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ACKNOWLEDGEMENT

In the name of Allah the praiseworthy, the

passionate whose blessings made it

possible for me to complete the project. It

is a matter of great enthusiasm and

pleasure for me to complete the report in

its real sequence. It is all because of

Almighty Allah’s great guidance that made

us so able.

We are, also thankful to our respected

teacher Mam Jaweria Amjad, because of

whose generous co-operation and help, the

accomplishment of this Project became

possible.

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DEDICATION

We dedicate this project to our Instructor,

Mam Jaweria Amjad who assigned this project

to me and also to my beloved Parents who

always pray for us.

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Abstract:

A communications channel is a pathway over which information can be conveyed. It may be

defined by a physical wire that connects communicating devices, or by a radio, laser, or other

radiated energy source that has no obvious physical presence. Information sent through a

communications channel has a source from which the information originates, and a destination

to which the information is delivered. Although information originates from a single source,

there may be more than one destination, depending upon how many receive stations are linked

to the channel and how much energy the transmitted signal possesses.

In a digital communications channel, the information is represented by individual data bits,

which may be encapsulated into multibit message units. A byte, which consists of eight bits, is

an example of a message unit that may be conveyed through a digital communications channel.

A collection of bytes may itself be grouped into a frame or other higher-level message unit.

Such multiple levels of encapsulation facilitate the handling of messages in a complex data

communications network.

Introduction:

The project problem is to design a digital communication system that can convey an image

across a channel.

an A/D convertor to convert the image to a digital signal,

a digitial modulator for the transmission of the digital signal through the channel,

a digitial demodulator for the reception of the transmitted signal,

a D/A convertor to convert the received digital signal back to an image,

This task can be accomplished by transmitting an image. The image file is in the JPEG format.

MATLAB function "imread" to read the file into MATLAB can be used. The image file contains

samples of a grey image .You can treat the sampled values at each pixel as analog values, and

thus the image loaded into MATLAB as a representation of the original analog image signal. It

can be quantized further into fewer quantization levels. Converting the image into a sequence

of digital symbols (say bits).

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Block Diagram Representation:-

Fig(1)

The source is an image having JPEG format.It must be converted in 1-D dimension

before processing it Otherwise the dimensions will mismatch throughout its processing.

The digital modulation used in this project is ‘PSK’.

We used ifft on the transmitter side so that we can transmit aur signal in time domain

Initially there were sub carriers which were bulky so ifft and fft technique used.

Cyclic prefix is added and used as a guard band for secure transmission.

The channel used is Rayleigh Channel with 4 tapping points.

FFT at the receiver to get it back from time to frequency domain.

Demodulation is done at the end and the final received signal is of 3-Dimension which is our

need.

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Constellation Diagram Representation:-

A representation of a signal modulated by a digital modulation scheme such as quadrature amplitude

modulation or PSK.It displays the signal as two dimensional scatter diagram. Measured constellation

diagrams can be used to recognize the type of reference and distortion in a signal.

Following Constellation diagram was obtained while transmitting an Image

Rayleigh Channel Model Simple definition of Rayleigh Channel is a channel which shows Rayleigh distribution of

power profile as shown below.

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Apart from multipath reflection there might also be dispersive time varying effects in the

channel that is being modeled. One such effect is Doppler Shift that is caused when the

receiver and/or transmitter is in motion with respect to each other. In such cases the

dispersive effect is also modeled along with the chosen multipath model.Here the

frequency-flat fading Rayleigh Fading model with Doppler shift is considered for our

simulation.In wireless communication, it is important because this is very important

modeling for faded channels in wireless communication. In most cases, the channels for

reflected path is modeled in Rayleigh model as shown below.

Signal Generation for Rayleigh channel

There are a couple of ways to generate the signal for Rayleigh channel. The simplest way is

as shown below and overall procedure is as follows. i) Generate a random signal with Guassian distribution ii) Generate another random signal with Guassian distribution iii) Combine the signal i) and ii) to make a complex signal. iv) Take the magnitude of the complex signal and the distribution of the magnitude

value follows Rayleigh distribution.

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Mathematical Presentation of Rayleigh Channel

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Results And Simulations:-

1) Through AWGN Channel

Transmitted Image

Received Image

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2)Through Rayleigh Channel

Received Image

Differences Between the Tx and Rx Images:-

Since the image is transmitted through a Rayleigh Channel,having 4 tapping points with delay and gain

So it is not possible to recover the image even through filter also. The noise is like salt and pepper

because the pixels are received as they were transmitted but they cannot place themselves in correct

order due to Rayleigh Channel.

