Method and apparatus for selecting optimum frequency for upstream data transmission in a network system utilizing cable modems

• US 6,570,913 B1
• Filed: 04/05/1999
• Issued: 05/27/2003
• Est. Priority Date: 04/05/1999
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Chen, Wei-Sing
• Primary Examiner(s): Bayard, Emmanuel
• Application Number:
  US09/286,202
• Time in Patent Office: 1,513 Days
• Field of Search: 375/220, 375/221, 375/222, 375/223, 375/302, 375/271, 455/557, 455/5.1, 455/71, 455/76, 370/278, 370/282, 348/11, 348/12, 348/13, 348/193
• US Class Current: 375/223
• CPC Class Codes: H04H 60/97 using uplink of the CATV systems
• CPC Class Codes: H04L 12/2801 Broadband local area networks
• CPC Class Codes: H04N 7/17309 Transmission or handling of upstream communications

Abstract

Provided are methods and apparatuses for quickly and efficiently locating a frequency band for upstream transmission of data in a data communications network system utilizing cable modems. In a preferred embodiment, a cable modem termination system (CMTS) at the headend performs a lookahead in order to determine the noise power spectrum allocated to its upstream channels. Free bands (noise-free bands available for upstream data transmission) may then be determined based on the noise power spectrum and the upstream channel capacity requirements according to a process that is preferably implemented in computer code at the headend. The lookahead is preferably accomplished by using a spectrum analyzer, which is preferably incorporated into the CMTS at the headend, to collect a table of samples of the noise power versus frequency. This table of samples is input to a computational algorithm which determines free band sets for one or more preferred modulation formats rapidly and efficiently in software without the stepping of the upstream receiver frequency as in the blind frequency hop process. Once a band has been located, the CMTS assigns its frequency to an upstream channel and signals the cable modem of the frequency update.

Claims

1. A method of selecting an upstream data transmission frequency band in a network system utilizing cable modems, comprising:

sampling noise power for a set of allocated upstream data transmission frequency bands when there is no data transmission;

determining a set of noise bands within the allocated frequency bands, said noise bands being bands in which noise exceeds a reliable transmission threshold for a modulation format;

determining a set of free bands within the allocated frequency bands, said free band set being the set difference of the allocated bands and the noise bands; and

performing a first-fit on the free bands for a channel to be transmitted to select an upstream data transmission frequency band having capacity for the channel.

2. The method of claim 1, wherein said network system is a hybrid fiber coaxial cable television system.

3. The method of claim 1, further comprising determining a set of in-use bands within the allocated frequency bands, said in-use bands being bands already assigned to another channel, and wherein said set of free bands is the set difference of the allocated bands and the combination of noise bands and in-use band.

4. The method of claim 1, further comprising assigning the allocated band to upstream transmission of the channel.

5. The method of claim 1, wherein said modulation format is at least one of QAM-16 and QPSK.

6. The method of claim 5, wherein said first-fit is first performed for the QAM-16 modulation format.

7. The method of claim 1, wherein said first-fit is a process comprising:

selecting a band in the free set;

where a channel width attributed to an upstream data channel is less-than-or-equal-to the band width, assigning the band to upstream transmission of the channel.

8. The method of claim 7, further comprising, where a channel width attributed to an upstream data channel is greater than the band width, selecting an untried band from the free set for comparison to the channel width.

9. The method of claim 8, further comprising, where no untried bands remain in the free set, and the channel width is greater than a minimum channel width, halving the channel width and restarting the band selection and comparison from the free set.

10. A computer program product comprising a computer-usable medium having computer-readable program code embodied thereon relating to selecting an upstream data transmission frequency band in a network system utilizing cable modems, the computer-readable program code effecting the following steps within a computing system:

sampling noise power for a set of allocated upstream data transmission frequency bands when there is no data transmission;

determining a set of noise bands within the allocated frequency bands, said noise bands being bands in which noise exceeds a reliable transmission threshold for a modulation format;

determining a set of free bands within the allocated frequency bands, said free band set being the set difference of the allocated bands and the noise bands; and

performing a first-fit on the free bands for a channel to be transmitted to select an upstream data transmission frequency band having capacity for the channel.

11. The computer program product of claim 10, further comprising determining a set of in-use bands within the allocated frequency bands, said in-use bands being bands already assigned to another channel, and wherein said set of free bands is the set difference of the allocated bands and the combination of noise bands and in-use band.

12. The computer program product of claim 10, further comprising assigning the allocated band to upstream transmission of the channel.

13. The computer program product of claim 10, wherein said modulation format is at least one of QAM-16 and QPSK.

14. The computer program product of claim 12, wherein said first-fit is first performed for the QAM-16 modulation format.

15. The computer program product of claim 10, wherein said first-fit is a process comprising:

selecting a band in the free set; and

where a channel width attributed to an upstream data channel is less-than-or-equal-to the band width, assigning the band to upstream transmission of the channel.

16. The computer program product of claim 15, further comprising, where a channel width attributed to an upstream data channel is greater than the band width, selecting an untried band from the free set for comparison to the channel width.

17. The computer program product of claim 16, further comprising, where no untried bands remain in the free set, and the channel width is greater than a minimum channel width, halving the channel width and restarting the band selection and comparison from the free set.

