CHADALAWADA RAMANAMMA ENGINEERING COLLEGE Communication Lab... · CHADALAWADA RAMANAMMA ENGINEERING COLLEGE (AUTONOMOUS) Chadalawada Nagar, Renigunta Road, Tirupati – 517 506 Department

DIGITAL COMMUNICATION SYSTEMS

LABORATORY MANUAL

Subject Code :

Regulations :

Class : III B.Tech I-Sem(ECE)

CHADALAWADA RAMANAMMA ENGINEERING COLLEGE (AUTONOMOUS)

Chadalawada Nagar, Renigunta Road, Tirupati – 517 506

Department of Electronics and Communication Engineering

17CA04510

R17

CHADALAWADA RAMANAMMA ENGINEERING COLLEGE (AUTONOMOUS)

Chadalawada Nagar, Renigunta Road, Tirupati – 517 506

Department of Electronics and Communication Engineering

INDEX

S. No Name of the Experiment Page No

1 Time division multiplexing. 1-4

2 Pulse code modulation. 5-8

3 Differential pulse code modulation. 9-10

4 Delta modulation. 11-13

5 Frequency shift keying. 14-17

6 Differential phase shift keying. 18-21

Experiments using MATLAB

7 Verification of Sampling Theorem 23-25

8 Pulse code modulation. 26-28

9 Differential pulse code modulation. 29-30

10 Frequency shift keying. 31-32

11 PSK Modulation and Demodulation 33-35

12 Differential phase shift keying. 36-39

Experiments Beyond the syllabus Using MATLAB

13 Quadrature Phase Shift Keying. 40-42

14 Delta modulation. 43-44

15 ASK Modulation and Demodulation 45-47

Digital Communication Systems Lab

Department of ECE-CREC-Tirupati Page 1

Expt-no:1

TIME DIVISION MULTIPLEXING AND DEMULTIPLEXING

Aim:

1. To study the 4 channel analog multiplexing and demultiplexing

2. To study the effect of sampling frequency on output signal characteristics.

3.To study the effect of input signal amplitude on the output signal characteristics .

Apparatus required:

1. Time Division Multiplexing and de multiplexing trainer Kit.

2. Dual Trace oscilloscope

Theory:

In PAM, PPM the pulse is present for a short duration and for most of the time

between the two pulses no signal is present. This free space between the pulses can

be occupied by pulses from other channels. This is known as Time Division

Multiplexing. Thus, time division multiplexing makes maximum utilization of the

transmission channel. Each channel to be transmitted is passed through the low

pass filter. The outputs of the low pass filters are connected to the rotating

sampling switch (or) commutator. It takes the sample from each channel per

revolution and rotates at the rate of f s . Thus the sampling frequency becomes fs

the single signal composed due to multiplexing of input channels. These channels

signals are then passed through low pass reconstruction filters. If the highest signal

frequency present in all the channels is f m , then by sampling theorem, the

sampling frequency f s must be such that f s ≥2f m . Therefore, the time space

between successive samples from any one input will be T s =1/f s, and T s ≤ 1/2fm.



Fig: Time Division Multiplexing And Demultiplexing Circuit

Procedure:

There are 4 signal sources;

a) AF Signal generator

b) Triangular wave generator

c) Square wave generator and

d) Sine wave generator

1. Connect these four signals to four inputs of the Multiplexer. Adjust each

signal amplitude to be with in +/-2V (p-p) and frequency non-over lapping

within a frequency band of 300Hz.

2. Connect A, B output of 7476 to AI, BI inputs of Multiplexer.

3. Adjust the frequency of IC 8038 (Square wave, triangular wave

generator) to be around 32 KHz, so that each of the Four channels are

sampled at 8 KHz.



4. Adjust the pulse width of 555 timers to be around 10μsecs.

5. Observe the 4 output pin 11 of 7476 on one channel 1and TDM output pin 13

of CD4052 on second channel of oscilloscope. Synchronize scope Internal-CH

1 mode. All the multiplexed channels are observed during the full period of the

clock (1/32 KHz).

6. Connect TDM output to comparator –ve input and saw tooth wave to +ve

Input. Observe the Comparator output. The PAM pulses are now converted in

to PWM pulses.

