Method and apparatus for using a spectrum analyzer for locating ingress noise gaps

• US 6,775,840 B1
• Filed: 12/19/1997
• Issued: 08/10/2004
• Est. Priority Date: 12/19/1997
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Millet, Mark E., Naegel, Charles J.
• Primary Examiner(s): Faile, Andrew
• Assistant Examiner(s): Koenig, Andrew Y
• Application Number:
  US08/993,334
• Time in Patent Office: 2,426 Days
• Field of Search: H04/N.7173, H04/B 1.700, H04/B.110, H04/B 1.500, G06/F 1.900, G01/R 2.310, 725/107, 725/111, 725/124, 725/125, 455/67.3, 455/67.4, 455/62, 455/63, 455/67.1, 702/76-78, 324/76-1-
• US Class Current: 725/111
• CPC Class Codes: H04L 12/2801 Broadband local area networks
• CPC Class Codes: H04N 17/00 Diagnosis, testing or measuring for television systems or their details
• CPC Class Codes: H04N 21/4384 involving operations to reduce the access time, e.g. fast-tuning for reducing channel switching latency
• CPC Class Codes: H04N 21/44245 Monitoring the upstream path of the transmission network, e.g. its availability, bandwidth
• CPC Class Codes: H04N 21/4425 Monitoring of client processing errors or hardware failure
• 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 device, system and method are disclosed for locating clean channels for upstream data carriers that are certain to have lower noise levels than the currently utilized channel used for carrying data upstream, thereby enabling intelligent placement of an upstream data carrier in a cable television system utilizing cable modems for two-way data transmission. A spectrum analyzer is placed in a cable modem termination system located in a headend of a cable television system. The spectrum analyzer contains a programmable device comprised of programmable circuitry. The circuitry is operable in a first mode to receive a signal having an associated frequency spectrum made up of several channels. The circuitry also determines a noise level for each of the channels. The circuitry is also operable in a second mode to receive the signal described above and filter the signal to generate several filtered signals where each filtered signal corresponds to one of the channels. The circuitry is also operable in the second mode to monitor another noise level associated with each of the filtered signals. The channels associated with the filtered signals are selected based on the noise levels determined in the first mode.

Claims

1. A programmable device comprising programmable circuitry:

operable in a first mode to receive a first signal having a frequency spectrum associated therewith, the frequency spectrum including a plurality of channels, and to determine a first noise level for each of the plurality of channels; and

operable in a second mode to filter the first signal, thereby generating a plurality of filtered signals each filtered signal corresponding to one of the plurality of channels, and to monitor a second noise level associated with each of the filtered signals;

wherein the channels associated with the filtered signals are selected for monitoring in the second mode based on the first noise levels determined in the first mode.

2. A device as recited in claim 1 wherein the programming circuitry determines the first noise level for each of the plurality of channels at predetermined time intervals when operating in the first mode.

3. A device as recited in claim 1 wherein the programming circuitry filters the first signal and monitors the second noise level associated with each of the filtered signals continuously.

4. A device as recited in claim 1 further comprising control circuitry for instructing the programmable circuitry to operate in one of the first mode and the second mode.

5. A device as recited in claim 4 wherein the control circuitry further comprises a microprogrammer for containing instructions for operating the programmable circuitry and a microcontroller for implementing the instructions for operating the programmable circuitry.

6. A device as recited in claim 1 wherein the programmable circuitry performs a fast Fourier transformation when operating in the first mode.

7. A device as recited in claim 6 further comprising data storage circuitry for use by the programmable device when operating in the first mode.

8. A device as recited in claim 1 wherein the programmable circuitry operates as a finite impulse response filter in the second mode.

9. A device as recited in claim 1 further comprising an input latch for receiving the first signal.

10. A device as recited in claim 1 wherein the channels selected correspond to filtered signals with first noise levels below a predetermined threshold.

11. A device as recited in claim 1 wherein the channels selected correspond to filtered signals with the low first noise levels.

12. A programmable device for receiving a first signal having a frequency spectrum associated therewith, the frequency spectrum comprising a plurality of channels, the programmable device comprising:

signal processing circuitry which;

in a first mode comprises frequency transformation circuitry which generates a second signal representative of a noise spectrum associated with the first signal, the noise spectrum comprising a plurality of first noise levels each associated with one of the plurality of channels; and

in a second mode comprises a plurality of filters each of which corresponds to a selected one of the plurality of channels;

noise monitoring circuitry for determining a second noise level of each of the selected channels; and

control circuitry for controlling the signal processing circuitry.

13. A programmable device as recited in claim 12 wherein the programmable device is a field programmable gate array.

14. A programmable device as recited in claim 12 wherein the frequency transformation circuitry of the first mode further comprises data storage circuitry for storing data necessary when performing a frequency transformation.

15. A programmable device as recited in claim 12 wherein the frequency transformation circuitry of the first mode generates the second signal representative of the noise spectrum by monitoring the first signal at predetermined time intervals.

16. A programmable device as recited in claim 12 wherein the plurality of filters of the second mode filter the first signal continuously.

17. A programmable device as recited in claim 12 wherein the filters of the signal processing circuitry operating in the second mode are finite impulse response filters.

18. A programmable device as recited in claim 12 wherein the noise monitoring circuitry comprises a plurality of threshold comparators, such that each threshold comparator is coupled to a filter for determining the second noise level of the selected channel corresponding to the filter.

19. A programmable device as recited in claim 12 wherein the control circuitry comprises a microprogrammer for storing instructions on operating the signal processing circuitry and a microcontroller for implementing the instructions contained in the microprogrammer.

