OCDMA SYSTEM USING optic system 15 for simulation

1. A
PROJECTP ROGRESS REPORT
On
OPTICAL CDMA
SUBMITTED BY:
BRIJESH BHARTI
CIT-06/16
Under the Guidance of
Dr. GausiaQazi
Department of Electronics & Communication Engineering
National Institute of Technology, Srinagar
Jammu and Kashmir 190006

2. Table of Contents
1. Abstract
2. Project overview
2.1 Introduction
2.2Principles of coding in OCDMA
3. Find major Challenges
3.1 BER (major issue)
3.2 OCDMA, MAI (multi user interference)
3.3Component cost and complexity
3.4Signal Loss in Multimode and Single-Mode Fiber-Optic Cable
3.5 Attenuation and Dispersion in Fiber-Optic Cable
4. Methods to overcomethe challenges
4.1Using Spectral Amplitude Coding (SAC)
4.2Spectral Phase Coding (SPC)
4.3Based on fiber Bragg grating (FBG) encoder/decoder
5. Simulation of OCDMABased on (FBG) encoder/decoder
5.1measurement of BERfor 1km distance
5.2 measurementof BER for 100 km distance
6. Applicationof OCDMA
6.1From LAN to PON
6.2 OCDMA for access networks
6.3Metro-level optical VPN
6.4 Optical control signaling and OBS
6.5 All-optical switching and label routing
6.6 Network monitoring and OCOTDR
6.7 All-optical multicasting
7. References

3. Abbreviations
BER bit error rate
MAI multiple access interference
TDMA time division multiple access
CDMA code division multiple access
LAN local area network
PON passive optical network
VPN OpticalVirtual Private Network
OTDR optical time-domain reflectometry
OCLS label switch

4. 1. Abstract
In this project report we try to enhance the performance of optical fiber communication using
the optical CDMA technology, using different modulation techniques and coding and
decoding techniques. And main focus on reduce the BER and MAI in optical CDMA
system.Because of consumer bandwidth demands are rapidly growing at huge rate, and are
expected to keep growing for years to come. This growth applies not only to the internet
usage, but to a large range of individual institutions. Most ofthe downstream traffic is web
media which is mainly due to photo and video communication and real-time streaming.so we
to improve the performance of Optical CDMA .for high speed data communication
.nowadays Meany researcher are working on optical CDMA technology .in optical fiber
communication .

5. 2.1Introduction
Optical CDMA stands for Optical Code Division Multiple Access. OCDMA Technologyis
one of the promising technologies to implement alloptical networks, which has the potential
to exploit the unmannedbandwidth of optical fiber and take advantage of the predominance of
CDMA technology. OCDMA is a category of multiplexing and internetworking technologies
that encodes/decodes signals through employing simple and costeffective passive optical
components such that the signal multiplexing, routing and switchingcan be implemented
smoothly.Driven by the rapid increasing demands of communication bandwidth, multiplexing
is essential in bothwireless radio and fiberoptic networks. Codebased network access has the
tendency to simplify the network control and management with enhanced information
security. The efficient multipleaccessprotocol also allows many users to access the fiber
channel asynchronously and simultaneously without delay and scheduling. OCDMA is based
on the principle.that codesare mapped to the identities or addresses of users following a code-
user relation. Accordingly OCDMA was initially proposed to implementultrafast
asynchronous broadcast LAN.The OCDMA cam be implemented in various method .and
class show in fig (1.1)

6. Fig (1.1) optical CDMA classification
2.2Principles of coding in OCDMA
An encoding operation optically transforms each data bit before transmission. At the receiver,
the reverse decoding operationis required to recover the original data. The encoding and
decoding operations alone constitute optical coding. OCDMA is the use ofOCDM technology
to arbitrate channel access among multiple network nodes in a distributed fashion. Code
sequence either in the time domain, the wavelength domain, or a combination of both. The
latter method is called two-dimensional coding (2D-coding) illustrates the three coding
principles. In a time-encoded signal, the bit is split into smaller time components called chips.
Time-domain coding that manipulates the phase of the optical signal is usually bipolar and
requires phase-accurate coherent sources. Alternatively, positive encoding manipulates the
power of the optical signal but not its phase and typically uses incoherent sources. In
wavelength- domain coding, transmitted bits consist of a unique subset of wavelengths
forming the code. 2D-coding combines both wavelength selection and time spreading. A data
bit is encoded as consecutive chips of different wavelengths, the unique wavelength sequence
constituting the code. Decoding consists of applying the reverse time/wavelength operations.
Regardless of the coding domain, the coding operation broadens the spectrum of the data
signal, hence the designation of spread spectrum. Note that encoding can also be performed
in the space-domain, whereby the code determines the positions of chips within a dense fiber
array or a multicore fiber.
3. Find major Challenges [1]
3.1BER The bit error rate (BER) is the number of bit errors per unit time. The bit error ratio
(also BER) is the number of bit errors divided by the total number of transferred bits during a
studied time interval. Bit error ratio is a unit less performance measure, often expressed as a
percentage. The bit error probabilitype is the expectation value of the bit error ratio. The bit
error ratio can be considered as an approximate estimate of the bit error probability. This
estimate is accurate for a long time interval and a high number of bit errors. Bit error in
optical CDMA due to noise in optical fiber channel .bit error is major issue in
communication.

