Method for time synchronization in a communications network

Patent metadata

Field	Value
Publication number	US-9288037-B2
Application number	US-201113825532-A
Country	US
Kind code	B2
Filing date	Sep 1, 2011
Priority date	Sep 24, 2010
Publication date	Mar 15, 2016
Grant date	Mar 15, 2016

Abstract

A method for time synchronization in a communications network having multiple nodes, wherein the nodes comprise a first node and at least one second node, where the first node generates first cycle counter states according to a reference clock frequency and the second node or nodes each generate second cycle counter states according to an internal clock frequency, where a time synchronization is carried out in sequential synchronization cycles, in which synchronization messages originating from the first node are sequentially transmitted from one node to another node, and a synchronization message transmitted by a node contains information used for time synchronization in the at least one second node receiving the synchronization message such that a time synchronization is performed in a given second node based on an estimation of a first cycle counter state and a compensation factor in combination with a linear quadratic regulator.

First claim

The invention claimed is:

1. A method for time synchronization in a communications network having a first node and at least one second node, comprising:
i) sending, within a synchronization cycle, a synchronization message from the first node to the at least one second node; and
ii) providing, by the first node, a first cycle counter state in accordance with a reference clock frequency and providing, by a respective second node of the at least one second node, a second cycle counter state in accordance with an internal clock frequency;
wherein time synchronization of the respective second node of the at least one second node is implemented such that:
(a) the synchronization message is received at the respective second node;
(b) an estimated first cycle counter state and an estimated compensation factor are estimated for a measured second cycle counter state of the respective second node based on information contained in the received synchronization message by a stochastic state estimator, the estimated first cycle counter state estimating the first cycle counter state of the first node for a point in time at which the synchronization message is received by the respective second node, and the estimated compensation factor estimating a duty cycle ratio of the reference clock frequency to a respective internal clock frequency for the synchronization cycle;
(c) a linear-quadratic regulator is utilized to determine from both the estimated first cycle counter state and the estimated compensator factor a controlled first cycle counter state and a controlled compensation factor based on a controlled system which contains a correction term for the controlled compensation factor as a control variable, the controlled compensation factor estimating a duty cycle ratio of the reference clock frequency to the respective internal clock frequency, and the controlled first cycle counter state indicating a synchronized timing; and
(d) a two-dimensional model is utilized for the stochastic state estimator and the linear-quadratic regulator, the two-dimensional model comprising the estimated first cycle counter and the estimated compensation factor as states.

2. The method in accordance with claim 1 , wherein, in step b), a variation of the compensation factor based on a stochastic process is modeled.

3. The method in accordance with claim 1 , wherein the control variable is updated after each receipt of the synchronization message in the respective second node and supplied to a control loop.

4. The method in accordance with claim 2 , wherein the control variable is updated after each receipt of the synchronization message in the respective second node and supplied to a control loop.

5. The method in accordance with claim 3 , wherein the control loop for the linear-quadratic regulator at a time of receipt of the synchronization message in a kth synchronization cycle in an nth second node and immediately before an updating of the manipulating variable is in accordance with the following relationship:

[

CT
n

⁡

(
k
)

o
n

⁡

(
k
)

]

=

A
n

⁡

(

k
-
1

)

⁡

[

CT
n

⁡

(

k
-
1

)

o
n

⁡

(

k
-
1

)

]

+

[

0

1

]

·

u
n
s

⁡

(

k
-
1

)

;

where CT n (k) is the regulated first cycle counter state at the time of receipt of the synchronization message in the kth synchronization cycle;
where o n (k) is the regulated compensation factor at the time of receipt of the synchronization message in the kth synchronization cycle;
where u n s (k−1) is a correction term for the regulated compensation factor used in a kth synchronization cycle;
where

A
n

⁡

(

k

Assignees

• Obradovic Dragan
• Scheiterer Ruxandra
• Wolfrum Philipp
• Steindl Günter
• Siemens Ag

Inventors

• Obradovic Dragan
• Scheiterer Ruxandra
• Wolfrum Philipp
• Steindl Günter

Classifications

• H04L7/04 Primary

  Speed or phase control by synchronisation signals {(H04L7/0075 takes precedence)} · CPC title

• H04J3/0667

  Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays (arrangements for monitoring round trip delays in packet switching networks H04L43/0864) · CPC title

• H04J3/0673 Primary

  using intermediate nodes, e.g. modification of a received timestamp before further transmission to the next packet node, e.g. including internal delay time or residence time into the packet · CPC title