An Adaptive Distributed Clock for Radar Networks
An adaptive distributed time, frequency, and phase synchronization system for radar networks is described. This clock consists out of multiple identical sync-modules that provide the time and frequency reference to the respective radar nodes. The modules are connected in a daisy-chain fashion and supports two-way time transfer. These modules are universal and independent of the time transfer medium. This system offers a solution to global navigation satellite system (GNSS) denied scenarios, and to applications where a more robust and precise network-wide timing solution is required. It supports a multi input multi output (MIMO) control loop that continuously steers the individual module clocks collectively and adaptively to ensure optimal synchronization. The steering is adjusted based on both the particular radar mode, and the availability and quality of the respective time transfer paths. Continuous monitoring hardens the system against time spoofing and attack. This idea is novel in that the radar and clock interacts. The radar can influence the synchronization parameters, while it can simultaneously adapt its own operation based on the reported level of node-to-node synchronization. Thus, the clock distribution is no longer a monolithic subsystem, as is often the case, but an integral part of the radar network. This paves the way to adaptive or fully cognitive radar networks where both the radar and timing system adapt to the circumstances. In this implementation, each module disciplines a stable local oscillator (STALO) to a 1 Hz time reference signal using two-way time transfer. The STALO then serves as the frequency reference to the radar node. This paper first develops the idea of an adaptive distributed clock. The system is fully modular and assembled from low-cost commercial off-the-shelf (COTS) parts. Its purpose is to serve as a research platform and software framework upon which sophisticated feedback and clock steering strategies could be developed and tested with the actual hardware in the loop. The initial prototype is verified using a preliminary PLL implementation and coax copper cable as time transfer medium. In the future, more sync-modules may be added and upgraded with Rubidium STALOs to offer two-way time transfer across RF for next generation radar networks.