7. 3.2 OCDMA, MAIan OCDMA local area network (LAN) is based on a broadcast
medium. Signals from different encoders are coupled and each decoder receives the sum of
the encoded signals. If a given encoder transmits a signal, only the decoder with the same
code is capable of recovering it. Unwanted signals appear as noise to the decoder and are
called multiple-access interference (MAI). MAI is the principal source of noise in OCDMA
and is the limiting factor to system performance. In a well-designed OCDMA LAN where
MAI is overcome, users can successfully communicate asynchronously and regardless of
network traffic.
3.3Component cost and complexity Component cost and complexity are key
issues in OCDMA system design. For instance, the tenability of encoders and decoders
represents a significant challenge compared to tenability of WDMA transceivers. In addition,
currently available broadband light sources required for spectral or 2D-OCDMA operation
are eitherexpensive or do not offer enough intensity OCDMA is limited in network reach by
dispersion due to the high encoded signal bit rateand high power budget required
3.4Signal Loss in Multimode and Single-Mode Fiber-Optic Cable
Multimode fiber is large enough in diameter to allow rays of light to reflect internally
(bounce off the walls of the fiber). Interfaces with multimode optics typically use LEDs as
light sources. However, LEDs are not coherent sources. They spray varying wavelengths of
light into the multimode fiber, which reflects the light at different angles. Light rays travel in
jagged lines through a multimode fiber, causing signal dispersion. When light traveling in the
fiber core radiates into the fiber cladding, higher-order mode loss results. Together these
factors limit the transmission distance of multimode fiber compared with single-mode fiber.
Single-mode fiber is so small in diameter that rays of light can reflect internally through one
layer only. Interfaces with single-mode optics use lasers as light sources. Lasers generate a
single wavelength of light, which travels in a straight line through the single-mode fiber.
Compared with multimode fiber, single-mode fiber has higher bandwidth and can carry
signals for longer distances. Exceeding the maximum transmission distances can result in
significant signal loss, which causes unreliable transmission.

8. 3.5 Attenuation and Dispersionin Fiber-Optic Cable
Correct functioning of an optical data link depends on modulated light reaching the receiver
with enough power to be demodulated correctly. Attenuation is the reduction in power of the
light signal as it is transmitted. Attenuation is caused by passive media components, such as
cables, cable splices, and connectors. Although attenuation is significantly lower for optical
fiber than for other media, it still occurs in both multimode and single-mode transmission. An
efficient optical data link must have enough light available to overcome attenuation.
Dispersionis the spreading of the signal over time. The following two types of dispersion can
affect an optical data link:
 Chromatic dispersion—spreading of the signal over time resulting from the different
speeds of light rays.
 Modal dispersion—spreading of the signal over time resulting from the different
propagation modes in the fiber.
For multimode transmission, modal dispersion, rather than chromatic dispersion or
attenuation, usually limits the maximum bit rate and link length. For single-mode
transmission, modal dispersion is not a factor. However, at higher bit rates and over longer
distances, chromatic dispersion rather than modal dispersion limits maximum link length. An
efficient optical data link must have enough light to exceed the minimum power that the
receiver requires to operate within its specifications. In addition, the total dispersion must be
less than the limits specified for the type of link in Telcordia Technologies document GR-
253-CORE (Section 4.3) and International Telecommunications Union (ITU) document
G.957.When chromatic dispersion is at the maximum allowed, its effect can be considered as
a power penalty in the power budget. The optical power budget must allow for the sum of
component attenuation, power penalties (including those from dispersion), and a safety
margin for unexpected losses.
4. Methods to overcome the challenges
4.1Using SpectralAmplitude Coding (SAC) [2]
In this project workwe are not consider this (SAC) coding techniques because is a promising,
cost effective,so little bit explanation about SAC. Method to reduce the BER ,The optical
spectral amplitude coding help to overcome the noise(BER) issue in optical CDMA system,
the code structure for spectral amplitude coding optical codedivision multiple access

