Design of 2B1Q transceiver for ISDN subscriber loops

A computationally efficient two-stage echo canceller is proposed. The first stage is a direct form adaptive FIR filter to cancel the main part of the echo response. The second stage cancels the "tail" part of the echo response. The proposed tail canceller is an adaptive version of the interpolated FIR (IFIR) filter in [11-[31. It is shown that the two-stage canceller meets the 60-dB echo cancellation accuracy for various typical loops. Extensive simulations were carried out to study the effects of the main canceller length as well as the interpolator parameters on the performance of the proposed two-stage echo canceller in the U-interface transceiver for basic rate ISDN. It is shown that the proposed structure compares favorably with a recently published two-stage canceller.

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Simplified adaptive IIR filters based on optimized orthogonal prefiltering

Kaelin

Lindgren²,

Moschytz³

1995

IEEE Trans. Circuits Syst. II

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Abstract-In order to reduce the circuit complexity associated with the estimation of echoes coming from systems with a long impulse response, we consider an estimator which is based on prefiltered input data. We propose a design of this prefilter which is optimal for a given system environment. In doing so, we represent the unknown discrete-time system by a set of characteristic impulse responses, which adequately describe the variety of the system. For such an environment we determine the optimum poles of a recursive prefilter. These poles are assumed to befied during the on-line LMS estimation process, which estimates the unknown echo by linearly weighting the prefilter states. An echo canceler for a typical European telephone subscriber-loop environment is used as a practical example. For this example the prefilter is optimized and realized with an orthogonal-state (lattice) filter. This not only reduces the computational costs-if compared to a conventional FIR filter design-but also permits a substantial speed-up of the on-line LMS adaptation process.

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Design of 2B1Q transceiver for ISDN subscriber loops

Cited by 5 publications

References 4 publications

High bit rate digital subscriber line echo cancellation

High bit rate digital subscriber line echo cancellation

An echo tail canceller based on adaptive interpolated FIR filtering

Simplified adaptive IIR filters based on optimized orthogonal prefiltering

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