다중레벨 신호점에 대한 동시 블라인드 등화 기법
A Concurrent Blind Equalization Technique for Multilevel Constellations
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초록
본 논문에서는 비 동시 등화기가 갖는 알고즘 전환에 따른 문제점을 해결하기 위해 연판정과 경판정을 결합한 새로운 동시 블라인드 등화기를 제안한다. 제안한 동시 SSDD-HDD 등화기는 계산 복잡성을 개선한 단순화된 연판정의거(SSDD: Simplified Soft Decision-Directed) 알고리즘에 기초하며, SSDD 알고리즘에 사용되는 시그모이드 함수의 평균과 분산을 조절함으로써 동시 SSDD-HDD 등화기의 연판정(SSDD) 알고리즘과 경판정(HDD: Hard Decision-Directed) 알고리즘이 구현되는 특징을 갖는다. 또한 제안한 동시 등화 기법에서는 등화기 출력의 이동평균 제곱오차(moving-average squared error)에 기초하여 등화기의 수렴을 검출하고 동시 동작을 중지함으로써 정상상태 성능을 개선하였다. 제안한 동시 등화기의 성능을 검증하기 위해, 다중레벨 신호점에 대한 블라인드 등화 기법으로 최근에 소개된 동시 CMA-DD 등화기 및 동시 CMA-SDD 등화기와 모의실험을 통하여 비교하였다. 제안한 방법은 기존 방식에 비해 잔류 ISI 및 MSE 성능을 개선하였다.
Abstract
This paper presents a novel concurrent blind equalizer combining soft decision with hard decision, which solves the difficulty in algorithm-switching of non-concurrent equalizers. The proposed concurrent SSDD and HDD equalizer is based on the simplified soft decision-directed (SSDD) algorithm that reduces computational complexity. It is characterized that both SSDD algorithm and HDD algorithm of the concurrent SSDD and HDD equalizer are implemented by controlling the mean and variance of the sigmoid function used in the SSDD algorithm. In addition, as the proposed concurrent equalization technique detects initial convergence based on moving-average squared error of the equalizer output, and then the concurrent operation is stopped, which enhances steady-state performance. For assessing the performance of the proposed concurrent equalizer, it is compared to the concurrent CMA and DD equalizer and concurrent CMA and SDD equalizer recently introduced to equalize multilevel constellations by computer simulations. The proposed method improves the residual intersymbol interference (ISI) and mean squared error (MSE) performance compared to the conventional methods.
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