Synchronization for digital cable network

• US 20020056133A1
• Filed: 03/02/2001
• Published: 05/09/2002
• Est. Priority Date: 03/03/2000
• Status: Abandoned Application

• Current Assignee: AVAZ Networks Incorporated (Quartics Incorporated)
• Original Assignee: AVAZ Networks Incorporated (Quartics Incorporated)
• Inventors: Fung, Danny, Usman, Mohammad
• Application Number:
  US09/798,539
• Publication Number:
  US 20020056133A1
• Time in Patent Office: Days
• US Class Current: 725/118
• CPC Class Codes: G06Q 40/02 Banking, e.g. interest calculation or account maintenance credit or loans G06Q40/03
• CPC Class Codes: G06Q 40/08 Insurance
• CPC Class Codes: H04J 3/0638 Clock or time synchronisation among nodes; Internode synchronisation synchronization for ring networks H04L12/422; data switching networks with synchronous transmission H04L12/43
• CPC Class Codes: H04L 7/0029 interpolation of received data signal
• CPC Class Codes: H04N 2007/17372 the upstream transmission being initiated or timed by a signal from upstream of the user terminal
• CPC Class Codes: H04N 21/234 Processing of video elementary streams, e.g. splicing of video streams or manipulating encoded video stream scene graphs
• CPC Class Codes: H04N 21/2365 Multiplexing of several video streams
• CPC Class Codes: H04N 21/242 Synchronization processes, e.g. processing of PCR [Program Clock References] arrangements for synchronising broadcast or distribution via plural systems in broadcast distribution systems H04H20/18
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• CPC Class Codes: H04N 21/4302 Content synchronisation processes, e.g. decoder synchronisation
• CPC Class Codes: H04N 21/4305 Synchronising client clock from received content stream, e.g. locking decoder clock with encoder clock, extraction of the PCR packets arrangements for synchronising receiver with transmitter by comparing receiver clock with transmitter clock H04L7/0012; arrangements for synchronising receiver with transmitter wherein the receiver takes measures against momentary loss of synchronisation H04L7/0083
• CPC Class Codes: H04N 21/4347 Demultiplexing of several video streams
• CPC Class Codes: H04N 21/44 Processing of video elementary streams, e.g. splicing a video clip retrieved from local storage with an incoming video stream or rendering scenes according to encoded video stream scene graphs
• CPC Class Codes: H04N 5/04 Synchronising for television systems using pulse code modulation H04N7/56
• CPC Class Codes: H04N 7/10 Adaptations for transmission by electrical cable H04N7/12 takes precedence
• CPC Class Codes: H04N 7/56 Synchronising systems therefor

Abstract

A communication system, such as a digital cable network, achieves synchronization using data rate synchronization, clock frequency synchronization, or clock recovery synchronization techniques. The communication system includes a conversion clock at a transmitter and a conversion clock at a receiver. The data rate synchronization techniques adjust data rates by resampling digital data sent from the transmitter to the receiver to compensate for frequency variations in the conversion clocks. The clock frequency synchronization techniques use time stamps to adjust the receiver conversion clock frequency to substantially match the transmitter conversion clock frequency. The clock recovery techniques use a reference clock to adjust the transmitter conversion clock frequency and the receiver conversion clock frequency to be approximately the same.

Claims

1. A digital cable television network comprising:

a transmitter comprising;

an analog-to-digital converter configured to receive an analog video signal and produce corresponding digital values at a rate determined by a transmitter clock; and

a transmitter synchronizer coupled to said transmitter clock and configured to produce a time signal indicative of the transmitter clock frequency, said transmitter synchronizer comprising a first counter incremented by a multiple of said transmitter clock; and

a receiver comprising;

a digital-to-analog converter configured to receive said analog video signal represented by said digital values and to produce analog equivalents at a rate determined by a receiver clock; and

a receiver synchronizer coupled to said receiver clock and configured to receive said time signal for comparison and adjustment of receiver operation to account for a difference between the transmitter clock frequency and the receiver clock frequency, said receiver synchronizer comprising a second counter and a comparator, said second counter incremented by a multiple of said receiver clock, and said comparator configured to receive inputs from said first counter and said second counter and to produce control information indicative of a difference in rates of change of the respective first and second counters.

2. The digital cable television network of claim 1 wherein said transmitter resides at a headend and said receiver resides at a node.

