Timing recovery over packet networks
First Claim
Patent Images
1. A method of recovering timing information over packet networks, comprising:
- measuring raw network time delays from timing packets of a single stream sent between a transmitter and a receiver over a packet network;
predicting a current delay estimate using a minimum statistics adaptive filter to track local minima of the measured raw network time delays over a series of successive smoothing windows of L received timing packets of the single stream, by;
maintaining a first variable tracking a local minimum measured raw network time delay within a smoothing window,maintaining a second variable representing the current delay estimate, said second variable being regularly updated within each smoothing window and being set equal to a minimum between the current value thereof and the measured raw network time delay for the current timing packet,after L received timing packets at the start of a new smoothing window setting said second variable equal to the current value of said first variable and subsequently updating the value of said first variable, andadaptively varying the value of L based on estimated delay variations between the transmitter and the receiver to change the tracking characteristics of the minimum statistics adaptive filter;
selecting those incoming timing packets of the single stream within the smoothing window which meet a particular criterion relative to the current delay estimate; and
making frequency adjustments determined from the measured raw network time delays of the selected timing packets of the single stream for a local clock at the receiver.
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Abstract
In a method of recovering timing information over packet networks, raw network delays are measured using timing packets sent between a transmitter and receiver. The expected delay is predicted using a minimum statistics adaptive filter to track local minima of measured time delays over a smoothing window. Only those incoming timing packets which meet a particular criterion relative to the expected delay within a smoothing window are selected, and a local clock is adjusted based on the measured timing delays from the selected timing packets.
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Citations
16 Claims
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1. A method of recovering timing information over packet networks, comprising:
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measuring raw network time delays from timing packets of a single stream sent between a transmitter and a receiver over a packet network; predicting a current delay estimate using a minimum statistics adaptive filter to track local minima of the measured raw network time delays over a series of successive smoothing windows of L received timing packets of the single stream, by; maintaining a first variable tracking a local minimum measured raw network time delay within a smoothing window, maintaining a second variable representing the current delay estimate, said second variable being regularly updated within each smoothing window and being set equal to a minimum between the current value thereof and the measured raw network time delay for the current timing packet, after L received timing packets at the start of a new smoothing window setting said second variable equal to the current value of said first variable and subsequently updating the value of said first variable, and adaptively varying the value of L based on estimated delay variations between the transmitter and the receiver to change the tracking characteristics of the minimum statistics adaptive filter; selecting those incoming timing packets of the single stream within the smoothing window which meet a particular criterion relative to the current delay estimate; and making frequency adjustments determined from the measured raw network time delays of the selected timing packets of the single stream for a local clock at the receiver. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A timing recovery unit for recovering timing information over packet networks, comprising:
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a block for measuring raw network time delays from timing packets of a single stream sent between a transmitter and a receiver over a packet network; a minimum statistics adaptive filter to track local minima of the measured raw network time delays over a smoothing window to predict a current delay estimate over a series of successive smoothing windows of L received timing packets of the single stream, and wherein the minimum statistics filter is configured to; maintain a first variable tracking a local minimum raw network time delay within a smoothing window, maintain a second variable representing the current delay estimate, said second variable being regularly updated within each smoothing window and being set equal to a minimum between the current value thereof and the measured raw network time delay for the current timing packet, after L received timing packets at the start of a new smoothing window, to set the second variable equal to the current value of the first variable and subsequently update the value of said first variable, and to adaptively vary the size of smoothing window based on estimated delay variations between the transmitter and the receiver to change the tracking characteristics of the minimum statistics adaptive filter; a selection block for selecting those incoming timing packets of the single stream within the smoothing window which meet a particular criterion relative to the current delay estimate; and a phase locked loop for outputting a local clock at the receiver using frequency adjustments determined from the measured raw network time delays of the selected timing packets of the single stream. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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Specification