A Precise RF Time Transfer Method for Coherent Distributed System Applications

A method for creating an absolute common time reference between distributed RF systems was demonstrated using software-defined radios by exchanging RF time-alignment waveforms. A timestamp-free protocol was implemented to reduce the non-deterministic sources of latency typical of digital timestamp exchange methods. The protocol is synthesized on the field-programmable gate array of National Instruments Universal Software Radio Peripheral transceivers. Measurements indicate time alignment can be achieved with a standard deviation of less than 100 ps. A demonstration using the protocol to align L-band transmissions from distributed nodes is presented.