Binary Passband Echo Canceller in a 4800 Bit/s Two-Wire Duplex Modem

This paper deals with the echo cancellation applied to highspeed (4800 bit//s or higher) voiceband data modems. Simple echo cancellers are presented for the whole range of data bit rates from 1200 bit//s to 9600 blt/s. Their structure full=y integrates the modulation process and especially exploits the various relationships existing between the modulation rate and the carrier frequency. The generation of the echo replica is performed by duplicating components of the line echo from simple coded binary symbols processed at the modulation rate only. The implementation of these binary passband echo cancellers can be made quite simple by properly selecting the coded binary symbols from the user´s data. The application of these principles to a 4800 bit/s two-wire duplex modem is then highlighted. The essential characteristics of the modem echo canceller are outlined and its implementation with bit slice processors is described. Finally, test results on the switched telephone network and on satellite links are presented.