Coherent Optical Code Division Multiple Access (OCDMA) Systems Pedro Bertarini

University of São Paulo
Engineering School of São Carlos
Department of Electrical Engineering

University of São Paulo
Engineering School of São Carlos
Department of Electrical Engineering
POSTDOCTORAL RESEARCHER: PH.D. PEDRO LUIZ LIMA BERTARINI
PH.D. CANDIDATES: ANDERSON L. SANCHES
DANIEL B. MAZULQUIM
LEONE M. VEIGA
JOSÉ V. REIS JR.
THIAGO R. RADDO
THIAGO VASCONCELOS (UFPE)
MS.C. CANDIDATES: ACHILES F. MOTA
DANIEL MARCHESI
HEINZ SUADICANI
LARISSA LIMA
COLLABORATORS: PH.D. FREDERICO D. NUNES (UFPE)
COLLABORATORS: PH.D. LUIZ G. NETO (SEL/USP)

› Metamaterials
› Chiral Metamaterials
› Cavity sensors
› Plasmonic lenses
› SOI/SPP based devices
› Supercontinuum generation
› Optical Code Division Multiple Access (OCDMA)
P. L. L. BERTARINI - Coherent Optical Code Division Multiple Access (OCDMA) Systems 4
 Different Applications:
 Antennas
 Biosensors

 OCDMA encoding technologies
 SPECTS-OCDMA systems
 Optimal code-set selection
 Concluding remarks
P. L. L. BERTARINI - Coherent Optical Code Division Multiple Access (OCDMA) Systems 5

 Multiple access technologies
WDMA TDMA CDMA
f
...
1
n
t
B
f
B ... ...
1 n 1 n
T
f
B
t
c
t
1
n
6P. L. L. BERTARINI - Coherent Optical Code Division Multiple Access (OCDMA) Systems

 Encoding -> to spread in one or more
dimensions:
 Time
 Frequency
 Space
 Polarization
 Maximize
› Cardinality (number of simultaneous users)
› Orthogonality (differentiation between users)

 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 *
* Optical Access Seamless Evolution (OASE), “Survey of next-generation optical access system concepts,” FP7/2007–2013, deliv. D4.1;
http://www.ict-oase.eu/.

DataLight
Source
Phase Mask – A(w)
Prism or grating SLM
Star
Couple
and
Optical
Channel
Data
Modulator
 Spectral Phase-Coding Time Spreading
Encoder
Fourier
Transform
Inverse
Fourier
Transform
Spetral Phase
Code – user K
Gaussian
Optical
Pulse Encoder

10
Fourier
Transform
Inverse
Fourier
Transform
Spetral 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

 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

 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.

 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

 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).

 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

 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
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
16
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.

 W-H 64 optimal code-set
6 simultaneous users :
409600 (0.543%) out of almost 75
million → BER<10-12
262144 (0.042%) out of almost more
than 621 million → BER<10-12
65536 (0.0015%) out of more than 4
billion → BER<10-12
A random choice of the code-set will
compromise the overall system
performance
17
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.

 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

Coherent Optical Code Division Multiple Access (OCDMA) Systems Pedro Bertarini

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