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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
recherche & développementSlide 3
Outline
Introduction Contexte
Experimentation Low-cost MB-OFDM for remote modulation of colorless ONU Direct modulation of DFB laser at a bit rate of 10Gbit/s
Conclusion and perspective
1
2
3
recherche & développementSlide 4
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
recherche & développementSlide 5
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
1. Introduction (2)Interest of OFDM for the optical access network
recherche & développementSlide 6
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
recherche & développementSlide 7
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 (3)Interest of OFDM for the optical access network
recherche & développementSlide 8
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)
recherche & développementSlide 9
Outline
Introduction Contexte
Experimentation Low-cost MB-OFDM for remote modulation of colorless ONU Direct modulation of DFB laser at a bit rate of 10Gbit/s
Conclusion
1
2
3
recherche & développementSlide 10
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
recherche & développementSlide 11
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
recherche & développementSlide 12
Received signal's constellation
2. Experimentation (3)Low-cost MB-OFDM for remote modulation of colorless ONU, EAM solution
BTB transmission, upstream transmission for 1x16
splitting ratio
recherche & développementSlide 13
Remote modulation was possible on a single fiber hybrid architecture
There are 2dB penalty for 1x8 splitting ratio and 6dB for 1x16 splitting ratio
2. Experimentation (4)Low-cost MB-OFDM for remote modulation of colorless ONU, EAM solution
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
recherche & développementSlide 14
2. Experimentation (7)Comparison with NRZ signal
SOA1 CWDM EAM NRZ
SO
A2
recherche & développementSlide 15
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)
2. Experimentation (8)Comparison with NRZ signal
recherche & développementSlide 16
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
2. Experimentation (9)Comparison with NRZ signal
recherche & développementSlide 17
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
recherche & développementSlide 18
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
recherche & développementSlide 19
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
recherche & développementSlide 20
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
recherche & développementSlide 21
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
recherche & développementSlide 22
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
recherche & développementSlide 23
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
recherche & développementSlide 24
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
recherche & développementSlide 25
Outline
Introduction Contexte
Experimentation Low-cost MB-OFDM for remote modulation of colorless ONU Direct modulation of DFB laser at a bit rate of 10Gbit/s
Conclusion and perspective
1
2
3
recherche & développementSlide 26
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
recherche & développementSlide 27
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
recherche & développementSlide 28
Annexe (1)
Definition of EVM
2max
2
log10log20V
VEVMSNR
m
mSNR
erfcm
BER2log
2231
12
recherche & développementSlide 29
1. Introduction (4)Interest of OFDM for the optical access network