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DIRECT DETECTION IN OPTICAL COMMUNICATION USING INTENSITY MODULATION V.Vadivu #1 , M.Sathya #2 , S.Anjugam #3 ,R.Ramya #4 , #1, #2, #3 PG students [Communication system], Dept.of ECE, As-salam engineering and technology, Aduthurai, Tamilnadu, India. #4 Assistant Professor [O.G], Dept.of ECE, As-salam engineering and technology, Aduthurai , Tamilnadu, India. [email protected] #1 [email protected] #2 [email protected] #3 [email protected] #4 AbstractOptical wireless communication (OWC) refers to communication through an unguided medium using modulated light. In this paper, the performance of OWC systems employing intensity modulation and direct detection (IM-DD), established by modulating light intensity at the source and using an intensity detector at the destination is proposed. The capacity of the intensity- modulation direct-detection optical broadcast channel (OBC) is investigated, under both average and peak intensity constraints. An outer bound on the capacity region is derived by adapting Bergmans’ approach to the OBC. Inner bounds are derived by using superposition coding with either truncated-Gaussian (TG) distributions or discrete distributions. At high signal-to-noise ratio (SNR), it is shown that the TG distribution is nearly optimal. KeywordsIntensity-modulation; optical broadcast; capacity region; truncated Gaussian; discrete inputs. I. INTRODUCTION The Optical Wireless Communications is a type of communications system that uses the atmosphere as a communications channel. The OWC systems are attractive to provide broadband services due to their inherent wide bandwidth, easy deployment and no license requirement. The idea to employ the atmosphere as transmission media arises from the invention of the laser. However, the early experiments on this field did not have any baggage of technological development derived from the fiber optical communications systems, because like this, the interest on them decreased. At the beginning of the last century, the OWC systems have attracted some interest due to the advantages mentioned above. However, the interaction of the electromagnetic waves with the atmosphere at optical frequencies is stronger than that corresponding at microwave. The intensity of a laser beam propagating through the atmosphere is reduced due to phenomena such as scattering and molecular absorption, among other. The changes in the refractive index of the atmosphere due to optical turbulence affect the quality of laser beam through distortion of its phase front and random modulation of its optical power. Also the presence of fog may completely prevent the passage of the optical beam that leads to a no operational communications link. The information signal analog or digital is applied to the optical transmitter to be sent through the atmosphere using an optical antenna. At the receiver end the optical beam is concentrated using an optical antenna to the photo-detector sensitive area which output is electrically processed in order to receiver the information signal. II. EXISTING SYSTEM In the existing systems the direct detection is used in optical communication. By using direct detection the signal from input side is directly given to the receiver side with an unwanted noise. Orthogonalizing users this way allows serving multiple users in the OBC without interference. Hence, the channel from the transmitter to each receiver reduces to an IM-DD P2P, and capacity results on IM-DD P2P channels can be applied. For a Gaussian broadcast channel which is physically degraded by nature, superposition coding (SC) is optimal and orthogonalizing users is not efficient. The performance of SC in the OBC in terms of bit- error rate and throughput III. PROPOSED SYSTEM The goal of this paper is to study the capacity of the N-user OBC, which models the downlink in VLC. The main focus is finding simple closed-form statements on the channel capacity. This requires developing outer and inner bounds on the capacity region of the channel. To this end, we modify Bergmans’ outer bound to obtain outer bounds on the capacity

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DIRECT DETECTION IN OPTICAL

COMMUNICATION USING INTENSITY

MODULATION V.Vadivu#1, M.Sathya#2, S.Anjugam#3,R.Ramya #4,

#1, #2, #3 PG students [Communication system], Dept.of ECE,

As-salam engineering and technology, Aduthurai, Tamilnadu, India.

#4Assistant Professor [O.G], Dept.of ECE, As-salam engineering and technology, Aduthurai , Tamilnadu, India.

[email protected]#1

[email protected]#2

[email protected]#3

[email protected]#4

Abstract— Optical wireless communication (OWC) refers

to communication through an unguided medium using

modulated light. In this paper, the performance of OWC

systems employing intensity modulation and direct

detection (IM-DD), established by modulating light

intensity at the source and using an intensity detector at

the destination is proposed. The capacity of the intensity-

modulation direct-detection optical broadcast channel

(OBC) is investigated, under both average and peak

intensity constraints. An outer bound on the capacity

region is derived by adapting Bergmans’ approach to the

OBC. Inner bounds are derived by using superposition

coding with either truncated-Gaussian (TG) distributions

or discrete distributions. At high signal-to-noise ratio

(SNR), it is shown that the TG distribution is nearly

optimal.

