SAE/OCDM System

ICEIC Indonesia 2013

SAE/OCDM SYSTEMS USING APD RECEIVER OVER LINEAR DISPERSIVE CHANNEL

Nguyen Tat Thang & Anh T. PhamThe University of Aizu

Computer Communications Lab

Wednesday, April 12, 2023 SAE/OCDM Systems


Contents

• Introduction• Optical code-division multiplexing (OCDM) techniques• Dispersion in optical fiber• Motivation

• Theoretical Model and Analysis• Spectral amplitude encoding (SAE) OCDM System• Linear Dispersive Channel• Theoretical BER over Linear Dispersive Channel

• Simulation Model• Results & Discussions• Conclusions


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Overview• SAE/OCDM has been considered as a promising technique for

the next-generation optical access and local networks

• Impact of dispersion is one of critical factors to performance of SAE/OCDM system• This has been analyzed theoretically and experimentally [3][5]

• In this work, we implement a simulation model using OptiSystem® software suite for analyzing the performance of SAE/OCDM systems• We especially focus on modeling and analyzing the impact of dispersion


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• Time Domain Encoding:

• Spectral Amplitude Encoding (Freq. domain):


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OCDM (Optical Code Division Multiplexing)

1 0

t t

Tb

Tc = Tb / NTc01010101

t

f

01010101

01010101

Broadband source

t

f

Tc=Tb

Dispersionphenomena

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3

4


Impact of Dispersion

Wednesday, April 12, 2023

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SAE/OCDM Systems

1

0

1

0

0

0

1

• Chromatic dispersion (group velocity dispersion, aka. GVD)• Peak reduction• Pulse Broadening• Time Skewing

ICEIC Indonesia 2013 6

Motivation (1)• Experimental study on the impact of dispersion has been reported

• H. Tamai et al., “Experimental study on time-spread/wavelength-hop optical code division multiplexing with group delay compensating en/decoder,” IEEE Photon. Technol. Lett., 2004.

• It is the experimental study with real implementation• Limitation: expensive, not flexible, delayed, difficult to analyze when

scalability is required

• Theoretical study using the Linear dispersive channel model for analyzing the performance of SAE/OCDM systems• Ngoc T. Dang et al., “Performance Analysis of Spectral Amplitude Encoding

OCDM Systems over a Linear Dispersive Optical Channel”, IEEE/OSA J. Optical Comm. & Netw., 2009.

• Could easily analyze with different configuration, settings• Validation required, some assumption is still far from practical conditions

SAE/OCDM SystemsWednesday, April 12, 2023


Motivation (2)• Understanding the impact of dispersion is critical and needed to be

carefully considered in the system design• Our proposal

• A trade-off solution• Analyze the performance of SAE/OCDM system over dispersive channel

using optical simulation system• Advantages

• Closer to the real implementation• However, it is

• Cheaper• Flexible: Easy to modify system’s parameters, • More quickly faster R&D process• Scalable: easily analyze with a large number of users


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THEORETICAL ANALYSIS


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SAE/OCDM System: Principle

Transmitter - User #1Code C1

Transmitter - User #2Code C2

…

Transmitter - User #KCode CK

Receiver - User #1Code C1

Receiver - User #2Code C2

Receiver - User #KCode CK

…

Combiner K • 1

Splitter1 • K

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Dispersive optical channel


APD2C1

C1 APD1



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Linear Dispersive Channel Model• The optical pulse propagation model with modified factors

was used for analytical modeling:

*Average received power of chip number i transmitting over L km of fiber

Gaussian pulse peak power

attenuation

*Ps: Transmitted power per bit K: Number of users N: Code length T0: half width of Gaussian Pulse


System’s BER over Linear Dispersive Channels (APD Receiver)• Received desired signal power (after decoding):

• Received MAI signal power (after decoding):

• BER:

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SAE/OCDM Systems

*Additive branch

*Subtractive branch

*Additive branch



CONSTRUCTION OF SIMULATION MODEL AND ANALYSIS


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Simulation Model for Transmitter


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Hadamard code – N=12 ω=6 λ=3

Optical Power Combiner

Ps

Other Users

γw

γ0

Ps

101010101010

Fiber Bragg Gratings


Simulation Model with APD Receiver


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Cm

Cm

Optical Splitter

Optical Power Splitter

Other User:1010101010100101

bit 1

bit 1

bit 0

bit 0


Results (Theoretical vs. Simulation)• The performances of system with two cases: considering

dispersive channel and non-dispersive (only attenuation) channel.

