METHOD AND APPARATUS FOR ADJUSTING A DIGITAL EQUALIZING FILTER IN SIMULTANEOUS ADAPTIVE ECHO ELIMINATION AND ADAPTIVE ELIMINATION OF NOISE CAUSED BY INTERSYMBOL INTERFERENCE.

摘要

A method and apparatus for adjusting a digital equalizing filter (U) in a hybrid circuit in a telecommunication system for transmitting digital information in duplex on a single line pair with simultaneous adaptive echo elimination and adaptive elimination of noise caused by intersymbol interference, where a first and a second compensation signal (ê(t), î(t)), which are respectively dependent on the stored parameters of a digital balance filter (B) and the equalizing filter (U), are subtracted from a received signal (a(t) + e(t) + i(t)) to form a difference signal (r(t)) which is compensated for noise respectively caused by echoes and intersymbol interference, the balance filter parameters being corrected with the aid of a correction signal ( epsilon Bk) dependent on the difference signal (r(t)). The equalizing filter parameters are adjusted with the aid of a further correction signal ( epsilon Uk) formed by the balance filter correction signal ( epsilon Bk) and the first compensation signal (ê(t)) such that the further correction signal ( epsilon Uk) will substantially agree with the balance filtercorrection signal ( epsilon Bk), but obtain the value zero when the first compensation signal (ê(t)) and the balance filter correction signal ( epsilon Bk) are both positive simultaneously or negative simultaneously. There is thus prevented the correction sequence of the equalizing filter parameters when the balance filter parameters are changed in a direction such that the absolute amount of the estimated echo (ê(t)) increases.