A hardware method for time-stamping asynchronous serial data streams relative to GNSS time

Abstract

A method for precisely synchronizing an external serial data stream to the pulse-per-second (PPS) output signal from global navigation satellite-based systems (GNSS) receiver is described in this paper. A signal timing device was designed that used a digital signal processor (DSP) with serial inputs and input captures to generate time-stamps based on an internal timer. All temporal measurements were made directly in hardware, which eliminated any concerns of software latency. The resolution of the signal timing device was 17.1μs. Testing showed that time measurements made on the signal timing device were consistent with measurements made using a digital oscilloscope. The standard error between the signal timing device and digital oscilloscope was 47.2μs which translated to less than a millimeter of horizontal position error for agricultural operations at speeds less than 10m/s. The signal timing device was shown to be useful for synchronizing GNSS receivers with ground based position measurement systems used to assess dynamic accuracy in agricultural applications by mitigating error due to latency.