Equalização adaptativa em sistemas radio-digitais : das tecnicas em frequencia a teoria da desconvolução autodidata

AUTOR(ES)
DATA DE PUBLICAÇÃO

1992

RESUMO

Equalization in microwave digital-radio transmission systems is dealt with under a transient and steady-state point of view. The c1assical theory of digital transversal equalization is revisited and complemented concerning the c1assical aspects of mean square error minimization (MSEM) and zero forcing (ZF), and also in the proposal of an algorithm for the adjustement of the complex coeffjcients of an equalizer by the ZF criterium. Classical stochastic algorithms limitations operating in the directed-decision mode for initializations periods in digital-radio systems (under c1osed eyes diagram, corresponding to strong distortion) are confirmed in computer simulations, suggesting the need of using robust algorithms, specially in the autodictate mode. The non-minimum phase characteristics for the sampled impulse reponse version of the microwave channel, restricts the choice of such algorithms. This happens due to the impossible use of second-order statistics processing in the available receiver signals, for the proper equalization of amplitude and phase in a non-minimum phase channel. A few blind algorithms available in the literature are compared for digital-radio systems, concerning their robustness, convergence velocities and consistencies behavior. It is confirmed that, among ali tested algorithms, the Godard algorithm is the one that shows the best compromise concerning the analised aspects, confirming some experimental results. Finnaly, an equalization linear method for the complex modulation is proposed based on the matching between the fourth-order moments of the system input signals and the fourth-order moments of the channel ouput signals. Perhaps, this method allows the action, in the autodidacte mode, of blind algorithms based in the estimation of fourth-order moments. The analytical results obtained are comparable with those of the MSEM and ZF criteria

ASSUNTO(S)

microondas equalizadores (eletronica)

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