OVERVIEW

Dr. Messerschmitt is a Professor at the University of California at Berkeley, and was formerly with Bell Laboratories. He has worked and published extensively in digital voice and data transmission and digital signal processing, including both theoretical and implementation aspects.

4.1 INTRODUCTION

Echo cancellation is an application of adaptive filtering technology to the control of echoes in the telephone network. It has been studied in the research laboratory for two decades, and due to the advances in microelectronics technology is now finding widespread practical application. This chapter describes the echo-control problems addressed by echo cancellation for both voice and data transmission, describes and analyzes the echo-cancellation algorithms used in these applications, and discusses the implementation of echo cancelers.

Section 4.2 describes the application of echo cancellation to speech transmission and the principles of echo suppression, and Section 4.3 discusses applications in full-duplex data transmission. Section 4.4 outlines the algorithms used for adaptation of echo cancelers in all these applications and evaluates their performance. Finally, Section 4.5 summarizes advanced techniques in echo cancellation.

4.2 ECHO CANCELLATION IN SPEECH TRANSMISSION

The telephone network generates echoes at points within and near the ends of a telephone connection. Echo cancellation is one means used to combat this echo for both speech and data transmission. The requirements for speech and data are quite different, so this section concentrates on speech and Section 4.3 deals with data. The sources...