Echo measurement arrangement

A filter circuit for ranging and converging on each of a plurality of echoes occurring at respective locations along a communications line comprising

• means for storing in a memory samples of a signal that is being transmitted to said communications line and samples of a signal that is being simultaneously received from said communications line, and
• a plurality of filtering means each having a respective group of filter coefficients, each of said filtering means being arranged to generate a filtered signal by sequentially and iteratively filtering respective overlapping sequences of said transmitted signal samples supplied to its input, a first one of said filtering means receiving at another input a respective sequence of said received signal samples and other ones of said filtering means each receiving at its other input an error signal outputted by a respective preceding one of said filtering means, said first one of said filtering means generating its error signal as a function of the value of its respective filtered signal and a respective one of said received signal samples and each of said other ones of said filtering means generating its error signal as a function of the value of its respective filtered signal and the value of the error signal that it receives at its other input, each of said filtering means converging on a respective one of said echoes by changing the values of its respective coefficients as a function of the current value of the error signal that it generates and freezing said values when the value of said error signal that it generates reaches a minimum.

A method for ranging and converging on at least one of a plurality of echoes occurring at respective locations along a communications line, said method comprising the steps of

• storing in a memory samples of a signal that is being transmitted to said communications line and samples of a signal that is being simultaneously received from said communications line,
• filtering overlapping sequences of said stored samples of said transmitted signal into a plurality of filtered signals using at least one filtering means having a plurality of respective coefficients,
• changing the values of said respective coefficients as a function of each of said filtered signals and respective signals representative of respective ones of said stored received signal samples,
• freezing the values of said coefficients when they reach respective final values as an indication that said one filtering mean has converged on said at least one echo, and
• determining the propagation delay associated with said at least one echo as a function of the effective number of said transmitted signal samples that have been filtered up to the point at which said coefficients reach their respective final values.