@@ -66,7 +66,7 @@ that WR will continue to proliferate in scientific applications and should soon
\vspace{-0.1cm}
\section{Introduction}
White Rabbit (WR) \cite{biblio:whiteRabbit} is an innovative technology that provides sub-nanosecond
accuracy and picoseconds precision of synchronization as well as deterministic and
accuracy and \textcolor{red}{tens of}picoseconds precision of synchronization as well as deterministic and
reliable data delivery for large distributed systems.
% \textcolor{gray}{
% The project with the same name
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@@ -88,10 +88,13 @@ to meet the requirements of WR applications. A WR network
is a Bridged Local Area Network (IEEE 802.1Q) that uses Ethernet
(IEEE 802.3) to interconnect network elements and
Precision Time Protocol (PTP, IEEE 1588) to synchronize
them. A WR network consists of switches and nodes
that implement WR enhancements:
them. \textcolor{red}{The WR network elements, i.e. 802.1Q bridges and end stations,
are called WR switches and WR nodes, respectively, and}
implement WR enhancements:
% A WR network consists of \textcolor{red}{(802.1Q bridges and end stations, called switches and nodes respectively,)} and nodes
% \textcolor{red}{(802.1Q end stations)} that implement WR enhancements:
\begin{enumerate}
\item\textbf{Synchronization with sub-ns accuracy and picoseconds precision}\textcolor{red}{among} all
\item\textbf{Synchronization with \textcolor{red}{sub-nanosecond} accuracy and \textcolor{red}{tens of} picoseconds precision}\textcolor{red}{among} all
WR switches/nodes. Such synchronization is provided by the WR extension to PTP (WR-PTP,
\cite{biblio:WRPTP}) and its supporting hardware \cite{biblio:ISPCS2011}\cite{biblio:TomekMSc}\cite{biblio:WRproject}.
\item\textbf{Deterministic and low-latency communication} between WR nodes provided by
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@@ -274,7 +277,7 @@ The most basic application of WR is the transfer of time and frequency from the
Grandmaster WR switch/node (Grandmaster) to all other WR switches/nodes in
the WR network. WR ensures that the Pulse Per Second (PPS) outputs of all the
WR switches/nodes in the WR network are aligned to the PPS output of the
Grandmaster with a sub-ns accuracy and picoseconds precision. WR switches and
Grandmaster with a \textcolor{red}{sub-nanosecond} accuracy and \textcolor{red}{tens of} picoseconds precision. WR switches and
nodes use and can output a clock signal (e.g. 10MHz, 125MHz) that is traceable to that
of the Grandmaster.
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@@ -348,7 +351,7 @@ within their campus UTC(NIST) and UTC(OP), respectively. All
laboratories are studying WR with different types and lengths of fiber links and attempt to
increase its performance, see Table~\ref{tab:timelabs}.
These studies have shown that the stability (at \textcolor{red}{$\tau=1s$}) of the off-the-shelf
WR switch is 1e-11 (Alan deviation, ADEV, similar to a typical frequency counter e.g. Keysight 53230A)
WR switch is 1e-11
and can be improved to 1e-12 without any modifications to the WR-PTP Protocol, see
@@ -453,7 +456,7 @@ accelerators is yet to be implemented.
% China Spoliation Neutron Source (CSNS)\\
% General Machine Timing (GMT) and Beam Synchronous Timing (BST)\\
\newpage
% \newpage
\section{Precise Timestamping (TS)}
\label{sec:timestamping}
% \subsection{Basic Concept}
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@@ -673,10 +676,16 @@ the CERN accelerators, except LHC, should be running WR-BTrain operationally \ci
\section{Radio-Frequency Transfer (RF)}
\label{sec:RFoverWR}
% \subsection{Basic Concept}
Radio-frequency transfer allows \textcolor{red}{the digitization of} periodic input signals in a WR master node,
\textcolor{red}{the sending}
Radio-frequency (RF) transfer \textcolor{red}{over WR network} allows \textcolor{red}{the digitization of} periodic input signals in a WR master node,
\textcolor{red}{the sending of}
their digital form over a WR network, and \textcolor{red}{the subsequent regeneration of the} signal coherently with a fixed delay in many
WR slave nodes. In such schema, depicted in Figure~\ref{fig:RFoverWR} and detailed in \cite{biblio:WR-LIST},
WR slave nodes. \textcolor{red}{Such a digital RF transfer provides a number of advantages over an analogue transmission of RF signals. For example, it is
scalable and allows transmission of multiple RF signals from multiple sources over a single WR network
whereas analogue transmission typically requires dedicated network per source and signal. It also allows easy and automatic phase-alignment of the output
RF signals with compensation for temperature changes of transmission cables whereas such alignment and compensation in analogue transmission is very challenging. }
% Lastly, the digital RF transfer over WR network minimizes bandwidth of transmitted data allowing to use WR network also for other purposes.
