Method and apparatus for locating a cleaner bandwidth in a frequency channel for data transmission

• US 6,574,797 B1
• Filed: 01/08/1999
• Issued: 06/03/2003
• Est. Priority Date: 01/08/1999
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Yang, Xiong, Schwartzman, Alejandro H., Chen, Hung-San, Naegeli, Charles J.
• Primary Examiner(s): Miller, John
• Assistant Examiner(s): ROUVAS, NIKOLAOS
• Application Number:
  US09/227,991
• Time in Patent Office: 1,607 Days
• Field of Search: 725/120, 725/124, 725/125, 725/126, 725/111, 348/192, 348/193, 375/224, 375/227, 375/260, 370/252, 370/437, 370/447, 370/462, 370/463, 370/480, 370/465, 370/468, 370/485, 455/62, 455/63, 455/69, 455/3.05
• US Class Current: 725/120
• CPC Class Codes: H04N 17/00 Diagnosis, testing or measuring for television systems or their details
• CPC Class Codes: H04N 7/17309 Transmission or handling of upstream communications

Abstract

Apparatus, methods, and computer program products for utilizing a frequency channel determined to be unacceptably noisy by finding a cleaner, narrower bandwidth within the frequency channel. Initially data is received on a frequency channel at a CMTS, specifically an upstream receiver, and by a narrow bandwidth detector, connected to a processor also used by components in the CMTS. The narrow bandwidth detector performs a Fast Fourier Transform (FFT) on the frequency channel thereby creating multiple FFT points within the frequency channel. A clean bandwidth for transmitting data within the frequency channel is identified where the clean bandwidth is derived from a subset of FFT points from the full set of FFT points. The subset of FFT points are contiguous points that have a noise level below a predetermined noise threshold.

Claims

1. A method of utilizing a frequency channel for transmitting data upstream in a cable plant from one or more cable modems to a cable modem termination system, the method comprising:

receiving data from one or more cable modems at a cable modem termination system on a frequency channel of interest which is designated for upstream transmissions in the cable plant;

analyzing the frequency channel of interest thereby creating a plurality of analysis points at different frequencies within the frequency channel of interest;

identifying a clean bandwidth for transmitting data within the frequency channel of interest wherein the clean bandwidth is derived from a set of analysis points from the plurality of analysis points within the frequency channel; and

instructing the one or more cable modems in the cable plant to constrain their data transmissions to the clean bandwidth within the frequency channel of interest.

2. A method as recited in claim 1 wherein receiving data at a cable modem termination system on a frequency channel of interest further comprises narrowing a broader frequency channel to derive the frequency channel of interest.

3. A method as recited in claim 2 further comprising determining that the broader frequency channel is unreliable for accurate data transmission.

4. A method as recited in claim 3 further comprising examining a bit error rate associated with the data being transmitted on the broader frequency channel.

5. A method as recited in claim 2 further comprising receiving the broader frequency channel at an upstream receiver located in the cable modem termination system.

6. A method as recited in claim 1 wherein receiving data at a cable modem termination system on a frequency channel of interest further comprises:

digitizing the data; and

routing the data on the frequency channel of interest to a narrow bandwidth detector.

7. A method as recited in claim 1 wherein analyzing the frequency channel of interest thereby creating a plurality of analysis points within the frequency channel of interest further comprises configuring an FPGA to perform an FFT.

8. A method as recited in claim 1 wherein identifying a clean bandwidth for transmitting data within the frequency channel of interest further comprises:

comparing a noise level of an analysis point to a predetermined noise level; and

incrementing a counter if the noise level of the analysis point is below the predetermined noise level.

9. A method as recited in claim 8 further comprising saving a value corresponding to the counter and resetting the counter if the noise level of the analysis point is above the predetermined noise level thereby storing one or more values corresponding to the counter.

10. A method as recited in claim 9 further comprising determining the largest value from the one or more values corresponding to the counter.

11. A method as recited in claim 10 further comprising deriving the clean bandwidth from the largest value of the one or more values corresponding to the counter.

12. A method as recited in claim 11 wherein deriving the clean bandwidth further comprises taking the product of the largest value of the one or more values corresponding to the counter and the width of an analysis point.

13. A method as recited in claim 1 wherein instructing one or more cable modems in the cable plant to use the clean bandwidth to transmit data further comprises adjusting a symbol rate of an upstream receiver to reflect the clean bandwidth.

