Dual Transform Domain Echo Canceller for Discrete Multitone Systems

Abstract

In communication systems where full-duplex transmission is required, digital echo cancellers are employed to cancel echo by means of adaptive filtering. In order to reduce the computational complexity of these cancellers, the structure of the Toeplitz matrix containing the transmitted signal is usually exploited to transform the time domain signals and perform the emulation and adaptive update in a more convenient domain (e.g. frequency domain). In this paper, we consider a general decomposition of the Toeplitz matrix and examine the effect of different components of the decomposition on the computational complexity and convergence behaviour of the canceller. Based on this general decomposition, a new dual transform domain canceller is proposed which has improved convergence compared to the current echo cancellers and also does not require the transmission of dummy data on the unused tones.

Dual domain echo cancellers for multirate discrete multitone systems

“…In the symmetric decomposition, where the data matrix is decomposed using the DCT and the DST [5], the resulting submatrices of S k are either diagonal or have non-zero elements only on the superdiagonal or on the sub-diagonal [1]. This characteristics makes this decomposition a suitable candidate for implementing the DTDC structure.…”

“…This characteristics makes this decomposition a suitable candidate for implementing the DTDC structure. In [1], we refer to this implementation of Fig. 1.…”

“…In this section, we present the expansion of the DTDC algorithm in [1], [2] for the multirate DSL systems. Two implementations are presented for the cancellers both at the RT and the CO transceivers: the direct approach and the polyphase decomposition approach.…”

“…In [1], we introduced the dual transform domain canceller (DTDC) for DMT systems. In this method, a pair of unitary transforms is used to map the time-domain signals into alternate domains where echo emulation and weight update can be performed more conveniently.…”

“…For discrete multitone (DMT) modulated systems, the computational complexity of these cancellers can be reduced by using the structure present in the transmitted signal. In [1] and [2], we have proposed a novel dual domain echo canceller for symmetric rate DMT systems. In practical DSL systems, asymmetric bandwidths are used for the upstream and downstream transmissions, therefore, echo cancellers must be designed to work in multirate cases.…”