Technique for achieving the theoretical coding gain of digital signals incorporating error correction
First Claim
1. A point-to-point communications system which transmits digital signals from a first location to only one second location via a communications medium having varying transmission characteristics, said system comprisinga first adjustable equalizer at said first location for compensating for amplitude and phase distortion in said medium,a second adjustable equalizer at said second location for compensating for amplitude and phase distortion in said medium,means, responsive to digital signals received at said second location, for generating equalization coefficients for said second equalizer which are suitable for compensating for said amplitude and phase distortion, and for transmitting said generated equalization coefficients from said second location to said first equalizera first Nyquist filter at said first location,a second Nyquist filter at said second location, andcontrol means for assuring that only one of said first and second equalizers and only one of said first and second Nyquist filters is operative at any time.
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Accused Products
Abstract
The theoretical coding gain associated with an error correction technique can be realized in a digital communications system employing this error correction by providing the equalization in the transmitter instead of the receiver. In a first embodiment, an automatic equalizer in the receiver of a digital communications system is adjusted using a training sequence. The equalizer coefficients for optimum adjustment are then transmitted back to the transmitter and supplied to an equalizer therein. After the training period is over, this transmitter equalizer, now having optimum coefficients, is activated and the receiver equalizer is disabled. In a second embodiment, the use of a training sequence can be eliminated and the receiver equalizer can be adjusted in response to actual data using "blind" equalization. The generated coefficients, as in the first embodiment, are then transmitted back to the transmitter. In either embodiment, using the transmitter equalizer to predistort the transmitted signal in a manner opposite to that of the communications medium connecting the transmitter and receiver assures that the noise at the input to the receiver decoder is both Gaussian and white. As a result, the theoretical coding gain associated with the employed error correction is substantially realized.
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Citations
29 Claims
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1. A point-to-point communications system which transmits digital signals from a first location to only one second location via a communications medium having varying transmission characteristics, said system comprising
a first adjustable equalizer at said first location for compensating for amplitude and phase distortion in said medium, a second adjustable equalizer at said second location for compensating for amplitude and phase distortion in said medium, means, responsive to digital signals received at said second location, for generating equalization coefficients for said second equalizer which are suitable for compensating for said amplitude and phase distortion, and for transmitting said generated equalization coefficients from said second location to said first equalizer a first Nyquist filter at said first location, a second Nyquist filter at said second location, and control means for assuring that only one of said first and second equalizers and only one of said first and second Nyquist filters is operative at any time.
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14. A method of realizing the theoretical coding gain associated with an error correction technique used in a point-to-point communications system, said system transmitting a digital signal from a first location to only one second location via a communications medium having varying transmission characteristics, said method comprising the steps of
generating equalization coefficients for a first adjustable equalizer at said first location in response to received digital signals therein which are suitable for compensating for amplitude and phase distortion in said medium, generating equalization coefficients for a second adjustable equalizer at said second location in response to received digital signals therein which are suitable for compensating for amplitude and phase distortion in said medium, transmitting said generated equalization coefficients from said first location to said second location, and transmitting said generated equalization coefficients from said second location to said first location.
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15. A multi-point communications system of the type wherein digital signals at a central location are transmitted to a plurality of remote locations via separate communications paths each having varying transmission characteristics, said system comprising
an adjustable equalizer at one remote location for compensating for amplitude and phase distorting in an associated one of the communications paths, an adjustable equalizer at said central location for compensating for amplitude and phase distortion in said associated one of the communications paths, and means, responsive to digital signals received at said one remote location, for generating equalization coefficients for said adjustable equalizer at said one remote location which are suitable for compensating for said amplitude and phase distortion in said associated one of the communications paths, and transmitting these generated equalization coefficients from said one remote location to said equalizer at said central location.
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27. A method of realizing the theoretical coding gain associated with an error correction technique used in a point-to-point communications system, said system transmitting a digital signal from a first location to only one second location via a communications medium having varying transmission characteristics, said method comprising the steps of
generating equalization coefficients for an adjustable equalizer at said second location in response to received digital signals therein which are suitable for compensating for amplitude and phase distortion in said medium, and transmitting said generated equalization coefficients from said second location to an adjustable equalizer at said first location, and controlling the operation of the equalizers at said first and second locations and first and second Nyquist filters respectively disposed at said first and second locations so that only one of the equalizers and one of the Nyquist filters is activated at any time.
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28. A method of realizing the theoretical coding gain associated with an error correction technique used in a multi-point communications system, said system being of the type wherein a digital signal at a central location is transmitted to a plurality of remote locations via separate communications paths each having varying transmission characteristics, said method comprising the steps of:
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generating equalization coefficients for an adjustable equalizer at said one remote location in response to received digital signals therein which are suitable for compensating for amplitude and phase distortion in an associated one of said communications paths, and transmitting said generated equalization coefficients from said one remote location to a second adjustable equalizer at said central location, said transmitted equalization coefficients being used by said second adjustable equalizer for compensating for said amplitude and phase distortion in communications from said central location to said one remote location.
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29. A point-to-point digital communications system which transmits digital signals from a first location to only one second location via a communications medium having varying transmission characteristics, said system comprising
a first adjustable equalizer at said first location for compensating for amplitude and phase distortion in said medium, a second adjustable equalizer at said second location for compensating for amplitude and phase distortion in said medium, means, responsive to digital signals received at said first location, for generating equalization coefficients for said equalizer which are suitable for compensating for said amplitude and phase distortion, and for transmitting said generated equalization coefficients from said first location to said second location, said transmitted equalization coefficients being used at said second location for compensating for said amplitude and phase distortion in signal transmission from said second to said first location, and means, responsive to digital signals received at said second location, for generating equalization coefficients for said second equalizer which are suitable for compensating for said amplitude and phase distortion, and for transmitting said generated equalization coefficients from said second location to said first location, said transmitted equalization coefficients being used at said first location for compensating for said amplitude and phase distortion in signal transmission from said first to said second location.
Specification