International Journal of Engineering Trends and Technology (IJETT) – Volume 24 Number 2- June 2015
Design of multi user free space optical communication system
for Three Dimensional SPPDD for OCDMA
Amanpreet Kaur#1, Neetika Soni*2
#
Student & Communication Systems & Guru Nanak Dev University Regional Campus, Jalandhar
Punjab, India
Abstract— 3-D W/T/P encoded signal transmitted over free
space optical link under the effects of atmospheric
turbulences i.e. haze, fog and clear weather. System
performance is best when clear weather attenuation is
considered (0.1dB/Km) and results degrades in case of Haze
(4dB/Km) and worst in Fog (20dB/Km).This system
analyzed at varied distance for all the three turbulences,
also effect of amplifiers observed to mitigate the effects of
attenuation. In all the systems discussed earlier SPPDD
coding used (Single Pulse Per Plane with Direct Detection).
Keywords— OCDMA, 3-D codes, Wavelength, Time,
Polarization, W/T/P, SPPDD, FSO
I. INTRODUCTION
Optical CDMA over Free Space Optics (FSO)
communication is very efficient to provide high data
rate for transmission having low BER and Multiple
Access Interference (MAI). From previous papers it is
cleared that W T P (Wavelength Time Polarization)
provides better results than W T S (Wavelength Time
Space) for Q-factor. In this we use W T P for FSO at
W=T=4 keeping P=2. FSO is advancement over
optical fiber because in this communication which is
limited to the distance and require more resource
management.
Firstly we discuss about W T P. Author found that
extremely short pulses in 1-D (time domain) OCDMA
have limited ability to support large number of users.
To overcome the limitations of 1-D, 2-D OCDMA
networks (utilizing both time and wavelength) are
used. 2-D OCDMA reducing the collisions while
simultaneously increasing the number of supported
users in the system but these 2-D code sets does not
support enough number of users in LAN for large
scale. To increase the number of users 3-D code sets
are used for short distances optical LANs, polarization
states remains stable [1].
3-D time/wavelength/polarization encoding and
decoding OCDMA system. In this number of potential
users increased, by a factor 2k over a conventional 2D code given the same code constraints, “k” is number
of collisions the code set will allow. By varying the
data rates we find the effects of BER using 3-D
OCDMA codes having dimensions in time,
wavelength and polarization [2]. Q-factor decreases,
BER increases with increased data rate. At lower data
rates have good Q-factor. Simulations done till 4gbps
system gives good BER and these codes suitable for
LAN to transmit data for single user [2].
OCDMA are used for transmitting high definition
audio and video content, exploring sensor technology
in medical to military and hospital environment.
ISSN: 2231-5381
Increase in data in form of voice, video and text at
each user end there is need to send data within high
capacity channel catering more number of users. For
that OCDMA as multiple access technology is
explored. In this author presented a technique that,
when employed doubles the number of active users.
The transmission of 10 active users with data rate up
to 5gb/s per user at variable received power with
acceptable BER is presented using newly developed 3D codes [3] A 3-D wavelength/time/space Multiple
Pulses per Row (MPR) using zero transmission length
of the system provides acceptable BER less than 10e-9.
3-D W/T/S MPR OCDMA system suitable for LAN
[4]. To increase the number of users 3-D W/T/P MPR
codes into an OCDMA system. This system supported
eight simultaneously users with acceptable BER at 18
gbps with attenuation of -15 db for 100 km optical
fiber length [5]. W/T/S has many limitations that its
Q-factor in not so good for the increased fiber length
so here we find that W/T/P has good Q-factor.Author
proposed a wireless optical mesh network based on
the OCDMA coded free space optical links. This
network under the intermediate and strong turbulence
channel conditions is investigated for the synchronous
and asynchronous OCDMA [6]. An advanced wireless
technology cable of providing higher data rates than
current RF technologies is preferred to support
efficient
and
reliable
transmission.
FSO
communication that deploys optical links in the
atmosphere without the use of optical fibers. For Line
Of Sight (LOS) communication link, laser based FSO
communication has many advantages over RF
technologies. Author found security problem in
subcarrier intensity modulated air to ground FSO
communication system over the atmospheric
turbulence using the reciprocity property of the FSO
channel, by introducing the secret sharing and key
agreement approach [7]. In this author found that
Optical CDMA over the FSO communication systems
at data rate 2.5 Gbps for 8000m distance. NRZ
technique provides better performance as compared to
RZ in optical CDMA over FSO communication and
gives that transmission range decreases with increase
in transmitter power. Efficiency of OCDMA over FSO
communication system is decreased by increasing the
users [8].
FSO communication has been used through the
transmission of information which is loaded with
optical radiations from a transmitter to receiver,
separated by the atmosphere. Author gives description
of transmitting high data rate over FSO link by
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International Journal of Engineering Trends and Technology (IJETT) – Volume 24 Number 2- June 2015
employing two OCDMA coding techniques i.e NRZ
and RZ and finds that the performance of NRZ is
better than other techniques [9].
