R cents Travaux sur le CDMA Optique - Telecom Paris

Récents Travaux sur le CDMA Optique!

Philippe Gallion et al "

pour le Consortium CEM2 Montpellier, ENSIL & ENST, "

CDMA Marcoussis, 25 Oct 2005" 2"

Le Consortium !CEM2 Montpellier, ENSIL & ENST !

!! CEM2 Montpellier "

"! Yves MOREAU"

"! Guillaume PiLLE"

!! ENSIL "

"! Jean Michel DUMAS"

"! Christelle AUPETIT-BERTHELEMOT"

"! Anne JULIEN-VERGONJANNE"

!! ENST"

"! Philippe GALLION "

"! Catherine LEPERS"

"! Mounia LOURDIANE"

"! Ihsan FSAIFES"

!! Avec le soutien de"

"! CNRS"

"! France Télecom R&D (Philippe GUIGNARD)"


Outline"

1.! Le CDMA en RF"

2.! Le CDMA en Optique, Pourquoi ? Comment ?"

3.! Les Codes Optiques 1D et 2D"

4.! Les Implémentations «Tout Optique » "!! Temporelle par Réseaux de Bragg"

!! Spectrale par Optique intégrée"

5.! Les Implémentations Electrique/0ptique "

Conclusion"


Outline"

1.! Le CDMA en RF"



4.! Les Implémentations «Tout Optique » "

!! Temporelle par Réseaux de Bragg"


5.! Les Implémentations Electrique/0ptique"

Conclusion"


t

f

t

f

t

f

t

f

Attribution de

fréquence

FDMA

Radiodiffusion

Etalement

de spectre

TDMA

Saut de fréquence

GSM (Europe)

1ms X 200kz

Accés multiple par

code

CDMA

IS95 CDMA (USA)

Sharing 2 Increasingly Rare Resources:!Time and Frequency"

"!Allocation bidimensionnelle aléatoire et dynamique"

"!Signature (code) spectrale et temporelle"


Une Origine Hollywoodienne"

!! Actrice Hedy Lamar et George Antheil"

!! Brouillage du guidage radio des torpilles par des sauts de fréquence"

!! Brevet en 1941"


Initial CDMA Motivation"

!! Spread spectrum technique developed for the military"

"! Resistance to jamming"

"! Low probability of intercept"

!! “Civil” Properties"

"! Resistance to multi-path effect (selective fading)"

"! Multi-user interference turns to AGWN for a large number of it"

"! Opening of unlicensed Band (Trojan Horse)"

"! Software resource allocation"

"! Fair resource sharing"

"! Cell size adaptation"

!! Today applications"

"! Cellular mobile systems (IS95)"

"! Wireless local Area Networks (WLAN…)"


Data sequence"

t"

t"

Code sequence user #1"

t"

CDMA transmitted signal"

Bipolar Code Sequence"

1 –1 1 1 1 –1 –1 1 –1 -1"

t"

Unipolar Code Sequence"

1 0 0 0 0 0 1 0 0 1 0 0 "

t"

Antipodal Signal On Off Keying Signal

Time Domain CDMA Principle"

!! Bit duration is divided in L time slots (chips)""! TB is the bit duration"

"! Tc is the chip duration"


Excess bandwidth is not (necessarily) wasted"

!! Channels sharing the same spectrum are simultaneously used"

!! No intrinsic gain using hard (single user) decision"

"! No area gain in the Time-Frequency space"

"! Repartition of resource shortage effects between users"

!! Number of users may be improved by soft (multi user) decision"

"! Other users are considered as signals"

"! Their contributions must be larger than others noise"

"! Decision on chips is mandatory"

!! Total number of users : "

"! Equals the allowed number active of users by using deterministic code attribution"

"! Larger, by using random code attribution (Overbooking)"


Today CDMA Doubts in RF"

!! Near/far field effects leading to power divergence"

!! High density operation questioned"

!! Qualcomm patent monopole"

!! Is it a future for UMTS ??"

"! Price"

"! 200 000 subscribers in France 200kbit/s"

"! Killed by WiFi (Hot spots) and WiMax (WMAN i.e. wireless ADSL) ? "

!! Chinese 3G"

"! Required by only voice applications, "

"! Do not (exactly) use it (TD-SCDMA)"

!! 4G ??"

"! OFDM (Multicarrier MC) ? "

"! MC-CDMA ??"


Outline"

1.! Le CDMA en RF"







Conclusion"


!! Low loss-High bandwidth""! Optical “passive” transport between electronically

intelligent nodes"

"! Bottleneck of O/E and E/O conversions"

!! Non Linear Optical Signal processing ""! In line signal processing, GVD and PMD compensation,

Soliton"

"! All Optical , 3R…"

"! WDM, OTDM"

"! OXC, OAD, ! Routing"

"! MUX, deMUX"

!! RF/Opto"

!! New optical layer functions""! FTTx"

"! From circuit to packet"

"! Transparency"

"! Quantum Cryptography"

"! CDMA"

"! Digital Optics…."

