Etude des nouveaux formats de modulation pour la montée en débit dans le réseau d'accès optique

recherche & développement

Etude des nouveaux formats de modulation pour la montée en débit dans le réseau d'accès optique28/03/2008 – Journée de doctorant ENSTB

DUONG Thanh Nga

Encardrant à FT: GENAY NaveenaDirecteur de thèse: SIMON Jean-Claude

recherche & développementSlide 2

Outline

Introduction Contexte

Experimentation Low-cost MB-OFDM for remote modulation of colorless ONU Direct modulation of 2.5GHz DFB laser at a bit rate of 10Gbit/s

Conclusion and perspective

1

2

3


Outline


Experimentation Low-cost MB-OFDM for remote modulation of colorless ONU Direct modulation of DFB laser at a bit rate of 10Gbit/s


1

2

3


1. Introduction (1)Interest of OFDM for the optical access network

Application Débit requis

Téléchargement des données 2 Mb/s

VoIP, Video-telephony, Videoconferencing 1 Mb/s

Musique à la demande (contenu multimédia)

2 Mb/s

Jeux en ligne 1 Mb/s

TV numérique SD 3 Mb/s

TV numérique HD 10 Mb/s

TV numérique HD canaux additionnels (2 HD DTV)

20 Mb/s


Increase the capacity and decrease the cost of the system in optical access network Increase the bit rate up to 10Gbit/s and more Increase the transmission distance up to 100km without chromatic

dispersion compensation

1. Fiber chromatic dispersion2. Rayleigh Backscattering in architecture colorless ONU3. Cost of system

Solution Low-cost ONU module Direct modulation of laser To use advanced modulation format which is robust to fiber chromatic

dispersion like DB, DPSK or OFDM modulation format



Interest of OFDM Duo-binary (DB)

Un spectre est plus comprimé que celui du NRZ Plus tolérance à la dispersion chromatique Détection simple Complexité de l'émetteur

DPSK/DQPSK Appliquer la technique remodulation La complexité du récepteur → coût élevé

DPSK/DQPSK-ASK Forte tolérance à la DC La complexité de l'émetteur et du récepteur Faible sensibilité au récepteur

OFDM Technique de transmission multi-porteuses Utiliser l'algorithme FFT/IFFT Chaque sous-porteuse est modulé par un format de modulation numérique

différent

Spectre de DB, NRZ, DPSK et RZ

Le signal modulé DPSK


What is OFDM ?

Widely use in the radio communication• DAB (Digital Audio Broadcasting)

• DVB-T (Digital Video Broadcasting-Terrestrial)

• DRM (Digital Radio Mondiale)

• Wireless system Multi-carriers modulation format which uses a large number of

closely-spaced orthogonal sub-carriers• Use FFT/IFFT algorithm

• Each sub-carrier is modulated with a conventional modulation (QPSK, m-QAM, etc…)



1. Introduction (5)Interests of OFDM for optical access network

Why we use OFDM for optical access network? High density of information (Bit/s/Hz) → increase the bit rate without

increasing RF cost (using low bandwidth component)

More tolerant to fiber chromatic dispersion (multi-path resilience) and we can optimize the transmission performance by adjusting the modulation format on each sub-carrier → 10G compatible

Could be implemented with DSP technique on fast and low cost devices

Reuse existing development in radio system (ISO/IEC DIS26908 UWB standard for MB-OFDM)

Improve the transmission performance with the help of FEC (BER = 10-4 without FEC)


Outline



Conclusion

1

2

3


2. Experimentation (1) Low-cost MB-OFDM for remote modulation of colorless ONU

Bidirectional transmission on 20km single-fiber hybrid WDM/TDM-PON architecture

CW laser at 1550nm sent downstream Upstream data was generated by MB-OFDM at 1.92Gbit/s (3 OFDM

bands at a bit rate of 640Mbit/s for each band)