7. Connect the PWM pulses to TDM input of De multiplexer at pin 3 of second

CD4052. Observe the individual outputs Y0, Y1, Y2, and Y3 at pin 1, 5, 2 & 4

of CD4052 respectively. The PWM pulses corresponding to each channels

are now separated as 4 streams.

8. Take one output and connect it to Low Pass Filter and the Low Pass Filter

output to Amplifier. Observe the output of the amplifier in conjunction with the

corresponding input. Repeat this for all 4 inputs. This is the Demodulated

TDM output. Any slight variation in frequency, amplitude is reflected in the

corresponding output.

Observations:



Model Waveform:

Multiplexed output

RESULT:



Expt-no:2

PULSE CODE MODULATION & DEMODULATION

AIM:

To generate a PCM signal using PCM modulator and detect the message signal

using PCM demodulator.

APPARATUS REQUIRED:

1. PCM kit

2. CRO

3. Connecting probes

THEORY:

Pulse code modulation is a process of converting an analog signal into digital. The

voice or any data input is first sampled using a sampler (which is a simple switch)

and then quantized. Quantization is the process of converting a given signal

amplitude to an equivalent binary number with fixed number of bits. This

quantization can be either midtread or mid-raise and it can be uniform or non-

uniform based on the requirements. For example in speech signals, the higher

amplitudes will be less frequent than the low amplitudes. So higher amplitudes are

given less step size than the lower amplitudes and thus quantization is performed

non-uniformly. After quantization the signal is digital and the bits are passed

through a parallel to serial converter and then launched into the channel serially.

At the demodulator the received bits are first converted into parallel frames and

each frame is de-quantized to an equivalent analog value. This analog value is thus

equivalent to a sampler output. This is the demodulated signal.

In the kit this is implemented differently. The analog signal is passed through a

ADC (Analog to Digital Converter) and then the digital codeword is passed

through a parallel to serial converter block. This is modulated PCM. This is taken

by the Serial to Parallel converter and then through a DAC to get the demodulated

signal. The clock is given to all these blocks for synchronization. The input signal

can be either DC or AC according to the kit. The waveforms can be observed on a

CRO for DC without problem.AC also can be observed but with poor resolution.



PROCEDURE:

1. Make the connections as per the diagram as shown in the Fig.1.and switch on

the power supply of the trainer kit.

2. Clock generator generates a 20 KHz clock .This can be given as input to the

timing and control circuit and observe the sampling frequency fs= 2 KHz

approximately at the output of timing and control circuit.

3. Apply the signal generator output of 6V(p-p) approximately to the A to D

converter input and note down the binary word from LED’s i.e. LED “ON”

represents ‘1’ & “OFF” represents ‘0’

4. Feed the PCM waveform to the demodulator circuit and observe the waveform

at the output of D/A which is quantized level.

Circuit Diagram:



Wave forms:



Calculations:

Result:



Expt No:3

DIFFERENTIAL PULSE CODE MODULATION

AIM: To Study & understand the operation of the DPCM

EQUIPMENT REQUIRED:

1. DPCM Modulator & Demodulator trainer

2. Storage Oscilloscope

3. Digital Multimeter

4. 2 No’s of coaxial cables (standard accessories with trainer)

5. Patch chords

THEORY:

In this DPCM instead of transmitting a base band signal m(t) we send the

difference signal of Kth sample and (k-1) th sample value. The advantage here is

fewer levels are required to quantize the difference than the required to quantize

m(t) and correspondingly, fewer bits will be needed to encode the levels. If we

know the post behaviour of a signal up to a certain time, it is possible to make

some interference about its future values this is called prediction. The filter

designed to perform the prediction is called a predictor. The difference between the

interest and the predictor o/p is called the prediction error.

Circuit Diagram:



Procedure:

1. Switch on the experimental kit.

2. Apply the variable DC signal of amplitude 6v(p-p) with frequency of 80Hz

to the input terminals of DPCM modulator.

3. Observe the sampling signal of amplitude 5v (p-p) with frequency 20KHz

on channel 1 of a CRO.

4. Observe the output of DPCM on the second channel.

5. By adjusting the DC voltage potentiometer, observe the DPCM output.

6. During the demodulation connect DPCM output to the input of

demodulator and observe the output of DPCM demodulator.

