What is GNSS Simulation?And how can simulation help reduce your time to market?
What is GNSS Simulation?Accuracy, integrity and availability are all major challenges forsatellite-based navigation system...
The primary aim of this paper will be to explain what a GNSSsimulator does and to present some of the key design questions...
IntroductionGlobal Navigation Satellite System (GNSS) is a general term fora system that provides navigation and other ser...
Since the early days of GNSS, there have essentially been two majoralternatives available to those wishing to test a navig...
Global Positioning System (GPS), GLONASS and Other GNSSsystemsWhile the US sponsored GPS system and the Russian GLONASSsys...
Global Positioning System (GPS)The GPS satellite navigation system was originally designed andfunded as a military navigat...
The United States continues to invest in the GPS system.This investment includes the specification, design and launch of n...
GLONASSDevelopment of the Russian GLONASS system began in 1976 andwas completed in 1995. Recently Russia has, with India a...
GalileoThe European Union has committed to the design and validation ofthe Galileo system. A prime difference between this...
Quasi-Zenith Satellite System (QZSS)The Quasi-Zenith Satellite System (QZSS) is a regional multi satellitesystem, partly d...
Beidou / CompassChina has indicated it intends to expand the current geostationaryBeidou navigation system into a full med...
Augmentation systemsGPS alone does not always provide adequate performance,particularly in demanding environments or where...
Space based Augmentation Systems (SBAS)Space Based Augmentation Systems (SBAS) are typically designedto improve GPS /GNSS ...
Ground based Augmentation Systems (GBAS)An alternative approach to space-based augmentation is to transmitcorrection messa...
GNSS Simulation: General PrinciplesThe core requirement of any GNSS receiver test, whether fordevelopment, integration or ...
Advantages of Simulation•	  Signal effects such as atmospheric disturbances, multipath and  obscuration are quantified, co...
Drawbacks of live sky•	 end user or test site cannot have any control over the GNSS  An  signal being transmitted•	  The s...
Questions Facing Modern DevelopersIn the past, designers of satellite-based navigation systems have beenmostly restricted ...
While questions surrounding the pure accuracy of any given receiverusing either one or multiple GNSS systems or services n...
What is a GNSS simulator and how can it help solve yourproblems?A GNSS simulator reproduces the environment of a GNSS rece...
A GNSS simulator provides a superior alternative for most testingcompared to using actual GNSS signals in a live environme...
With a GNSS simulator, users can easily generate and run many differentscenarios for diverse kinds of tests, with complete...
Environmental conditionsSimulators model effects that impact GNSS receiver performance,such as atmospheric conditions, obs...
Why use a GNSS Simulator?Testing with simulators is the widely-accepted best practice forvalidating the performance of GNS...
GNSS simulators provide many benefits, including:•	  Control. Simulators allow complete control over all aspects of test  ...
•	  Reliability. Because all test conditions are controlled, test results  are reliable, and equipment performance can be ...
•	  ealism. The performance of GNSS receivers and systems are   R   tested end-to-end using real signals. Simulators with ...
A summary of the advantages of testing with GNSS simulators,compared to live testing with actual GNSS constellations, is s...
Spirent GNSS SimulatorsSpirent is the industry leader for GNSS simulator products. Spirentoffers several different models ...
For more comprehensive testing, Spirent also offers products thatsimulate additional system elements simultaneously with t...
With almost 25 years of GNSS simulator experience, Spirent providesGNSS simulators with unparalleled performance, features...
Where Next?If you found this eBook of interest, you may now like to do oneof the following:•	Visit our Resources page to b...
About SpirentSpirent has been the global leader in GNSS testing for 25 years. Spirent deliversnavigation and positioning t...
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What is GNSS Simulation? And how can it reduce your time to market?

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Global Navigation Satellite System (GNSS) simulation is a technique used to professionally assess the performance of devices that use satellite navigation and positioning. But how does it work?

Discover:
- How GPS is no longer the only GNSS in town
- The general principles of GNSS simulation, and its role in location-aware device R&D
- How simulation can help get higher-performance products to market faster

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What is GNSS Simulation? And how can it reduce your time to market?

