Nanosecond Time Synchronization over a 2.4 GHz Long-Range Wireless Link.

Time synchronization between geographically separated equipment, such as, for example, that required in sensor networks for radio localization, is often based on global navigation satellite systems (GNSSs). However, in environments that are GNSS-denied due to signal blockage or interference, alternative timing synchronization methods are necessary. In this work, an experimental wireless time synchronization system based on long-range (LoRa) modulation has been developed and tested in the field. LoRa modulation operating in the license-free 2.4 GHz industrial, scientific and medical (ISM) band was chosen due to the potentially large coverage area of several kilometers and the availability of a ranging engine in the SX1280 transceiver by Semtech, which facilitates the implementation of time synchronization. The prototype system was tested over 170 m, where it achieved a time deviation (TDEV) of 30 ps for an average time of 1 s and a maximum TDEV of 3 ns over one day of measurement, improving over existing work on time synchronization with LoRa modulation by around three orders of magnitude. The field tests showed that ns accuracy can be achieved using LoRa modulation, making it suitable for the synchronization of remote sites, for example, for radio localization.