Waveform:

Result:



Expt-No:4

DELTA MODULATION & DEMODULATION

AIM: To study the characteristics of Delta Modulation and Demodulation.

EQUIPMENT REQUIRED:

1. DM Modulator & Demodulator trainer

2. Storage Oscilloscope

3. Digital multimeter.

4. 2 No’s co-axial cables (standard accessories with trainer)

THEORY:

Delta modulation is almost similar to differential PCM. In this, only one bit is

transmitted per sample just to indicate whether the present sample is larger or

smaller than the previous one. The encoding, decoding and quantizing process

become extremely simple but this system cannot handle rapidly varying samples.

This increases quantizing noise. It has also not found wide acceptance.

Circuit Diagram:



Procedure:

1. Switch on the experimental board.

2. Connect the clock signal of frequency of 10KHz,with amplitude of 5v(p-p)

to the delta modulator circuit.

3. Connect the modulating signal of amplitude 5v(p-p) and frequency of of

0.2KHz modulating input of the delta modulator

And observe the same on channel 1 of a Dual Trace oscilloscope.

4. Observe the Delta Modulator output on channel 2.

5. Connect this Delta modulator output to the Demodulator

6. Also connect the clock signal to the demodulator.

7. Observe the Demodulator output with and without RC filter on CRO.



Model Waveforms:

Result:



Expt-No:5

FREQUENCY SHIFT KEYING

AIM: To study the characteristics of Frequency Shift keying

EQUIPMENT REQUIRED:

1. Frequency Shift Keying system trainer

2. Dual trace Oscilloscope

3. Digital multimeter

4. Digital frequency counter

THEORY:

Frequency Shift Keying (FSK) is a modulation/ Data transmitting technique in

which carrier frequency is shifted between two distinct fixed frequencies to

represent logic 1 and logic 0. The low carrier frequency represents a digital 0

(space) and higher carrier frequency is a 1 (mark). FSK system has a wide range of

applications in low speed digital data transmission systems. Wave forms are

shown in Figure. FSK Modulating & Demodulating circuitry can be developed in

number of ways, familiar VCO and PLL circuits are used in this trainer.

Procedure:

1. Connect the circuit as shown in fig.1

2. Apply the (binary) Data input of amplitude 20V (p-p) with frequency of 6 KHz

from function generator to pin no.7.

3. Give the power supply of 10v to the appropriate pins.

4. Observe the FSK output at pin no.2.

5. Now note down the mark and space frequencies for different carrier

frequencies.

6. Calculate the maximum frequency deviation and modulation index.



7. Repeat the steps (5) and (6) for different pulse durations of binary input.

Circuit Diagram:

Fig: Block diagram for Frequency Shift Keying

Procedure:

1 Connect the AC Adaptor to the mains and the other side to the

Experimental Trainer. Switch‘ON’ the power.

2 Connect ‘Data Input’s socket to ground

3 Connect the FSK output to the Ch1 of the Oscilloscope and trigger the

scope from Ch1.

4 Set the ‘ Freq. Adj ’ Potentiometer So that the output is around 30 kHz

approx.

5 Set the Switches for required word pattern. Push the load switch

momentarily and release . This will parallel load the word pattern and then

shifts the pattern that is set Adjust the required frequency of the clock.

6 Connect the Data input to ‘ Ground’, Measure the frequency.

7 Connect the ‘ Data output ‘ to ‘ Data input ‘ .

8 Observe the Data output on CH1 and FSK output on CH2.



9 Observe that at each negative transition’ ‘ the carrier switches from high to low

and every positive transition ‘ ‘ the frequency switches from low to high.

10 Connect ’FSK output ‘ to ‘ FSK input ’ of the Demodulator.

11 Adjust P3 to regenerate the Data correctly.

12 Compare the Demod output to the Data output which are identical in nature.

13 Change the Data Pattern as mentioned in sl No 6, and Observe the Demod

output again.

Model Waveform:



Tabulations:

Result:



Expt-No:6

Differential phase shift keying

AIM: To study the characteristics of differential phase shift keying.