CW

1xN

ONU

Rx

20km

OLT 1.92Gbit/s OFDM

CW

CW laser

CWDM

Splitter

Remote modulation


Filter: CWDM having 0.6dB insertion losses and bandwidth of 20nm

EAM: 14dB insertion losses, 10dB extinction ratio and bandwidth of 12GHz

2SOAs: 18dB optical gain 3 OFDM bands centred at 744MHz, 1272MHz and 1800MHz. 128

sub-carriers modulated by QPSK format each band

SOA1 CWDM EAM OFDM Signal

SO

A2

CW signal 1

Modulated upstream signal 1

2. Experimentation (2)Low-cost MB-OFDM for remote modulation of colorless ONU, EAM solution


Received signal's constellation


BTB transmission, upstream transmission for 1x16

splitting ratio


Remote modulation was possible on a single fiber hybrid architecture

There are 2dB penalty for 1x8 splitting ratio and 6dB for 1x16 splitting ratio


1E-12

1E-11

1E-10

1E-09

1E-08

1E-07

1E-06

1E-05

-26 -24 -22 -20 -18 -16Received power (dBm)

Bit

erro

r rat

e

1x8 band 3 1x8 band 2 1x8 band 11x16 band 3 1x16 band 2 1x16 band 1BTB band 3 BTB band 2 BTB band 1

BTB

1x8

1x16

2dB 6dB


2. Experimentation (7)Comparison with NRZ signal

SOA1 CWDM EAM NRZ

SO

A2


Remote modulation was also possible on a single fiber hybrid architecture Only a splitting ratio of 1x8 was achieved for EAM solution and no splitter

could be added for R-EAM solution (at 1.3Vp-p input at R-EAM)-error floor for 1x2 splitting ratio at 2Vp-p

1E-11

1E-10

1E-09

1E-08

1E-07

1E-06

1E-05

1E-04

1E-03

-32 -29 -26 -23 -20 -17Received power (dBm)

Bit

erro

r rat

e

1x8, 1,3Vp-p 1x8, 2Vp-p1x16, 1,3Vp-p 1x16, 2Vp-p

1E-11

1E-10

1E-09

1E-08

1E-07

1E-06

1E-05

1E-04

1E-03

-33 -29 -25 -21 -17Received power (dBm)

Bit

erro

r rat

e

no splitter, 1,3Vpp no splitter, 2Vp-p1x2, 1.3Vp-p 1x2, 2Vp-p1x4, 1,3Vp-p 1x4, 2Vp-p

EAM solution R-EAM solution

1x8

1x16

No splitter

1x4

1x2 (pour 2Vp-p)



Measured factor OFDM remote modulation

NRZ remote modulation

Architecture WDM/TDM-PON WDM/TDM-PON

Launched power laser

2dBm 2dBm

Bit rate 1.92Gbit/s 2Gbit/s

SNR 19dB (BER<10-9) 19dB (BER>10-6)

Achieved splitting Ratio (BER<10-9)

1x16 (SNR = 19dB) 1x8 (SNR = 23dB)

For EAM solution



Discussion

OFDM modulation is a good candidate as a cost effective solution for colorless ONU

OFDM format is more tolerant to Rayleigh backscattering than NRZ format in a bidirectional link

Increase the bit rate in optical access network

GPON → 10G in access

1. Fiber chromatic dispersion

2. Expensive component

3. Chirp of components

Low cost infrastructure and low cost ONU module

1. Low cost components

2. Colorless ONU

3. RF cost vs optical cost

4. Fiber single architecture

Colorless ONU 1. Rayleigh Backscattering


Outline

Introduction Interest of OFDM modulation for the optical access network

Experimentation Low-cost MB-OFDM for remote modulation of colorless ONU Direct modulation of low-cost laser at a bit rate of 10Gbit/s

Conclusion

1

2

3


Direct modulation of 2.5GHz DFB laser by 10Gbit/s AMOOFDM signal

64 sub-carriers The m-QAM mapping varies from 4-QAM to 32-QAM Transmission distance was taken to be 20km, 50km and 110km No dispersion compensation