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SAE/OCDM Systems

* 3 x 500 Mb/s active users in total 8 users, 10 km optical fiber with attenuation 0.2dB/km, D = 16.75 ps/nm/km

BER vs. APD gain,Ps=-17dBm

BER vs. Ps,APD gain = 7


0.5 dB


Conclusions & Summary• We have built the computer simulation model for

SAE/OCDM system using APD receiver with 3 activating users in 8 users total

• The well-matched simulation and theoretical results has validated the simulation model. The simulation model therefore could be used for OCDM system R&D

• Next step: we will build the simulations for more complete models, with more practical parameters and more practical devices such as EDFA, dispersion shifted fiber.

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Question time

Thank you!

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Some of recent experimental model for SAE/OCDM systems

• Julien Penon et al., “Spectral-Amplitude-Coded OCDMA Optimized for a Realistic FBG Frequency Response”, Journal of Lightwave Technology, 2007.

• Mohammad Reza Salehi et al., “Code Performance Comparison in SAC-OCDMA Systems under the Impact of Group Velocity Dispersion”, J. Opt. Commun., 2012


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Simulation of Linear Dispersive Channel

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SAE/OCDM Systems

Without GVD

With GVD

1549 nm 1554 nm



Transmitter: Principle


Laser Source

Spectral Encoder

Data (0,1)

channel (OF)

Transmitter

λ1 … λ5 … λ8 λ2 λ4 λ6 λ8

Ps

Ps

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Cm: 0 1 0 0 1 1 1 0 λ1λ2λ3λ4λ5λ6λ7λ8


Hadamard code:• Code length: N – number of chips• Code weight: ω – number of chip 1s• In-phase cross correlation: λ – number

of similar chip 1s of two codes. •

•

SAE/OCDM Systems


Motivation (2) (Obsoleted)

• Problem• Theoretical model required to be validated• The practical experiments: expensive, not scalable, not flexible and

delayed• Some proposed models have assumption is far from practical

implementation. The dispersive characteristic of OF has not been consider in experiment.

• Advantages• Scalable: large and flexible number of users• Easy to modify system’s parameters• Get the result quickly faster R&D process• Cheaper than the real implementation


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Multiplexing Techniques


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Time t

λ

Wav

elen

gth

Time t

Wav

elen

gth

λ

t

λ

Code

• Codes used for multiplexing

• Asynchronous access ability

• Flexible number of users

• Possibly cheaper

Time division multiplexing(TDM)

Wavelength division multiplexing(WDM)

Code division multiplexing (CDM)

• Time synchronization required

• Limited speed by electronic processing

• Wavelength management required

• Expensive


Simulation Systems


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Other Users

λ1=1549 λ2=1549.5 λ3=1550 λ4=1550.5

User 1 code: 11110000

λ5, λ6, λ7, λ8,

Cm

Cm


Optical Splitter

Optical Power Splitter

Optical Power Combiner

Gratings

Ps


SAE/OCDM Receiver


Coupler (3dB)

Decoder 1

Decoder 2

Threshold Detection

Data (0,1)

PD1

PD2I2

I = I2-I1

I1

channel (OF)

Receiver

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delay

APD1

APD2

Balanced detection

λ2

λ7

λ5

λ6

λ2

λ7

λ6

λ5


• Received power at receiver #1 (designate for user #1):• Complement code branch - data:

• Direct code branch-data :

• Multiple Access Interfering:

• Balanced Detection:


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Theoretical Calculation


Spreading Sequence (Code)

• m-sequence (N, (N+1)/2, (N+1)/4), Hadamard (N, N/2, N/4),

MQC (N=p2+p, ω=p+1, λ=1) (p is odd prime number).

• There are several construction of these code sets.


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SAE/OCDM System

Technology

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