Abstract
Echo signal is the delayed form of an electrical or acoustic signal and it occurs when it returns to its source, in other words when acoustic signal finds its way from sending route through receiving one. One of the important parameters in discussing echo is delay time. In practical applications, if round trip time exceeds 30 milliseconds and echo power also exceeds 30 decibels, echo cancellation should be done. Today given the developments in utilizing communication system and transmitting acoustic information, echo cancellation becomes very important. There are different algorithms for cancelling echo of acoustic signals and each of them has both advantages and disadvantages. Adaptive filters are appropriate for echo cancellation. In such filters, minimization of the computational complexity and quick convergence of adapting is done within frequency domain owing to long impact response. In this study, different adaptive algorithms such as LMS, NLMS, VSLMS, VSNLMS and RLS have been suggested which can be used for echo cancellation and finally, a combination of them as an optimal algorithm was simulated for echo cancellation. In this paper, the stages of determining filter coefficients and the level of computational work in terms of convergence behavior, simulation results and other methods’ results were compared and it was found that using NLMS and MAX-E algorithms would offer best results in different situations. Innovative aspects of this paper include using adaptive algorithms in their real time and we can minimize the computational work of these algorithms and maximize the convergence speed by selecting accurate filter coefficients and the window used in computations. Also, we can use it in current applications and even in sound conversations on some communication networks like internet. Other aspects include using adaptive algorithms in implementing echo cancellation that have better function and convergence compared to blind methods of echo cancellation and they contribute to quality improvement of sent signals in conversations.
Highlights
Echo signal is the delayed form of an electrical or acoustic signal and it occurs when it returns to its source, in other words when acoustic signal finds its way from sending route through receiving one
In communication systems such as telephone, when acoustic signal echo reflects from barriers like door, wall, ceiling, etc. it reflects back to our ears through a microphone embedded in the second acoustic source
Each of the above algorithms have been simulated by a software and in every simulation, echo signal has been obtained by specifying impact response and its convolution with input acoustic signal
Summary
Echo signal is the delayed form of an electrical or acoustic signal and it occurs when it returns to its source, in other words when acoustic signal finds its way from sending route through receiving one. In the late 1970s, the system designed by Comsat Tele Systems found many applications and for the first time it sold commercial analog echo canceller. [3] When the output of an adaptive filter changes into signal, error signal becomes zero and in this way echo is completely cancelled so that acoustic source does not receive its own transmitted signal reflection. Nowadays, different algorithms such as LMS, NLMS, VSLMS, VSNLMS, RLS and so on are used for echo cancellation. Different algorithms such as LMS, NLMS, VSLMS, VSNLMS, RLS and so on are used for echo cancellation. [9]
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