  1. 1. What is GNSS Simulation?And how can simulation help reduce your time to market?
  2. 2. What is GNSS Simulation?Accuracy, integrity and availability are all major challenges forsatellite-based navigation systems, particularly in safety criticalenvironments. Previously the sole system providing commercialsatellite navigation was the US funded global positioning system’sGPS L1 C/A code. The current revolution in new GNSS signalavailability is requiring the navigation system designer to answer anumber of new key design questions.There are also many techniques and technologies currently existing,and under development, to improve the performance of GNSSsystems. Examples include augmentation such as inertial sensors andWi-Fi positioning techniques, as a compliment to GNSS.SPIRENT eBook Page 2
  3. 3. The primary aim of this paper will be to explain what a GNSSsimulator does and to present some of the key design questionsand solutions for testing navigation and positioning systems undercontrolled laboratory conditions using simulation techniques.SPIRENT eBook
  4. 4. IntroductionGlobal Navigation Satellite System (GNSS) is a general term fora system that provides navigation and other services to usersworldwide. Each GNSS employs a constellation of satellites, whichbroadcast signals that are then processed by GNSS receivers todetermine location, speed, and time for users anywhere withinrange of the satellites. This is normally on or just above the Earth’ssurface, but can be in space as well. There have been a significantnumber of developments in the availability of new satellite navigationsystems and services (GPS, Galileo, GLONASS, QZSS, Beidou, IRNSSetc.) correspondingly driving a need for more testing to confirmthe performance of these systems and associated enhancementsin relation to the design, qualification and validation of navigationequipment, whereas in the past, GPS C/A code was the only availableservice for the majority of commercial applications.SPIRENT eBook Page 4
  5. 5. Since the early days of GNSS, there have essentially been two majoralternatives available to those wishing to test a navigation system:• Field test• Laboratory simulationToday, best practice indicates that mosttesting is done under controlled, repeatableconditions in a secure laboratory. This enablesboth nominal and adversarial conditionstesting, including testing to the limits ofboth real and theoretical performance.It also allows development of receiversfor GNSS systems that are currentlyunavailable or lacking a full constellation.SPIRENT eBook
  6. 6. Global Positioning System (GPS), GLONASS and Other GNSSsystemsWhile the US sponsored GPS system and the Russian GLONASSsystems are the only GNSS with fully deployed constellationsof operational satellites, other systems are either in planning ordeployment stages. Laboratory testing here becomes of utmostimportance due to the lack of the real live-sky signals.SPIRENT eBook Page 6
  7. 7. Global Positioning System (GPS)The GPS satellite navigation system was originally designed andfunded as a military navigation system. The removal of selectiveavailability (a deliberate degradation of the satellite’s clock stability)in 2000 improved the accuracy for non-military applications using theL1 Coarse Acquisition (C/A) code to much better than 10m in manyoperational scenarios. This improved accuracy has enabled GPS tobe used in many applications and led to the explosion of commercialGPS applications that we are seeing today.In the military sphere, the L1 and L2 P(Y) code encrypted signalsremain the NATO standard for military Precise Positioning System(PPS) receivers.SPIRENT eBook Page 7
  8. 8. The United States continues to invest in the GPS system.This investment includes the specification, design and launch of newsatellites including the new Military Code or M-code signal.The initial M-code satellites have already been launched, withadditional launches planned over the next decade as the currentsatellites reach end of life. Additional civil GPS signals are alsoplanned at L2C and L5. The first L2C satellites have already beenlaunched, although full operational capability is stillseveral years away.SPIRENT eBook Page 8
  9. 9. GLONASSDevelopment of the Russian GLONASS system began in 1976 andwas completed in 1995. Recently Russia has, with India as a programpartner, restored the system to full operational capability (FOC).Spirent has seen a recent upsurge in interest in combined GPS/GLONASS simulators. This is due to people wanting to takeadvantage of additional signals today to improve theavailability of their receiver and systemimplementations.SPIRENT eBook Page 9