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Distribution Of Workload:-

Rana Ahtisham Ali Coding Of Rayleigh Channel

M Shams Ul Haq Image Processing and the Modulation Schemes

References:-

http://www.camiresearch.com/Data_Com_Basics/data_com_tutorial.html

http://www.realworldengineering.org/index.php?page=project&project=468

http://www.wu.ece.ufl.edu/projects/channelEstimation/

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Complete MATLAB Code clc clear all close all %**~~~~~~~ reading an image to be processed~~~~~~~~**% y=imread('images.jpg')

%**~~~~~~~ Converting the Image to Binary~~~~~~~~**% b=im2bw(y,0.4) imshow(b)

%**~~~~~~~ Resizing the image to 65536*1~~~~~~~~**% a=reshape(b,256*256,1)

%**~~~~~~~ System Object Creation For Modulation~~~~~~~~**% hModulator = comm.PSKModulator(256,pi/16,'BitInput',true) modData=step(hModulator,a)

%**~~~~~~~ IFFT Of the Data~~~~~~~~**% d=ifft(modData)

%**~~~~~~~Adding Cyclic Prefix~~~~~~~~**% Cp=length(d) * .25; end1=length(d); tx=[d(end1-Cp+1:end1,:)]; tx1=vertcat(tx,d);

%**~~~~~~~ Constellation Diagram representation~~~~~~~~**% %constellation(hModulator)

%**~~~~~~~ Creation of AWGN channel Object For comparison with rayleigh

Channel~~~~~~~~**% %hAWGN = comm.AWGNChannel('EbNo',200,'BitsPerSymbol',3) %modData1=step(hAWGN,tx1)

%**~~~~~~~ Passing Through Rayleigh Channel~~~~~~~~**% modData1=relaigh(tx1);

%**~~~~~~~ Removing Cyclic Prefix~~~~~~~~**% rec=[modData1(Cp+1:length(modData1),:)];

%**~~~~~~~ FFT of the data~~~~~~~~**% e=fft(rec)

%**~~~~~~~ System Object Creation For Demodulation~~~~~~~~**% hDemod = comm.PSKDemodulator(256, 'PhaseOffset',pi/16) modData2=step(hDemod,e)

%**~~~~~~Converting Back the Image to 256*256~~~~~~~~**% y=decimalToBinaryVector(modData2) y=logical(y(:)); s=reshape(y,256,256,1)

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%**~~~~~~~ Plot Of the Recieved Image through Channel~~~~~~~~**% figure(2) imshow(s)

function data_channel=relaigh(x)

N=10240;

Taps=4; % Number of Taps p1=0.5/2.3; % Power of Tap1 p2=0.9/2.3; % Power of Tap2 p3=0.7/2.3; % Power of Tap3 p4=0.2/2.3; gain1=sqrt(p1/2)*[randn(1,N) + j*randn(1,N)]; % Gain for Tap1 gain2=sqrt(p2/2)*[randn(1,N) + j*randn(1,N)]; % Gain for Tap2 gain3=sqrt(p3/2)*[randn(1,N) + j*randn(1,N)]; % Gain for Tap3 gain4=sqrt(p4/2)*[randn(1,N) + j*randn(1,N)]; % Gain for Tap4 x11=x(:); x12=reshape(x11,1,length(x11)); i=1:length(x12); delay1=1; for i=delay1+1:length(x12) % Producing one sample delay in Tap2 w.r.t. Tap1 x13(i)=x(i-delay1); end delay2=2; for i=delay2+1:length(x12) % Producing two sample delay in Tap2 w.r.t. Tap1 x14(i)=x(i-delay2); end delay3=3; for i=delay3+1:length(x12) % Producing three sample delay in Tap2 w.r.t. Tap1 x15(i)=x(i-delay3); end x1=reshape(x13,(1),length(x13)/(1)); x2=reshape(x14,(1),length(x14)/(1)); x3=reshape(x15,(1),length(x15)/(1)); x=reshape(x,(1),length(x13)/(1));

ch1=repmat(gain1,(1),1); ch2=repmat(gain2,(1),1); ch3=repmat(gain3,(1),1); ch4=repmat(gain4,(1),1);

data_channel=(x.*ch1)+(x1.*ch2)+(x2.*ch3)+(x3.*ch4);% Passing data through

channel

data_channel=data_channel';