GNSS simulators Essential tools for satellite navigation test

1. GNSS simulatorsEssential tools for satellite navigation test

2. Agenda Testing GPS • Why test at all? • Where is testing required? • What to test for? • How to test? • What is a simulator? • Application areas • Test Characteristics

3. Why Test? • To satisfy • Yourself, and to prove to others, that your GNSS product performs as well as you say it does • To determine • and show how well your GNSS product actually works in its intended application • and investigate if your product can be used in other applications or situations • To evaluate • How your product interacts with other systems • To check • That most (or all) of your manufactured product has been assembled correctly • To verify • That your product is still working before it needs to be used in anger A + B = C

4. GSS6560 GSS4100 STR4500 GSS7700 GSS4200 Where is testing required? Research Integration Qualification Development Verification Manufacturing

5. Test ‘figures of merit’ examples • Parametric • Sensitivity • Ability to reliably track low-power signals • Carrier-to-Noise ratio • A measure of how well the receiver has correlated with the coded signal • Dynamic tracking • Ability to maintain signal tracking as the user’s platform rapidly moves or changes orientation • Time-to-First-Fix (TTFF) • How long after a cold or warm start does it take to obtain the first position solution?

6. Test ‘figures of merit’ examples • Parametric • Re-acquisition time (REAC) • How long does it take the receiver to track a signal again after the signal has been ‘obscured’ for a given period? • Accuracy • Compared to truth in ideal conditions

7. Test ‘figures of merit’ examples • Operational • Accuracy • Estimated from the residuals of the position estimator and other data (can also be compared to truth) • Availability • Derived from number of signals currently usable and the receiver’s ability to provide continuous, uninterrupted output of position or time • Integrity • Reliability of data available; is it consistent and is quality high? ~16:59:10.297,$GPVTG,,T,,M,0.00,N,0.0,K,N*1C ~16:59:11.250,$GPGGA,001007.000,3936.0009,N,11934.9992,W,6,00,50.0,525.5,M,-21.1,M,,0000*51 ~16:59:11.266,$GPRMC,001007.000,V,3936.0009,N,11934.9992,W,0.00,,070425,,,E*70 ~16:59:11.282,$GPVTG,,T,,M,0.00,N,0.0,K,N*1C

8. Testing to the Limits • Sensitivity • Fine control, signal stability and repeatability • Tracking ability • Extreme dynamics simulated accurately • Accuracy • One-effect-at-a-time flexibility needed to build error budget • Dealing with fault conditions • FDE, RAIM – simulation flexibility and complexity, control • Creating Anomalies • simulation flexibility and complexity, control to introduce errors • Urban Canyon • Multipath, Occultation

9. How to test? • Option 1: Live-Sky and conventional test gear • Use the RF signals from actual GNSS satellites • Spectrum Analyzers, Frequency Counters, Power Meters, Logic Analysers, etc • Option 2: Specialised Laboratory Test Gear • Use a GNSS Simulator • Spectrum Analyzers, Frequency Counters,Power Meters , Logic Analysers, etc • Option 2 has become the approach of choice.Live-sky or field test is often used as a quick check, but also wrongly relied upon for real testing.

10. Live Sky • Advantages • Signals are freely available • Quick operational check • Usually includes an actual reception antenna • Disadvantages • Lack of Control (GPS owned by US Govt) • Cannot repeat • Little flexibility • Multiple unknowns • Especially where there is dynamic motion • Very high costs • Especially where there is dynamic motion

11. GNSS simulator testing • Advantages • Lacks ambiguity • High degree of control • Inherent repeatability • Flexibility • Test to the limits • Lower costs overall • Disadvantages • Usually does not include the reception antenna in the loop • But can do in a controlled RF screened chamber • Representative, not always realistic • Not a problem in most test situations

12. What is a simulator? • Most GNSS ‘Simulators’ are in fact ‘Emulators’ • “Simulator” or “RFCS” is the accepted industry term • Simulators create RF signals that are designed to be as representative as possible of the signals that would actually be incident at the antenna of a GNSS Receiver under specified conditions • Realistic modulation, content and bandwidth • Realistic values for satellite pseudoranges • The ‘simulation’ takes place in real-time • Like the real world • A running simulation cannot be slowed down or speeded up • Without hardware, simulations can be run many times real time

13. GNSS Constellation Simulator Your constellation (GPS, GLONASS, Galileo), under your control RTCM NMEA L-band RF

14. Simulator Control - SimGEN • Test definition, test execution, data analysis

15. Starting SimGEN Desktop Icon Menu Start

16. Selecting a Scenario Default is to highlight last successful scenario

17. Scenario file Hierarchy Default Location Shared Area! Your Scenarios! Pre-installed scenarios

18. SimGEN Main Window Toolbar Scenario ContentsWindow Simulation DataWindow MessageWindow

19. Key Areas Context Sensitive Help! Header Menu Bar Stop Scenario Toolbar Rewind Turbo Mode on/off Turbo Mode Speed Run Scenario Amber – No Hardware Mode Simulation Time Status Bar

20. Sat Signal Data Data Display Ground Track Signal Levels Data Plots RX Ant Pattern Data Logging Channel Assignment Scenario Contents Vehicle/Ant Selection Level Control P-Range Ramp Date/Time Sky Plot RTCM Antenna Position Vehicle Dynamics Window Selection

21. Scenario Contents Window Scenario name, date, time & duration General Files Atmosphere definition File GPS Constellation File LAAS Definition File (if applicable) Vehicles, Antennas and Signals

22. What is a Scenario? • Series of files used to define the simulation environment. (source files) • GPS Constellation • GLONASS Constellation • GALILEO Constellation • LAAS Definition • SBAS Constellations • Atmospheric parameters • Vehicle parameters • Vehicle Motion • Antenna position and it’s gain and phase pattern etc. • XML based file structure

23. Scenario Source Files • Consists of a top level file and subordinate files • Top level is “scenario file” (.scn extension) and contains pointers to subordinate files • Defaults used if not specified in scenario. <XML ID="XMLID"> <vehicles> 1 </vehicles> <veh_file> agp_test_v1.veh </veh_file> <networks> 1 </networks> <net_file> agp_test_tn_GPS.net </net_file> <atmos_file> agp_test_at1.atc </atmos_file> <start_time> 01-May-2003 00:00:00 </start_time> <duration> 777600 </duration> <user_actions> </user_actions> <quick_look> </quick_look> <rtcm> </rtcm> <nmea> </nmea> <laas> </laas> <rtcm_enabled> 0 </rtcm_enabled> <nmea_enabled> 0 </nmea_enabled> <laas_enabled> 0 </laas_enabled> <user_actions_enabled> 0 </user_actions_enabled> <ql_setup_enabled> 0 </ql_setup_enabled> </XML> Example .scn file But of course no need to edit directly, SimGEN is there for that.

24. Editing Scenario Source Files • Standard Windows ™ protocol • Double-click the file in the scenario contents window • Or press the EDIT button at the foot of the scenario contents window NOTE: If a shared file is edited it will change all of the other scenarios that access it as well

25. Save Source file • For edits a filename is required • Changes are overwritten unless a new filename is specified • File extension added automatically .atm added by SimGEN

26. Scenario file selection

27. Recap