14. A method as recited in claim 1 wherein the set of analysis points includes contiguous analysis points such that each contiguous analysis point has a noise level that meets a predetermined criteria.

15. A method as recited in claim 1 wherein the analysis performed is a Fast Fourier Transform and an analysis point is an FFT point.

16. A method of identifying a usable bandwidth in a noisy frequency channel capable of transmitting data using one of a first modulation scheme and a second modulation scheme, the method comprising:

(a) performing an FFT on the noisy frequency channel thereby creating a plurality of FFT points and deriving a plurality of noise level measurements, each one of the noise level measurements corresponding to an FFT point from the plurality of FFT points;

(b) comparing a noise level measurement from the plurality of noise level measurements to a first noise threshold associated with a first modulation scheme and incrementing a first counter associated with the first modulation scheme and a second counter associated with a second modulation scheme if the noise level measurement is less than the first noise threshold;

(c) comparing the noise level measurement to the second noise threshold and incrementing the second counter if the noise level measurement is less than the second noise threshold;

(d) repeating steps (b) and (c) until each noise level measurement from the plurality of noise level measurements has been compared to the first noise threshold and to the second noise threshold; and

(e) determining whether to use the first modulation scheme or the second modulation scheme from comparing the first counter with the second counter.

17. A method as recited in claim 16 wherein the FFT is a 32-point FFT.

18. A method as recited in claim 16 wherein comparing a noise level measurement to a first noise threshold further comprises:

saving the first counter; and

resetting the first counter to an initial value if the noise level measurement is greater than the first noise threshold.

19. A method as recited in claim 16 wherein comparing the noise level measurement to the second noise threshold further comprises:

saving the second counter; and

resetting the second counter to an initial value if the noise level measurement is greater than the second noise threshold.

20. A method as recited in claim 16 wherein the first noise threshold is based on the QPSK modulation scheme and the second noise threshold is based on the QAM16 modulation scheme.

21. A method as recited in claim 16 wherein determining whether to use the first modulation scheme or the second modulation scheme from comparing the first counter with the second counter further comprises:

identifying the largest first counter and the largest second counter; and

comparing a multiple of the largest first counter to the largest second counter.

22. A method as recited in claim 21 wherein the first counter is associated with the QPSK modulation scheme and the second counter is associated with the QAM16 modulation scheme and the multiple is two.

23. A method as recited in claim 22 wherein determining whether to use the first modulation scheme or the second modulation scheme from comparing the first counter with the second counter further comprises:

using the first modulation scheme if twice the largest first counter is greater than the largest second counter; and

using the second modulation scheme if twice the largest first counter is less than the largest second counter.

24. A method as recited in claim 16 wherein deriving a usable bandwidth based on one of the first counter and the second counter and the width of an FFT point further comprises taking the product of the width of an FFT point and one of the first counter and the second counter.

25. A method as recited in claim 16 further comprising deriving a usable bandwidth based on one of the first counter and the second counter and the width of an FFT point.

26. A system for detecting a usable bandwidth within a frequency channel, the system comprising:

a processor; and

a narrow bandwidth detector comprising;

a memory;

a processor interface; and

a data processor configured to perform an FFT on a signal carried on the frequency channel which is designated for upstream transmissions in a cable plant, thereby creating a set of FFT points within the frequency channel wherein a subset of contiguous FFT points from the set of FFT points is identified as being a clean usable bandwidth for transmitting data, the data processor also being configured to instruct one or more cable modems using the frequency channel in the cable plant to constrain their data transmissions to the clean bandwidth within the frequency channel.

27. A system as recited in claim 26 further comprising a filter for narrowing a broader upstream channel to the frequency channel as input to the narrow bandwidth detector.

28. A system as recited in claim 27 wherein the filter is a receiver.

29. A system as recited in claim 26 further comprising an analog/digital converter for digitizing an analog signal.

30. A system as recited in claim 26 further comprising an upstream receiver having an adjustable input symbol rate that receives the signal carried on the frequency channel, thereby allowing the upstream receiver to receive data on varying size frequency channels.

31. A system as recited in claim 26 wherein the narrow bandwidth detector is located outside a headend of a cable plant.

32. A system as recited in claim 26 wherein the narrow bandwidth detector is located within a headend of a cable plant.

33. A system as recited in claim 26 wherein the narrow bandwidth detector is a digital signal processor programmed to perform an FFT on the signal carried on the frequency channel.