EQUIPMENT REQUIRED:

1. Differential Phase Shift Keying Kits

2. C.R.O

3. Digital multimeter.

4. No’s of coaxial cables (standard accessories with trainer)

THEORY:

DPSK: Phase Shift Keying requires a local oscillator at the receiver which is

accurately synchronized in phase with the un-modulated transmitted carrier, and in

practice this can be difficult to achieve. Differential Phase Shift Keying (DPSK)

over comes the difficult by combining two basic operations at the transmitter (1)

differential encoding of the input binary wave and (2) phase shift keying – hence

the name differential phase shift keying. In other words DPSK is a non - coherent

version of the PSK. DPSK DEMODULATOR: Fig shows the DPSK modulator.

This consists of PSK modulator and differential encoder. PSK Modulator: IC CD

4052 is a 4 channel analog multiplexer and is used as an active component in this

circuit. One of thecontrol signals of 4052 is grounded so that 4052 will act as a

two channel multiplexer and other control is being connected to the binary signal

i.e., encoded data. Un shifted carrier signal is connected directly to CH1 and carrier

shifted by 1800 is connected to CH2. Phase shift network is a unity gain inverting

amplifier using Op-Amp (TL084).

When control signal is at high voltage, output of the 4052 is connected to CH1

and un-shifted (or 0 phase) carrier is passed on to output. Similarly when control

signal is at zero voltage output of 4052 is connected to CH2 and carrier shifted by

1800 is passed on to output.



Differential encoder: This consists of 1 bit delay circuit and an X-NOR Gate. 1 bit

delay circuit is formed by a D-Latch. Data signal i.e., signal to be transmitted is

connected to one of the input of the X-NOR gate and other one being connected to

out of the delay circuit. Output of the X-NOR gate and is connected to control

input of the multiplexer (IC 4052) and as well as to input of the D-Latch. Output

of the X-NOR gate is 1 when both the inputs are same and it is 0 when both the

inputs are different.

Circuit Diagram:



Procedure:

1. Switch on the experimental board.

2. Check the carrier signal and the data generator signals initially.

3. Apply the carrier signal of amplitude 6v (p-p) with frequency of1KHz to the

carrier input, the data input of amplitude 5v (p-p) with frequency of 600Hz

to the data input and bit clock of amplitude 5v (p-p) with and frequency of

1 KHz to the DPSK modulator.

4. Observe the DPSK wave of amplitude 5.6v (p-p) and frequency of 1 KHz

with respect to the input data generated signal of dual trace oscilloscope.

5. Give the output of the DPSK modulator signal to the input of demodulator,

give the bit clock output to the bit clock input to the demodulator and also

give the carrier output to the carrier input of demodulator.

6. Observe the demodulator output with respect to data generator signal.



Waveform:

Result:



Software Programs using MATLAB



Verification of Sampling Theorem

AIM :

To write a MATLAB program for the process of sampling and to reconstruct the signals and

observe the output waveforms.

Requirements: PC and MATLAB software

THEORY:

A message signal may originate from a digital or analog source. If the message signal is analog

in nature, then it has to be converted into digital form before it can transmitted by digital means.

The process by which the continuous-time signal is converted into a discrete time signal is called

Sampling. Sampling operation is performed in accordance with the sampling theorem.

Sampling Theorem For Low-Pass Signals:-

Statement:- “If a band –limited signal g(t) contains no frequency components for ׀f |f| > W,

then it is completely described by instantaneous values g(kTs) uniformly spaced in time

with period Ts ≤ 1/2W. If the sampling rate, fs is equal to the Nyquist rate or greater (fs ≥

2W), the signal g(t) can be exactly reconstructed”.

Program:

clear all;

close all;

clc;

t=-10:.01:10; %t vector

T=8; %time period

fm=1/T; %frequency

x=cos(2*pi*fm*t); %cos wave

fs1=1.6*fm; %fs<2fm

fs2=2*fm; %fs=2fm

fs3=8*fm; %fs>2fm

n1=-4:1:4; %index vector

xn1=cos(2*pi*n1*fm/fs1);%aliasing

EXPT. NO-7



subplot(2,2,1);

plot(t,x);

xlabel('time in sec');

ylabel('x(t)');

title('continuous time signal');

subplot(2,2,2);

stem(n1,xn1); %aliasing discrete

hold on;

plot(n1,xn1); %aliasing cont

xlabel('n');

