Near-end Echo Research Articles

Data-driven echo cancellation for a multitone modulation system

The problem of echo cancellation in a multitone modulation (MTM) scheme is addressed. A general model for the near-end echo is derived and is used to identify candidate data-driven echo canceller (DDEC) structures. The stability, steady state performance, and associated system complexity of an adaptive DDEC based on the stochastic gradient approach is developed. It is further shown how the symmetry in the derived echo path model can be exploited to enable a reduction in canceller complexity, enhancing convergence speed without sacrificing final SNR. Simulation results are provided that confirm the analytical predictions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A data-driven multitone echo canceller

A data-driven echo canceller for full-duplex data transmission with multitone modulation is presented. This multitone echo canceller (MTEC) is not impaired by eigenvalue-spread problems that are inherent in signal-driven echo cancellers-it has numerical performance and cancellation range that equals, and in most cases exceeds, that of data-driven echo cancellers used in data transmission with baseband or quadrature amplitude modulation. The method makes use of frequency-domain updating, but time-domain implementation of the canceller. It introduces no delay into the received signal path and presents no special difficulties for interframe interpolation between near-end echo, far-end echo, or far-end data signal. The authors also investigate the fast initialization and the special case of far-end frequency offset in the echo signal. >

Transhybrid loss with RC balance circuits for primary-rate ISDN transmission systems

The authors report a method for the reduction of the near-end echo in the subscriber loop environment for primary-rate ISDN full-duplex data transmission. The technique uses an RC network as the matching input line impedance at the transmitter to reduce the near-end echo. Data rates ranging from the ISDN basic rate with (2B+D) channels to primary rate with (23B+D) channels are covered. The results indicate that a single basic configuration for the balancing line impedance may be adapted to keep the transhybrid loss in the range of about 22 dB in the worst case over the entire frequency range of interest. The balancing procedure for the hybrid takes place in a training sequence during which the component values of the RC matching circuit are adjusted from their initial values by an iterative adaptation procedure. Two techniques for optimizing the component values have been verified. For all cases examined, including worst-case line configurations, the components of the RC matching circuit have converged to final values, for which the minimum transhybrid loss had a maximum above 20 dB. >