34. A system as recited in claim 26 wherein the processor is in communication with components of a cable modem termination system and the processor interface of the narrow bandwidth detector is an interface to the processor thereby enabling the processor to communicate with the narrow bandwidth detector and for the narrow bandwidth detector to communicate with components in the cable modem termination system.

35. A computer program product for utilizing a frequency channel for transmitting data upstream in a cable plant from one or more cable modems to a cable modem termination system, comprising:

a computer code that receives data from one or more cable modems at a cable modem termination system on a frequency channel of interest which is designated for upstream transmissions in the cable plant;

a computer code that performs an analysis on the frequency channel of interest thereby creating a plurality of analysis points at different frequencies within the frequency channel of interest;

a computer code that identifies a clean bandwidth for transmitting data within the frequency channel of interest wherein the clean bandwidth is derived from a set of analysis points from the plurality of analysis points within the frequency channel;

a computer code that instructs the one or more cable modems in the cable plant to constrain their data transmissions to the clean bandwidth within the frequency channel of interest; and

a computer-readable medium that stores the computer codes.

36. The computer program product of claim 35, wherein the means for receiving data further comprises means for narrowing a broader frequency channel to derive the frequency channel of interest.

37. The computer program product of claim 35, wherein the means for receiving data further comprises:

means for digitizing the data; and

means for routing the data on the frequency channel of interest to a narrow bandwidth detector.

38. The computer program product of claim 35, wherein the means for analyzing the frequency channel of interest further comprises means for configuring an FPGA to perform an FFT.

39. The computer program product of claim 35, wherein the means for identifying a clean bandwidth further comprises:

means for comparing a noise level of an analysis point to a predetermined noise level; and

means for incrementing a counter if the noise level of the analysis point is below the predetermined noise level.

40. The computer program product of claim 35, wherein the means for instructing the one or more cable modems further comprises means for adjusting a symbol rate of an upstream receiver to reflect the clean bandwidth.

41. The computer program product of claim 35, wherein the set of analysis points includes contiguous analysis points such that each contiguous analysis point has a noise level that meets a predetermined criteria.

42. A computer program product for identifying a usable bandwidth in a noisy frequency channel capable of transmitting data using one of a first modulation scheme and a second modulation scheme, comprising:

a computer code that performs an FFT on the noisy frequency channel thereby creating a plurality of FFT points and deriving a plurality of noise level measurements, each one of the noise level measurements corresponding to an FFT point from the plurality of FFT points;

a computer code that compares a noise level measurement from the plurality of noise level measurements to a first noise threshold associated with a first modulation scheme and increments a first counter associated with the first modulation scheme and a second counter associated with a second modulation scheme if the noise level measurement is less than the first noise threshold;

a computer code that compares the noise level measurement to the second noise threshold and increments the second counter if the noise level measurement is less than the second noise threshold;

a computer code that repeats the computer code that compares a noise level measurement from the plurality of noise level measurements to a first noise threshold associated with a first modulation scheme and that repeats the computer code that compares the noise level measurement to the second noise threshold until each noise level measurement from the plurality of noise level measurements has been compared to the first noise threshold and to the second noise threshold;

a computer code that determines whether to use the first modulation scheme or the second modulation scheme by comparing the first counter with the second counter; and

a computer-readable medium that stores the computer codes.

43. A computer readable medium on which is provided a computer code for detecting a usable bandwidth within a frequency channel, the computer code comprising:

instructions for performing an FFT on a signal carried on the frequency channel which is designated for upstream transmissions in a cable plant, thereby creating a set of FFT points within the frequency channel; and

instructions for instructing one or more cable modems using the frequency channel in the cable plant to constrain their data transmissions to the clean bandwidth within the frequency channel;

wherein a subset of contiguous FFT points from the set of FFT points is identified as being a clean usable bandwidth for transmitting data.

44. A system for utilizing a frequency channel for transmitting data upstream in a cable plant from one or more cable modems to a cable modem termination system, the system comprising:

means for receiving data from one or more cable modems at a cable modem termination system on a frequency channel of interest which is designated for upstream transmissions in the cable plant;

means for analyzing the frequency channel of interest thereby creating a plurality of analysis points at different frequencies within the frequency channel of interest;

means for identifying a clean bandwidth for transmitting data within the frequency channel of interest wherein the clean bandwidth is derived from a set of analysis points from the plurality of analysis points within the frequency channel; and

means for instructing the one or more cable modems in the cable plant to constrain their data transmissions to the clean bandwidth within the frequency channel of interest.