Keywords— Intensity-modulation; optical broadcast;

capacity region; truncated Gaussian; discrete inputs.

I. INTRODUCTION

The Optical Wireless Communications is a type of

communications system that uses the atmosphere as a

communications channel. The OWC systems are attractive to

provide broadband services due to their inherent wide

bandwidth, easy deployment and no license requirement. The

idea to employ the atmosphere as transmission media arises

from the invention of the laser. However, the early

experiments on this field did not have any baggage of

technological development derived from the fiber optical

communications systems, because like this, the interest on

them decreased. At the beginning of the last century, the

OWC systems have attracted some interest due to the

advantages mentioned above. However, the interaction of the

electromagnetic waves with the atmosphere at optical

frequencies is stronger than that corresponding at microwave.

The intensity of a laser beam propagating through the

atmosphere is reduced due to phenomena such as scattering

and molecular absorption, among other. The changes in the

refractive index of the atmosphere due to optical turbulence

affect the quality of laser beam through distortion of its phase

front and random modulation of its optical power. Also the

presence of fog may completely prevent the passage of the

optical beam that leads to a no operational communications

link. The information signal analog or digital is applied to the

optical transmitter to be sent through the atmosphere using an

optical antenna. At the receiver end the optical beam is

concentrated using an optical antenna to the photo-detector

sensitive area which output is electrically processed in order

to receiver the information signal.

II. EXISTING SYSTEM

In the existing systems the direct detection is used in

optical communication. By using direct detection the signal

from input side is directly given to the receiver side with an

unwanted noise. Orthogonalizing users this way allows

serving multiple users in the OBC without interference.

Hence, the channel from the transmitter to each receiver

reduces to an IM-DD P2P, and capacity results on IM-DD

P2P channels can be applied. For a Gaussian broadcast

channel which is physically degraded by nature, superposition

coding (SC) is optimal and orthogonalizing users is not

efficient. The performance of SC in the OBC in terms of bit-

error rate and throughput

III. PROPOSED SYSTEM

The goal of this paper is to study the capacity of the

N-user OBC, which models the downlink in VLC. The main

focus is finding simple closed-form statements on the channel

capacity. This requires developing outer and inner bounds on

the capacity region of the channel. To this end, we modify

Bergmans’ outer bound to obtain outer bounds on the capacity

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region of the OBC. Then, we develop inner bounds on the

capacity region based on SC, where the source sends the sum

of several symbols, each of which is desired by one user.

The main contributions of the paper can thus be

summarized as providing:

1) Outer and inner bounds on the OBC capacity region,

2) The high-SNR capacity within a small constant gap, and

3) The low-SNR capacity.

OPTICAL BROADCAST CHANNEL

Consider an N-user optical broadcast system, where

information needs to be conveyed from a light source to users.

Coherent receivers in which the received optical field is mixed

with the field generated by a local optical oscillator (laser)

through a beam combiner or coupler, and the resulting signal

is photo-detected.

Fig. 1 Optical Broadcast Channel

BLOCK DIAGRAM OF OPTICAL COMMUNICATION

Fig. 2 Optical Communication diagram

The input signal is generated as binary symbols. This

signal doesn’t have polarity at this stage. If the binary signals

are generated we need to process encoding. Encoding is a

method which converts the individual binary bit to another

format of binary data’s. In our implementation we are using

Convolutional encoding. Now we have to modulate the binary

signal using QPSK. Then we need to spit those polarized

signal into two sections. X- Real part and Y- imaginary part of

the symbol. Again we need to do the symbol mapping. IFFT

and FFT is the process of Frequency division multiplexing

and demultiplexing respectively.

DETAILED WITH OPTICAL CHANNEL

Fig. 3 Detailed with optical channel diagram

Then we have to convert those parallel signals into serial

for transmission of symbols into single channel or medium. So

the signals we are having is digital. To pass through the fiber

channel we have to change to analog. Then the signals are

transmitted to the channel as dual signal. In fiber optic

channel, the first and initial process is the IQ-modulator

(In-phase and Quadrature –phase).

