Calibration-Free Feedforward Temperature Compensation for Wireless Clock Synchronisation

Wireless systems are entering the arena of time-critical applications, including industrial controls. This makes clock synchronisation vital. A relevant source of synchronisation errors, especially in heavy-duty applications and harsh environments, is given by temperature variations that affect the quartz oscillators. This article takes a control theory-based approach and proposes to augment clock synchronisation schemes—that are typically feedback-based—with a feedforward compensation path using temperature measurements to quickly react to temperature change. Unlike previous approaches relying on per-device data, our solution takes advantage of the combined feedforward-feedback nature of the control scheme to perform compensation using only nominal crystal parameters. When implemented in conjunction with the FLOPSYNC-2 feedback-based clock synchronisation scheme and tested both in simulation and experimentally, the approach resulted in a greatly reduced synchronisation error during temperature transients. In detail, Monte Carlo simulations show that the proposed solution can reduce the peak clock synchronisation error on average by 5.3 \(\times\) and in the worst case by 2.2 \(\times\) , thus proving applicable and effective without the need for a costly per-device calibration. When tested experimentally on a network of sensor nodes, a 3.3 \(\times\) peak clock synchronisation error improvement was observed, confirming the simulation predictions.