Adaptive filter for reducing ingress noise in CATV return signals

• US 6,757,910 B1
• Filed: 06/08/2000
• Issued: 06/29/2004
• Est. Priority Date: 06/08/2000
• Status: Expired due to Term

• Current Assignee: ARRIS Enterprises LLC (CommScope Holding Company, Inc.)
• Original Assignee: C-COR.net Corp. (CommScope Holding Company, Inc.)
• Inventors: Bianu, Dan
• Primary Examiner(s): Miller, John
• Assistant Examiner(s): BELIVEAU, SCOTT E
• Application Number:
  US09/590,933
• Time in Patent Office: 1,482 Days
• Field of Search: 725/125, 725/127, 725/128, 725/129, 725/149, 725/126, 327/552, 370/290, 379/406.08, 379/406.09, 381/71.11, 333/17.1, 455/125, 455/339, 455/340, 348/725, 348/731, 348/735
• US Class Current: 725/125
• CPC Class Codes: H04H 20/78 CATV [Community Antenna Television] systems
• CPC Class Codes: H04N 7/102 Circuits therefor, e.g. noise reducers, equalisers, amplifiers H04N7/108 takes precedence

Abstract

An adaptive high pass filter is used to reduce signal noise such as that occurring on a CATV upstream carrier. A signal detector senses a lowest active frequency on a CATV transmission. A high pass filter is then adjusted to cut off transmissions at frequencies below the lowest active frequency. This reduces ingress noise present in the upstream channel.

Claims

1. A method for reducing ingress noise from upstream signals in a communication network, the method comprising:

monitoring frequencies of a desired signal in an upstream path on an ongoing basis;

detecting a first lowest signal frequency and a second lowest signal frequency used by the desired signal in the upstream path at a first time and at a second time later than the first time, respectively;

electronically adjusting a first cutoff frequency of a filter circuit in response to detection of the detected first lowest signal frequency, to a frequency below the first lowest signal frequency used by the signals in an upstream spectrum; and

electronically adjusting a second cutoff frequency of a filter circuit in response to detection of the second lowest signal frequency, to a frequency below the second lowest signal frequency used by the signals in the upstream path, by using a first selected time constant for exponentially lowering the cutoff frequency from the first cutoff frequency to the second cutoff frequency, and by using a second selected time constant for exponentially raising the cutoff frequency from the second cutoff frequency to the first cutoff frequency, thereby blocking a signal component having a frequency below at least one of the first and second cutoff frequencies, to an extent permitted by a frequency plan used in the upstream spectrum, where at least one of the first and second time constants is selected to reduce the likelihood of false or spurious signal detection.

2. The method of claim 1, further comprising using artificial intelligence to separate noise from signal by determining which transmissions are desired signal and filtering transmissions which do not meet predetermined criteria for signal transmissions, the predetermined criteria comprising detection of a predetermined signal characteristic and detection of said lowest signal frequency associated with detection of a signal associated with the predetermined signal characteristic.

4. The method of claim 1, wherein artificial intelligence is used to separate noise from signal by determining which transmissions are desired signal and filtering transmissions which do not meet predetermined criteria for signal transmissions, the predetermined criteria comprising detection of a predetermined signal characteristic and detection of said lowest signal frequency associated with detection of a signal associated with the predetermined signal characteristic.

3. A multichannel signal carrier filter circuit comprising:

a circuit for detecting first and second lowest signal frequencies used by a desired signal in an upstream path at a first time and at a second time later than the first time, respectively;

an adaptive high pass filter, having a dynamically and electronically adjustable cutoff frequency; and

a control circuit, responsive to the circuit for detecting, for adjusting the cutoff frequency of the adaptive high pass filter to a first cutoff frequency and to a second cutoff frequency, below the lowest signal frequency used by the desired signals in the upstream path at the first time and at the second time, respectively, thereby blocking a signal component having a frequency below at least one of the first and second cutoff frequencies, to an extent permitted by a frequency plan used in an upstream spectrum, where a first selected time constant is used for exponentially lowering the cutoff frequency from the first cutoff frequency to the second cutoff frequency, and a second selected time constant is used for exponentially raising the cutoff frequency from the second cutoff frequency to the first cutoff frequency, where at least one of the first and second time constants is selected to reduce the likelihood of false or spurious signal detection.

5. A CATV system comprising:

a circuit for detecting a lowest signal frequency used by a desired signal in an upstream path at a first time and at a second time later than the first time, respectively;

an adaptive frequency selective filter, having a dynamically and electronically adjustable cutoff frequency; and

a control circuit, responsive to the circuit for detecting, for adjusting the cutoff frequency of the adaptive frequency selective filter to a first cutoff frequency and to a second cutoff frequency, below the lowest signal frequency used by the desired signals in the upstream path at the first time and at the second time, respectively, thereby blocking a signal component having a frequency below at least one of the first and second cutoff frequencies, to an extent permitted by a frequency plan used in an upstream spectrum, where a first selected time constant is used for exponentially lowering the cutoff frequency from the first cutoff frequency to the second cutoff frequency, and a second selected time constant is used for exponentially raising the cutoff frequency from the second cutoff frequency to the first cutoff frequency, where at least one of the first and second time constants is selected to reduce the likelihood of false or spurious signal detection.

6. The method of claim 5, wherein artificial intelligence is used to separate noise from signal by determining which transmissions are desired signal and filtering transmissions which do not meet predetermined criteria for signal transmissions, the predetermined criteria comprising detection of a predetermined signal characteristic and detection of said lowest signal frequency associated with detection of a signal associated with the predetermined signal characteristic.