Exploring Wireless Clock Synchronization with OCP-TAP Time Cards and RTL-SDRs

Wireless clock synchronization between data centers is a topic of interest due to a variety of applications and services in the cloud needing to fuse data based on a common time reference. The need to discipline local clocks at each data center presents a synchronization challenge for an application or service when Global Navigation Satellite System (GNSS) is disrupted. We seek to explore a resilient wireless clock synchronization approach leveraging RTL-SDRs and Internet of Things (IoT) when GNSS is disrupted on the Time Cards part of the Open Compute Project. The Open Compute Project - Time Appliances Project (OCP-TAP) Time Cards provide an open timing architecture and a source of time for data centers leveraging a GNSS receiver built into a Receiver Carrier Board (RCB) and include a stable time reference (i.e. CSAC or TCXO) when GNSS signals are disrupted. We seek to explore how best to wirelessly synchronize a network of OCP-TAP Time Cards with RTL-SDRs to wirelessly distribute a common clock source between OCP-TAP Time Cards when GNSS signals are unavailable. Our wireless clock synchronization approach seeks to support the development of a modified RCB that combines a GNSS chipset with an RTL-SDR and an IoT device to provide wireless two-way interferometry (Wi-Wi). Fusing an IoT chipset with an RTL-SDR and a GNSS receiver provides an inexpensive way to add wireless clock synchronization between OCP-TAP Time Cards if GNSS signals are disrupted. An RTL-SDR based RCB primarily functions to provide clock synchronization information between the OCP-TAP Time Cards for relative clock synchronization across a network of OCP-TAP Time Cards based on the exchange of messages between the IoT devices. A LoRa based IoT device is considered to provide the wireless clock synchronization signal between OCP-TAP Time Cards but any type of IoT device that can be captured in the frequency range of the RTL-SDR is sufficient for this approach.