In \textcolor{red}{the RF transfer over WR Network} schema, depicted in Figure~\ref{fig:RFoverWR} and detailed in \cite{biblio:WR-LIST},
\begin{figure}[!ht]
\centering
\vspace{0.2cm}
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@@ -688,22 +697,36 @@ a digital direct synthesis (DDS) based on the WR reference clock
signal (125MHz) is used to generate an RF signal in the WR master node. The generated RF signal is then compared by a phase detector to the
input RF signal. The error measured by the phase detector is an input to a
loop filter (e.g. Integral-Proportional controller) that steers the DDS to produce a signal identical to the RF input -
effectively locking the DDS to the input signal..
effectively locking the DDS to the input signal.
The tuning words of the DDS are the digital form of the RF input
that is sent over WR network. Each of the receiving WR slave nodes recreates the RF input signal
by using the received tuning words to control the local DDS with a fixed delay.
In such way, the WR slave nodes produce RF outputs that are syntonized with
the RF input, phase-aligned among each other, and delayed with respect to the RF input --
all with sub-ns accuracy and picoseconds precision.
all with \textcolor{red}{sub-nanosecond} accuracy and \textcolor{red}{tens of} picoseconds precision.
\textcolor{red}{Such a performance is possible because the noise of the DDS and the reference clock signal provided by WR to digitize/synthesize
the RF signal are much lower than the required characteristics
of the digital RF signal transmission, thus negligible.}
% \subsection{Example Applications}
The WR-based radio-frequency transfer is being implemented in the European Synchrotron Radiation
Facility (ESRF) \cite{biblio:ESRF}. The operation of the ESRF accelerator facility
is controlled by a "Bunch Clock" system that delivers to accelerator subsystems a
Facility (ESRF) \cite{biblio:ESRF}\cite{biblio:ESRF-WR}. The operation of the ESRF accelerator facility
is controlled by a "Bunch Clock" system\textcolor{red}{\footnote{
\textcolor{red}{Bunch Clock is a clock signal that is synchronous with particle bunches
circulating in a synchrotron or an accelerator. The "Bunch Clock" system generates such a clock signal.}
}}
that delivers to accelerator subsystems a
$\approx$352 MHz RF signal and triggers initiating sequential actions synchronous
to the RF signal, such as "gun trigger", "injection trigger" or "extraction trigger".
to the RF signal, such as
"gun trigger", "injection trigger" or "extraction trigger"\textcolor{red}{\footnote{
\textcolor{red}{
"Gun trigger" initiates generation of an electron bunch at the LINAC input,
"injection trigger" initiates transfer of the bunch from the LINAC into the Booster,
"extraction trigger" initiates extraction of the bunch from the Booster into the
Storage Ring at the end of acceleration. Detailed description is provided in \cite{biblio:ESRF-WR}.
}}}.
The jitter of the output RF signal is required to be below 50~ps. The RF signal is continuously
trimmed around the 352~MHz value as the tuning parameter in the "fast orbit feedback"
process. Apart from the 352~MHz signal, other frequencies are distributed, such as the
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@@ -1138,8 +1161,7 @@ have shown that the performance of a WR switch currently commercially available
improved:
\begin{itemize}
\item ADEV clock stability (tau=1s) from 1e-11 to 1e-12,
\item Random jitter from \textcolor{red}{1.1 to 11~ps} RMS
over 1Hz-100kHz.
\item Random jitter from 11 to 1.1~ps RMS \textcolor{red}{(integration bandwidth from} 1Hz to 100kHz\textcolor{red}{)}.
\end{itemize}
This prompted the development of the Low-Jitter Daughterboard
\cite{biblio:WR-LJD}\textcolor{red}{, which} improves the performance of the WR switch to 1e-12 without any
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@@ -1156,7 +1178,7 @@ within the WRITE project.
The studies \cite{biblio:wr-cngs} have shown that the temperature variation
of WR nodes and switches degrades synchronization performance, still