comm lab file

8/10/2019 Comm Lab File

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DIGITAL COMMUNICATION LAB

Submitted By

Kodamanchili Rahul

60/EC/09


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CONTENTS

S. No Experiment Teachers Sign

1To evaluate the performance and compute the

SNR of Uniform and -law companding

quantizer

2 To evaluate the performance of DPCM and DM

schemes

3 To perform M-ary ASK/FSK/PSK Modulation

4

Generate four symbols with the given

probabilities a = 0.4, b = 0.3, c = 0.2, d = 0.1. Do

Huffman Coding and decoding of the signal and

compute the data rate compression

5

Generate a random sequence of 0s and 1s.

Generate the linear block code, add noise and

perform decoding

6To sample a signal of given amplitude and

frequency using Flat top and natural sampling

and reconstruct it back at the receiver

7Convert a sine wave to PCM data stream using

PCM encoder and reconstruct it back at the

receiver using PCM decoder

8 To observe the effect of limited bandwidth on

transmission of digital data

9

To evaluate performance of M-ary

ASK/PSF/FSK/QPSK/QAM signal and evaluate

its performance in the presence of Additive

White Gaussian Noise


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EXPERIMENT 1

Aim: - To evaluate the performance and compute the SNR of Uniform and -law compandingquantizer

[I] Uniform Quantizer

MATLAB Code: -

clear all;

clc;

N=2000;

a=rand(1,N)-0.5;

b=a;

for L=3:80

Linv=1/L;

for n=1:N

c(n)=0;

d(n)=0;

for j=0:L-1

if ( ( a(n)>(j*Linv-0.5) ) & ( a(n)


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Output: -

0 10 20 30 40 50 60 70 800

1000

2000

3000

4000

5000

6000

7000

Quantisation Levels---->

SNR

----

>

Uniform Quantizer

[II] -Law Companding Quantizer

MATLAB Code: -

clear all;

clc;

A = 10000; %Number of valuesMax =256; %Maximum value with minimum = 0

DATA = Max*rand(1,A);

Power=0;

for i=1:length(DATA)

Power = Power + DATA(i).^2;

end

Power;

u=1;

for i=1:length(DATA)

b(i)=Max*((log10((DATA(i)/Max)*u+1)) / (log10(1+u)));

endT = 100;%Number of maximum levels

N = zeros(1,T);

for z = 2:T

L = z;%Number of levels

d = zeros(1,length(b));

Diff = zeros(1,length(b));

M = (max(b))/L; %Interval

for i=1:length(b),

j=1;


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while b(i) > (j*M)

d(i) = d(i) + M;

j = j+1;

end

end

Diff = DATA-d;

Noise = 0;for i=1:length(Diff)

Noise = Noise + Diff(i).^2;

end

N(z)=Noise;

SNR(z) = Power/N(z);

end

plot(SNR,'k')

xlabel('Number of levels---->');

ylabel('SNR');

title('u Law quantizating');

Output: -

0 10 20 30 40 50 60 70 80 90 1000

50

100

150

200

250

Number of levels---->

SNR

u Law quantizating


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EXPERIMENT 2

Aim: - To evaluate the performance of DPCM and DM schemes.

[I] DPCM (Differential Pulse Code Modulation)

MATLAB Code: -

%perform DPCM

% 7 level quantizer

clear all;

clc;

N = 100;

X = rand(N,1);

X = X-1/2;

for i = 1:length(X)

if(i>3)

Xp(i) = 0.3*u(i-1)+0.2*u(i-2)+0.5*u(i-3); %Depends upon past 3 valueselse

Xp(i) = 0;

end

e(i) = X(i)-Xp(i);

if (e(i)>5/12)

eq(i) = 3/6;

elseif (e(i)>3/12)

eq(i) = 2/6;

elseif (e(i)>1/12)

eq(i) = 1/6;

elseif (e(i)>-1/12)

eq(i) = 0;

elseif (e(i)>-3/12)

eq(i) = -1/6;

elseif (e(i)>-5/12)

eq(i) = -2/6;

else

eq(i) = -3/6;

end

u(i)=eq(i)+Xp(i);

end

plot(1:length(X),X,1:length(u),u)

xlabel('x--->');ylabel('y--->');

title('DPCM');

figure(2)

stem(e,eq)

xlabel('Vin--->');

ylabel('Vo--->');

title('Transfer Characteristic');

%proceed further

QN = 0;


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SN = 0;

for i= 1:length(e)

QN = QN + (X(i)-u(i))^2;

