US 5,710,792 AGranted

Adaptive equalizer

AssigneeNTT Mobile Communications Network, Inc.

InventorsKazuhiko Fukawa, Hitoshi Yoshino, Hiroshi Suzuki

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Abstract

A baseband signal, obtained by quasi-coherent detecting a received signal, is sampled and written as a sequence of baseband signal samples into a buffer memory. For each baseband signal sample read out from the buffer memory, a maximum likelihood sequence estimation part generates a desired symbol sequence and feeds it to a transversal filter having a characteristic based on an estimated impulse response of the transmission path in correspondence with the timing of the baseband signal sample. A phase error between an estimated received signal from the transversal filter and the corresponding baseband signal sample is sequentially detected by a phase error detecting part. The phase error thus obtained is fed to an offset correcting signal generating part, which calculates an estimated offset angular frequency .DELTA..omega..sub.e on the basis of the phase error, generates an offset correcting signal of an angular frequency equal in absolute value to the estimated offset angular frequency but opposite thereto in the direction of rotation and feeds the offset correcting signal to a correcting multiplier. The correcting multiplier multiplies the baseband signal sample by the offset correcting signal to correct it to cancel an angular frequency offset, and a subtractor calculates a difference between the corrected baseband signal sample and the estimated received signal from the transversal filter.

An adaptive equalizer for use in a receiver which receives a burst-like received signal, comprising:

buffer memory means into which a sequence of samples of digital signals obtained by sampling a baseband signal obtained through quasi-coherent detection of said received signal is written as a sequence of baseband signal samples and from which the sequence of baseband signal samples is read out with predetermined timing;
control signal generating means which generates a control signal for controlling the write and read of said buffer memory means;
maximum likelihood sequence estimation means which generates and outputs a desired symbol sequence for said baseband signal samples read out from said buffer memory means;
transversal filter means which has a characteristic based on the estimation of the impulse response of a transmission path and is supplied with said symbol sequence in correspondence with the timing of said baseband signal sample and outputs an estimated received signal;
phase error detecting means which detects a phase error between said estimated received signal from said transversal filter means and the baseband signal corresponding to said baseband signal sample;
offset correcting signal generating means which is supplied with said phase error, calculates an estimated offset angular frequency .DELTA..omega..sub.e on the basis of said phase error and generates an offset correcting signal of an angular frequency equal in absolute value to said estimated offset angular frequency but opposite thereto in the direction of rotation;
multiplying means which multiplies said baseband signal sample and said offset correcting signal to generate a corrected baseband signal sample;
and
subtracting means which calculates the difference between said corrected baseband signal sample and said estimated received signal from said transversal filter means and outputs it as an estimation error;
wherein said maximum likelihood sequence estimation means obtains likelihood information from said estimation error and makes a signal decision by a maximum likelihood sequence estimation algorithm on the basis of said likelihood information.

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Abstract

Claims6