Timing, Communications, and Ranging SDR (TCR-SDR) for IoT Wireless Synchronization

Wireless clock synchronization approaches leveraging Internet of Things (IoT) could provide an inexpensive and scalable way to wirelessly distribute time between stable clock sources if time transfer clock errors are minimized and proper timing interfaces are created for IoT devices. Most IoT devices are focused on just providing reliable wireless Communications and do not expose the parameters and metrics needed to perform timing and ranging functionality from their transceivers. This paper explores developing an IoT device that adds timing and ranging functionality to an existing IoT device while maintaining its original communications capability. This is a hybrid architecture integrating an existing IoT transceiver with a stable clock source and an IoT I/Q transceiver to generate the parameters and metrics needed for wireless clock synchronization between IoT devices. This modified IoT device is known as a Timing, Communications, and Ranging Software Defined Radio (TCR-SDR) where timing and ranging functions are primary features being provided from SDR capabilities. SDR capabilities are providing by combining an IoT based I/Q transceiver with an FPGA and microcontroller. The current TCR-SDR is in a Receiver Carrier Board (RCB) form factor for exploring wireless clock synchronization algorithms with the Open Compute Project Timing Applications Project (OCP-TAP) Time Card. The OCP-TAP Time Card provides an open timing architecture and a source of time for data centers leveraging a GNSS receiver and a stable time reference (i.e. CSAC or TCXO) for holdover when GNSS signals are disrupted. In this paper we explore how to generate timing precision performance bounds of the TCR-SDR. This provides insights into performance limitations for distributing 10 MHz and 1 PPS reference sources from OCP-TAP Time Cards to other IoT devices. This discussion is focused on using LoRa to distribute the reference sources since LoRa is the IoT transceiver being used in the current TCR-SDR instantiation.