3. The digital cable television network of claim 1 wherein said transmitter resides at a node and said receiver resides at a headend.

4. The digital cable television network of claim 1 wherein said receiver further comprises a resampler configured to receive said control information and change a data rate of said analog video signal represented by said digital values.

5. The digital cable television network of claim 1 wherein said receiver synchronizer adjusts the receiver clock frequency with said control information.

6. A digital cable television network comprising:

a transmitter comprising;

an analog-to-digital converter configured to receive an analog video signal and to produce corresponding digital values at a rate determined by a transmitter clock; and

a transmitter synchronizer coupled to said transmitter clock and configured to produce a time signal indicative of the transmitter clock frequency, said transmitter synchronizer comprising a program clock reference, a first system time clock controlled by said transmitter clock, and a first comparator configured to compare values of said program clock reference with said first system time clock and adjust said transmitter clock based on a difference; and

a receiver comprising;

a digital-to-analog converter configured to receive said analog video signal represented by said digital values and to produce analog equivalents at a rate determined by a receiver clock; and

a receiver synchronizer coupled to said receiver clock and configured to receive said time signal for comparison and adjustment of receiver operation to account for differences between the transmitter clock frequency and the receiver clock frequency, said receiver synchronizer comprising an extractor, a second system time clock and a second comparator, said extractor configured to extract value of said program clock reference from data stream sent by said transmitter, said second system time clock controlled by said receiver clock, and said second comparator configured to compare values of said program clock reference and said second system time clock and adjust said receiver clock based on a difference.

7. A method of synchronizing a transmitter and a receiver in a digital cable television network comprising the acts of:

comparing a first count with a second count, wherein said first count is representative of a transmitter data rate and said second count is representative of a receiver data rate;

producing control information for a resampler based on said comparison;

and

resampling digital data produced by said transmitter in accordance with said control information before converting said digital data to an analog equivalent in the receiver.

8. The method of synchronizing a transmitter and a receiver in a digital cable television network of claim 7, further comprising the acts of:

generating said first count at said transmitter using a transmitter clock;

inserting value of said first count into a data stream at the transmitter;

and

extracting said value of said first count from the data stream at the receiver.

9. The method of claim 8, wherein the value of the first count is inserted into the data stream during framing at the transmitter, and the value of the first count is extracted from the data stream during deframing at the receiver.

10. A method of synchronizing a transmitter and a receiver in a digital cable television network comprising the acts of:

comparing a first count with a second count, wherein said first count is representative of a transmitter data rate and said second count is representative of a receiver data rate;

producing control information based on said comparison; and

adjusting a receiver clock in accordance with said control information.

11. The method of synchronizing a transmitter and a receiver in a digital cable television network of claim 10, further comprising the acts of:

generating said first count at said transmitter using a transmitter clock;

inserting value of said first count into a data stream at the transmitter;

and

extracting said value of said first count from the data stream at the receiver.

12. The method of claim 11, wherein the value of the first count is inserted into the data stream during framing at the transmitter, and the value of the first count is extracted from the data stream during deframing at the receiver.

14. The method of claim 13, wherein the signal is inserted into a data stream at the receiver, and the signal is extracted from the data stream at the receiver.

15. The method of claim 14, wherein the signal is inserted into the data stream during framing, and the signal is extracted during deframing.

13. A method of synchronizing a transmitter and a receiver in a digital cable television network comprising the acts of:

adjusting a transmitter clock frequency to follow a program clock reference frequency in the transmitter;

sending a signal indicative of said program clock reference frequency to the receiver; and

adjusting a receiver clock frequency based on said signal.

16. A digital cable television network comprising:

means for digitizing analog signals at a first data rate;

means for producing a first count that is representative of said first data rate;

means for producing a second count that is representative of a second data rate; and

means for converting said digitized analog video signals from said first data rate to said second data rate based on a comparison of said first count and said second count.

17. A digital cable television network comprising:

means for digitizing analog signals at a first data rate;

means for producing a first count that is representative of said first data rate;

means for producing a second count that is representative of a second data rate; and

means for adjusting said second data rate based on a comparison of said first count and said second count.

18. A digital cable television network comprising:

means for digitizing analog video signals at a first data rate;

means for producing a reference clock;

means for adjusting said first data rate based on said reference clock;

means for processing said digitized analog video signals at a second data rate; and

means for adjusting said second data rate based on value of said reference clock.