DESIGNING AN ECHO CANCELLER SYSTEM USING THE TMS320C50 DSP

This application report describes an echo canceller system using the Texas Instruments (TI™) TMS320C50 digital signal processor (DSP). The system is based on based on low resolution time-delay estimation, using the knowledge that mainly one or two active regions (depending on the number of reflections in the communication channel) characterize the impulse response of a typical echo-path in telephony communications.

These active regions usually have a duration that is only a small fraction of the total supported length. Low-resolution time-delay estimators track those active regions where short-length adaptive filters are centered, assuring an accurate echo-path estimation.

A speech detector is employed to avoid erroneous time-delay estimates and adaptive filter coefficient drift. Using a single TM5320C50 DSP with no external memory, the system detects and cancels an echo with a delay of more than 380 ms. Considering a configuration with 64Kwords of data memory, the maximum supported delay is greater than 2.5s.

The resulting system enables long delay echo cancellation with reduced computational effort, while achieving greater convergence speed and lower residual error, when compared with other systems reported in recent literature.

This document was part of the first European DSP Education and Research Conference that took place September 26 and 27, 1996 in Paris. For information on how TI encourages students from around the world to find innovative ways to use DSPs, see TI's World Wide Web site at www.ti.com.

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(c) Copyright 1998 Texas Instruments Incorporated. All rights reserved.
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