ylabel('x(n)');

title('discrete time s/g with fs<2fm');

n2=-5:1:5; %time index

xn2=cos(2*pi*n2*fm/fs2); %fs=2fm

subplot(2,2,3);

stem(n2,xn2); %sampling for fs=2fm

hold on;

plot(n2,xn2); %ploting fs=2fm

xlabel('n');

ylabel('x(n)');

title('discrete time s/g with fs=2fm');

n3=-20:1:20; %time index

xn3=cos(2*pi*n3*fm/fs3); %fs>2fm

subplot(2,2,4);

stem(n3,xn3); %samples for fs>2fm

hold on;

plot(n3,xn3); %ploting fs>2fm

xlabel('n');

ylabel('x(n)');

title('discrete time s/g with fs>2fm');



Waveforms:

Result:


Department of ECE-CREC-Tirupati

Pulse Code Modulation

AIM:To write a MATLAB program for Pulse Code Modulation and to observe the output wave

forms.

Requirements:PC and MATLAB software

Description: Pulse code modulation (PCM) is a digital scheme for transmitting analog data.

The signals in PCM are binary; that is, there are only two possible states, represented by

logic 1 (high) and logic 0 (low). This is true no matter how complex the analog waveform

happens to be. Using PCM, it is possible to digitize all forms of analog data, including

full-motion video, voices, music, telemetry, and virtual reality (VR).

To obtain PCM from an analog waveform at the source (transmitter end) of a

communications circuit, the analog signal amplitude is sampled (measured) at regular time

intervals.The sampling rate, or number of samples per second, is several times the

maximum frequency of the analog waveform in cycles per second or hertz. The

instantaneous amplitude of the analog signal at each sampling is rounded off to the nearest

of several specific, predetermined levels. This process is called quantization. The number

of levels is always a power of 2 -- for example, 8, 16, 32, or 64. These numbers can be

represented by three, four, five, or six binary digits (bits) respectively. The output of a

pulse code modulator is thus a series of binary numbers, each represented by some power

of 2 bits.

At the destination (receiver end) of the communications circuit, a pulse code demodulator

converts the binary numbers back into pulses having the same quantum levels as those in

the modulator. These pulses are further processed to restore the original analog waveform.

Program:

clc;

close all;

clear all;

n=input('Enter n value for n-bit PCM system : ');

n1=input('Enter number of samples in a period : ');

L=2^n;

x=0:2*pi/n1:4*pi; % n1 nuber of samples have tobe selected

s=8*sin(x);

subplot(3,1,1);

plot(s);

title('Analog Signal');

ylabel('Amplitude--->');

xlabel('Time--->');

Page 26

EXPT. NO-8

http://searchcio-midmarket.techtarget.com/definition/digital

http://searchcio-midmarket.techtarget.com/definition/analog

http://searchmobilecomputing.techtarget.com/definition/hertz



subplot(3,1,2);

stem(s);grid on; title('Sampled Signal'); ylabel('Amplitude--->'); xlabel('Time--->');

% Quantization Process

vmax=8;

vmin=-vmax;

del=(vmax-vmin)/L;

part=vmin:del:vmax;

code=vmin-(del/2):del:vmax+(del/2);

[ind,q]=quantiz(s,part,code);

l1=length(ind);

l2=length(q);

for i=1:l1

if(ind(i)~=0) ind(i)=ind(i)-1;

end

i=i+1;

end

for i=1:l2

if(q(i)==vmin-(del/2)) % q(i)=vmin+(del/2);

end

end

subplot(3,1,3);

stem(q);grid on;

title('Quantized Signal');


xlabel('Time--->');

% Encoding Process

figure

code=de2bi(ind,'left-msb');

k=1;

for i=1:l1

for j=1:n

coded(k)=code(i,j);

j=j+1;

k=k+1;

end

i=i+1;

end

subplot(2,1,1); grid on;

stairs(coded);

axis([0 100 -2 3]); title('Encoded Signal');


xlabel('Time--->');

% Demodulation Of PCM signal

qunt=reshape(coded,n,length(coded)/n);

index=bi2de(qunt','left-msb');

Page 27



q=del*index+vmin+(del/2);

subplot(2,1,2); grid on;

plot(q);

title('Demodulated Signal');


xlabel('Time--->');

