Turbo-synchronization

Turbo-synchronization

Friday, March 19 2004 Sébastien de la Kethulle de Ryhove – Turbo-synchronization

Introduction

• Communication systems based on the turbo principle

• Remarkable performances

• Ideal synchronization


Transmission System


The Turbo Principle

Compute soft information on the transmitted symbols using an

iterative receiver


Soft / Hard Information

• Hard approach

• Soft approach


The Turbo Principle

• Applicable to a wide variety of problems:

– Decoding: Turbo-decoding– Decoding + equalization: Turbo-equalization– Decoding + demodulation: Turbo-demodulation– …

• Turbo detection


Example: Turbo-demodulation

Transmitter


NSC Encoder


Grouping and Mapping


Example: Turbo-demodulation

Receiver – Exchange of soft information


Synchronization

• Find estimates for

– The carrier frequency

– The carrier phase

– The sampling time


Synchronization

Classical receiver


Turbo-synchronization

Soft receiver


Soft Synchronization – Example

• Traditional DD synchronization

• Soft DD synchronization


Algorithm: Soft Phase SynchronizationInitialize /* many possibilities */

do {

Correct the phase of the received sequence

Perform one soft det./dec. iteration on the corrected sequence

Find a new estimate for using the newly obtained soft information

} while ( changes a lot)

/* Continue with detection / decoding */


BER Performance

-150 -100 -50 0 50 100 15010

-5

10-4

10-3

10-2

10-1

100

Performances d'un système turbo codé en présence d'une erreur de phase

Erreur de phase (degrés)

Taux

d'e

rreu

r bi

naire

Eb/N

0 = 1 dB

Eb/N

0 = 2 dB

Eb/N

0 = 3 dB

Phase offset [degrees]

BE

R

BER Performance vs. Phase Offset for a Turbo Coded system


Mean Estimated Phase Offset

0 20 40 60 80 100 120 140 160 180-100

-50

0

50

100

150

200

Eb/N

0 = 1.0 dB


Pha

se m

oyen

ne e

stim

ée (

degr

és)

Idéal Méthode traditionnelle (ML NDA)Méthode douce (Soft DD)


Me

an

Est

ima

ted

Ph

ase

Off

set

[de

gre

es]


Estimator Variance

0 20 40 60 80 100 120 140 160 18010

0

101

102

103

104

105


Var

ianc

e de

l'es

timat

eur

(deg

rés2 )

Eb/N

0 = 1.0 dB

Borne théorique Méthode traditionnelle (ML NDA)Méthode douce (Soft DD)


Est

ima

tor

Va

rian

ce [

de

gre

es2

]


BER Performance

0 20 40 60 80 100 120 140 160 18010

-3

10-2

10-1

100

Eb/N

0 = 1.0 dB


Taux

d'e

rreu

r bi

naire

Idéal Méthode traditionnelle (ML NDA)Méthode douce (Soft DD) Pas d'estimateur


BE

R


Estimator Variance

0 0.5 1 1.5 2 2.510

0

101

102

Erreur de phase = 30 degrés

Eb/N

0 (dB)

Var

ianc

e de

l'es

timat

eur

(deg

rés2 )

Borne théorique Méthode traditionnelle (ML NDA)Méthode douce (Soft DD)

Phase offset = 30 degreesE

stim

ato

r V

aria

nce

[d

eg

ree

s2]

Eb / N0 [dB]


Performances – Acquisition

1 1.5 2 2.5 3 3.5 4 4.5 510

-5

10-4

10-3

10-2

10-1

100

Préambule: 7 symboles 16-QAM

Eb/N

0 (dB)

Taux

d'e

rreu

r bi

naire

Méthode Soft DD Méthode Hard DD Méthode DD TraditionnelleIdéal

BE

R

Preamble: 7 16-QAM symbols

Eb / N0 [dB]


Conclusions

• Performance enhancement– Synchronization algorithms– Overall system

• Encouraging results

Documents

Turbo-synchronization