Testing Multi-GNSS in an R&D Environment: From GPS to Multi-GNSS


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Increasingly, Global Navigation Satellite System (GNSS) receivers are capable of receiving and processing signals from multiple satellite systems. Multi-GNSS brings many new market opportunities, but it also creates new challenges for R&D teams.

- The differing requirements of GLONASS, Galileo, GPS and Compass GNSS
- How Multi-GNSS simulators can help

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Testing Multi-GNSS in an R&D Environment: From GPS to Multi-GNSS

  1. 1. Testing Multi-GNSSin an R&D EnvironmentFrom GPS to Multi-GNSS
  2. 2. A host of benefitsThe shift from individual satellite navigation systems using GPSto next-generation receivers capable of exploiting multiple globalnavigational satellite systems (Multi-GNSS) offers a host of benefitsin terms of improved coverage and accuracy and in new services.However, this switch to Multi-GNSS dictates that manufacturers takea different approach to testing their products to ensurethat they will function as desired, regardless ofwhich satellite signals can be acquired atany given time. And that new approach hasto start at the beginning of the productdevelopment process – in the researchand development lab.SPIRENT eBook
  3. 3. So many systemsThe problem is that while systems such as GLONASS, Galileo, thesoon to be upgraded GPS and Compass are functionally similar, thereare major differences in the way they go about their respective tasks.Different constellations broadcast on different frequencies. Modulationschemes differ. Timebases differ. Different systems even use differentmathematical models for ionospheric modelling.SPIRENT eBook Page 3
  4. 4. As a result, the range of tests required in the R&D laboratoryis considerably wider than those traditionally used in thedevelopment of “vanilla” GPS receivers.SPIRENT eBook Page 4
  5. 5. The simulation solutionA Multi-GNSS simulator provides an effective and efficient meansto test GNSS receivers and the systems that rely on them. With aMulti-GNSS simulator, every time a test scenario is run, the signalsproduced are identical. The scenario will start at the same time andon the same date, and the satellite positions will be identical – evendown to the relative phase offsets between the different signals.SPIRENT eBook Page 5
  6. 6. In this way you can guarantee that the receiver is being simulatedwith exactly the same signals every time the test is run. Only this waycan you fully determine any improvement (or otherwise) the designalterations have made.What’s more, a suitable simulator will be capable of upgrading tosimulate other GNSS signals as soon as they have been defined bythe system operator.SPIRENT eBook Page 6
  7. 7. The tests requiredIn the development process of any GNSS receiver, thereare two distinct levels of tests that will be applied.SPIRENT eBook Page 7
  8. 8. Basic tests are those that exercise the simplest underlyingfunctionality of the receiver.Advanced tests cover those that recreate “unusual” situationsand also those that exploit novel applications outside the basicfunctionality of the receiver.SPIRENT eBook Page 8
  9. 9. Basic R&D testingIn testing the underlying functionality of any GNSS receiver designin the laboratory, it is essential that the equipment is subjected to aknown and repeatable stimulus so that the correct response can beassessed and the performance can be adjusted accordingly.SPIRENT eBook Page 9
  10. 10. At the simplest level, the receiver is supplied with a referencesignal with a navigation message consistent with the relevant ICDor interface control document. This allows the designer to verify thereceiver’s algorithms for decoding the messages and recovering timesynchronisation. It also allows the designer to optimise the accuracyand sensitivity of the receiver.Other basic tests at this level include the receiver’s one pulseper second (1PPS) performance, together with static and dynamicaccuracy and time to first fix (TTFF).SPIRENT eBook Page 10
  11. 11. Advanced R&D testingThe key to any advanced R&D testing is the ability to simulate aspecific scenario with absolute repeatability so that adjustmentscan be made and the test can be re-applied. These scenarios can be ofalmost any nature, and while each onemay be unlikely to occur in real life,a reliable Multi-GNSS receiver willbe expected to perform reliablyunder all possible conditions.SPIRENT eBook Page 11
  12. 12. Clearly, because these scenarios are unlikely, it is impossible to“create” them in real life without a simulator (let alone recreate themfor a second test). The simulator enables easy creation of a library ofperformance tests ready to apply to the receiver.These tests can then be combined and enhanced to create ever morecomplex test scenarios that can be saved and used over again withabsolute repeatability.SPIRENT eBook Page 12
  13. 13. The Multi-GNSS angle Even at the most basic level, it is important to test the Multi-GNSS capabilities of the receiver. The basic tests of signal and truth data references should be repeated for each GNSS with which the receiver is intended to operate. So (currently) this will mean applying GPS, GLONASS and Galileo reference signals and decoding their respective navigation messages.SPIRENT eBook Page 13
