What does particle physics at CERN have in common with tracking ships off the coast of Cape Town? The answer lies in ultra-precise timing—specifically, how we clock distributed sensor networks.
In a doctoral thesis completed at the University of Cape Town (UCT) under the Radar Remote Sensing Group, Dr. Simon Alexander Cole Lewis put two clocking mechanisms head-to-head in a coherent multistatic radar system: GPS-Disciplined Oscillators (GPSDOs) vs. CERN’s White Rabbit Network.
Here is a look at why this comparison matters, how the test was conducted in the field, and what it means for the future of radar sensing.
The Core Challenge: Keeping Multistatic Nodes Coherent
Single-station monostatic radars rely on an internal clock to send out a radio frequency pulse and measure its return time. In contrast, multistatic radar systems use multiple spatially separated transmitters and receivers.
Working cooperatively allows multistatic systems to detect stealth targets, defeat electronic counter-measures, and achieve high-resolution spatial tracking. However, combining signals from nodes located kilometers apart requires strict spatial, temporal, and phase synchronization. If the individual clocks drift by even a few nanoseconds or introduce phase jitter, the combined radar image degrades into spatial ambiguity and noise.
Comparing the Contenders
The UCT doctoral research evaluated two Time and Frequency Transfer (TFT) protocols:
- GPS-Disciplined Oscillators (GPSDOs): Wireless synchronization using multi-channel GPS timing receivers operating under common-view time transfer. While cost-effective and easy to deploy without physical cabling between radar nodes, satellite timing remains vulnerable to weather, signal degradation, line-of-sight blockage, and RF interference/jamming.
- White Rabbit (WR) Network: A fiber-optic timing technology initially designed at CERN for particle accelerators. Combining Synchronous Ethernet (SyncE) with IEEE 1588 Precision Time Protocol (PTP), White Rabbit delivers sub-nanosecond precision and picosecond-level phase jitter over dedicated optical links.
Field Testing on NeXtRAD & The Lighthouse Benchmark
To move beyond laboratory predictions, the synchronization networks were integrated into NeXtRAD - UCT’s dual-band (X-band and L-band) polarimetric multistatic radar system.
During field trials across False Bay, South Africa, the team aimed the radar nodes at the Roman Rock Lighthouse—a static, stationary reflection point off the coast. By analyzing the Doppler spectra and direct line-of-sight signal paths from this fixed target, the research directly measured phase drift, Doppler noise, and timing alignment between nodes.
Results
- Phase Coherence: The White Rabbit network achieved superior timing stability and near-zero phase drift compared to GPSDOs.
- Radar Processing Gain: The sub-nanosecond precision of White Rabbit allowed NeXtRAD to successfully perform fully coherent spatial processing gain across distributed nodes.
Primary Sources & Reading
- UCT Doctoral Thesis Repository: Read Dr. Simon A. C. Lewis's full dissertation via the University of Cape Town Open Access Repository.
- IEEE Publication: Read the peer-reviewed field comparison in IEEE Transactions on Aerospace and Electronic Systems.
- Project Details: Overview of UCT’s Radar Remote Sensing Group (RRSG).
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