Parallel blind equalizer suitable for QAM signal

Abstract

In digital communication system the Constant Modulus Algorithm (CMA) based FIR equalizer is by far the most popular blind equalization to combat the Inter-Symbol Interference (ISI). The major problem of CMA, however, is that it only achieves moderate convergence rate and steady state mean square error (MSE). Furthermore, the CMA and such blind equalization techniques must rely on the observations of system outputs and some a priori statistical information of transmitted signals, so when they are used in some special fields such as military filed, electronic counter measures and many others, these blind equalization techniques cannot operate, because the priori statistical information of intercepted signals cannot be obtained. Consequently a parallel scheme for blind equalizer is proposed, which combines Modified Modulus Algorithm (MCMA) and Modified Decision Directed (MDD) algorithm. Compared with CMA, the proposed method can obtain faster convergence rate and lower MSE, and more important is that it can detect which order QAM signal is transmitted in the communication system.

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