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
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