  10. 10. GalileoThe European Union has committed to the design and validation ofthe Galileo system. A prime difference between this and the othersystems is the proposed civil focus of the Galileo programme. Galileois designed to be inter-operable with GPS raising the possibility ofcombined GPS/Galileo receivers in future, bringing benefits to usersof additional satellite availability and improved integrity. Spirentis an official supplier of RF Constellation Simulators (RFCS) to theGalileo programme. The RFCS are being used for testing the groundmonitoring stations and prototype user receivers. In early 2010 theGalileo project office announced that it had placed contracts for thefirst satellites, launch services and satellite control. In March 2010the Galileo signal specification (ICD, interface control document) wasissued formally with a free licence available to anyone who wants touse the information to develop Galileo receivers or services.SPIRENT eBook Page 10
  11. 11. Quasi-Zenith Satellite System (QZSS)The Quasi-Zenith Satellite System (QZSS) is a regional multi satellitesystem, partly designed to provide ‘GPS-like’ signals from satellites ina Highly Elliptical Orbit (HEO) over Japan. The constellation and orbitshave been designed to allow each satellite to dwell over the Japanland mass for more than 12 hours a day with an elevation above 70°providing improved coverage in urban and mountainous areas wherethe line-of-sight limitation of classic GNSS systems may be impaired.The first launch of QZSS is planned in 2010.SPIRENT eBook Page 11
  12. 12. Beidou / CompassChina has indicated it intends to expand the current geostationaryBeidou navigation system into a full medium-earth-orbit GNSSconstellation, according to China news agency Xinhua. Details arecurrently awaited by the industry on the capability and internationalavailability of this system. In principle the Compass open civil signalsshould be interoperable with the other GNSS systems.SPIRENT eBook Page 12
  13. 13. Augmentation systemsGPS alone does not always provide adequate performance,particularly in demanding environments or where a high level ofintegrity is required. The accuracy and integrity of GPS / GNSS can begreatly enhanced by the use of information derived from observationsfrom others sensor technologies. The use of augmentation systemstakes many forms but all share the same basic objective of improvingGPS / GNSS performance and/or trustworthiness.SPIRENT eBook Page 13
  14. 14. Space based Augmentation Systems (SBAS)Space Based Augmentation Systems (SBAS) are typically designedto improve GPS /GNSS system integrity and accuracy for aircraftnavigation and particularly landing. SBAS satellites broadcastcorrection messages back to Earth, where suitably enabled receiversuse the SBAS corrections and integrity information to improveaccuracy and integrity. The USA, Europe and Asia are developing theirown SBAS systems. In Europe, the European Geostationary NavigationOverlay Service (EGNOS) system exists and is now operational. In theUSA there is the Wide Area Augmentation System (WAAS), in Japanthe Multi-functional Satellite Augmentation System (MSAS) and Indiais focusing on the GPS Aided Geo Augmented Navigation (GAGAN)system.SPIRENT eBook Page 14
  15. 15. Ground based Augmentation Systems (GBAS)An alternative approach to space-based augmentation is to transmitcorrection messages from ground-based systems. An exampleis the Local Area Augmentation Systems (LAAS), which allows asuitably equipped receiver to derive enhanced accuracy and integrityinformation in a local area, at an airport for example, where thereare stringent requirements necessary to be met to land a commercialaircraft. LAAS can be tested using Spirent’s unique LAAS VHF databroadcast signal simulator, the GSS4150.SPIRENT eBook Page 15
  16. 16. GNSS Simulation: General PrinciplesThe core requirement of any GNSS receiver test, whether fordevelopment, integration or production purposes, is for a controlled,repeatable signal. For many tests, the signal control includes flexibilityover test case, or scenario, conditions that enable performance testingat nominal and extreme or error-state conditions.Real-world, live-sky testing has significant drawbacks which, inpractice, preclude controlled testing. Some of the drawbacks of live-sky testing and the advantages of simulation are summarised below:SPIRENT eBook Page 16
  17. 17. Advantages of Simulation• Signal effects such as atmospheric disturbances, multipath and obscuration are quantified, controlled and precisely repeatable• Vehicle and satellite trajectory and associated dynamics are modelled• Future signals (e.g. Galileo, GLONASS and modernised GPS signals) can be generated to allow testing against new signals before a complete constellation of satellites are transmitting the Signals in Space (SIS)• GNSS RF constellation simulators can be used in various configurations enabling, for example, use of remotely generated trajectories and generation of interference signals as well as simulated GNSS signalsSPIRENT eBook Page 17