II. SIMULATION SETUP
In FSO simulation has been done in three different
environment in clear weather (0.1db/km), in haze
(4db/km) and fog (20db/km). In this simulation setup
W=T=4 at P=2 (W T P FSO) as shown in fig.1 for
clear weather. W T P FSO consists of a transmitter,
encoder at transmitter side, decoder at receiver side
and FSO for transmission of data. Same as above at
transmitter side two polarization channel. At P=2 there
are total eight wavelengths and these wavelengths are
range from polarization channel wavelength range
from 1549 to 1551.4 nm. Each wavelength differs
from a frequency spacing 0.8 nm. The input data bit
sequence is at rate of 1Gbps after that coded light
signal modulates the input data. The modulator is
driver by modulator driver which decides the input
data format and modulator uses in both setups is
Mach-Zehnder modulator. The input data is NRZ. The
modulated data is encoded in the encoder first four
channels and other channels at polarization 0˚ and
90˚respectively. Output of all encoder combine and
sent to FSO at length (0.1km, 0.5km, 1km, 4km and
8km respectively). After that decoder is placed which
decodes the data, it is just inverse of encoder and then
receiver is placed.
(4db/km) and fog (20db/km). We find that in clear
weather Q-factor is better than in haze and fog. Fig. 2
shows that as the distance varied Q-factor is also
varied and the Q-factor decreases in haze and fog as
the distance increases. By varying the distance at in
three different environments in clear weather
(0.1db/km), in haze (4db/km) and fog (20db/km) with
attenuation for W T P FSO, correspondingly Q-factor
is measured and compares this varied distance versus
Q-factor for all the wavelengths and find out that at
which wavelength and time provides better results in
which environment. By observing this graph we find
out that in clear weather W T P FSO gives better Qfactor.
Fig. 2 Q-factor versus length of fiber
Fig 3-5 shows the eye diagram taken for W T P
with FSO of distance 0.1km, 0.5km, 1km, 4km and
8km respectively. It can be shown from these
diagrams as the distance increases eye opening is
considerably decreasing and found that for W=T=4 at
P=2 (in clear weather) W T P FSO gives maximum
opening of eye with less distortions as compared to
others. Table I shows the values of W=T=4 at P=2 (W
T P FSO) at different fiber length.
Fig. 1 Subsystem for the implementation of 3D
codes W T P FSO under clear weather.
III. RESULTS AND DISCUSSION
W T P for FSO. FSO is advancement over optical
fiber because in this communication which is limited
to the distance and require more resource management.
In FSO simulation has been done in three different
environment i.e. are clear weather (0.1db/km), in haze
ISSN: 2231-5381
a)
W=T=4, S=2 (W T P FSO) for fiber length
fiber length 0.1km
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International Journal of Engineering Trends and Technology (IJETT) – Volume 24 Number 2- June 2015
b)
W=T=4, S=2 (W T P FSO) for fiber length
fiber length 8km
Fig.4 Eye Diagrams at S=2 for W=T=4 (W T P
FSO under haze attenuation 4db/km) at fiber
lengths 0.1km and 8km respectively.
b)
W=T=4, S=2 (W T P FSO) for fiber length
fiber length 8km
Fig.3 Eye Diagrams at S=2 for W=T=4 (W T
P FSO under clean weather attenuation
0.1db/km) at fiber lengths 0.1km and 8km
respectively.
a)
W=T=4, S=2 (W T P FSO) for fiber length
fiber length 0.1km
a)
W=T=4, S=2 (W T P FSO) for fiber length fiber
length 0.1km
b)
W=T=4, S=2 (W T P FSO) for fiber length fiber
length 8km
Fig.5 Eye Diagrams at S=2 for W=T=4 (W T P FSO
under fog attenuation 20db/km) at fiber lengths 0.1km
and 8km respectively.
ISSN: 2231-5381
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International Journal of Engineering Trends and Technology (IJETT) – Volume 24 Number 2- June 2015
TABLE I
EVALUATION W/T/P FSO AT DIFFERENT DISTANCE
(KM) IN TERMS OF Q-FACTOR
Distance
under haze
attenuation
4db/km
under fog
attenuation
20db/km
0.1km
under
clean
weather
attenuation
35.5984
0.1db/km
35.6785
88.6817
0.5km
34.864
33.9379
25.8209
1km
33.2688
28.1524
0
4km
17.0776
0
0
5km
5.7621
0
0
a)
Input signal at Transmitter
Fig.6 to 8 shows the input signal at transmitter side,
after that the data send to W T P FSO and received
signal at receiver side.
b) Output signal at Receiver
Fig.7 Input and output signal for W T P FSO under
haze at 0.1km
a)
Input signal at Transmitter
a)
Input signal at Transmitter
b) Output signal at Receiver
Fig.6
Input and output signal for W T P FSO under
clear weather at 0.1km
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International Journal of Engineering Trends and Technology (IJETT) – Volume 24 Number 2- June 2015
REFERENCES
[1]
[2]
[3]
[4]
b) Output signal at Receiver
[5]
Fig.8 Input and output signal for W T P FSO under
haze at 0.1km
[6]
Conclusions
[7]
3-D W/T/P encoded signal transmitted over free space
optical link under the effects of atmospheric
turbulences i.e. haze, fog and clear weather. System
performance is best when clear weather attenuation is
considered (0.1dB/Km) and results degrades in case of
Haze (4dB/Km) and worst in Fog (20dB/Km).This
system analyzed at varied distance for all the three
turbulences, also effect of amplifiers observed to
mitigate the effects of attenuation. In all the systems
discussed earlier SPPDD coding used (Single Pulse
Per Plane with Direct Detection).
ISSN: 2231-5381
[8]
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