Title :
Precision-efficient use of block adaptive algorithms in data-driven echo cancellers
Author_Institution :
Inf. Syst. Lab., Stanford, CA, USA
Abstract :
Data-driven echo cancellers are used in full-duplex voiceband data transmission at rates of 4800 b/s and above, and in digital subscriber loops for ISDN (integrated services digital network) at rates of 160 kb/s (or above). It is well-known that the required 60 dB of cancellation mandates high coefficient and processor precision if the stochastic-gradient (least-mean-squares (LMS)) adaptive algorithm for the echo canceller is implemented in fixed-point arithmetic. However, the use of block LMS or block adaptive algorithms significantly improves this situation without increasing computation. The improvement in numerical accuracy is traded (almost linearly) for a decrease in tracking speed of the echo canceller, which, however, is often an acceptable tradeoff as the echo channel does not exhibit significant time variation. A drawback of the block adaptive algorithms, their requirement of more temporary internal variables, is also discussed
Keywords :
ISDN; data communication systems; echo suppression; least squares approximations; subscriber loops; telecommunication equipment; 160 kbit/s; 4800 bit/s; ISDN; LMS; block adaptive algorithms; data-driven echo cancellers; digital subscriber loops; fixed-point arithmetic; full-duplex voiceband data transmission; least-mean-squares; precision efficient use; stochastic gradient adaptive algorithm; tracking speed; Adaptive algorithm; DSL; Data communication; Echo cancellers; Fixed-point arithmetic; ISDN; Information systems; Laboratories; Least squares approximation; Roundoff errors;
Conference_Titel :
Communications, 1988. ICC '88. Digital Technology - Spanning the Universe. Conference Record., IEEE International Conference on
Conference_Location :
Philadelphia, PA
DOI :
10.1109/ICC.1988.13590