  14. 14. This multiple signal testing will also exercise the frequency agility ofthe receiver design. For while both GPS and Galileo broadcast theirL1 civilian signals in a band centred on 1575.42MHz, the GLONASScivilian signal is broadcast in a band from 1598MHz to 1605MHz.And the ability to apply all these tests from the same simulator willremove a number of potential error sources from the test setup.SPIRENT eBook Page 14
  15. 15. Advanced Multi-GNSS testingOne critical difference in testing a Multi-GNSS receiver compared withone destined for use on a single system is in its ability to handle allthe various different models used by each satellite system. And whileGPS, Galileo and GLONASS use the same co-ordinate frames, GPS hasits own timebase, which differs from the other two systems, whichare tied to the global UTC time system.SPIRENT eBook Page 15
  16. 16. Similarly, while GPS uses the Klobuchar model to correct for errorsinduced by ionospheric effects, Galileo will use the NeQuick model.Fortunately, a Multi-GNSS simulator can account for these differences,and will supply the signals exactly as they would appear to thereceiver in the real world, allowing R&D testing to predict real-worldperformance way in advance of the “real” signals being available.SPIRENT eBook Page 16
  17. 17. Mixed messagesSo while the designer will want to assess any new receiverdesign for its performance against all the standard GNSS tests,it is essential that these tests are run for each GNSS for whichthe receiver is designed.SPIRENT eBook Page 17
  18. 18. • Time to first fix• Acquisition sensitivity• Tracking sensitivity• Reacquisition time• Static navigation accuracy• Dynamic navigation accuracy• Radio frequency interferenceBut the true Multi-GNSS receiver should be able to produceworkable results even when working with partial signals frommultiple systems. It is only by using a multichannel Multi-GNSS simulator that this performance can be readily assessedand the design refined to improve it.SPIRENT eBook Page 18
  19. 19. Application-specific testingCertain tests at this stage will depend on the intended endapplication of the Multi-GNSS receiver. These might be automotive-specific tests, avionics-specific tests (which might involve thereceiver and its antenna being at any range of angles depending onvehicle manoevres) or space-specific tests.SPIRENT eBook Page 19
  20. 20. In each case, the simulator will either provide suitable ready-writtentests, or can be programmed with the relevant scenarios, which canthen be replayed with absolute repeatability, time and time again.SPIRENT eBook Page 20
  21. 21. State-of-the-art simulationsimplifies R&DThe switch from simple GPS navigation to theuse of multiple satellite systems is bringing a newset of challenges to receiver designers. However,exhaustive testing in the R&D laboratory can givedesigners the confidence that their new Multi-GNSS receiver designs will perform as intendedonce they enter service.The list of tests required is extensive, and“live-sky” testing using “real” signals from“real” satellites is not an option.SPIRENT eBook Page 21
  22. 22. A multichannel Multi-GNSS simulator will allow all the necessarytests to be run using signals from single and multiple GNSSs.And the ability to “mix and match” signals from different systemswill allow designers to create receivers that can perform reliablyanywhere in the world.SPIRENT eBook Page 22
  23. 23. The Spirent GNSS and Wi-Fi SolutionsSpirent is the industry leader for GNSS simulator products. Spirentoffers several different models of GNSS simulators that support avariety of different applications and cover the full spectrum of civilianand military GNSS testing needs. Spirent products range from basicsingle-channel simulators, suitable for simple production testing,through multi-channel, multi-constellation simulators, suitable forthe most demanding research and engineering applications.SPIRENT eBook Page 23
  24. 24. For more comprehensive testing, Spirent also offers products thatsimulate additional system elements simultaneously with the GNSSconstellation signals, such as inertial sensors, various automotivesensors, Assisted GPS (A-GPS) + Assisted GLONASS (A-GLONASS)data, SBAS and GBAS augmentation system signals, interferencesignals, GNSS Record & Playback and Wi-Fi Positioning.Spirent GSS8000 Spirent GSS6700 Spirent GSS6300 Spirent GSS6400 Spirent GSS5700Multi-GNSS Constellation Multi-GNSS Constellation Multi-GNSS Signal Record & Playback Wi-Fi Access PointSimulator system generator System simulatorSPIRENT eBook Page 24
  25. 25. We hope you found this Spirent Testing Multi-GNSS in an R&DEnvironment E-Book of interest.We are continually adding new content to our websiteon a regular basis. Bookmark this link:www.spirent.com/positioningVisit the Spirent GNSS Blog, there are currentlymore than 90 posts with 2 to 3 new posts addedper week. Catch up on what’s new:www.spirent.com/Blog/PositioningNeed more information?gnss-solutions@spirent.comShare?Facebook LinkedIn Twitter Technorati Google Buzz Digg Delicious Reddit Stumbleupon MCD00172 Issue 1-02
  26. 26. Spirent Spirent Federal Systems Got a smartphone?+44 1803 546325 +1 714 692 6565 Scan the QRglobalsales@spirent.com info@spirentfederal.com Code for morewww.spirent.com/positioning www.spirentfederal.com information