Using GPS/GNSS Simulators in Development, Debug and Testing

This paper reviews the application of GPS/GNSS Simulators in the development, debug and testing of products and systems incorporating GPS/GNSS receivers. The GPS/GNSS simulator was originally envisioned for GPS or GNSS receiver development and testing. However, the applications of GPS/GNSS simulator are rapidly expanding to include products and system’s integrating or embedding GPS/GNSS receivers. In the near future, distributed application using position, navigation or Time/Frequency inputs from GPS/GNSS receivers will require GPS/GNSS simulation to test their operating conditions and failure modes. Positioning and Navigation products require testing to ensure correct operation under a variety of signal conditions and use cases. Manufacturers can test their GPS/GNSS based products for operation and quality metrics. Developers can use case verification using GPS/GNSS simulator to perform design verification. A GPS/GNSS simulator provides for consistent and repeatable test conditions unmatched by field or lab testing. Location based services for telematics, navigation, tracking, or location restricted licensing operation require system integrators to devise GPS/GNSS test cases. The ability to repeat, revise and reuse GPS/GNSS test data and test cases allows for rapid regression testing in any simulated location or time. The ability of a GNSS simulator to output multiple constellations allows for new feature testing requiring simultaneous constellations or operation using individual constellations. Solution providers and product manufacturers need to verify their product meets specifications for typical and under minimally specified GPS/GNSS conditions. The GNSS simulator allows test conditions to vary from typical to minimal to denied. Time and Frequency product developers require the ability to evaluate their products under a variety of signal conditions. The stability of the 1PPS output and other frequency outputs derived from GPS/GNSS receivers needs to be characterized under typical and worst case conditions which are not always possible with an antenna installation. Furthermore, long term testing for time and frequency products with exactly repeatable signal conditions can be performed to verify time and frequency disciplining algorithms. Time and frequency distribution systems based on GPS/GNSS receivers add great complexity to GPS/GNSS simulation. Now GPS/GNSS simulators can drive distributed systems consisting of Serial Time distribution networks, IRIG distribution, frequency outputs, and network time and frequency protocols such as IEEE 1588 (PTP), NTP, and Synchronous Ethernet. Large scale systems can be synchronized involving time distribution for large numbers of computers, database driven enterprise applications or widely distributed time and frequency distribution systems for power, telecom and financial trading networks. Errors in time synchronization and loss of frequency synchronization can lead to costly service outages, database corruption, stock trading errors or system control and measurement errors. GPS/GNSS simulators allow testing of conditions like leap seconds, loss of tracking, reception issues and GPS errors to test system susceptibility to GPS/GNSS problems.