Metropolitan network"

Access Network"

Transport network"

Optical Technologies Down to the End User"


CDMA Interest in Optics"

!!Achieving communication access, free of network control"

!!Asynchronous emission of the users"

!!Cost reduction of network installation"

!! Improvement of multiplexing capacity"

!!Transformation of low elementary access application bit rate into high bandwidth signals more appropriate to the high optical channel bandwidth"

!!Multiple Access Interference (MAI) apparition threshold higher in the noisy amplified optical channel (ASE)"

!!Privacy, Security"


Difficulties for CDMA Implementation in Optics"

!!Bandwidth extension is not free of fiber dispersion"

"!Not strongly relevant for access"

"! 1300nm"

!!Only direct detection is compatible with low cost implementation"

!!Difficulty for numerical optical random sequence generation""!Only analog (chaotic) optical signal is easy generated"

"!Deterministic digital code attribution"

#! Reduction of the number of active users "

#! No statistical multiplexing"

#! Privacy reduction"

!!Difficulty for classical electronic logic function implementation"

"! Single XOR (addition mod 2) gate demonstrated with bulk optics"

"!No large scale integration expectable today"


Time and/or Frequency Domain!Optical CDMA Techniques?"

!! Temporal coding Techniques"

"! Standard Optical sources "#! Narrow band (Coherent)"

#! Low noise"

#! High power"

#! Low cost"

"! Low dispersion sensitivity"

!! Spectral coding Techniques"

"! Sliced or filtered wideband optical Source"#! Amplified Spontaneous Emission (ASE)/Supercontinum"

#! High relative intensity noise"

#! Beatings noise"

"! High dispersion sensitivity"

!! Multi-wavelength & temporal Techniques""! WDM/CDMA : Independent CDMA on different wavelength"

"! Fast (Optical) Frequency Hoping (FFH)/CDMA : A given sequence uses several wavelengths"


Outline"

1.! Le CDMA en RF"




!! Temporelle par Réseau de Bragg"



Conclusion"


Code Sequence Properties"

!!Code Sequence = Address Code = Signature Sequence"

!!Extraction of data encoded with a given sequence from all other sequences"

!!Each sequence easily distinguished from any time delayed version "

"!Of itself"

"!Of every other sequence in the set"

!! “Good” correlation properties"

"!Nearly Dirac delta autocorrelation functions"

"! Low level cross correlation functions"

"! Robust (or improved) by asynchronism"


!!Code parameters"

"! Code length L : number of chips "

Frequency spreading"

"! Code weight w : number of chips equals to 1"

Energy per bit"

"!Maximum number of active user N!Multiplexing capacity!

!!Code Sequence is a periodic signal with period LTc :"

0123456789…………………………l…….. L-1

Sequence: {0,4,9,l}

Weight = 4

Code length = L

T = L Tc

Code Sequence Parameters"


!! Optical codes are Quasi-Orthogonal Codes"

!! Correlation function are not equals to 0"

"! For any sequence x = {xn}, and any shift l , self correlation is : !•! Less or equal to 1 for l #0, "

•! Equal to code weight w and for l =0 the "

"! For each pair of sequence x = {xn} and y = {yn}, and any shift l , the cross correlation is less than 1"

!! Only a one chip collision is allowed"

!! Intrinsic multi user interference"

!! Unsynchronized chip may reduces the residual correlation"

Optical Codes"


Selecting an Optical Code"

Optical Orthogonal Codes"

(OOC)"

" " - L : Code Length"

" " - ! : Code weight "

" " - N : Number of users"

Code 1 : 110001000000000000000"

Code 2 : 101000001000000000000"

Code 3 : 100100000010000000000"

3"21"3"

Optical Orthogonal Codes (OOC)"!!L!N!

Prime Sequences"

(PS)"

" p is a prime number:"

" - L = p2 : Code Length"

" - ! = p : Code weight "

" - N = p : Number of users"

Code 1 : 100100100"

Code 2 : 100010001"

Code 3 : 100001010"

3"9"3"

Prime Sequences (PS)"!!L!N!

