Optimizing upstream transmission in a cable television distribution plant

• US 6,725,462 B1
• Filed: 04/19/2000
• Issued: 04/20/2004
• Est. Priority Date: 04/19/2000
• Status: Expired due to Term

• Current Assignee: AT&T Corporation (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Kaplan, Alan Edward
• Primary Examiner(s): Srivastava, Vivek
• Assistant Examiner(s): Ma, Johnny
• Application Number:
  US09/552,628
• Time in Patent Office: 1,462 Days
• Field of Search: 725/124, 725/125, 725/127, 725/128, 725/111, 370/480, 370/485, 370/488
• US Class Current: 725/124
• CPC Class Codes: H04J 1/12 Arrangements for reducing cross-talk between channels in line transmission systems H04B3/32; in cables or lines H04B3/26 - H04B3/30
• CPC Class Codes: H04N 21/6118 involving cable transmission, e.g. using a cable modem
• CPC Class Codes: H04N 21/6168 involving cable transmission, e.g. using a cable modem
• CPC Class Codes: H04N 7/17309 Transmission or handling of upstream communications

Abstract

A method and apparatus for reducing delay distortion of upstream transmissions in a cable television (CATV) distribution plant. Upstream transmission in a CATV distribution plant, i.e., from the customer premises toward the head-end, is made difficult by delay distortion caused by diplexing filters used in bi-directional amplifiers and other components in the CATV distribution plant. A database storing information relating to each cable modem (CM) in the CATV distribution plant is maintained, and the delay distortion for each upstream transmission is calculated using information queried from the database. Delay distortion in the upper portion of the upstream bandwidth in a CATV distribution plant is preferably minimized by assigning CMs having a transmission path that causes relatively minimal delay distortion to the upper portion of the upstream bandwidth. Alternatively, the upper portion of the upstream bandwidth is preferably assigned to the largest number of CMs that have the same number of bi-directional amplifiers in their respective transmission paths. For either frequency assigning technique, a fixed equalizer may be used to further minimize delay distortion. Alternatively, delay distortion for upstream transmissions transmitted on any frequency in the upstream bandwidth may be minimized using a variable equalizer. The delay distortion for an upstream path is calculated using information queried from the database. The tap weights for the variable equalizer are adjusted depending on the calculated distortion for each upstream transmission.

Claims

1. A method of assigning upstream bandwidth to a downstream cable modem communicating with a cable modem termination system in a cable television distribution plant, the method comprising steps of:

obtaining identity of said cable modem

determining characteristics of said cable television distribution plant between said identified cable modem and said cable modem termination system by means of a database lookup; and

assigning a frequency for the upstream transmission based said characteristics.

2. The method of claim 1, where said characteristics relate to delay distortion between said cable modem and said cable modem termination system.

10. The method of claim 2, wherein the step of assigning a frequency firer includes assigning a frequency in the upstream bandwidth near a split between the upstream and downstream bandwidths, when the delay distortion is less than the predetermined threshold.

11. The method of claim 2, wherein the step of assigning upstream bandwidth further includes a step of assigning bandwidth in the upper portion of the upstream bandwidth, when the delay distortion is approximately equal to the predetermined threshold.

12. The method of claim 11, further comprising steps of:

identifying a largest number of subscribers having the same number of bi-directional amplifiers in their respective transmission paths; and

setting the predetermined threshold approximately equal to the delay distortion of a transmission path having the same number of bi-directional amplifiers as each the largest number of subscribers.

13. The method of claim 11, wherein the threshold is a range of delay distortion values and the upstream transmission is assigned to the upper portion of the upstream bandwidth when the delay distortion of the upstream transmission is within the range.

14. The method of claim 12, further including a step of minimizing delay distortion using a fixed equalizer.

15. The method of claim 14, wherein the fixed equalizer is configured to minimize delay distortion for the largest number of subscribers having the same number of bi-directional amplifiers in their respective transmission paths.

20. The method of claim 1, wherein the distribution plant is a hybrid fiber-coaxial distribution plant.

30. The method of claim 2 further comprising a step of comparing the calculated delay distortion to a predetermined threshold.

3. A method of assigning upstream bandwidth in a cable television distribution plant, comprising steps of:

calculating delay distortion of an upstream transmission caused by diplexing filters in a transmission path for the upstream transmission;

assigning a frequency for the upstream transmission based upon the calculated delay distortion for the transmission path; and

comparing the calculated delay distortion to a predetermined threshold;

wherein the step of assigning upstream bandwidth further includes a step of assigning bandwidth in the upper portion of the upstream bandwidth, when the calculated delay distortion is less than the predetermined threshold.

4. The method of claim 3, wherein the upper portion of the upstream bandwidth is approximately 38-42 MHz.

5. The method of claim 3, further comprising a step of setting the predetermined threshold so the calculated distortion of an upstream transmission having a relatively minimal number of a bi-directional amplifiers in its transmission path is less than the predetermined threshold.

