+ All Categories
Home > Documents > Equalization Techniques By: Nader Mohammed Abdelaziz.

Equalization Techniques By: Nader Mohammed Abdelaziz.

Date post: 18-Jan-2018
Category:
Upload: frank-woods
View: 228 times
Download: 0 times
Share this document with a friend
Description:
 What is the ISI Inter-symbol-interference, takes place when a given transmitted symbol is distorted by other transmitted symbols. Inter-symbol-interference, takes place when a given transmitted symbol is distorted by other transmitted symbols.  Cause of ISI ISI is imposed due to band-limiting effect of practical channel, or also due to the multi-path effects (delay spread). ISI is imposed due to band-limiting effect of practical channel, or also due to the multi-path effects (delay spread).
25
Equalization Equalization Techniques Techniques By: Nader Mohammed By: Nader Mohammed Abdelaziz Abdelaziz
Transcript
Page 1: Equalization Techniques By: Nader Mohammed Abdelaziz.

Equalization TechniquesEqualization Techniques

By: Nader Mohammed By: Nader Mohammed AbdelazizAbdelaziz

Page 2: Equalization Techniques By: Nader Mohammed Abdelaziz.

IntroductionIntroduction Wireless communication is the most Wireless communication is the most

interesting field of communication interesting field of communication these days, because it supports these days, because it supports mobility (mobile users). However, mobility (mobile users). However, many applications of wireless comm. many applications of wireless comm. now require high-speed now require high-speed communications (high-data-rates).communications (high-data-rates).

Page 3: Equalization Techniques By: Nader Mohammed Abdelaziz.

What is What is thethe ISI ISI Inter-symbol-interference, takes Inter-symbol-interference, takes

place when a given transmitted place when a given transmitted symbol is distorted by other symbol is distorted by other transmitted symbols.transmitted symbols.

Cause of ISICause of ISI ISI is imposed due to band-limiting ISI is imposed due to band-limiting

effect of practical channel, or also effect of practical channel, or also due to the multi-path effects (delay due to the multi-path effects (delay spread).spread).

Page 4: Equalization Techniques By: Nader Mohammed Abdelaziz.

Definition of the Equalizer:Definition of the Equalizer: the equalizer is a digital filter that the equalizer is a digital filter that

provides an approximate inverse of provides an approximate inverse of channel frequency response.channel frequency response.

Goal of equalization:Goal of equalization: is to mitigate the effects of ISI to is to mitigate the effects of ISI to

decrease the probability of error that decrease the probability of error that occurs without suppression of ISI, but occurs without suppression of ISI, but this reduction of ISI effects has to be this reduction of ISI effects has to be balanced with prevention of noise balanced with prevention of noise power enhancement.power enhancement.

Page 5: Equalization Techniques By: Nader Mohammed Abdelaziz.

ISI-Free Transmission System:ISI-Free Transmission System:

Page 6: Equalization Techniques By: Nader Mohammed Abdelaziz.
Page 7: Equalization Techniques By: Nader Mohammed Abdelaziz.

Components of ISI-free Components of ISI-free transmission system:transmission system: BACK> BACK>

• Pulse shape g(t), used to improve the spectral Pulse shape g(t), used to improve the spectral properties of the transmitted signal.properties of the transmitted signal.

• Matched filter, which is matched to the pulse shape Matched filter, which is matched to the pulse shape g(t), used to maximize SNR of the received signal.g(t), used to maximize SNR of the received signal.

• Sampler, to sample the signal with higher rate than Sampler, to sample the signal with higher rate than symbol-rate, and equalizer designed for the over-symbol-rate, and equalizer designed for the over-sampled signal (fractionally-spaced-equalization).sampled signal (fractionally-spaced-equalization).

• Decision device, used to round the estimated symbol Decision device, used to round the estimated symbol (o/p of the equalizer) to the training sequence.(o/p of the equalizer) to the training sequence.

• Tap-update algorithm, to update the tap coefficients Tap-update algorithm, to update the tap coefficients to improve the performance of equalizer filter.to improve the performance of equalizer filter.

Page 8: Equalization Techniques By: Nader Mohammed Abdelaziz.

BACK> BACK> ( ) ( )k

k

d t d t kT

*( ) ( ) ( ) ( )mf t g t c t g t ( ) ( ) ( )h t g t c t

( ) ( ) ( ) ( ) ( ) ( )g k b gy t d t f t n t d f t kT n t [ ] ( ) ( ) [ ] [ ] [0] [ ] [ ]k s s g s k n k

k k k n

y n d f nT kT n nT d f n k v n d f d f n k v n

Page 9: Equalization Techniques By: Nader Mohammed Abdelaziz.

methods of implementation of methods of implementation of equalizers:equalizers: Transversal structureTransversal structure which is a digital filter with N-taps that which is a digital filter with N-taps that

have a tunable complex coefficients, have a tunable complex coefficients, and N-1 delay elements.and N-1 delay elements.

