1 Jitendra kumar Pathak, Krishna Raj International Journal of Computer & Mathematical Sciences IJCMS ISSN 2347 – 8527 Volume 5, Issue 3 March 2016 Survey on Echo Cancellation using Adaptive Filter Algorithm Jitendra kumar Pathak Dept. of Electronics Engineering H.B Technological Institute Kanpur, India Krishna Raj Dept. of Electronics Engineering H. B. Technological Institute Kanpur India Abstract: Echo cancellation is the one of the Essential and challenging part of the digital signal processing. Echo adversely affects the quality of signal which we want to process. Adaptive digital filter algorithms (like LMS, NLMS, PNLMS and IPNLMS etc.) are one of the important ways to remove Echo from the signals. In this paper we provide a survey of the main work on Echo cancellation to date. Keywords- Echo Cancellation, adaptive filter, digital signal processing, LMS, NLMS, PLMS and IPLMS. I Introduction Echo is the repetition of a waveform due to reflection from points where the characteristics of the medium through which the wave propagates changes. Echo is usefully employed in sonar and radar for detection and exploration purposes. In telecommunication, echo can degrade the quality of service, and echo cancellation is an important part of Communication systems. Echo Cancellation in Telecommunication requires identification of unknown Echo path impulse response. The length of network echo path is typically in the range between 32 to 128 milliseconds. This is characterized by bulk delay, depending on network loading, encoding and jitter delay [3]. Because of this, “active” region of echo path is in the range between 8 and 12 milliseconds, so it contains mainly “inactive” components where coefficient magnitudes are close to zero, making the impulse response sparser. In general, adaptive filters have been used to estimate the unknown echo path by using algorithms such as least-mean-square (LMS) Normalized least-mean square (NLMS) Proportionate normalized least mean square (PNLMS) and improved proportionate normalized least mean square (IPNLMS).[4] This paper is organized as follow, in section II we discuss about types of echo and their characteristics, after that in section III discuss the principle of Echo canceller in section IV we discuss about the recent work related to the Echo cancellation and finally in the last section conclusion of this literature is given. II Types of Echo A. Telephone Line Hybrid Echo Hybrid echo is the main source of echo generated from the public-switched telephone network (PSTN). Echoes on a telephone line are due to the Reflection of signals at the points of impedance mismatch on the Connecting circuits. Conventionally, telephones in a given geographical area are connected to an exchange by a 2-wire twisted line, called the subscriber's line, which serves to receive and transmit signals. For a local call, there is usually no noticeable echo either because there is not a significant impedance mismatch on the connecting 2-wire local lines or because the distances are relatively small and the resulting low-delay echoes are perceived as a slight amplification and “livening” effect. For long-distance communication between two exchanges, it is necessary to use repeaters to amplify the speech signals; therefore a separate 2-wire telephone line is required for each direction of transmission. Figure: 1 Telephone line Hybrid Echo Telephone-A Telephone-B Echo of B Echo of A Hybrid A Hybrid B Speaker Speaker