6. The method of claim 5, further including a step of minimizing delay distortion for the upstream transmission using a fixed equalizer.

7. The method of claim 6, wherein the fixed equalizer is configured to minimize delay distortion for an upstream transmission path having a relatively minimal number of a bi-directional amplifiers.

8. The method of claim 6, wherein the fixed equalizer is configured to minimize delay distortion for a relatively large number of subscribers having the same number of bi-directional amplifiers in their respective transmission paths.

9. The method of claim 5, wherein the relatively minimal number of bi-directional amplifiers is one.

16. A method of assigning upstream bandwidth in a cable television distribution plant, comprising steps of:

calculating delay distortion of an upstream transmission caused by diplexing filters in a transmission path for the upstream transmission;

assigning a frequency for the upstream transmission based upon the calculated delay distortion for the transmission path;

identifying a source of the upstream transmission; and

retrieving information from a database that corresponds to the source

wherein the information includes at least one of a cable modem type, a bi-directional amplifier type, number of bi-directional amplifiers of each type and fiber node type.

17. The method of claim 16, wherein the step of calculating the delay distortion filter includes summing delay distortion caused by the retrieved cable modem type, number of bi-directional amplifiers of each type and the fiber node type.

18. A method of assigning upstream bandwidth in a cable television distribution plant, comprising steps of:

calculating delay distortion of an upstream transmission caused by diplexing filters in a transmission path for the upstream transmission;

assigning a frequency for the upstream transmission based upon the calculated delay distortion for the transmission path;

identifying a source of the upstream transmission; and

retrieving information from a database that corresponds to the source

wherein the retrieved information includes a number of diplexing filters and the number of diplexing filters of each type associated with the source.

19. The method of claim 18, wherein the step of calculating the delay distortion further includes summing delay distortion caused by the retrieved number of diplexing filters for each type.

21. A hybrid-fiber coaxial distribution plant, comprising:

a fiber node;

multiple cable modems connected to the fiber node,

a transmission path between each cable modem and the fiber node; and

a cable modem termination system connected to the fiber node, the cable modem termination system assigning an upstream transmission frequency for each cable modem based on a database lookup that contains information for each of said multiple cable modem, which information is reflective of delay distortion for each upstream transmission path associated with each cable modem.

22. The hybrid-fiber coaxial distribution plant of claim 21 further comprising a database, wherein the database stores information corresponding to each cable modem.

28. The hybrid-fiber coaxial distribution plant of claim 21 further comprising a fixed equalizer at the fiber node for minimizing delay distortion.

23. A hybrid-fiber coaxial distribution plant, comprising:

a fiber node;

multiple cable modems connected to the fiber node;

a transmission path between each cable modem and the fiber node,

a cable modem termination system connected to the fiber node, the cable modem termination system assigning an upstream transmission frequency for each cable modem based on calculated delay distortion for each upstream transmission path associated with each cable modem; and

a database that stores information corresponding to each cable modem;

wherein the calculated delay distortion is calculated from information stored in the database corresponding to each cable modem.

24. The hybrid-fiber coaxial distribution plant of claim 23 wherein the information comprises cable modem type, a bi-directional amplifier type, number of bi-directional amplifiers of that type and fiber node type.

25. The hybrid-fiber coaxial distribution plant of claim 23 wherein the information comprises the type of diplexing filters and the number of diplexing filters for each type in the transmission path.

26. A hybrid-fiber coaxial distribution plant, comprising:

a fiber node;

multiple cable modems connected to the fiber node;

a transmission path between each cable modem and the fiber node; and

a cable modem termination system connected to the fiber node, the cable modem termination system assigning an upstream transmission frequency for each cable modem based on calculated delay distortion for each upstream transmission path associated with each cable modem; and

wherein the assigned frequency is in the upper portion of the upstream bandwidth or near the split between the upstream and downstream bandwidths, when the calculated delay distortion is less a predetermined threshold.

27. A hybrid-fiber coaxial distribution plant, comprising:

a fiber node;

multiple cable modems connected to the fiber node;

a transmission path between each cable modem and the fiber node, and a cable modem termination system connected to the fiber node, the cable modem termination system assigning an upstream transmission frequency for each cable modem based on calculated delay distortion for each upstream transmission path associated with each cable modem; and

wherein the assigned frequency is in the upper portion of the upstream bandwidth or near the split between the upstream and downstream bandwidths, when the calculated delay distortion is approximately equal to a predetermined threshold.

29. A cable television distribution plant comprising:

multiple cable modems;

a database storing information relating to each cable modem, which information is reflective of transmission distortion suffered by said each cable modem when transmitting upstream; and

a cable modem termination system assigning an upstream transmission frequency for each cable modem based upon information stored in the database for each cable modem.