Motorola Corporation

Universal Data Systems, Inc.

Jack L Hayes

Richard Lee Goodson

Mickey C Rushing

Michael D Turner

A modem with nonlinear equalization (100) receives a signal (101) that includes linear and nonlinear distortion. The modem includes a multiplier (107) that frequency shifts the signal to form a baseband signal, which is then sampled by an A/D converter (114) to provide a complex receiver input sample, R(n). A first equalizer (117) equalizes R(n) to form a first equalized result (n). A nonlinear generator (129) forms .vertline.R(n).vertline..sup.2 R(n), which is then equalized by a second equalizer (133) to form a second equalized result (n). A summing device (121) combines the first equalized result (n) with the second equalized result (n) to form a composite equalized result (n). The modem includes a data recovery circuit (125) that determines a received signal point (n) based on the composite equalized result (n) and a predetermined constellation.

Modem receiver with nonlinear equalization

A modem receiver circuit comprises one or more phase jitter canceling circuits for reducing sinusoidal components of phase jitter in a telecommunications channel. The receiver circuit automatically tracks multiple sinusoidal frequency components and jitter components varying slowly in amplitude and frequency. Each phase jitter canceling circuit is responsive to a phase angle error signal, which is scaled by an adaptive gain constant and appropriately signed. The corrected error signal is passed through a second order loop filter which contains an accumulator with a jitter frequency estimate. The output is integrated into an estimate of the phase of the sinusoidal jitter, which is converted into an estimate of the jitter angle by using a sine lookup table. The resulting estimated jitter component angle is added to the carrier loop phase angle estimate to derive a total receiver phase estimate. The circuit provides rapid acquisition of an accurate initial estimate for the jitter component. It also decouples the operation of the jitter canceling circuitry from the existing carrier phase loop circuitry to avoid harmful interactions.

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Huntsville, AL, United States of America

Jack L Hayes