SN = SN + u(i)^2;

end

QN = QN/length(QN);

SN = SN/length(SN);SNR = SN/QN

Outputs: -

SNR = 12.63


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[II] DM

MATLAB Code: -

%perform DM

% 2 level quantizer

clear all;

clc;

N = 100;

X = sin(0.05*(1:N));X = X-1/2;

for i = 1:length(X)

if(i>1)

Xp(i) = u(i-1);

else

Xp(i) = 0;

end

e(i) = X(i)-Xp(i);

if (e(i)>0)

eq(i) = 1/9;

else

eq(i) = -1/9;

end

u(i)=eq(i)+Xp(i);

end

plot(1:length(X),X,1:length(u),u)

xlabel('x--->');

ylabel('y--->');

title('DM');


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figure(2)

stem(e,eq)

xlabel('Vin--->');

ylabel('Vo--->');

title('Transfer Characteristic');

%proceed further

QN = 0;

SN = 0;

for i= 1:length(e)

QN = QN + (X(i)-u(i))^2;

SN = SN + u(i)^2;

end

QN = QN/length(QN);

SN = SN/length(SN);

SNR = SN/QN

Outputs: -

SNR = 122.53


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Experiment 3

Aim: - To perform M-ary ASK/FSK/PSK Modulation

[I] Binary ASK

MATLAB Code: -

clc;

clear all;

X = rand(10,1);

X=X-0.5;

Ai = 5;

fc = 1000;

Tb = 0:.00001:.002;%Bit duration

for i=1:length(X),

if X(i)>0X(i)=1;

else

X(i)=0;

end;

for(j = 1:length(Tb))

Y(j+(i-1)*length(Tb)) = Ai*X(i)*sin(2*pi*fc*Tb(j));

end;

end;

plot(1:length(Y),Y,'k');

xlabel('Time--->');

ylabel('Amplitude--->');

title('ASK');

Output: -

0 200 400 600 800 1000 1200 1400 1600 1800 2000-5

-4

-3

-2

-1

0

1

2

3

4

5

Time--->

Amp

litude--

->

ASK


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[II] Binary PSK

MATLAB Code: -

clc;

clear all;

X = rand(10,1);

X=X-0.5;

Ai = 5;

fc = 1000;

Tb = 0:.00001:.002;%Bit duration

for i=1:length(X),

if X(i)>0

X(i)=1;

else

X(i)=0;

end;

for(j = 1:length(Tb))Y(j+(i-1)*length(Tb)) = Ai*sin(2*pi*fc*Tb(j)+X(i)*pi);

end;

end;


xlabel('Time--->');


title('PSK');

axis([0 2000 -5 5]);

Output: -

0 200 400 600 800 1000 1200 1400 1600 1800 2000-5

-4

-3

-2

-1

0

1

2

3

4

5

Time--->

Amp

litude--->

PSK


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[IV] 4-ary ASK

MATLAB Code: -

clc;clear all;

n=2;

X = rand(20,1);

X=X-0.5;

Ai = 5;

fc = 1000;

Tb = 0:.00001:.002;%Bit duration/half symbol duration

for i=1:length(X),

if X(i)>0

X(i)=1;

elseX(i)=0;

end;

if(mod(i,2)==0)


for(p=1:n)

Y(j+(i-p)*length(Tb)) = Ai*(X(i)+2*X(i-1))*sin(2*pi*fc*Tb(j));

end

end;

end

end;


xlabel('Time--->');


title('ASK');

axis([0 4003 -16 16]);


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Output: -

0 500 1000 1500 2000 2500 3000 3500 4000

-15

-10

-5

0

5

10

15

Time--->

Amp

litude--->

ASK

[V] 4-ary PSK

MATLAB Code: -

clc;

clear all;

n=2;

X = rand(10,1);

X=X-0.5;

Ai = 5;

fc = 1000;

Tb = 0:.000001:.002;%Bit duration/half symbol duration

for i=1:length(X),if X(i)>0

X(i)=1;

else

X(i)=0;

end;

if(mod(i,2)==0)


for(p=1:n)

Y(j+(i-p)*length(Tb)) = Ai*sin(2*pi*fc*Tb(j)+(((X(i)+2*X(i-1)))*pi/2));

end;

end

end

end;


xlabel('Time--->');


title('PSK');

axis([0 20003 -6 6]);


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Output: -

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

x 104

-6

-4

-2

0

2

4

6

Time--->

Amp

litude--->

PSK

[VI] 4-ary FSK

MATLAB Code: -

clc;

clear all;

clc;

clear all;

n=2;