20. A programmable device as recited in claim 12 further comprising an input latch for receiving and storing the first signal.

21. In a cable television system, a method of locating a low-noise channel for data transmission from a subscriber to a headend including:

receiving a first signal having a frequency spectrum associated therewith, the frequency spectrum comprising a plurality of channels;

generating a second signal representative of a noise spectrum associated with the first signal, the noise spectrum comprising a plurality of first noise levels each corresponding to one of the plurality of channels;

selecting a first subset of the plurality of channels as selected channels based on the first noise levels;

band pass filtering the first signal in the selected channels thereby generating a plurality of filtered signals;

monitoring a plurality of second noise levels, each second noise level corresponding to one of the filtered signals; and

selecting for data transmission one of the selected channels based on a second noise level.

22. A method as recited in claim 21 wherein the frequency spectrum is in the range of 5 MHz to 42 MHz.

23. A method as recited in claim 21 wherein generating the second signal comprises performing a frequency transformation on the first signal.

24. A method as recited in claim 21 further comprising evaluating the plurality of first noise levels comparing each noise level to a current noise level of a current channel.

25. A method as recited in claim 21 wherein the band pass filtering comprises filtering the first signal with a finite impulse response filter.

26. A method as recited in claim 21 wherein monitoring a plurality of second noise levels comprises comparing each second noise level to a predetermined threshold and accumulating data on each second noise level.

27. A cable television system capable of two-way transmission of data comprising:

a downstream data path to subscribers on the cable television 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 television system;

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

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

a spectrum manager for receiving and monitoring the first signal carried on the upstream data path comprising;

signal processing circuitry for generating a second signal representative of a noise spectrum associated with the first signal, the noise spectrum comprising a plurality of first noise levels, each associated with one of a plurality of channels, and for determining a second noise level for selected channels of the plurality of channels, the selected channels being selected based on the plurality of first noise levels; and

control circuitry for controlling operation of the signal processing circuitry.

28. A cable television system as recited in claim 27 wherein the upstream and downstream paths comprise a hybrid fiber coaxial cable television system.

29. A cable television system as recited in claim 27 wherein the headend contains a cable modem termination system.

30. A cable television system as verified in claim 29, wherein the spectrum manager is coupled to the upstream data path within the cable modem termination system.

31. A cable television system as recited in claim 27 further comprising a cable modem for receiving data on the downstream data path and transmitting data on the upstream data path.

32. A cable television system as recited in claim 27 wherein the spectrum manager is coupled to the upstream data path within the headend.

33. A cable television system as recited in claim 27 wherein the spectrum manager is coupled to the upstream data path outside the headend.

34. A cable television system as recited in claim 33 wherein the spectrum manager is coupled to the upstream data path at a subscriber location.

35. A cable television system as recited in claim 27 wherein the spectrum manager further comprises a low-pass filter for eliminating portions of the first upstream signal above a predetermined frequency.

36. A cable television system as recited in claim 27 wherein the spectrum manager further comprises an external processor interface for communicating data from the signal processing circuitry to an external processor.

37. 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 receiver for receiving a first signal having an upstream frequency spectrum associated therewith, the upstream frequency spectrum made up of a plurality of channels;

a spectrum manager for receiving and monitoring the first signal comprising;

signal processing circuitry for generating a second signal representative of a noise spectrum associated with the first signal, the noise spectrum comprising a plurality of first noise levels each associated with one of a plurality of channels, and for determining a second noise level for selected channels of the plurality of channels, the selected channels being selected based on the first noise levels; and

control circuitry for controlling the signal processing circuitry.

38. A system headend as recited in claim 37 further comprising a cable modem termination system containing the downstream transmitter, the upstream transmitter, and the spectrum manager.

39. A system headend as recited in claim 37 further comprising a media access control unit for storing data regarding cable modems in the cable television system.

40. A system headend as recited in claim 37 further comprising a data network interface for receiving data from sources external to the cable television system.

41. A system headend as recited in claim 37 further comprising a converter for converting the first signal from an analog signal to a digital signal before the first signal is received by the spectrum manager.

42. A system headend as recited in claim 37 wherein data corresponding to the second noise levels for the selected channels is retrievable by an external processor with minimal latency between the time the first signal is received by the upstream receiver and the second noise levels for the selected channels are determined by the signal processing circuitry.

43. At least one computer readable medium including programmed instructions arranged to locate a low-noise channel for data transmission from a subscriber to a headend, comprising:

computer programming instructions for receiving a first signal having a frequency spectrum associated therewith, the frequency spectrum comprising of a plurality of channels;

computer programming instructions for generating a second signal representative of a noise spectrum associated with the first signal, the noise spectrum comprising a plurality of first noise levels each corresponding to one of the plurality of channels;

computer programming instructions for selecting a first subset of the plurality of channels as selected channels based on the first noise levels;

computer programming instructions for band pass filtering the first signal in the selected channels thereby generating a plurality of filtered signals;

computer programming instructions for monitoring a plurality of second noise levels, each second noise level corresponding to one of the filtered signals; and

computer programming instructions for selecting for data transmission one of the selected channels based on the second noise levels.

44. A computer readable medium as recited in claim 43 wherein the computer programmed instructions for generating the second signal comprises programmed instructions for performing a frequency transformation on the first signal.

45. A computer readable medium as recited in claim 43 further including programmed instructions for evaluating the plurality of first noise levels whereby each first noise level is compared to a current noise level of a current channel.

46. A computer readable medium as recited in claim 43 wherein the computer programmed instructions for monitoring comprises programmed instructions for comparing the second noise level to a predetermined threshold and accumulating data on the second noise level.