EECS0712 Adaptive Signal Processing 2 Introduction to ...€¦ · EECS0712 Adaptive Signal...

EECS0712 Adaptive Signal Processing

2

Introduction to Adaptive Signal Processing (II)

Assoc. Prof. Dr. Peerapol Yuvapoositanon

Dept. of Electronic Engineering

EECS0712 Adaptive Signal Processing http://embedsigproc.wordpress.com/eecs0712

Assoc. Prof. Dr. P.Yuvapoositanon ASP2-1

Content

• Digital Filters

• Overview of Adaptive Signal Processing Applications



Digital Filters

• Digital Filters is a digital device adjusting frequency and magnitude

• There are two types of Finite Impulse Response (FIR) and Infinite Impulse Response (IIR)

– FIR has no feedback

– IIR has feedback



• An FIR filter has no feedback

Finite Impulse Response (FIR)

DelayDelay



Infinite Impulse Response (IIR)

• An IIR filter has feedback

FeedbackFeedback



Transfer Function I

• Transfer function= A ratio of z-transform

• Z-Transform

z -Transform



Transfer Function

• Transfer function



Use z-Transform to find Frequency Response

• Replace z with ,



Frequency Response from Poles and Zeros



Zk= Zeros

Pk= Poles

Magni tude of

response at omega

Example

Example for Frequency Response



Example for Frequency Response

• Put together



To Summarise…

The coefficients of a Digital Filter determine the desired

frequency response.



Overview of Adaptive

Signal Processing



Why we need adaptive?

• Because environment is always changing.

• System needs to be adaptable.

• In electrical engineering, the environment is systems defined by transfer function.



Multipath in Wireless Communications



• Signal from transmitter may reach receiver with multipath signals

Multipath

Channel Equalisation

11 00 11 00

11 00 11..33

..66

Without multipath

With multipath


Assoc. Prof. Dr. P.Yuvapoositanon 16

Channel

Loss of Info.

set(gcf, 'Color', [1 1 1]) movie2avi(M,'tx_signal')


Frequency fading channel

• Multipath Channel is also called Frequency fading channel

ff tt

Fourier Transform

ff tt

H(f)=1

H(f)



Without multipath

With multipath

Fading

Channel Equalization

11 00 11 00

11 00



Channel

ff

ff

H(z)=1

H(z) 11..33

..66



Basic Equalization II

• If we knew the channel H(z), we put a filter W(z) at the receiver



Channel Digital

Filter

H(z)

xx 11 00 11 00

11..33

..66

W(z)

H(z) x W(z) = 1




Basic Equalization III

• Equaliser is an inverse channel estimation

Channel Equalizer

H(z) W(z)=1/H(z)

xx



11 00 11 00

11..33

..66

W(z)= H-1(z)




Basic Equalization II

• Adaptive Equaliser finds H-1(z) automatically

Channel Adaptive

Equalizer

H(z)

xx

++ ee

dd

yy ++

-- xx



11 00 ..66

11..33




LMS Adaptive Algorithm

• error= d-y New value = Old Value + Step * Error* Input

w(n)=w(n-1) + mu*e(n)*x(n)

For n=1:N

end

e(n)= d(n)-y(n)

AlgorithmAlgorithm



To Summarise…

The coefficients of Adaptive Equaliser are adapted to the

inverse channel H-1(z).



LMS Algorithm Block

• บล็อก LMS

Normalization



Example of Adaptive Equalization

• Least Mean Square (LMS) for Adaptive Equalizer



Signal+Noise, Signal and Error2



Trend of Error2

Equalizer Response



Final Tap weights



• Anti phase =Cancellation

Basic of Noise Cancellation

FeedbackFeedback ANCANC

NoiseNoise Pilot MicPilot Mic

LoudspeakerLoudspeaker

Quiet zone Quiet zone

nn

nn --nn



Active Noise Cancellation Headphones

• ANC Headphones

LXLX--18 18 Active Noise Cancelling HeadphonesActive Noise Cancelling Headphones



Diagram of Active Noise Cancellation Headphones

H(z)H(z)

nn nn

yy

11 22

33

H(z) =Acoustic Transfer Function

Ext.MicExt.Mic

Pilot Mic Quiet Zone



Speaker

DSP Adaptive Algorithm

ANC

LoudspeakerLoudspeaker

AlgorithmAlgorithm

++

Exterior MicExterior Mic

ee

yy nn

Pilot MicPilot Mic

nn

ANCANC

FIRFIR



ANC Simulink Model

• Dspanc_win32.mdl



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