X = rand(10,1);

X=X-0.5;

Ai = 5;

fc = 1000;Tb = 0:.000001:.002; %Bit duration/half symbol duration

for i=1:length(X),

if X(i)>0

X(i)=1;

else

X(i)=0;

end;

if(mod(i,2)==0)


for(p=1:n)

Y(j+(i-p)*length(Tb)) = Ai*sin(2*pi*(fc+200*(X(i)+2*X(i-1)))*Tb(j));

end

end;

end

end;


xlabel('Time--->');


title('FSK');

axis([0 20003 -6 6]);


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Output: -

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

x 10

4

-6

-4

-2

0

2

4

6

Time--->

Amp

litude--->

FSK


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Outputs: -

H = 1.8464

Sym = 0 0 0 0 1 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0

Tx = 0 0 1 0 1 0 0 1 0 1 0 1 0 1 0 0

Lbar = 1.9000

Efficiency = 97.1810

Tx(j+1)=0;

Tx(j+2)=0;j=j+3;

endend

TxLbar=1*p(1)+2*p(2)+3*p(3)+3*p(4)Efficiency=H*100/Lbar


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[II] Huffman Decoder

MATLAB Code: -

clc;clear all;num=10;

% Probabilities a=0.4, b=0.3, c=0.2, d=0.1j=1;

X=rand(1,num);

for i=1:numif(X(i)0.9)Rx(j)=1;

Rx(j+1)=0;

Rx(j+2)=0;j=j+3;

endend

j=1;i=1;% for i=1:length(Rx)while(i~=length(Rx)+1)

if(Rx(i)==0)Sym(j)=0;

Sym(j+1)=0;

j=j+2i=i+1

elseif(Rx(i)==1)if((Rx(i+1)==0)&&(Rx(i+2)==1))

Sym(j)=1;Sym(j+1)=0;

j=j+2i=i+3

elseif((Rx(i+1)==0)&&(Rx(i+2)==0))

Sym(j)=1;S m +1 =1;


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Outputs: -

Rx= 1 0 1 1 0 0 1 1 1 0 1 0 1 0 0 0 0 1 0 1 1 0 1

Sym = 1 0 1 1 0 1 1 0 0 0 1 1 0 0 0 0 1 0 1 0

j=j+2

i=i+3elseif(Rx(i+1)==1)

Sym(j)=0;

Sym(j+1)=1;j=j+2

i=i+2end

endend


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EXPERIMENT 5

Aim: - Generate a random sequence of 0s and 1s. Generate the linear block code, add noiseand perform decoding.

[I] Linear Block Code

MATLAB Code: -

clear all;clc;

a=rand(1,4);for i=1:length(a)

if(a(i)


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Outputs: -

DATA =

0 1 1 0

C =

1 0 0 0 1 1 0

R =

0 0 0

S =

1 1 0 0 0 1 0

E =

0 0 1


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Observations:

Natural sampling of Sine Wave Flat top sampling of Sine Wave

Natural Sampling at higher sampling frequency Reconstruction of message signal

Input Signal and the Reconstructed Signal


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EXPERIMENT 7

Aim: - Convert a sine wave to a PCM data stream using PCM encoder and reconstruct the

message at the receiver using PCM decoder

Apparatus:Emona Telecoms Kit 101, BNC Connectors, Digital Storage Oscillicope, Patch leads

Theory:

In Pulse Code Modulation, a message signal is represented by a sequence of coded pulses,

which is accomplished by representing in discrete form in both time and amplitude. The basic

operations performed in the transmitter of a PCM system are sampling, quantizing and

encoding, the low pass filter before sampling the signal is used for preventing aliasing of the

message signal. The quantizing and encoding operations are usually performed in the same

circuit, which is called an analog-to-digital converter. The basic operations in the receiver are

regeneration of impaired signals, decoding and reconstruction of the train of quantized

samples. When TDM is used, it becomes necessary to synchronize the receiver to thetransmitter for the overall system to operate satisfactorily.

Pulse Code Encoding

Pulse Code Decoding

In combining the processes of sampling and quantization, the specification of a continuous

message baseband signal becomes limited to a discrete set of values, but not in the form best

suited to transmission over a telephone line or radio path. To exploit the advantages of

sampling and quantizing for the purpose of making the transmitted signal more robust to noise,

interference and other channel impairments, we require use of encoding process to translatethe discrete set of values to a more appropriate form of digital signal. Maximum advantage

over the effects of noise in a medium is obtained by using a binary code because a binary

symbol withstands high level of noise and is easy to regenerate.


