Why are we Talking About Multi GNSS?

A few years ago the Sat Nav system in your car was considered a luxury now almost every PDA, mobile phone and PC has built-in GPS technology. However, navigation and positioning technology is no longer just about GPS L1 C/A code. The GPS constellation is being modernized, the GLONASS constellation is nearly complete with 19 satellites transmitting as you read, new systems including the Japanese QZSS, the European Galileo and the Chinese Compass constellations are on the way.

GPS, the backbone of our current satellite navigation systems for the past 10 years will be only one of four Global Navigation Satellite Systems (GNSS) and four Satellite Based Augmentation Systems (SBAS) which will be available by the middle of this decade. There are already over 60 GNSS and SBAS satellites in operation (including 32 from GPS) and more than 130 are planned.

This multi-GNSS environment offers opportunities to improve performance to meet increasing user demands. In particular, end user availability is potentially improved by using more than one constellation. Benefits to end users can also include improved integrity, continuity and accuracy, depending on the situation and priorities of the application. However this multi-GNSS environment also offers significant opportunities and challenges to GNSS technology, system and application developers’ to meet these increasing user demands e.g.

  • How can I test future signals which do not yet exist in space such as L5 and L2C on GPS
  • How can I test GNSS constellations which are partially deployed or not yet deployed (e.g. Galileo)

Well, there is a solution. GPS/GNSS simulators generate the same kinds of signals transmitted by GPS/GNSS satellites, thus GPS/GNSS receivers process the simulated signals in exactly the same way as signals from actual satellites. GPS/GNSS simulators are the most powerful test method for GNSS receivers and applications and have three core attributes which are more difficult (or impossible) to achieve using live-sky test methods, these are repeatability, control and scalability:

  • A simulator can repeat exactly the scenario time-after-time enabling test results to be accurately compared during the development process. Further, repeatable test scenarios can be created to include failure conditions which may only occur sporadically or randomly in the real-world and are difficult to capture with live-sky methods
  • Simulators give full control over all the performance characteristics for GNSS. This means that single scenario can be created which tests a GNSS receiver or application in ways which might require several live-sky sessions to emulate. The control of GNSS parameters offered by a simulator also means clearly defined, repeatable and rigorous test standards can be established and documented
  1. Simulators offer a scalable test method
  2. Only simulators can test for GNSS constellations which are partially deployed (e.g. Galileo) and future signals such as L5 and L2C on GPS
  3. Simulators are the best solution for establishing test standards across dispersed development centers
  4. Simulators generate data for multiple scenarios and locations compared to live-sky, which are single-scenario single-location solutions
  5. Simulator test scenarios can be quickly added or modified through software whereas changing test conditions for live-sky requires new data to be collected

GNSS simulators are the test method of choice for developers and test engineers. They offer a rigorous, repeatable and cost effective means of exploring, benchmarking and testing GNSS receivers, applications and systems. No other method can offer the same flexibility in generating new test scenarios or the ability to incorporate both current and future GNSS and frequencies.  

If you’re not working on multi-GNSS projects right now, you probably will be soon. Find out more on how Spirent’s multi-GNSS product portfolio could help you today.


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