!!Prime Sequences offers shorter code length for given number of users"

!!Low weight leading to low SNR"

!!Importance of correlations properties


Type de codage 1D"

(temps/longueur d’onde)"

Dimension du code"(m,n)"

Cardinalité"N"

Valeur de l’inter corrélation"

Prime/OOC" L.p2" L. Nooc. p" 1"

Prime/prime" p.p2" p.(p-1)" 1"

EQC/prime" p2.(2p-1)" p.(p-1)2" 2"

prime/EQC" p.p2" p2.(p-1)" 2"

OOC/prime" p*L" Nooc.p2" 1"

OOC/OOC" L*L" Nooc. L.(L+1)" 1"

Codage en 2D ( Longueur d’onde -Temps)"

!! Code 2D = 2 x codes 1D"

"! En temps (n)"

"! En longueur d’onde (m) "

!! Plus grande capacité

p : nombre premier; L longueur du code OOC; Nooc cardinalité du code OOC


Outline"

1.! Le CDMA en RF"


3.! Les Codes Optiques 1D, 2D"





Conclusion"


From Bits to Chips and Chips to Bits Optically ?!(All Optical CDMA Technique)!

!! Temporal coding Techniques :"

"! Bragg grating fiber"

"! Fiber parallel optical delay lines"

"! Series/parallel fiber cascade"

!! Spectral Coding"

"! AWG and MMI optical integrated circuit"

"! Fourier focal plane intensity or phase filtering"

!! Advantages"

"! Overcome O/E and E/O conversion bottleneck"

"! Passive and low cost implementation"

!! Drawbacks"

"! Deterministic (Hardware) sequence allocation"

"! Multi-user detection impossible"

"! Sequences generation limited"


Sampling Bragg Grating (SBG) Encoder"

!! Passive, Integrability, Compactness and Low Cost "

!! 50ps initial chip pulse is launched in a SBG"

!! Bragg grating reflexions produce the chip sequence"

!! Reflected chip pulses collected by an optical circulator "

!! Bit duration is (9+1) = 10 times the chip duration"

!! A maximun rate of 2Gbit/s per user can be implemented"

Input pulse

Tc =50ps LFBG1-FBG2 LFBG2-FBG3

FBG1 FBG2 FBG3

S-FBG

R1

R2

R3

"B =1551nm

Bit rate : 2 Gb/s"

Chip rate : 20 Gb/s"


Photodiode and Oscilloscope

BG1 BG2 BG3

Decoder 1 or 2

Optical

Fiber

Data

EOM ILM

SG

Circulator

Encoder 1

BG1 BG2 BG3

Clock

EOM ILM

3 dB Coupler

SG

Data Circulator

BG1 BG2 BG3

Clock

Encoder 2

Optical

Amplifier

DS-OCDMA Multiplexing System"

May be! by-passed!

for back to back configuration"


Experimental results (1)"

Code 1 (100100100)" Code 2 (100010001)"

Code Generation Checking"


Experimental results (2)"

(a)! Back to back self correlation function"

(b)! Self-correlation function after 15 km optical fiber"

(a)! Back to back self-correlation function (2 users)"

(b)! Back to back cross-correlation function (Mismatched decoder)"

Negligible impact of dispersion in short range metropolitan and access networks

Auto and Cross-Correlation Functions"


Multiuser "Maximun "

Theoritical"

Single User"Theoritical"

Single User"Measured"

Assynchronous Multi User"Measured"

Optical Power at the amplifier Input (dBm) "

BER"

Bit Error Rate (BER) Measurement"

Multi user"Synchronous "

A theorytical model has been developped for the amplified CDMA channel"


Outline"

1.! Le CDMA en RF"


3.! Les Codes Optiques 1D, 2D"





Conclusion"


Système CDMA Spectral en Optique Intégrée !!!CDMA spectral"

"!Haut débit : pas de subdivision temporelle du bit

"!Dispersion élevée mais peu sensible en accès

!!Optique intégrée"

"! Fabrication de masse

"! Pas d’alignement"

"!Compact"

Les codes spectraux (combinaisons de longueurs d’onde) sont synthétisés grâce à des filtres en ! et des coupleurs en Y pour

regrouper les sorties.

0

0,05

0,1

0,15

0,2

0,25

0,3

1,302 1,3036 1,3052 1,3068 1,3084 1,31 1,3116 1,3132 1,3148 1,3164

Spectre 0

Spectre 1


Encodeurs/Décodeurs : Filtres en !!!!Emission"

!!Detection différentielle"

!!Deux types étudiés à l’Université de Montpellier: "

"! Réseaux de guides avec MMI ( codes de type Hadamard Walsh)"

"! Star-couplers avec AWG ( codes de type M séquences)"


Encodeur/Décodeur :! Réseaux de Guides et MMIs -1/2 !

