Low-Power and High Speed Robust Sub Band Adaptive

7/29/2019 Low-Power and High Speed Robust Sub Band Adaptive

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Low-Power and high speed Robust

sub band adaptive echo

cancellation on FPGA hardware

By Under the Guidance of

A.Geetha Pravallika M.Madhusudan Reddy

119X1D6801 Asst.Professor


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Aim of the Project

The term echo cancellation is used in telephony todescribe the process of removing echo from a voicecommunication in order to improve voice quality ona telephone call.

Echo cancellation involves first recognizing theoriginally transmitted signal that re-appears, withsome delay, in the transmitted or received signal.

Once the echo is recognized, it can be removed by'subtracting' it from the transmitted or receivedsignal.


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Block diagram of Echo Cancellation


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The main blocks are:

DDS(Direct Digital Frequency synthesizer)

Analysis Filter bank

DLMS

Synthesis Filter bank


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Block diagram of Direct Digital

Frequency Synthesizer (DDS)


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Direct Digital Frequency Synthesizer is a

technique to produce desired output

waveforms with full digital control.

DDS consists of

Registers

Adders LUTS


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The phase accumulator consists of phase

increment register, adder and phase register.

The phase increment register stores the

instantaneous phase increment values

resulting from frequency modulation control

block.

The phase register holds the instantaneous

phase for each clock pulse.


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Analysis filter bank

In Analysis filter bank, wide band of frequency

will be divided into many sub-bands and those

sub-bands are then subjected to equalization.

The divided sub-bands are then combined at

the synthesis filter bank. The block diagram is

shown below.


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Block diagram of Analysis Filter

Channe

l Receiver

SUB BAND OF FREQUECY




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Delayed Least mean square(DLMS)

In this algorithm, the estimated signal in each

data interval is computed and subtracted from

the desired signal .

DLMS algorithm can be used to adjust the

filter coefficients to reduce the interference.

DLMS algorithms are a class of adaptive filter.


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Block diagram of DLMS algorithm


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Synthesis filter bank

After the signal is decomposed by the analysis

bank, each signal is reconstructed using a

synthesis bank structure.

This structure is composed of filters and

up-sampling that reconstructs each signal to

its original sampling rate.


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Block diagram of synthesis Filter


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Applications

Total Echo Removal

1. No echo at the beginning of the call

2. No Echo throughout the call - call is stablewithout bursts or distortion

3. Residual Echo (low-level) is absent

throughout the call


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Future scope

Effective implementation of echo cancellation

across the network holds the key to improving

call quality and ultimately, strengthen

customer satisfaction, boost revenues, and

reduce subscriber churn.


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References

Low-Power Reconfgurable Acceleration of Robust

Frequency-domain Echo Cancellation on FPGA

Wai-Chung Tang*, C. H. Hot, Chiu-Wing Sham and K. F C. Yiut

IEEE 2010

Reconfigurable acceleration of robust frequency-domain echocancellation

ChunHokHo,KaFaiCedricYiu ,JiaquanHuo ,SvenNordholm andWayneLuk

Low-Power and High Speed Robust Sub Band Adaptive

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