Cselt-centro Studi E Laboratori Telecomunicazioni S.p.a.

Sip - Societa Italiana Per L'esercizio Telefonico S.p.a.

Valerio Zingarelli

Giancarlo Pirani

An adaptive equalizer for high-speed binary signals, operating in baseband, comprises a transversal filter receiving digitized samples of incoming symbols and feeding them to a decision stage. An error signal derived from the difference between the filtered and the decided samples, for each coefficient of the transversal filter and for each iteration of the processing by that coefficient, is fed to an updating unit, where its sign is compared with the sign of the corresponding filtered sample to determine their identity or disparity. The result is a binary discriminating signal sent to a coefficient calculator and to a threshold generator which receives from that calculator the current coefficient and, dependent on the polarity of that coefficient and on the logical value of the discriminating signal, produces a threshold value to be compared with the absolute magnitude of the error signal. Whenever that absolute magnitude exceeds the existing threshold, it causes the count of an up/down counter to be incremented or decremented, depending on whether the two compared signs are different or equal. Whenever the up count of the down count reaches a predetermined limit in any cycle, the counter resets itself to zero and triggers the calculator to update the existing coefficient, again on the basis of the discriminating signal, by either halving or doubling that coefficient.

Adaptive equalizer for binary signals and method of operating same

An adaptive equalizer for high-speed binary signals, operating in baseband, comprises a transversal filter receiving digitized samples of incoming symbols and feeding them to a decision stage. The samples also go to a coefficient computer, in parallel with that filter, which includes a filter simulator, an error calculator and a processor delivering corrective coefficients to the filter. A register in the filter simulator accumulates a predetermined multiplicity of received samples (e.g. 150) which are jointly convoluted with an initial set of coefficients to yield a mean square error supplied by the error calculator to the processor; the latter, for each coefficient of the initial set, selects two collateral values which are successively substituted for that coefficient to yield two further mean square errors. Using an algorithm based upon a parabolic function, the processor computes an optimized coefficient which is rounded to the nearest power of 2 constituting a new coefficient replacing the corresponding coefficient of the initial set. After all coefficients of the initial set have been thus replaced to produce an updated set, the processor determines whether the resulting mean square error is less than that obtained with the initial set and, if so, substitutes the updated set for the initial set in the transversal filter.

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Turin, Italy

Valerio Zingarelli