Frequency-domain Echo Canceller Research Articles

Research on VoIP Acoustic Echo Cancelation Algorithm Based on Speex

Echo cancellation has been a major problem to be solved in VoIP, although the integrated echo cancellation module in Speex, it does not consider thread synchronization issues. The frequency domain echo cancellation algorithm MDF of speex is analyzed, and then a synchronization method of playing thread and recording thread is proposed. The results show that the acoustic echo canceller which achieved by the proposed method meet the requirements of voice communication, implementation is easier and therefore provides a reference for the VoIP voice communication and mobile communication terminal .

Errata to “Frequency Domain Echo Canceller for DMT-Based Systems” [Dec 11 713-716

In the above titled letter (ibid., vol. 18, no. 12, pp. 713-716, Dec. 2012), equation (6) was incorrect. The correct equation is presented here.

Reconfigurable FPGA-based switching path frequency-domain echo canceller with applications to voice control device

Acoustic echo control is of vital interest for hands-free operation of telecommunications equipment. An important property of an acoustic echo canceller is its capability to handle double-talk and be able to operate in real time. When it is applied to intelligent voice control device, it is important to suppress the speech from the device and enhance the speech of the user for speech recognition, where double-talk situation is frequently occurred. In this paper, we propose a novel hardware architecture to support a robust adaptive algorithm in combination with a switching path model to tackle the double-talk situation. The proposed switching path model avoids adapting two filters at the same time during double-talk and prevents the disadvantage of the conventional two-path model. In order to achieve computational efficiency and to meet the rigorous timing requirements, the echo canceller is operated in the frequency domain and its computing power is raised by a hardware accelerator implemented in the FPGA fabric surrounding a PowerPC on a Xilinx XUP V2P platform. Results obtained show the echo canceller is successful in handling double-talk situation and the sub-band implementation has improved convergence significantly. An overall improvement by 82.5 times is achieved when a hardware accelerator is used to perform the critical part of the algorithm over a pure software implementation running on a 300 MHz embedded PowerPC processor.

On Adjusting the Learning Rate in Frequency Domain Echo Cancellation With Double-Talk

One of the main difficulties in echo cancellation is the fact that the learning rate needs to vary according to conditions such as double-talk and echo path change. In this paper we propose a new method of varying the learning rate of a frequency-domain echo canceller. This method is based on the derivation of the optimal learning rate of the NLMS algorithm in the presence of noise. The method is evaluated in conjunction with the multidelay block frequency domain (MDF) adaptive filter. We demonstrate that it performs better than current double-talk detection techniques and is simple to implement.

Fast unbiased echo canceller update during ADSL transmission

This paper presents an efficient method for updating echo canceller (EC) coefficients in asymmetric digital subscriber line transceivers during transmission that removes the dependency of updates on the far-end signal. The new method improves on the frequency-domain EC architecture by Ho et al. (1996), in that it converges faster, improves the stability to perturbation, and is not prone to bias from pilot tones. The new EC updating system architecture is presented for both the central office and remote terminal systems and is fully compliant with the ITU-T G.DMT standard.

Frequency-domain echo cancellation in digital multicarrier modulation systems

The data driven frequency-domain echo canceller (EC) for a multicarrier modulation system is considered. An EC in such a system has to deal with both the interchannel and intersymbol interference occurring in the echo signal. For this reason, the main disadvantage of the data driven EC structure is the large computational complexity. Here, the solution of the computational complexity problem is presented. It is based on assumption that in practice, interchannel interference has a limited range. The number of operations per symbol as a measure of the EC computational complexity is given. Simulation results present echo attenuation in the frequency-domain EC, operating in the orthogonally multiplexed quadrature amplitude-shift keying system. Modifications of the proposed EC structure and its computational complexity in the systems with pulse shaping are discussed.

Zipper discrete multi-tone echo-canceller

A data-driven frequency-domain echo canceller for full-duplex data transmission with Zipper discrete multitone modulation is presented. It is shown that echo cancellation leads to a substantial increase in the aggregate throughput of the system while the implementational complexity is kept to a minimum of one complex multiplier per FFT output.

Frequency-domain echo canceller with phase adjustment

The frequency-domain filter is an efficient realization of an echo canceller that provides a simple and elegant solution to the problem of jitter compensation. An essential requirement for a low-error digital transmission system is that the echo canceller retains high accuracy while the sampling instant is being adjusted. One of the most attractive features of discrete Fourier transform is its capacity to reconstruct time-shifted signals using phase shifts in the frequency-domain. The signals involved, however, are not always alias-free (nor are they in telecommunications), which seriously degrades the echo cancellation. This paper introduces a de-aliasing technique, which results in an algorithm that is largely insensitive to the spectral content of cancelled signals. The de-aliasing technique allows preservation of high-performance echo cancellation during rapid changes in the sampling phase of the input signal. Computer simulations confirm the theoretically predicted behavior and accuracy.

Frequency domain echo cancellation for discrete multitone asymmetric digital subscriber line transceivers

An asymmetric digital subscriber line (ADSL) is an emerging technology for the transport of video dial tone and other new services over the telephone copper loop plant. Discrete multitone (DMT) has been selected by ANSI as the modulation scheme for ADSL transmission. Echo cancellation can be used to increase the reach or noise margin of an ADSL system by allowing both upstream and downstream channels to use the low frequency portion of the twisted pair spectrum. Previous papers have described an efficient time and frequency domain echo canceler (TAFDEC) for potential DMT ADSL application. This paper presents a generalization of this previously described canceler which, when properly optimized, results in significant complexity reduction. The generalization applies to the cyclic echo synthesizer (CES), which forms the time-domain processing portion of the canceler. By expanding the achievable CES input range and optimizing the temporal alignment between transmitter and echo canceler, ADSL CES complexity is reduced to approximately one-half of that previously described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>