Acoustic echo:  they are generated with analog digital technique and there degree is related to their quality and quantity. When the coupling between devices like microphone and earphone are poor then this type echo is produced.

Hybrid echo: they are primary source of echo generated from PSTN (public switched telephone network. They are generated when hybrid connection is created with four wire PSTN conversion point

Cause: they are created when background noise through network is interfered and when analog and digital signals are operated from hands free mode. Sometimes additional sounds are mixes in the microphone and that is transmitted back to the user or sometimes due to bad quality of wireless network.

Echo cancellation: Echo problems can be overcome by some following some principles. We record the voice going in loudspeaker and later remove it from microphone when coming out. Also adaptive filtering

Echo suppression: first identify the echo then suppress it with help of gain control, this prevents howling effect, or we can also interrupt other party speech.

Importance: to deliver best quality of communications over telephone conversation as hybrid is still not proper for transmitting electrical energy or voice transmission because they are reflected back or perceived as echo.

During telephone conversation sound waves is transmitted that travel earpiece and when we speak it return through microphone.

Today, in AEC systems multipath-path echo, time difference echo, grouped echo and noise reduction have been major problems to be thoroughly studied when designing system.

Conclusion: echo cancellation has become complex device for highly complex networks. All cellular networks are using this technique to make their service better, better network performance and reduce customers complain.

Download Echo Cancellation PPT and Seminar Report .