MULTI INPUT TIMING RECOVERY OVER PACKET NETWORK

• US 20100296524A1
• Filed: 05/04/2010
• Published: 11/25/2010
• Est. Priority Date: 05/22/2009
• Status: Active Grant

• Current Assignee: Microsemi Semiconductor ULC (Microchip Technology Incorporated)
• Original Assignee: Zarlink Semiconductor Inc. (Microchip Technology Incorporated)
• Inventors: Rahbar, Kamran
• Granted Patent: US 8,774,227 B2
• Time in Patent Office: Days
• US Class Current: 370/516
• CPC Class Codes: H04J 3/0644 External master-clock
• CPC Class Codes: H04J 3/0661 using timestamps
• CPC Class Codes: H04J 3/0667 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 Class Codes: H04J 3/0679 by determining clock distribution path in a network
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04L 43/0852 Delays
• CPC Class Codes: H04L 43/087 Jitter
• CPC Class Codes: H04L 43/106 using time related information in packets, e.g. by adding timestamps
• CPC Class Codes: H04L 47/283 in response to processing delays, e.g. caused by jitter or round trip time [RTT]
• CPC Class Codes: H04L 7/0331 with a digital phase-locked loop [PLL] processing binary samples, e.g. add/subtract logic for correction of receiver clock H04L7/0337 takes precedence

Abstract

In a method of recovering timing information over packet networks, a receiver receives a plurality of packet streams over different paths from the same source. The raw delays experienced by the timing packets for each stream are filtered to provide a filtered delay for each stream. The filtered delays are weighted based on the quality of each stream, and the weighted filtered delays are then combined to form an aggregate delay estimate. Frequency adjustments for a local clock at the receiver are derived from the aggregate delay estimate.

Claims

1. A method of recovering timing information over packet networks wherein a receiver receives a plurality of packet streams over different paths from the same source, comprising:

receiving timing packets from each stream;

measuring the raw delays experienced by the timing packets for each stream;

filtering the measured raw delays to account for network packet delay variations so as to provide a filtered delay for each stream;

weighting the filtered delays based on the quality of each stream;

combining the weighted filtered delays to form an aggregate delay estimate; and

determining frequency adjustments from the aggregate delay estimate for a local clock at the receiver.

2. A method as claimed in claim 1, wherein the quality of each stream is determined by the variance of the packet delay and the packet rate for each stream.

4. A method as claimed in claim 1, wherein the weights of the individual streams are calculated based on a non-linear function of the packet rate and an estimated residual error for the filtered delay.

5. A method as claimed in claim 1, wherein the aggregate delay estimate is determined in accordance with the formula:

6. A method as claimed in claim 5, wherein the weighting coefficients are calculated in accordance with the formula:

7. A method as claimed in claim 6, wherein the aggregate delay estimate is passed through a loop filter of a phase locked loop to provide an update for a digital controlled oscillator that provides said local clock.

8. A method as claimed in claim 2, wherein the streams of filtered timing delay packets are re-sampled to the same uniform sampling rate.

9. A method as claimed in claim 1, wherein the timing packets for each stream are filtered using a minimum statistics adaptive filter.

10. A timing recovery unit for recovering timing information over packet networks wherein a receiver receives a plurality of packet streams over different paths from the same source, comprising:

a block for receiving timing packets from each stream;

a block for measuring the raw delays experienced by the timing packets for each stream;

a filter for filtering the measured raw delays to account for network packet delay variations so as to provide a filtered delay for each stream;

a weighting block for weighting the filtered delays based on the quality of each stream;

a combiner for combining the weighted filtered delays to form an aggregate delay estimate; and

a phase locked loop for outputting a local clock at the receiver using frequency adjustments determined from the aggregate delay estimate.

11. A timing recovery unit as claimed in claim 10, wherein the weighting block determines the quality of each stream based on the variance of the packet delay and the packet rate for each stream.

12. A timing recovery unit as claimed in claim 10, wherein the weighting block calculates the weights of the individual streams based on a non-linear function of the packet rate and an estimated residual error for the filtered delay.

13. A timing recovery unit as claimed in claim 12, wherein the aggregate delay estimate is determined in accordance with the formula:

14. A timing recovery unit as claimed in claim 13, wherein the weighting coefficients are calculated in accordance with the formula:

15. A timing recovery unit as claimed in claim 14, wherein the phase locked loop includes a loop filter for filtering the aggregate delay estimate to provide an update for a digital controlled oscillator that provides said local clock.

16. A timing recovery unit as claimed in claim 10, further comprising a re-sampler for re-sampling the streams of filtered timing delay packets to the same uniform sampling rate.

17. A timing recovery unit as claimed in claim 10, further comprising a minimum statistics adaptive filter for filtering the timing packets for each stream.