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Observations:

Sampling frequency for PCM Encoder

PCM Encoded Sine Wave

PCM Decoded Sine wave at the receiver and the input sine wave


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EXPERIMENT 8

Aim:- To observe the effect of limited bandwidth on the transmission of digital data


Theory:

In classical model, intelligence moves from transmitter to a receiver over a channel. A number

of transmission media can be used for the channel including metal conductors. Regardless of

the medium used, all channels have a bandwidth. That is, the medium lets a range of signal

frequencies pass relatively unaffected while frequencies outside the range are mode smaller.

The issue has important implications. If the mediums bandwidth isnt wide enough some of the

sine waves are attenuated and others are lost completely.

Square Wave through a channel through a band limited channel

Bandwidth limiting in a channel can distort digital signals and upset the operation of the

receiver. A solution to the problem of limited bandwidth of the channel is to use a transmission

medium that has a sufficiently wide bandwidth for the digital data. As digital technologyspreads there are demands to push more data down existing channels. To do so without

slowing things down requires that the transmission bit rate be increased. This ends up having

the same basic effect as reducing the channels bandwidth.

Eye diagrams give us idea about the signals quality and the channels bandwidth. As bandwidth

limiting degrades the signals quality the eyes begin to close.

Eye Diagram


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Observations:

PCM Data with full bandwidth PCM Data with restricted bandwidth using a LPF

Eye Diagram

Restored Digital Signal using Comparator


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EXPERIMENT 9

Aim:- To generate binary ASK/FSK/QPSK signal and evaluate its performance in the presence of

Additive White Gaussian Noise


Theory:

Amplitude-shift keying is a form of modulation that represents digital data as variations in

the amplitude of a carrier wave. The amplitude of an analog carrier signal varies in accordance

with the bit stream (modulating signal), keeping frequency and phase constant. The level of

amplitude can be used to represent binary logic 0s and 1s.

The simplest and most common form of ASK operates as a switch, using the presence of a

carrier wave to indicate a binary one and its absence to indicate a binary zero. This type of

modulation is called on-off keying, and is used at radio frequencies to transmit Morse code(referred to as continuous wave operation).

More sophisticated encoding schemes have been developed which represent data in groups

using additional amplitude levels. For instance, a four-level encoding scheme can represent

two bits with each shift in amplitude; an eight-level scheme can represent three bits; and so on.

These forms of amplitude-shift keying require a high signal-to-noise ratio for their recovery, as

by their nature much of the signal is transmitted at reduced power.

Frequency-shift keying (FSK)is a frequency modulation scheme in which digital information is

transmitted through discrete frequency changes of a carrier wave. The simplest FSK is

binary FSK(BFSK). BFSK literally implies using a pair of discrete frequencies to transmit binary

(0s and 1s) information. With this scheme, the "1" is called the mark frequency and the "0" iscalled the space frequency.

Phase-shift keying (PSK)is a digital modulation scheme that conveys data by changing, or

modulating, the phase of a reference signal (the carrier wave). Any digital modulation scheme

uses a finite number of distinct signals to represent digital data. PSK uses a finite number of

phases, each assigned a unique pattern of binary digits. Usually, each phase encodes an equal

number of bits. Each pattern of bits forms the symbol that is represented by the particular

phase. The demodulator, which is designed specifically for the symbol-set used by the

modulator, determines the phase of the received signal and maps it back to the symbol it

represents, thus recovering the original data.

Alternatively, instead of using the bit patterns to setthe phase of the wave, it can instead be

used to changeit by a specified amount. The demodulator then determines the changesin the

phase of the received signal rather than the phase itself. Since this scheme depends on the

difference between successive phases, it is termed differential phase-shift keying (DPSK). DPSK

can be significantly simpler to implement than ordinary PSK since there is no need for the

demodulator to have a copy of the reference signal to determine the exact phase of the

received signal (it is a non-coherent scheme). In exchange, it produces more erroneous

demodulations. The exact requirements of the particular scenario under consideration

determine which scheme is used.
http://en.wikipedia.org/wiki/Signal_(electrical_engineering)http://en.wikipedia.org/wiki/Signal_(electrical_engineering)


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Observations:

Digital Signal and its ASK Signal

Input Signal and its Regenerated signal after ASK

Digital Signal and its FSK modulation


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Demodulated FSK Signal and input signal Cleaned up demodulated signal and input signal

Signal Demodulated from the BPSK version BPSK (Even and Odd bits)

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