile Terminals
Exx SW
NordNav Soft GPS

11. 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

12. NordNav-RXX Architecture
Acqusition
Engine
Correlator
Data
Interface
Acqusition &
Tracking
Navigation
Hard drive
API
User
App.
SampleStreamer GUI
Receiver GUI
GPS Antenna RF
USBv2
Multibit L1
Front End
IF Samples
Microprocessor

13. 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 realtime depending on configuration)
Configurable parameters
Add multiple correlators – New feature!
Tracking loop framework – Updated framework
Signal Injection – example study interference effects

14. Baseband Configuration

15. Receiver GUI Examples Monitor the antenna frequency spectrum
Horizontal scatter plot
Monitor AGC
level
Monitor the antenna frequency spectrum

16. Real-Time GUI Correlator Plot
Add multiple correlator pairs
Each channel can be individually configured
User can set the tracking pairs & spacing

17. Impact of Tracking Loop Parameters
10 Hz PLL
20 Hz PLL

18. 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
Visual C Framework
User implemented code - dll
Example implementation included
NordNav R30 API
NordNav R30 Receiver
CloseLoops API
CloseLoops.dll

19. 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

20. 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)

21. Signal Combiner 2(4) GPS Signal Stored GPS samples Sample Streamer
Multiplication factor
Antenna
R30 Software Receiver
Front end
A/D
Stored external signal samples Example : Simulated CW, Noise
Signal Combiner

22. Included example signal generation scripts
Signal Combiner 3(4)
>> cw_gen(5e5, 1e6, 0.05, 'cw_500kHz.sim')
Included example signal generation scripts
CW tone noise

23. Signal Combiner 3(4)
Example of GPS L1 frequency spectrum with a injected 20 dB CW tone (sinusoid) at 500 KHz off L1 frequency

24. 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

25. Fault Detection Example (severe multipath reflection)
Normal Processing – R30
With Fault Detection Processing – R30
Reference Receiver Processing

26. 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)

27. 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)

28. GNSS Frequency Spectrum
Modernized GPS and Glonass signals not included

29. GPS Signals Carrier at 1575.42 MHz (L1) 19 cm (L1) 1227.60 MHz (L2)
Code at Mcps (C/A)
10.23 Mcps (P(Y))
300 m (CA)
6000 km
Navigation Data at 50 bps

30. Galileo – Open Service Signal L1 Band, BOC(n,m)

31. GPS and Galileo Sharing L1 Spectrum : C/A and BOC(1,1)
Galileo BOC(1,1) (data bearing signal)
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
GPS C/A
Code length 1023 chips
1.023 MHz chipping rate (1 ms period time)
50 Hz data rate (20 code periods per data bit)
~90 % of signal power within ~2 MHz bandwidth
~4 MHz BW

32. 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