9. (CDMA) is proposed and analyzed. It is shown that such codes can effectively suppress the
intensity noise and in turn increase the number of active users and improve the bit error rate
performance.
4.2SpectralPhaseCoding (SPC)[3]
The spectral phase coding help to reduce the MAI in optical CDAM system
Spectral phase coded OCDMA system architecture is illustrated by Fig. (2.1). The SPC-
OCDMA system requires a broadband multi wavelength source, one of the most popular
sources is mode-locked laser (MLL).By this kind of spectral phase encoders the modulated
spectrum separated into spectral bins and applies a distinct phase shift to each bin. The phase
components could be simple binary codes (0 &1) or more advanced multilevel phase codes.
Spectral Phase Encoder/Decoder Technologies
The fundamental function of SPC - OCDMA technology is the ability to access and modify
uniformly the phase of spectrum components. The basic operation of such encoder/decoders
consists of three processes, DE multiplexing the optical pulse into addressable spectral
components, adding a prescribed phase change uniformly across the spectral components,
and multiplexing the phase encoded spectral components back into fiber. DE multiplexing
and multiplexing processes can be done in series or parallel depending on theapplied
technology. There are three technologies that have been applied in SP Encoder/Decoders,
diffraction gratings, virtually imaged phased array, and cascaded micro-ring resonators

10. Fig 3. Block diagram of SPC-OCDMAsystem.
4.3 Basedon fiber Bragg grating[4]
A fiber Bragg grating (FBG) is a type of distributed Bragg reflector constructed in a short
segment of optical fiber that reflects particular wavelengths of light and transmits all others.
This is achieved by creating a periodic variation in the refractive index of the fiber core,
which generates a wavelength-specific dielectric mirror. A fiber Bragg grating can therefore
be used as an inline optical filter to block certain wavelengths, or as a wavelength-specific
reflector.

11. The fundamental principle behind the operation of an FBG is reflection, where light traveling
between media of different refractive indices may both reflect and refract at the interface. The
refractive index will typically alternate over a defined length. The reflected wavelength (𝜆𝐵),
called the Bragg wavelength.
(FBG) encoder/decoder
The encoding/decoding scheme based on Fiber Bragg Grating (FBG) for Optical Code
Division Multiple Access (OCDMA) system is analyzed and the whole process from
transmitting end to receiving end is are simulated in this project work Having the properties
of large system capacity, great security, asynchronous connectivity, and high anti-jamming
ability, Optical Code Division Multiple Access (OCDMA) system, a very attractive multiple-
access technology, is receiving more and more attention and being researched well One of the
key technologies required on the practical application of OCDMA is the design of its core
parts, encoder/decoder. Fiber Bragg Grating (FBG) has been applied inmany fields of optical
communication and tailor technique for it has been improved largely in recent years.
Benefited from its unique filtering property, FBG is also becoming the major choice as the
material of optical encoder/decoder in OCDMA system. Uniform FBG is a kind of short-
period fiber grating, of which the reflection is utilized. The periodical variation of the
refraction index along the fiber axis makes FBG act as an optical band rejection filter, whose
center reflecting wavelength is AB, called the Braggwavelength. In non-coherent OCDMA

12. system, we employ the users' signature codes to control the center reflecting wavelength of
FBGs in order to reflect the broadband signal.
5. Simulation of OCDMABasedon (FBG)encoder/decoder
The spectral amplitude coded optical code division multiple access system for three users
where third user id off the detection technique we have chosen is single photo detection
(SPD) technique. The BER for user 1 and user 2 are 0.0092 and 0.00621 respectively. But
still we are searching how to improve theBER.
Simulation parameters in FGB based Optical CDMA
Optical channel
Distance 1KM
Attenuation 0.2 dB/Km
Reference wave length 1550 nm
Dispersion 16.75 ps/nm/km
Dispersion slop 0.075 ps/nm/km
Uniform FGB
Bit rate 10e+009 bps
Time window 0.1024e-006 s
Number per sample 64
Signal bit rate200mbps
Sequence length1024 bits
Samples rate 640e+009Hz
5.5 measurement of BER for 1km distance
For distance 1 km
Distance 1 Km
Attenuation 0.2 dB/Km
Reference wave length 1550 nm
Dispersion 16.75 ps/nm/km
Dispersion slop 0.075 ps/nm/km