Encoded data out

Optical receiver

A/D converte

r

DSP demodulati

on

Negotiation between Tx and Rx

S/PM-QAM mappe

r

IFFTP/S AWG DFB

laserEncoded data in

20km, 50km, 110km SMF

DSP modulation

-42

-36

-30

-24

-18

-12

-6

0

130 2130 4130 6130 8130 10130

Frequency (MHz)

Ampl

itude

(dB)

AOV

2. Experimentation (1)Direct modulation of DFB laser at a bit rate of 10Gbit/s


2. Experimentation (2)Direct modulation of DFB laser at a bit rate of 10Gbit/s

Sub No.1 Sub No.31

Sub No.23 Sub No.10


2. Experimentation (3)Direct modulation of low-cost laser at a bit rate of 10Gbit/s – DFB laser

1E-05

1E-04

1E-03

1E-02

1E-01

-16,5 -16 -15,5 -15 -14,5 -14Received Optical Power (dBm)

Bit E

rror

Rate

Back To Back20km Fiber50km Fiber110km Fibre

BERk is the bit error rate of kth sub-carrier ND is the number of sub-carrier which contain the real data

ND

kktotal BER

NDBER

1

1

The transmission is possible on 110km SMF A BER of 10-3 was obtained at a received optical power of -16dBm The penalties for 20km and 50km optical links are negligible (the sensibility is considering at BER of 10-4) The penalty on 110km optical link was approximately 2dB because of chromatic dispersion


1E-05

1E-04

1E-03

1E-02

1E-01

-20 -19 -18 -17 -16 -15 -14 -13 -12 -11 -10

Received Optical Power (dBm)

Bit

Err

or

Ra

te

20km Fiber

Back To Back transmission

Modulate directly with signal NRZ-OOK at a bit rate of 10Gb/s using the same DFB laser and receiver

There was an error-floor at a bit rate of 9x10-4 for BTB curve and at a bit rate of 3x10-2 for 20km transmission.

Transmission over 50km and 110km SMF were impossible due to the effect of chromatic dispersion AMOOFDM is more tolerant to fiber chromatic dispersion than NRZ-OOK signal

2. Experimentation (4)Comparison with NRS modulation – DFB laser


Considering factors

Direct modulation with AMOOFDM signal

Direct modulation with NRZ-OOK signal

Architecture TDM-PON TDM-PON

Launch power 9.6dBm 9.6dBm

Bit rate 10Gb/s 10Gb/s

Transmission distance possible

110 km 0

2. Experimentation (5)Comparison with NRZ modulation – 2.5GHz DFB laser


Discussion

AMOOFDM modulation is a good candidate as a cost effective solution for optical access network in order to increase the capacity (bit rate and transmission distance)

AMOOFDM format is more tolerant to fiber dispersion chromatic than NRZ format

Increase the capacity in optical access network

GPON → 10G in access

Transmission distance → 100km

1. Fiber chromatic dispersion

2. Expensive component

3. Chirp of components


Outline




1

2

3


3. Conclusion A remote modulation scheme was presented for upstream

transmission in hybrid WDM/TDM-PON single fiber architecture A solutions are proposed for the colorless ONU: EAM solution. A

bit rate of 1.92Gbit/s was archived for each wavelength Comparison between NRZ and OFDM remote modulation for both

solutions was performed OFDM format is more robust to Rayleigh Backscattered light than

NRZ-OOK modulation 10Gb/s transmission is experimentally demonstrated over 110km

SMF by direct modulation of 2GHz bandwidth DFB laser without dispersion compensation

A comparison between NRZ-OOK format and AMOOFDM format was performed at a bit rate of 10Gb/s

AMOOFDM modulation format is more tolerant with fiber chromatic dispersion than NRZ-OOK format


Thank you for your attention

Any question ?

This work was performed in the framework of E-Photon One network of excellence and the French ANTARES project


Annexe (1)

Definition of EVM

2max

2

log10log20V

VEVMSNR

m

mSNR

erfcm

BER2log

2231

12



Documents

Etude des nouveaux formats de modulation pour la montée en débit dans le réseau d'accès optique