A Calibrated Precision GNSS Simulator for Timing Applications

Testing GNSS receivers specifically for timing applications to determine the accuracy of the receiver’s 1PPS output presents challenges in measuring accuracy to sub nanosecond levels. Using the live sky signals as a test reference has many problems. It has been shown that receiver biases vary at different frequency bands because of varying group delay in the RF circuitry: Biases vary across different GNSS signal types because of the different modulation, various decoding techniques and different correlator sizes, and biases even vary from satellite to satellite for the same signal type because of different transmitter characteristics. Moreover, changing atmospherics over time makes the live sky signals a poor reference for repeatable tests. For all of these reasons, it is desirable to use a GNSS simulator to generate the various constellation signals in a repeatable, reliable fashion.

This white paper will show the results of a project that takes an affordable but fully capable precise GNSS simulator and calibrates its RF output so a receiver’s 1PPS can be measured. The goal is to calibrate the 1PPS output reference output of the simulator relative to the simulator’s RF output to a resolution of 0.1 ns for any particular constellation signal.