Methods and systems for estimating offset and skew using linear programming
AssigneesKhalifa University of Science, Technology, and Research, British Telecommunications pic, Emirates Telecommunications Corporation
InventorJames Aweya
Life of this patent
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Abstract
This invention relates to methods and systems for estimating offset and skew using linear programming. Embodiments of the invention relate to methods and systems which apply linear programming principles to links with asymmetric transmission rates which are estimated from an exchange of timing messages (for example under IEEE 1588 PTP). Further embodiments provide for the estimation of clock offsets using linear programming techniques when the skew is known or estimated.
Claims24
A slave device connected to a master device having a master clock over a network, wherein the slave device includes a slave clock and a processor, and wherein the processor is arranged to:
- exchange with the master device, timing messages and record timestamps which are:
- the time of sending of said timing messages from the master device according to the master clock;
- the time of receipt of said timing messages according to the slave clock;
- the time of sending of said timing messages according to the slave clock;
- and the time of receipt of said timing messages according to the master clock;
- formulate a linear programming problem which includes in its constraints said timestamps along with variables relating to:
- the skew and offset of the slave clock compared to the master clock;
- and the relationship between the forward and reverse transmission speeds in the network between the master device and the slave device;
- solve the linear programming problem to derive an estimate of the skew and offset of the slave clock relative to the master clock;
- and
- synchronize the slave clock to the master clock based on the estimated skew and offset to produce a master time estimate.
A method of synchronizing the time and frequency of a slave clock in a slave device to a master clock in a master device which is connected to the slave device over a network, the method including the steps of:
- exchanging, between the master device and the slave device, timing messages and recording timestamps which are:
- the time of sending of timing messages from the master device according to the master clock;
- the time of receipt of said timing messages according to the slave clock;
- the time of sending of said timing messages according to the slave clock;
- and the time of receipt of said timing messages according to the master clock;
- formulating a linear programming problem which includes in its constraints said timestamps along with variables relating to:
- the skew and offset of the slave clock compared to the master clock;
- and the relationship between the forward and reverse transmission speeds in the network between the master device and the slave device;
- solving the linear programming problem to derive an estimate of the skew and offset of the slave clock relative to the master clock;
- and
- synchronizing the slave clock to the master clock based on the estimated skew and offset to produce a master time estimate.
A time and frequency synchronisation system for a network, the system including:
- a master device having a master clock;
- a slave device having a slave clock;
- and
- a network connecting the master and slave devices, wherein:
- the slave clock comprises a slave clock and a processor;
- and
- the processor is arranged to:
- exchange with the master device, timing messages and record timestamps which are:
- the time of sending of said timing messages from the master device according to the master clock;
- the time of receipt of said timing messages according to the slave clock;
- the time of sending of said timing messages according to the slave clock;
- and the time of receipt of said timing messages according to the master clock;
- formulate a linear programming problem which includes in its constraints said timestamps along with variables relating to:
- the skew and offset of the slave clock compared to the master clock;
- and the relationship between the forward and reverse transmission speeds in the network between the master device and the slave device;
- solve the linear programming problem to derive an estimate of the skew and offset of the slave clock relative to the master clock;
- and
- synchronize the slave clock to the master clock based on the estimated skew and offset to produce a master time estimate.
Dependencies are inferred from the claim text.