Lattice structureLattice structure which uses a sophisticated recursive which uses a sophisticated recursive

structure that has some advantages structure that has some advantages such as, better stability, flexibility to such as, better stability, flexibility to change length of equalizer.change length of equalizer.

Page 10: Equalization Techniques By: Nader Mohammed Abdelaziz.

BACK>BACK>

Page 11: Equalization Techniques By: Nader Mohammed Abdelaziz.
Page 12: Equalization Techniques By: Nader Mohammed Abdelaziz.

Types of Equalization Types of Equalization techniquestechniques

Linear Equalization techniquesLinear Equalization techniques which are simple to implement, but which are simple to implement, but

greatly enhance noise power because greatly enhance noise power because they work by inverting channel frequency they work by inverting channel frequency response.response.

Non-Linear Equalization techniquesNon-Linear Equalization techniques which are more complex to implement, which are more complex to implement,

but have much less noise enhancement but have much less noise enhancement than linear equalizers.than linear equalizers.

Page 13: Equalization Techniques By: Nader Mohammed Abdelaziz.

Linear Equalizers

Zero-Forcing(ZF)

Minimum-Mean-Square-Error

(MMSE)

Page 14: Equalization Techniques By: Nader Mohammed Abdelaziz.

• Linear equalizer with N-taps, and (N-Linear equalizer with N-taps, and (N-1) delay elements.1) delay elements.

BACK>BACK>

Page 15: Equalization Techniques By: Nader Mohammed Abdelaziz.

Zero-Forcing techniqueZero-Forcing technique• It cancels all ISI effect by inverting It cancels all ISI effect by inverting

the channel frequency response, and the channel frequency response, and accordingly leads to large noise accordingly leads to large noise enhancement.enhancement.

BACK>BACK>

Page 16: Equalization Techniques By: Nader Mohammed Abdelaziz.

• Its goal of design is to minimize the Its goal of design is to minimize the expected MSE between transmitted expected MSE between transmitted symbol and its estimation.symbol and its estimation.

Page 17: Equalization Techniques By: Nader Mohammed Abdelaziz.

Non-Linear Equalizers

Decision-FeedbackEqualizer

(DFE)

Maximum-LikelihoodEqualizer(MLSE)

Page 18: Equalization Techniques By: Nader Mohammed Abdelaziz.

• It consists of a feed-forward filter It consists of a feed-forward filter B(z), and a feedback filter D(z).B(z), and a feedback filter D(z).

• It suffers from Error propagation It suffers from Error propagation when bits are decoded in error, when bits are decoded in error, which leads to poor performance.which leads to poor performance.

BACK>BACK>

Page 19: Equalization Techniques By: Nader Mohammed Abdelaziz.

• It is the optimal equalization technique, It is the optimal equalization technique, but its complexity increases but its complexity increases exponentially with the delay spread.exponentially with the delay spread.

Page 20: Equalization Techniques By: Nader Mohammed Abdelaziz.

Difference between Difference between Adaptive Equalization, and Adaptive Equalization, and Blind Equalization.Blind Equalization.

Page 21: Equalization Techniques By: Nader Mohammed Abdelaziz.

Adaptive EqualizationAdaptive Equalization• Definition.Definition.

• What is meant by: Training, and What is meant by: Training, and TrackingTracking

Page 22: Equalization Techniques By: Nader Mohammed Abdelaziz.

Blind EqualizationBlind Equalization• In which the signal recovery is done In which the signal recovery is done

by prior knowledge concerning by prior knowledge concerning channel, or by array calibration channel, or by array calibration information (no need for training information (no need for training sequence).sequence).

Page 23: Equalization Techniques By: Nader Mohammed Abdelaziz.

Table of various algorithms and their Table of various algorithms and their trade-offs:trade-offs:

algorithalgorithmm

Multiplying-Multiplying-operationsoperations

complexitycomplexity convergenconvergencece

trackingtracking

LMSLMS LowLow slowslow poorpoorMMSEMMSE Very highVery high fastfast goodgoodRLSRLS HighHigh fastfast goodgoodFastFastkalmakalmann

FairlyFairlyLowLow

fastfast goodgood

RLS-RLS-DFEDFE

HighHigh fastfast goodgood

2 3N toN2 1N

22.5 4.5N N

20 5N

21.5 6.5N N

Page 24: Equalization Techniques By: Nader Mohammed Abdelaziz.

Some performance figures:Some performance figures:

Page 25: Equalization Techniques By: Nader Mohammed Abdelaziz.

Recommended