Multi-mode variable rate digital cable receiver
First Claim
1. In combination for use in a multi-mode variable rate digital cable receiver, first means for receiving through the cable carrier signals modulated by information signals in a particular frequency range, second means for reducing the frequency of the carrier signals to a particular intermediate frequency, third means for providing a digital conversion of the signals at the reduced frequency from the second means to obtain digital information signals, a variable interpolator responsive to the digital data signals for providing first signals, a complex multiplier responsive to the first signals for providing second signals, an adaptive equalizer responsive to the second signals for selecting, for each of the second signals, an individual one of a plurality of amplitude levels in quadrature amplitude modulation, fourth means responsive to the signals from the adaptive equalizer for operating upon the variable interpolator to provide a sampling of the digital information signals for obtaining the first signals in the middle of the period that each of such digital information signals is produced, and fifth means responsive to the first signals from the adaptive equalizer for operating upon the complex multiplier to maintain the frequency of the second signals at the frequency of the digital information signals.
6 Assignments
0 Petitions
Accused Products
Abstract
Carrier signals modulated by information (video and/or data) signals are received through a cable and are converted to modulated signals at an intermediate frequency. The IF signals are sampled at a particular frequency to produce digital information signals. The digital information signals are introduced to a variable interpolator which produces first digital signals. The first digital signals are introduced to a complex multiplier which produces second digital signals. The second digital signals pass to an adaptive equalizer which selects for each of the second signals in accordance with the amplitude of such second signals, an individual one of a multitude of amplitude levels involved in quadrature amplitude modulation. These selected amplitude levels represent the information (video and/or data). The output signals from the adaptive equalizer are introduced to a first signal recovery loop which includes a first numerically controlled oscillator. The oscillator operates upon the variable interpolator to obtain the production by the variable interpolator of the first digital signals in the correct subinterval of the time period that each of the digital information signals is produced. The output signals from the adaptive equalizer are also introduced to a second signal recovery loop which includes a second numerically controlled oscillator. This oscillator operates upon the complex multiplier to maintain the frequency of the second digital signals at the frequency of the digital information signals.
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Citations
23 Claims
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1. In combination for use in a multi-mode variable rate digital cable receiver,
first means for receiving through the cable carrier signals modulated by information signals in a particular frequency range, second means for reducing the frequency of the carrier signals to a particular intermediate frequency, third means for providing a digital conversion of the signals at the reduced frequency from the second means to obtain digital information signals, a variable interpolator responsive to the digital data signals for providing first signals, a complex multiplier responsive to the first signals for providing second signals, an adaptive equalizer responsive to the second signals for selecting, for each of the second signals, an individual one of a plurality of amplitude levels in quadrature amplitude modulation, fourth means responsive to the signals from the adaptive equalizer for operating upon the variable interpolator to provide a sampling of the digital information signals for obtaining the first signals in the middle of the period that each of such digital information signals is produced, and fifth means responsive to the first signals from the adaptive equalizer for operating upon the complex multiplier to maintain the frequency of the second signals at the frequency of the digital information signals.
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8. In combination for use in a multi-mode variable rate digital cable receiver,
first means for receiving through the cable carrier signals modulated by information in a particular frequency range, second means for converting the modulated carrier signals to digital information signals at a particular frequency, a variable interpolator responsive to the digital information signals for producing first signals, third means including an adaptive equalizer for converting each of the first signals to an individual one of a plurality of amplitude levels involved in quadrature amplitude modulation, and fourth means responsive to the amplitude levels produced by the adaptive equalizer for operating upon the variable interpolator to obtain the production by the variable interpolator of the first signals in the correct subinterval of the time period that each of the digital information signals is produced.
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15. In combination for use in a multi-mode variable rate digital cable receiver,
first means for receiving through the cable carrier signals modulated by information in a particular frequency range, second means for converting the modulated carrier signals to digital information signals at a particular frequency, third means including a complex multiplier responsive to the digital information signals for producing first signals, an adaptive equalizer for converting each of the first signals to an individual one of a plurality of amplitude levels involved in quadrature amplitude modulation, and fourth means responsive to the amplitude levels produced by the adaptive equalizer for operating upon the complex multiplier to maintain the frequency of the first signals at the frequency of the digital information signals.
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23. In a combination as set forth in claim 23,
the fifth means including a symbol recovery loop responsive to the operation of the adaptive equalizer for generating signals representing errors in the sampling of the second signals at the times other than the middle of the time period that each of the digital information signals is produced and further includes a numerically controlled oscillator responsive to the error signals from the symbol recovery loop for adjusting the production by the symbol recovery loop of the second signals at the middle of the time period that each of the digital information signals is produced.
Specification