Adaptive correction of phase errors in noncoherent demodulation of carrier asymmetrically modulated with digital signals
First Claim
1. A method of correcting distortions due to phase errors in a train of data signals recovered during successive clock cycles by noncoherent demodulation from an asymmetrically modulated carrier, comprising the steps of:
- deriving a train of raw bipolar quadrature signals from the train of recovered raw bipolar data signals;
cross-multiplying said raw data signals and said raw quadrature signals with two mutually conjugate trigonometric functions of a magnitude substantially compensating said phase errors, thereby generating corrected bipolar in-phase signals and corrected bipolar quadrature signals;
generating a series of reference signals by quantizing said corrected in-phase signals;
obtaining a succession of bipolar difference signals by subtractively combining said corrected in-phase signals and said reference signals;
multiplying at least parts of said difference signals with at least parts of said corrected quadrature signals to produce bipolar error signals of a polarity which is the product of the polarities of said difference signals and of said corrected quadrature signals;
averaging said error signals over a plurality of clock cycles to obtain a succession of corrective bipolar feedback signals; and
deriving said trigonometric functions from said feedback signals.
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Abstract
Digital signals asymmetrically modulated upon a carrier, with suppressed or vestigial second sideband, are recovered at a receiver by pseudo-coherent demodulation or periodic sampling and subsequent digitization to provide a train of raw data signals X from which a train of raw quadrature signals Y is derived by digital filtration. Signals X and Y are fed to a phase corrector where they are cross-multiplied with a sine function and a cosine function of a feedback signal W, approximating a corrective phase angle φ(t), to yield a corrected in-phase signal X'"'"' and a corrected quadrature signal Y'"'"'. Signal X'"'"' is quantized to provide a reference signal c which, upon subtraction from signal X'"'"', produces a bipolar difference signal whose sign bit is multiplied with either the entire signal Y'"'"' or its sign bit to provide an error signal V. The latter is averaged over a number of clock cycles, resulting in the feedback signal W whose trigonometric functions are read out from a memory for utilization in the generation of corrected signals X'"'"' and Y'"'"'.
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Citations
12 Claims
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1. A method of correcting distortions due to phase errors in a train of data signals recovered during successive clock cycles by noncoherent demodulation from an asymmetrically modulated carrier, comprising the steps of:
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deriving a train of raw bipolar quadrature signals from the train of recovered raw bipolar data signals; cross-multiplying said raw data signals and said raw quadrature signals with two mutually conjugate trigonometric functions of a magnitude substantially compensating said phase errors, thereby generating corrected bipolar in-phase signals and corrected bipolar quadrature signals; generating a series of reference signals by quantizing said corrected in-phase signals; obtaining a succession of bipolar difference signals by subtractively combining said corrected in-phase signals and said reference signals; multiplying at least parts of said difference signals with at least parts of said corrected quadrature signals to produce bipolar error signals of a polarity which is the product of the polarities of said difference signals and of said corrected quadrature signals; averaging said error signals over a plurality of clock cycles to obtain a succession of corrective bipolar feedback signals; and deriving said trigonometric functions from said feedback signals. - View Dependent Claims (2)
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3. In a system for recovering a train of bipolar data signals during successive clock cycles by noncoherent demodulation from an asymmetrically modulated carrier, including a local time base for establishing said clock cycles and a component circuit for correcting distortion of said data signals due to phase errors, the improvement wherein said component comprises:
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transformation means for deriving a train of raw bipolar quadrature signals from a train of recovered raw data signals; an arithmetic unit with a first input for receiving said raw data signals, a second input connected to said transformation means for receiving said raw quadrature signals, a first output for emitting corrected bipolar in-phase signals, and a second output for emitting corrected bipolar quadrature signals; decision means connected to said first output for producing a series of reference signals by quantizing said corrected in-phase signals; algebraic summing means with input connections to said first output and to said decision means for generating a succession of bipolar difference signals by subtractively combining said corrected in-phase signals and said reference signals; multiplication means connected to said algebraic summing means and to said second output for producing bipolar error signals of a polarity which is the product of the polarities of said difference signals and said corrected quadrature signals; integrating means controlled by said time base and connected to said multiplication means for producing a succession of corrective bipolar feedback signals representative of phase angle; conversion means connected to said integrating means for translating each of said feedback signals into a pair of conjugate trigonometric functions thereof; and calculating means in said arithmetic unit inserted between said inputs and outputs thereof and connected to said conversion means for synthesizing said corrected in-phase and quadrature signals by cross-multiplying said raw data signals and said raw quadrature signals with said conjugate trigonometric functions. - View Dependent Claims (4, 5, 6, 7, 8, 9, 10, 11, 12)
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Specification