US 5,111,484 A · Adaptive distortion canceller

Abstract

An adaptive distortion cancellation algorithm minimizes intersymbol interference (ISI) when demodulating signals in the presence of distortion over fading and dispersive channels. The algorithm computes preliminary estimates of received data and feeds them to a canceller structure. The canceller checks the preliminary estimates and then makes a series of subsequent estimates by modifying the elements of the original received estimated data sequence. Each estimate generates a distortion cancellation quantity which is added to the received data estimate to generate a sequence of values; a final decision is determined by that subsequent estimate which is closest to an ideal state. The preliminary estimates are made using a conventional transversal filter whose coefficients are controlled by one of the existing filter tap algorithms. The canceller algorithm corrects all incorrect elements of the preliminary estimates while maintaining relatively small error magnitudes at its output as compared to the transversal filter output error magnitudes.

Claims10

Dependent claims

In a digital communications system having a channel susceptible to linear and nonlinear distortions, a method for identifying the state of an observed data element from among a set of states, said method comprising the steps of:

a. receiving a preliminary sequence of data elements, said preliminary sequence including said observed data element;
b. estimating the states of each of said data elements of said preliminary sequence;
c. generating, for each of a plurality of cancellation coefficients corresponding to a plurality of data sequences having states which map closely adjacent to the states of said preliminary sequence, the value of said observed data element modified by said cancellation coefficient;
d. determining, for each value of said observed data element modified by said cancellation coefficient, a closest state from among a mapping of said set of states;
e. measuring, for each value of said observed data element modified by said cancellation coefficient, the error quantity resulting from the difference between said value of said observed data element modified by said cancellation coefficient and said closest state;
and
f. assigning to said observed data element the closest state of said determining step for which said error quantity of said measuring step results in a minimum value.

4 more elements

Dependencies are inferred from the claim text.

Adaptive distortion canceller

Life of this patent

Adaptive distortion canceller

Life of this patent

Abstract

Claims10