13. Fig-(2.1)
5.2 measurementof BER for 100 km distance

14. Parameters of optical channel and FBG are same only distances are increase
Fig(2.1)

15. 6 Application of OCDMA
6.1 From LAN to PON
LAN and PON contender techniques include TDMA, SCMA, and WDMA, denoting time-,
subcarrier-, and wavelength-division multiple access respectively. In TDMA, a time slot is
allocated to each user statically or dynamically. TDMA already is deployed in two forms:
asynchronous transfer mode PON (with various extensions) and Ethernet PON (EPON). In
WDMA, each user has a specific wavelength.Both TDMA and WDMA benefit from the
maturity of electrical multiplexing and optical transmission gained in backbone networks.
TDMA/WDM is proposed as a viable extension to TDMA that achieves dynamic bandwidth
allocation (DBA) on multiple wavelengths. In SCMA, microwave channels are multiplexed
electrically, and the composite signal modulates the optical carrier. SCMA is commonly used
in hybrid fiber-coax networks to carry broadcast community access television (CATV)
channels. SCMA/WDM has notable applications in radio-over-fiber networks
6.2 OCDMA for access networks
OCDMA is viewed as a candidate technology for future PON access networks. An OCDMA
PON uses a tree topology with passivepower splitters. Each optical network unit (ONU)
contains an encoder and decoder with unique fixed codes. The optical line terminal (OLT)
may contain all encoder-decoder pairs required for communication with each ONU or a
smaller number of tunable encoder decoders. In contrast to LAN, OCDMA PON is not fully
broadcast systems, because the signal transmitted by an ONU never reaches other ONU.
Hybrid OCDMA/WDM systems have been proposed. More ambitious contributions
introduce mapping universal IP addresses to OCDMA codes.
6.3 Metro-level optical VPN
Wavelength routing metropolitan optical network may provide light paths for VPN
connections. These links carry a multitude of OCDMA signals that are multiplexed and
demultiplexed at the end-points the primary goal of a VPN is to provide secure data links
over an insecure platform. The OCDMA signals provide enhanced security and can be
decoded only at the corresponding end point. The use of OCDMA for all-optical VPN
simplifies network design by replacing electronic multiplexing and grooming with optical
splitting and combining. Light-tree capabilities at the metropolitan network level can be used
to enable the establishment of multipoint VPN.

16. 6.4 Optical control signaling and OBS
Optical coding benefits from the fact that more information can be packed all-optically in a
coded pulse in a wavelength assignment. We use the term code wordto designate a pulse
encoded in a unique code and corresponding to a specific piece of information or set of
commands. Like an OC-label, a code word can carry photonic signaling information such as
the status of links and equipment for maintenance, the availability of communication
channels such as wavelength light paths, and control commands for dynamic switches. OC-
gate-like devices enable the photonic processing of code words at optical speeds. Condensing
relevant information in a code word inserted in a control packet is analternative to electronic
processing of an optical control packet. In addition to the elimination of electronic processing
time, code words reduce control packet overhead. The mapping of codes to relevant values
(quantities or commands) requires the provision of enough codes to span the entire set of
information values. Longer codes enable condensing more information in a single code word.
6.5 All-optical switching and label routing
OC label switching is among the most promising implementations of optical coding. In an
OC label-switched network, optically-encoded pulsesare added to fixed-length packets as
headers that specify the route or label-switched path (LSP). In an OC label switch (OCLS),
each output portis controlled by a header-sensitive switching device called an optical code
gate (OC-gate). OC-gates allow through only packets with a specificheader (OC-label).
6.6 Network monitoring and OCOTDR
The goal of optical time-domain reflectometry (OTDR) technology is to monitor fiber plant
quality and detect faults, particularly fiber cuts. It is based on the emission of out-of-band
optical pulses and the analysis of resulting reflections. Pulse reflection analysis reveals the
position of cuts, as well as any optical devices causing unusual reflection losses such as faulty
connectors. OTDR has found wide-scale applications in WDM backbone point-to-point links.
In reflections at any of the PON branches. The localization of an eventual faulty branch is
impossible, unless upstream OTDR is performed at each ONU.
6.7 All-optical multicasting
OC label switching may be extended to implement a multicast (MC) tree network where
optical codes denote MC groups as well as individual end-users. The network topology
considered is a tree where MC-enabled OC label switches reside at each node except the end
nodes. Packets are labeled with OC pulses corresponding to their MC group.

17. 7. References
[1]H. Fathallah, “Optical CDMA Communications and theUse of OFCs,” Optical Fiber
Components: Design andUse of OFCs,” Optical Fiber Components: Design andApplications,
H. Hamam, Ed., Research Signpost,Trivandrum, Kerala, India, Jan. 2006, pp. 201–43.
[1,2] HooshangGhafouri_Shiraz, M. MassoudKarbassian (auth.)-Optical CDMA Networks_
Principles, Analysis and Applications-Wiley-IEEE Press (2012)
[2] www.elsevier.de/ijleo/ Implementation of spectrally-coded FBG-based coder/decoder
optical CDMA network Accepted 6 September 2015