High-Precision Measurement of Sine and Pulse Reference Signals Using Software-Defined Radio

This paper addresses simultaneous high-precision measurement and analysis of generic reference signals by using inexpensive commercial off-the-shelf software-defined radio hardware. Sine reference signals are digitally downconverted to baseband for the analysis of phase deviations. Hereby, we compare the precision of the fixed-point hardware digital signal processing chain with a custom single instruction multiple data x86 floating-point implementation. Pulse reference signals are analyzed by a software trigger that precisely locates the time where the slope passes a certain threshold. The measurement system is implemented and verified using the Universal Software Radio Peripheral (USRP) N210 by Ettus Research LLC. Applying standard 10 MHz and 1 PPS reference signals for testing, a measurement precision (standard deviation) of 0.36 and 16.6 ps is obtained, respectively. In connection with standard PC hardware, the system allows long-term acquisition and storage of measurement data over several weeks. A comparison is given to the dual-mixer time difference and time interval counter, which are state-of-the-art measurement methods for sine and pulse signal analysis, respectively. Furthermore, we show that our proposed USRP-based approach outperforms measurements with a high-grade digital sampling oscilloscope.