coherent optical code division multiple access (ocdma) systems pedro bertarini
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Coherent Optical Code Division Multiple Access (OCDMA)
Systems
Pedro Luiz Lima Bertarini
University of São PauloEngineering School of São Carlos
Department of Electrical Engineering
International Workshop on Trends in Future Communications:High Performance Network Infrastructure for Future Internet23-25 February 2014, CPqD Auditorium, Campinas, SP- Brazil
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University of São PauloEngineering School of São Carlos
Department of Electrical Engineering
São Carlos~ 150 km to Campinas~ 240 km to São Paulo
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Telecomunications GroupSupervisor: Prof. Ph.D. Ben-Hur Viana Borges
University of São PauloEngineering School of São Carlos
Department of Electrical Engineering
POSTDOCTORAL RESEARCHER: PH.D. PEDRO LUIZ LIMA BERTARINI
PH.D. CANDIDATES: ANDERSON L. SANCHESDANIEL B. MAZULQUIMLEONE M. VEIGA JOSÉ V. REIS JR. THIAGO R. RADDO THIAGO VASCONCELOS (UFPE)
MS.C. CANDIDATES: ACHILES F. MOTADANIEL MARCHESIHEINZ SUADICANILARISSA LIMA
COLLABORATORS: PH.D. FREDERICO D. NUNES (UFPE)COLLABORATORS: PH.D. LUIZ G. NETO (SEL/USP)
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On-going Research Projects
› Metamaterials
› Chiral Metamaterials
› Cavity sensors
› Plasmonic lenses
› SOI/SPP based devices
› Supercontinuum generation
› Optical Code Division Multiple Access (OCDMA)
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Different Applications:
Antennas
Biosensors
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Outline
OCDMA encoding technologies
SPECTS-OCDMA systems
Optimal code-set selection
Concluding remarks
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OCDMA encoding technologies
Multiple access technologies
WDMA TDMA CDMAf
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Encoding -> to spread in one or more dimensions:
Time Frequency Space Polarization
Maximize › Cardinality (number of simultaneous users)› Orthogonality (differentiation between users)
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OCDMA encoding technologies
P. L. L. BERTARINI - Coherent Optical Code Division Multiple Access (OCDMA) Systems
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OCDMA encoding technologies
OCDMA technologies:
› Incoherent OCDMA systems Manipulates intensity of optical field
› Coherent OCDMA systems Manipulates phase and amplitude of optical
field It appears to be the most viable technology for
the implementation of OCDMA systems *
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* Optical Access Seamless Evolution (OASE), “Survey of next-generation optical access system concepts,” FP7/2007–2013, deliv. D4.1; http://www.ict-oase.eu/.
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Data
Light Sourc
e
Phase Mask – A(w)
Prism or grating
SLM
Star Couple
and Optical Chann
el
DataModulat
or
SPECTS-OCDMA systems
Spectral Phase-Coding Time Spreading
Encoder
Fourier Transfor
m
Inverse Fourier Transfor
mSpetral Phase Code
– user K
Gaussian Optical Pulse Encoder
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SPECTS-OCDMA systems
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Fourier Transfor
m
Inverse Fourier Transfor
mSpetral Phase Code
– user K
Gaussian Optical Pulse Encoder
Encoded Signal
Encoding / decoding process
› The pulse reconstruction, or decoding, requires a conjugate code to be used, otherwise it will remain spread out as multiple access interference (MAI)
› Other devices are necessary to distinguish between correctly and incorrectly decoded users Time gate devices – NOLM Nonlinear thresholder
P. L. L. BERTARINI - Coherent Optical Code Division Multiple Access (OCDMA) Systems
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SPECTS-OCDMA systems
System Performance
› Walsh-Hadamard and m-sequence codes› “1” and “-1” represent phase shifts of “0” and
“π”
› Synchronism between active users› Worst case scenario
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Methodology
A bit “1” is encoded with a given user's code, and then is imposed to all other users' decoders.
We are able to get the energy (interference) level received by each user.
This process is carried out for all possible code combinations.
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SPECTS-OCDMA systems
We showed for the first time in OCDMA literature that each user differently interferes in all other users in the system› Ideal scenario → orthogonality between
codes› Realistic scenario → the MAI produced by
incorrectly decoded users coincide with the correctly decoded user’s signal
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SPECTS-OCDMA systems Interference level caused by users (a) #12 and (b) #15 on
other users when a bit "1“ is sent. The dashed lines indicate the average energy value, equal to
0.286 for W-H 32 (left) and 0.277 for m-sequence (rigth).
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Optimal code-set
BER evaluation › based on the interference level between active
user› each user has a different performance depending
on the interference caused by others active users
Optimal code-set selection
› The goal is to select the code-set that represents the best scenario for all possible code combinations
› best scenario: code-set with lowest BER for all users
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Optimal code-set
W-H 32 optimal code-set 3 simultaneous users: 992 (20%) out of 4960 → BER<10-12
1120 (22.6%) out of 4960 → BER<10-9
4 simultaneous users: 416 (1.16%) out of 35690 → BER<10-12 656 (1.82%) out of 35690 → BER<10-9
The maximum number of active users allowed to W-H 32 with satisfactory BER levels is only 4
BERTARINI , P. L. L., et al. - "Optimal Code Set Selection and Security Issues in Spectral Phase-Encoded Time Spreading (SPECTS) OCDMA Systems," Journal of Lightwave Technology, vol. 30, no. 12, June, 2012.
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Optimal code-set
W-H 64 optimal code-set
6 simultaneous users : 409600 (0.543%) out of almost 75 million → BER<10-12
7 simultaneous users: 262144 (0.042%) out of almost more than 621 million → BER<10-12
8 simultaneous users:65536 (0.0015%) out of more than 4 billion → BER<10-12
A random choice of the code-set will compromise the overall system performanceBERTARINI , P. L. L., et al. - "Optimal Code Set Selection and Security Issues in Spectral Phase-Encoded Time Spreading (SPECTS) OCDMA Systems," Journal of Lightwave Technology, vol. 30, no. 12, June, 2012.
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Concluding remarks The code-set selection is necessary in order to
implement optical networks based on OCDMA technology
Code-set selection algorithm can be applied to any CDMA system, regardless the technology used
Some efforts have to be made to seek a STANDARD for CDMA technology in optical domain, such as G-PON for TDMA systems
We are currently working on security, robustness and scalability issues of coherent OCDMA networks
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Thank you!
Coherent Optical Code Division Multiple Access (OCDMA) Systems
Pedro Luiz Lima Bertarini
University of São PauloEngineering School of São Carlos
Department of Electrical Engineering
International Workshop on Trends in Future Communications:High Performance Network Infrastructure for Future Internet23-25 February 2014, CPqD Auditorium, Campinas, SP- Brazil