White Rabbit Clock Synchronization: Ultimate Limits on Close-In Phase Noise and Short-Term Stability Due to FPGA Implementation

Abstract

This paper investigates the ultimate limits of White Rabbit (WR), an high-accuracy time distribution system based on field-programmable gate array (FPGA). The knowledge of such limits is essential for new emerging applications that are evaluating WR. In this paper, we identify and study the key elements in the WR synchronization: the digital dual mixer time difference phase detector and the Gigabit Ethernet transceiver. The benchmarks and experimental analysis of these key elements allow us to determine the WR switch (WRS) performance limits and evaluate their evolution with newer FPGAs. The identified performance limits are achievable by the present-day generation of WRS. The ultimate limits of short-term synchronization performance due to FPGA implementation have been derived through analysis and then demonstrated using the existing WRS enhanced with an additional daughterboard. This combination (WRS and daughterboard) achieves a tenfold improvement in terms of phase noise, jitter, and short-term stability with respect to the current WR performance. Both phase detectors and Gigabit transceivers have a similar phase noise contribution equal to a short-term stability of modified Allan deviation 4E-13 at $\tau = 1$ s (dominated by flicker phase modulation noise).

A Multidisciplinary Approach for the Development of Smart Distribution Networks

“…In a IEC 61850 scenario [51], which is becoming a possible framework for communications also outside the electrical substations, the PMU can be conceived as the union of one or more merging units that acquire and tag samples (sampled values) and an IED that runs the algorithm needed to calculate measurements [52]. PMUs are traditionally equipped with a GPS receiver [37], but synchronization based on packet-network protocols have taken place (see Chapter 5 of [38]), considering both hardware [52] and software [53] implementations of precision time protocol and investigating also wireless connection potentialities [54] and recent White Rabbit synchronization perspectives [55].…”

Enhanced Timestamping Method for Subnanosecond Time Synchronization in IEEE 802.11 Over WLAN Standard Conditions

“…The algorithm is stated in Algorithm 1. The received signal is first introduced to the cross-correlator (9) and the frame start index is detected using a threshold (10).…”

“…TS.). The conventional timestamps are based on the detector stated in (10). The time synchronization accuracy is the combination of the precision and trueness of the measurement.…”

“…In addition, there are some applications that need to deploy a communication system just for performing time distribution. These networks are usually found in scientific experiments [10], where a system must gather data with very high time accuracy over large areas. In this case, the use of wireless links for time transfer, instead of wired links, could lead to more costeffective solutions, faster deployments, and lower failure possibility, due to the inexistence of cables.…”

Dwingeloo Telescope has Fringes (Again)

“…Dwingeloo Fringes the existing network, and limits the wavelength uncertainty to 0.1 nm. Secondly, the WR switches were augmented with the 'Low Jitter Board' extension, also developed at CERN [3]. Finally the WR switch at the Dwingeloo telescope contains a clean-up oscillator to further reduce the short term phase noise of the link.…”