  18. 18. Drawbacks of live sky• end user or test site cannot have any control over the GNSS An signal being transmitted• The signal seen incident upon the GNSS receiver antenna is never repeatable between two different tests. This is because of the constantly changing GNSS satellite positions, environmental effects and objects around the antenna (e.g. cars and trucks in different positions on different days)• There are signal errors, often unknown to the receiver at the time• Atmospheric conditions change significantly and have a significant impact on single frequency systemsSPIRENT eBook Page 18
  19. 19. Questions Facing Modern DevelopersIn the past, designers of satellite-based navigation systems have beenmostly restricted to using a single system and service, the GPS L1 C/Acode.With new systems and services available now, and even differentservice levels, the question of which system or blend of systems aGNSS designer should consider, along with the potential for multipleservices is thus an entirely new consideration.The application of the receiver under development may define theanswer to this new conundrum to some extent, but in many casesthe best way to answer the question fully before committing to aparticular design path is to investigate the performance of differentoptions available using a GNSS simulator.SPIRENT eBook Page 19
  20. 20. While questions surrounding the pure accuracy of any given receiverusing either one or multiple GNSS systems or services need tobe answered, there are also a multitude of associated questionsregarding device performance, such as power consumption, interface,multipath and interference resistance etc. that also need to beanswered.The availability of multi-frequency,multi system, multi service GNSSsimulators allows the GNSS developer toanswer these questions with completeconfidence in the final design choice.Furthermore, the simulator is invaluablein the actual design effort and integration Spirent’s GSS8000of the receiver into a given application. Multi-GNSS SimulatorSPIRENT eBook Page 20
  21. 21. What is a GNSS simulator and how can it help solve yourproblems?A GNSS simulator reproduces the environment of a GNSS receiver ona dynamic platform by modelling vehicle and satellite motion, signalcharacteristics, atmospheric and other effects, causing the receiver toactually navigate according to the parameters of the test scenario. Itprovides an effective and efficient means of testing GNSS receiversand the systems that rely on them.It provides control over the signals generated over the global testenvironment all within a box, so that testing can be conducted incontrolled laboratory conditions.SPIRENT eBook Page 21
  22. 22. A GNSS simulator provides a superior alternative for most testingcompared to using actual GNSS signals in a live environment.Unlike live testing, testing with simulators provides full control ofthe simulated satellite signals and the simulated environmentalconditions.SPIRENT eBook Page 22
  23. 23. With a GNSS simulator, users can easily generate and run many differentscenarios for diverse kinds of tests, with complete control over:Date, time, and locationSimulators generate GNSS constellation signals for any locationand time. Scenarios for any location around the world or in space,with different times in the past, present, or future, can all be testedwithout leaving the laboratory.Vehicle motionSimulators model the motion of the vehicles containing GNSSreceivers, such as aircraft, ships, or automobiles. Scenarios involvingvehicle dynamics for different routes and trajectories anywhere in theworld can all be run without moving the equipment being tested.SPIRENT eBook Page 23
  24. 24. Environmental conditionsSimulators model effects that impact GNSS receiver performance,such as atmospheric conditions, obscuration, multipath reflections,antenna characteristics, and interference signals. Various combinationsand levels of these effects can all be tested in the same controlledlaboratory environment.Signal errors and inaccuraciesSimulators provide control over the content and characteristicsof GNSS constellation signals. Tests can be run to determine howequipment would perform if various GNSS constellation signal errorsoccurred.SPIRENT eBook Page 24