18. The computer program product of claim 10, wherein the computer-usable medium comprises at least one of a magnetic medium, an optical medium, a hardware device specially configured to store and perform program instructions, and a carrier wave.

19. A network system utilizing cable modems capable of two-way transmission of data, comprising:

a downstream data path to subscribers on the cable network system originating from a headend;

a downstream modulator and transmitter for modulating and transmitting a downstream signal to be carried on the downstream data path to subscribers on the cable network system;

an upstream data path to the headend originating from subscribers on the cable network system;

an upstream demodulator and receiver in the headend for receiving and demodulating an upstream signal to be carried on the upstream data path;

a spectrum analyzer for scanning an upstream frequency band; and

an interface to a central processing unit;

said spectrum analyzer capable of receiving computer program instructions via said interface for a method of selecting an upstream data transmission frequency band comprising the following steps,

sampling noise power for a set of allocated upstream data transmission frequency bands when there is no data transmission,

determining a set of noise bands within the allocated frequency bands, said noise bands being bands in which noise exceeds a reliable transmission threshold for a modulation format,

determining a set of free bands within the allocated frequency bands, said free band set being the set difference of the allocated bands and the noise bands, and

performing a first-fit on the free bands for a channel to be transmitted to select an upstream data transmission frequency band having capacity for the channel.

20. The cable network system of claim 19, wherein the upstream and downstream paths comprise a hybrid fiber coaxial cable television system.

21. The cable network system of claim 19, further comprising a cable modem for receiving data on the downstream data path and transmitting data on the upstream data path.

22. The cable network system of claim 19, wherein the headend contains a cable modem termination system.

23. The cable network system of claim 19, wherein the spectrum analyzer is coupled to the upstream data path within the headend.

24. The cable network system of claim 23, wherein the spectrum analyzer is coupled to the upstream data path within the cable modem termination system.

25. The cable network system of claim 19, wherein the spectrum analyzer is coupled to the upstream data path outside the headend.

26. The cable network system of claim 25, wherein the spectrum analyzer is coupled to the upstream data path at a subscriber location.

29. The cable network system of claim 19, wherein said first-fit comprises:

selecting a band in the free set;

where a channel width attributed to an upstream data channel is less-than-or-equal-to the band width, assigning the band to upstream transmission of the channel.

30. The cable network system of claim 29, further comprising, where a channel width attributed to an upstream data channel is greater than the band width, selecting an untried band from the free set for comparison to the channel width.

31. The cable network system of claim 30, further comprising, where no untried bands remain in the free set, and the channel width is greater than a minimum channel width, halving the channel width and restarting the band selection and comparison from the free set.

27. A cable television system headend, comprising:

a downstream transmitter for transmitting to subscriber destinations a downstream signal having a downstream frequency spectrum associated therewith;

an upstream demodulator and receiver for receiving and demodulating an upstream signal having an upstream frequency spectrum associated therewith;

a cable modem termination system,

said cable modem termination system comprising,

a spectrum analyzer for scanning an upstream frequency band, and

an interface to a central processing unit; and

said cable modem termination system capable of receiving and implementing computer program instructions via said interface for a method of selecting an upstream data transmission frequency band comprising the following steps,

sampling noise power for a set of allocated upstream data transmission frequency bands when there is no data transmission,

determining a set of noise bands within the allocated frequency bands, said noise bands being bands in which noise exceeds a reliable transmission threshold for a modulation format,

determining a set of free bands within the allocated frequency bands, said free band set being the set difference of the allocated bands and the noise bands, and

performing a first-fit on the free bands for a channel to be transmitted to select an upstream data transmission frequency band having capacity for the channel.

28. The headend of claim 27, wherein said interface is an interface card.

32. The headend of claim 27, wherein said first-fit comprises:

selecting a band in the free set;

where a channel width attributed to an upstream data channel is less-than-or-equal-to the band width, assigning the band to upstream transmission of the channel.

33. The headend of claim 32, further comprising, where a channel width attributed to an upstream data channel is greater than the band width, selecting an untried band from the free set for comparison to the channel width.

34. The headend of claim 33, further comprising, where no untried bands remain in the free set, and the channel width is greater than a minimum channel width, halving the channel width and restarting the band selection and comparison from the free set.

35. A network system utilizing cable modems capable of two-way transmission of data, comprising:

a downstream data path to subscribers on the cable network system originating from a headend;

a downstream modulator and transmitter for modulating and transmitting a downstream signal to be carried on the downstream path to subscribers on the cable network system;

an upstream data path to the headend originating from subscribers on the cable network system;

an upstream demodulator and receiver in the headend for receiving and demodulating an upstream signal to be carried on the upstream data path;

means for performing a first-fit on a set of noise-free frequency bands in a set of allocated bands to select a noise-free band available for upstream data transmission.

36. The cable network system of claim 35, wherein said first-fit comprises:

selecting a band in the free set;

where a channel width attributed to an upstream data channel is less-than-or-equal-to the band width, assigning the band to upstream transmission of the channel.

37. The cable network system of claim 36, further comprising, where a channel width attributed to an upstream data channel is greater than the band width, selecting an untried band from the free set for comparison to the channel width.

38. The cable network system of claim 37, further comprising, where no untried bands remain in the free set, and the channel width is greater than a minimum channel width, halving the channel width and restarting the band selection and comparison from the free set.