!!En sortie n images de l’entrée avec phases différentes"

!!Changement d’entrée"

"! Permutations des phases"

"! Permutations des longueurs d’onde en sortie"

"! Changement de codes"

!!Les sorties donnent les longueurs d’onde dans un ordre aléatoire"

!!Sorties adjacentes : spectres cannelés"


Encodeur/Décodeur :! Réseaux de Guides et MMIs -2/2"

!!Souplesse du multiplexage"

"! Le même dispositif implémente tous les codes"

"! Simple changement d’entrée pour changement de code"

!!Contrôle de fabrication difficile si nombre d’entrées important "

!!Performances du filtrage en longueur d’ondes non contrôlable:"

"!Nombre de guides imposé = nombre de sorties "

!!Nombre de codes orthogonaux réduits"


Encodeur/Décodeur :!Star-Coupleur+Phasar (AWG)"

!! Fabrication mieux maîtrisée (AWG)"!! Performances théoriques supérieures (MMI)"!! Plus de bras, moins de MAI"!! Sorties ordonnées nécessitant un croisement des fibres"!! Peu de pertes si angles de croisement >40°"


CDMA avec dispositif AWG !!! Les Codes"

"! m-séquences possibles (générées à partir de 001101011110001)"

"! Propriétés statistiques de suite pseudo aléatoire : auto corrélation optimale … "

" " Chip de rang k : 1 =>ln utilisé pour le spectre du «$1$»"

" " Chip de rang k : 0 =>ln utilisé pour le spectre du «$0$»"

"! Un nouveau code quasi-orthogonal est obtenu par décalage"

!! Implémentation""! Décalage d’une entrée => Permutation des longueurs d’onde en

sortie "

"! Changement de code par changement d’entrée"

!!Réalisation d’un démonstrateur en cours""! Université -Montpellier"

"! KLOE S.A.


Outline"

1.! Le CDMA en RF"







Conclusion"


From Bits to Chips and Chips to Bits Electrically ?"

!!Advantages"

"! Random sequence allocation"

"! Easily implemented"

"! Realistic"

"! Electrical signal processing possible"

"!Multi-user detection possible"

"! Convenient for Hybrid Fiber Radio interface"

!! Drawbacks""! Enlarged electrical bandwidth"


Implantation Electrique du Codage/Décodage OCDMA"

Source

des données

Conversion

Optique/

Electrique

Décodage

CDMA

Conversion

Electrique/

Optique

Domaine Electrique – Réception

Domaine Electrique – Emission Domaine Optique

Codage

CDMA


Limitations !liées à la bande passante électrique"

!! Le produit débit x longueur de code (DxL) limité par la BP B"

!! Compromis entre""! Longueur du code L""! Nombre d’utilisateur N""! Performance (BER)"

!! Exemple, B = LD = 10Ghz"

"! Pour N=30 D = 155 Mbit/s ND = 4.65 Gbit/s"

"! L< 64 donc Interférences d’Accès Multiple"

Les codes courts génèrent plus d’IAM (à poids donné)"

Codage

Electronique

D"DxL

Conversion

Electronique-

Optique DxL"

Solution « électrique »" à l’émission"

Données


Les Différents Récepteurs"

1- Réception Conventionnelle (Intégateur comparateur)"

2 - Réception Conventionnelle"

" avec «$hard-limiter$»"

3- Réception par annulation successive d’interférences série"

4 - Réception par annulation successive d’interférences parallèle"

" (Multi user reciever)"

) ( 1 t c

) ( t c k

) ( t c N

Modulateur

Optique

Modulateur

Optique

Modulateur

Optique

C

o

u

p

l

e

u

r

Fibre

Optique

Utilisateur #1 ) 1 (

i b

Utilisateur #k ) ( k

i b

Utilisateur #N ) ( N

i b

PIN ou

APD

Signaux électriques Signaux optiques

Signaux électriques


Performances d’un Traitement Electrique"

CCR = Conventionnel"

HL+CCR = Hard Limiteur +CCR"

SIC = Serie Interference Cancellation"

PIC = Parallele interference Cancellation"

codage 1D OOC ( L,W)" Codage 2D OOC (5,56,5)"


Forward Error Coding (FEC)!

!!Shannon Limit""!BER = 0.1 corrected to 10-9 "

"!0.5 efficiency"

!!Reed Salomon ""!BER = 10-4 corrected to 10-9"

"!0.9 efficiency"


Conclusion"

!! Great interest in OCDMA for access networks "

!! Wide range of possible implementations"

"! Time domain, Direct sequence"

"! Spectral encoding"

!! Low cost implementation technology is a key issue"

"! Fiber Bragg gratings for time domain direct sequences"

"! Integrated optics for spectral en coding "

!! Electrical vs all optical receiver implementation"

"! Electrical signal processing"

"! Wireless Network interconnect"

!! Forward Error Coding"

!! Not yet a dynamic resource allocation ?"

R cents Travaux sur le CDMA Optique - Telecom Paris

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