PBC is the polarized beam combiner to pass into fiber.

Here we are using SSMF type of fiber. Then we have the

design of coherent receiver. Coherent receiver has number

steps to accurately recover the original signal of transmitter.

To reduce the phase offset and phase noise we use the

error compensation algorithm and MIMO equalizer is used to

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get the correct path of signal. Finally the FFT is performed to

get the original subcarriers. And ZF and SD are used to

recover original binary data from the dual polarized

subcarriers.

IV.PROJECT DESIGN

SOFTWARE DESCRIPTION

MATLAB® is a high-performance language for

technical computing. It integrates computation, visualization,

and programming in an easy to use environment where

problems and solutions are expressed in familiar mathematical

notation. Typical uses include

Math and computation

Algorithm development

Modeling, simulation, and prototyping

Data analysis, exploration, and visualization

Scientific and engineering graphics

Application development, including graphical user

interface building

The name MATLAB stands for matrix laboratory.

MATLAB was originally written to provide easy access to

matrix software developed by the LINPACK and EISPACK

projects. MATLAB has evolved over a period of years with

input from many users.

MATLAB features a family of application-specific

solutions called toolboxes. MATLAB has evolved over a

period of years with input from many users. In university

environments, it is the standard instructional tool for

introductory and advanced courses in mathematics,

engineering, and science.

In industry, MATLAB is the tool of choice for high-

productivity research, development, and analysis. Very

important to most users of MATLAB, toolboxes allow you to

learn and apply specialized technology.

Toolboxes are comprehensive collections of MATLAB

functions (M-files) that extend the MATLAB environment to

solve particular classes of problems. Areas in which toolboxes

are available include

signal processing,

control systems,

neural networks,

fuzzy logic,

wavelets,

simulation, and many others

V. RESULT

Fig .4 Simulation result – 1

Fig. 5 Simulation result – 2

Fig. 6 Simulation result – 3

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Fig. 7 Simulation result – 4

Fig. 8 Simulation result – 5

VI. CONCLUSION

In this paper, a signal strength using the capacity of

the IM-DD optical broadcast channel is achieved. For this

channel, we have derived capacity region outer and inner

bounds. The inner bounds are achieved using superposition

coding and either truncated-Gaussian distributions or discrete

input distributions. We have shown that a superposition of

truncated-Gaussian inputs achieves the capacity region within

a constant gap at high SNR. We have also shown that as far as

the symmetric capacity is concerned, time-sharing between

superposition coding strategies is not necessary at high SNR.

As an extension of this work, it would be interesting to study

the impact of fading on the capacity of the OBC.

ACKNOWLEDGMENT

I would like to thank our chairman Mr.M.J.A.Jamal,

Managing Director Mr.K.Karl Mark principal

Dr.M.Ravichandran, Ph.D for encouraging and providing

necessary facilities towards the growth carrying this work.

The authors knowledge with the help of Ms.R.Ramya,

M.E., As-salam college of engineering and technology,

aduthurai, Tamilnadu in assisting me towards implemented

the project work.

REFERENCES

1. Chaaban, Z. Rezki, and M.-S. Alouini, “On the capacity of the 2-

user IM-DD optical broadcast channel,” in IEEE Globe com

Workshop on Optical Wireless Communication, San Diego, CA, Dec. 2015.

2. M.A. Khalighi and M.Uysal, “Survey on free space optical communications: A communication theory perspective,” IEEE

Communication Surveys and Tutorials, vol. 16, no. 4, pp. 2231–

2258, 4th quarter 2014.

3. H.Elgala, R.Mesleh, and H. Haas, “Indoor optical wireless communication: Potential and state-of-the-art,” IEEE Comm.

Magazine, vol. 49, no. 9, pp. 56–62, Sep. 2011.

4. S.M.Moser, “Capacity results of an optical intensity channel with

input dependent Gaussian noise,” IEEE Trans. on Info. Theory,

vol. 58, no. 1, pp. 207–223, Jan. 2012.

5. A.A.Farid and S.Hranilovic, “Diversity gain and outage

probability for MIMO free-space optical links with

misalignment,” IEEE Trans. On Communications, vol. 60, no. 2, pp. 479–487, Feb. 2012.

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