NewCom dept 1 (CNRS 19)

Lab. SATIE

Benoit Geller, Jean-Pierre Barbot,

Christophe Vanstraceele, Stéphanie Bay

Phase turbo-synchronization scheme

SynchronizationProblem presentation

Transmitted Symbols Received symbols

phase rotation φNoise b

(receiver)(chanel)

00 01

10 11

ak

φk yk

1024-QAM

Synchronization

• Data Aided estimator: pilot symbols,

• Blind estimator : use properties of the signal,

• Semi-blind

Here : hight coding rate

=> use the properties of the turbo-decoder

Block Turbo-CodesProduct code

k1

k2Informative bits

redundancyon

redondancies

n2

redundancy on the columns

3. the n1 columns are coded by C2(n2,k2,d2).

The otained code C = C1 × C2

parameters are :

• n = n1 × n2

• k = k1 × k2

• d = d1 × d2

1. k1×k2 information bits in a matrix,

redundancy

on the

rows

n1

2. the k2 rows are coded C1(n1,k1,d1),

Turbo codes blocshalf an iteration of the R. Pyndiah’s Turbo decoder :

SISO decoder

(row or column)

Block Turbo codesComputation of the soft output : Log-likelihood

Evaluatation of the reliability of the Chase decision :

where :

with the concurrent code words of Ci such that

with the concurrent code words of Ci such that

Block Turbo codes

with :

= word of the code at minimal distance from R with its j ième bit at +1.

with : and

Extrinsic InformationSoft decision

Computation of the soft output : R. Pyndiah’s decoder

= word of the code at minimal distance from R with its j ième bit at -1.

Synchro : LLRLog_likelihood Distribution

Constant phase offset on a code word

demapping

turbo decoder LLR

Synchro : LLRMean of the LLR absolute value

R(l) = reliability of the l th code word.

Sort (growing order)

Rtri(l )

Absolute value

Synchro : LLRLinear drift

Phase error due to linear drift

demapping

turbo decoder M(l)

Synchro : LLREstimator definition

Transmitted symbols Received symboles

Built the sequence demapping

turbo decoder

k = 1 … K

Estimator :

Synchro : Maximisation des LLRAlgorithme du gradient

Soft demapper

Turbo decoder

Estimator

Synchro : LLRDependancy on mf

Synchro : LLRMean Square Errors

Synchro : Maximisation des LLRMean Square Errors

large constellations, low SNR,

no pilot symbols,

No Phase ambiguity,

easy to implement.

Brevet n°04O6290