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Precise clock synchronization is a fundamental requirement in real-time distributed embedded systems, yet low-cost microcontrollers typically rely on free-running crystal oscillators with non-negligible frequency drift. This paper explores a novel use of Wi-Fi Fine Timing Measurement (FTM) to estimate and compensate for the relative frequency drift between the quartz oscillators of two ESP32-S3 microcontrollers.
The proposed approach employs a minimalistic setup in which one node operates as a standard Wi-Fi FTM Responder, while the other acts as an FTM Initiator continuously issuing ranging requests. For each FTM exchange, the initiator records the timestamp quadruple (T1, T2, T3, T4), which is subsequently logged via a serial interface. By post-processing these timestamps with appropriate estimation algorithms, the relative frequency offset between the two oscillators can be derived, enabling the characterization of long-term drift behavior.
Beyond offline analysis, this work outlines a forward-looking vision in which drift estimation is performed directly on the initiator node and used to actively correct oscillator frequency via a Digitally Controlled Crystal Oscillator (DCXO) integrated with a modified ESP32 platform. Such closed-loop compensation has the potential to significantly improve clock alignment and long-term synchronization accuracy without external time references. The presented concept opens new possibilities for low-cost, wireless clock synchronization in distributed microcontroller-based systems using commodity Wi-Fi hardware.
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