Method and apparatus for controlling echo on both sides of a connection

Abstract

A single two-ended echo canceller (102) is provided that uses an adaptive FIR filter (112) to model the impulse response of the echo path and cancel the echo originating from the PSTN side of the connection, and a non-linear processor (114) controlled by input signal levels to cancel the echo originating from the mobile phone side of the connection. Since the linear processing function is not used for cancelling echoes of the mobile phone side, the algorithms directed to estimating and cancelling echoes on the two sides of the connection can be executed in a single DSP, with all of the attendant advantages.

Description

technical field [0001] The present invention relates generally to the field of telecommunications, and in particular to echo cancellation in telephone systems. Background technique [0002] "Echo" is a phenomenon that can occur in telephone systems when a portion of the energy of a transmitted voice signal is reflected back to the transmitter. These reflections are due to impedance mismatches in the analog portion of the telephone network. There may be many different echo sources, for example, a 4-wire to 2-wire hybrid in a public switched telephone network (PSTN) user interface, or acoustic crosstalk in a mobile radiotelephone. Echoes with substantial delays can severely degrade the quality of the processed speech signal. [0003] An echo canceller is a device commonly used in telephone systems to suppress or eliminate echoes from long-distance traffic. For example, in a cellular public land mobile network (PLMN), echo cancellers are used in mobile services switching cen...

AI Technical Summary

Problems solved by technology

[0010] Problems can arise if the echo on both sides of the switched connection is controlled with separate echo cancellers

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