Interference cancellation system for CATV return transmissions
First Claim
1. A method of canceling interference in a CATV return path signal that includes a time division multiple access data stream having a plurality of time slots within which frames of data are transmitted from subscriber units comprising the step:
- acquiring an interference reference signal from the CATV return path;
selecting at least one time slot for use in evaluating interference;
sampling said selected time slot when predetermined data is transmitted therein;
processing said interference reference signal to produce an interference cancellation signal; and
combining said interference cancellation signal with said CATV return path signal to cancel interference.
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Accused Products
Abstract
A CATV interference cancellation system reduces the presence of undesirable narrowband interference that corrupts return signal transmissions. The cancellation system first acquires a reference signal that contains components related to the interference present in the return signal. The reference signal is processed to derive estimates of the interference components appearing in the return signal and a cancellation signal is generated. The interference cancellation signal is then combined with the return signal, thereby reducing the interference components present in it. The interference cancellation system is deployed at a CATV headend and time division multiple access techniques (TDMA) are used for return transmission. The reference signal is derived from monitoring time slots within a TDMA frame that contain predetermined transmission data. Preferably the predetermined data is the absence of data resulting in an idle time slot. These time slots may be temporarily idle, or may deliberately be left unused to provide a window to a "noise-only" component of the return path signal. The signal thus obtained is passed through the same RF processing stage as the composite return signal and subsequently sampled and digitized. Thereafter, spectrum estimation techniques are applied to the samples of the signal to determine the frequencies of the interfering signals. Once an estimate of the interference frequencies is obtained from the spectrum, the reference signal comprising the same frequencies may be synthesized.
118 Citations
56 Claims
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1. A method of canceling interference in a CATV return path signal that includes a time division multiple access data stream having a plurality of time slots within which frames of data are transmitted from subscriber units comprising the step:
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acquiring an interference reference signal from the CATV return path; selecting at least one time slot for use in evaluating interference; sampling said selected time slot when predetermined data is transmitted therein; processing said interference reference signal to produce an interference cancellation signal; and combining said interference cancellation signal with said CATV return path signal to cancel interference. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of canceling interference in a CATV return path signal comprising the steps:
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acquiring an interference reference signal; processing said interference reference signal using a finite impulse response filter when related linearly with said return path signal to produce an interference cancellation signal; combining said interference cancellation signal with said CATV return path signal to cancel interference; and training said finite impulse response filter with a feedback signal acquired downstream of said combined cancellation signal and return path signal. - View Dependent Claims (17, 18, 19, 20)
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21. A method of canceling interference in a CATV return path signal comprising the steps:
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acquiring an interference reference signal; processing said interference reference signal using an infinite impulse response filter when related linearly with said return path signal to produce an interference cancellation signal; combining said interference cancellation signal with said CATV return path signal to cancel interference; and training said infinite impulse response filter with a feedback signal acquired downstream of said combined cancellation signal and return path signal.
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22. A method of canceling interference in a CATV return path signal comprising the steps:
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acquiring an interference reference signal; processing said interference reference signal using a feedforward neural network when related nonlinearly with said return path signal to produce an interference cancellation signal; combining said interference cancellation signal with said CATV return path signal to cancel interference; and training said neural network with a feedback signal acquired downstream of said combined cancellation signal and return path signal using a back propagation algorithm.
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23. A method of canceling interference in a CATV return path signal comprising the steps:
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acquiring an interference reference signal; processing said interference reference signal using a radial basis function network when related nonlinearly with said return path signal to produce an interference cancellation signal; combining said interference cancellation signal with said CATV return path signal to cancel interference; and training said radial basis function network with a feedback signal acquired downstream of said combined cancellation signal and return path signal.
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24. An interference cancellation system for a CATV return path signal having a time division multiple access data stream having a plurality of time slots within which frames of data are transmitted from subscriber units comprising:
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means for acquiring an interference reference signal; means for selecting at least one time slot for use in evaluating interference; means for sampling said selected time slot when predetermined data is transmitted therein; means for processing said interference reference signal to produce an interference cancellation signal; and means for combining said interference cancellation signal with said CATV return path signal to cancel interference. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38)
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39. A CATV return path interference cancellation system comprising:
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means for acquiring an interference reference signal by means of an antenna; means for processing said interference reference signal to produce an interference cancellation signal; means for combining said interference cancellation signal with said CATV return path signal to cancel interference; means for acquiring a second interference reference signal from said combined cancellation signal and return path signal; means for processing said second interference reference signal to produce a second interference cancellation signal; and means for combining said second interference cancellation signal with said combined cancellation signal and return path signal to cancel interference. - View Dependent Claims (40, 41, 42, 43)
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44. A CATV return path interference cancellation system comprising:
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means for acquiring an interference reference signal; means for processing said interference reference signal using a finite impulse response filter when related linearly with said return path signal to produce an interference cancellation signal; means for combining said interference cancellation signal with said CATV return path signal to cancel interference; and means for training said finite impulse response filter with a feedback signal acquired downstream of said combined cancellation signal and return path signal. - View Dependent Claims (45, 46, 47, 48)
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49. A CATV return path interference cancellation system comprising:
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means for acquiring an interference reference signal; means for processing said interference reference signal using an infinite impulse response filter when related linearly with said return path signal to produce an inteference cancellation signal; means for combining said interference cancellation signal with said CATV return path signal to cancel interference; and means for training said infinite impulse response filter with a feedback signal acquired downstream of said combined cancellation signal and return path signal.
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50. A CATV return path interference cancellation system comprising:
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means for acquiring an interference reference signal; means for processing said interference reference signal using a feedforward neural network when related nonlinearly with said return path signal to produce an interference cancellation signal; means for combining said interference cancellation signal with said CATV return path signal to cancel interference; and means for training said neural network with a feedback signal acquired downstream of said combined cancellation signal and return path signal using a back propagation algorithm.
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51. A CATV return path interference cancellation system comprising:
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means for acquiring an interference reference signal; means for processing said interference reference signal using a radial basis function network when related nonlinearly with said return path signal to produce an interference cancellation signal; means for combining said interference cancellation signal with said CATV return path signal to cancel interference; and means for training said radial basis function network with a feedback signal acquired downstream of said combined cancellation signal and return path signal.
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52. A method of canceling interference in a CATV return path signal comprising the steps:
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acquiring an interference reference signal by means of an antenna; processing said interference reference signal to produce an interference cancellation signal; combining said interference cancellation signal with said CATV return path signal to cancel interference; acquiring a second interference reference signal from said combined cancellation signal and return path signal; processing said second interference reference signal to produce a second interference cancellation signal; and combining said second interference cancellation signal with said combined cancellation signal and return path signal to cancel interference. - View Dependent Claims (53, 54, 55, 56)
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Specification