  25. 25. Why use a GNSS Simulator?Testing with simulators is the widely-accepted best practice forvalidating the performance of GNSS receivers and systems inmany different scenarios and operating conditions. Simulators areused extensively in academia and industry, in virtually all GNSSreceiver manufacturing and major system integration, and in manydifferent application fields, including navigation, positioning,telecommunications, aviation, automotive, and space, for both civilianand military applications. Using simulators facilitates several stages ofresearch and product development, including requirements analysis,design and development, integration, production, maintenance, andsupport.SPIRENT eBook Page 25
  26. 26. GNSS simulators provide many benefits, including:• Control. Simulators allow complete control over all aspects of test scenarios, including GNSS constellation signals and environmental conditions.• lexibility. Users can easily define different scenarios for different F testing needs.• Completeness. Equipment can be tested under different operating conditions, ranging from nominal to extreme, including conditions that are impractical or impossible to produce in live testing.• epeatability. Test scenarios are the same every time they R are executed.SPIRENT eBook Page 26
  27. 27. • Reliability. Because all test conditions are controlled, test results are reliable, and equipment performance can be evaluated against known truth data.• ost. Tests are conducted in the laboratory, without extra expenses C for field tests and test vehicles. Field testing is very often more costly and time consuming than laboratory testing.• Efficiency. Many different tests can be completed in the same laboratory test bed, without reconfiguring or relocating equipment. New test scenarios can be created and executed quickly.SPIRENT eBook Page 27
  28. 28. • ealism. The performance of GNSS receivers and systems are R tested end-to-end using real signals. Simulators with real-time control capabilities support advanced hardware-in-the-loop (HWIL) testing.• uture. Simulators provide effective means of testing new and F future GNSS capabilities that are not yet supported by actual constellations, such as the GPS L2C and L5 signals and the Galileo system.SPIRENT eBook Page 28
  29. 29. A summary of the advantages of testing with GNSS simulators,compared to live testing with actual GNSS constellations, is shown inthe table below. Live Testing with Actual GNSS Constellations Laboratory Testing with GNSS Simulators No control over constellation signals Complete control over constellation signals Limited control over environmental conditions Complete control over environmental conditions Not repeatable; conditions are always changing Fully repeatable Unintended interference from FM, radar, etc. No unintended interference signals Unwanted signal multipath and obscuration No unwanted signal effects No way to test with GNSS constellation errors Easily test scenarios with GNSS constellation errors Expensive field testing and vehicle trials Cost-effective testing in laboratory Limited to signals available in GNSS constellations Testing of present and future GNSS signals Competitors can monitor field testing Testing conducted in secure laboratorySPIRENT eBook Page 29
  30. 30. Spirent GNSS SimulatorsSpirent 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 for themost demanding research and engineering applications.SPIRENT eBook Page 30
  31. 31. 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) data, SBAS and GBAS augmentationsystem signals, and interference signals.SPIRENT eBook Page 31
  32. 32. With almost 25 years of GNSS simulator experience, Spirent providesGNSS simulators with unparalleled performance, features andcomprehensive support.Spirent’s Multi-GNSS simulation platforms Spirent GSS8000 Spirent GSS6700 Spirent GSS6300 Multi-GNSS Constellation Multi-GNSS Constellation Multi-GNSS Signal Simulator system generatorSPIRENT eBook Page 32
  33. 33. Where Next?If you found this eBook of interest, you may now like to do oneof the following:• Visit our Resources page to browse our other eBooks and Application Notes on relevant topics.• Read the Spirent GNSS Blog to keep up with news and insights on the latest GNSS developments.• Email us for more information at gnss-solutions@spirent.comShare this eBook on your favourite social media platform:Facebook LinkedIn Twitter Technorati Google +1 Digg Delicious Reddit Stumbleupon MC
  34. 34. About SpirentSpirent has been the global leader in GNSS testing for 25 years. Spirent deliversnavigation and positioning test equipment and services to governmental agencies,major manufacturers, integrators, test facilities and space agencies worldwide.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

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