Output:

Enter n value for n-bit PCM system : 8

Enter number of samples in a period : 8

Result:

0 10 20 30 40 50 60 70 80 90 100-2

-1

0

1

2

3Encoded Signal

Ampli

tude--

->

Time--->

0 2 4 6 8 10 12 14 16 18-10

-5

0

5

10Demodulated Signal

Ampli

tude--

->

Time--->

0 2 4 6 8 10 12 14 16 18-10

0

10Analog Signal

Am

plitu

de--

->

Time--->

0 2 4 6 8 10 12 14 16 18-10

0

10Sampled Signal

Am

plitu

de--

->

Time--->

0 2 4 6 8 10 12 14 16 18-10

0

10Quantized Signal

Am

plitu

de--

->

Time--->

Page 28



Expt no:

Differential Pulse Code Modulation

Aim: To write a MATLAB program for Differential Pulse Code Modulation

and to observe the output wave forms.

Apparatus:

Operating Systems: Windows

Software Tools: Matlab

Theory:

In this DPCM instead of transmitting a base band signal m(t) we send the

difference signal of Kth sample and (k-1) th sample value. The advantage

here is fewer levels are required to quantize the difference than the

required to quantize m(t) and correspondingly, fewer bits will be needed

to encode the levels. If we know the post behaviour of a signal up to a

certain time, it is possible to make some interference about its future

values this is called prediction. The filter designed to perform the

prediction is called a predictor. The difference between the interest and

the predictor o/p is called the prediction error.

Program:

Clc; Clear all; Close all; predictor = [0 1]; % y(k)=x(k-1) partition = [-1:.1:.9];

codebook = [-1:.1:1];

t = [0:pi/50:2*pi];

x = sawtooth(3*t); % Original signal

% Quantize x using DPCM.

9

Page 29



encodedx = dpcmenco(x,codebook,partition,predictor);

% Try to recover x from the modulated signal.

decodedx = dpcmdeco(encodedx,codebook,predictor);

plot(t,x,t,decodedx,'--')

legend('Original signal','Decoded signal','Location','NorthOutside');

distor = sum((x-decodedx).^2)/length(x) % Mean square error

Output:

The output is

distor = 0.0327

Result:

Page 30



FREQUENCY SHIFT KEYING

AIM:To write a MATLAB program for Frequency Shift Keying and to observe the output wave

forms.


Description:

Frequency-shift keying (FSK) allows digital information to be transmitted by changes or

shifts in the frequency of a carrier signal, most commonly an analog carrier sine wave. There are

two binary states in a signal, zero (0) and one (1), each of which is represented by an analog

wave form. This binary data is converted by a modem into an FSK signal, which can be

transmitted via telephone lines, fiber optics or wireless media. FSK is commonly used for caller

ID and remote metering applications. FSK is also known as frequency modulation (FM).

Program:

clc;

close all;

clear all;

fc1=input('Enter the freq of 1st Sine Wave carrier:');

fc2=input('Enter the freq of 2nd Sine Wave carrier:');

fp=input('Enter the freq of Periodic Binary pulse (Message):');

amp=input('Enter the amplitude (For Both Carrier & Binary Pulse Message):');

amp=amp/2;

t=0:0.001:1;

c1=amp.*sin(2*pi*fc1*t);% For Generating 1st Carrier Sine wave

c2=amp.*sin(2*pi*fc2*t);% For Generating 2nd Carrier Sine wave

subplot(4,1,1); %For Plotting The Carrier wave

plot(t,c1)

xlabel('Time')

ylabel('Amplitude')

title('Carrier 1 Wave')

subplot(4,1,2) %For Plotting The Carrier wave

plot(t,c2)

xlabel('Time')

ylabel('Amplitude')

title('Carrier 2 Wave')

m=amp.*square(2*pi*fp*t)+amp;%For Generating Square wave message

subplot(4,1,3) %For Plotting The Square Binary Pulse (Message)

Page 31

EXPT. NO-10



plot(t,m)

xlabel('Time')

ylabel('Amplitude')

title('Binary Message Pulses')

for i=0:1000 %here we are generating the modulated wave

if m(i+1)==0

mm(i+1)=c2(i+1);

else

mm(i+1)=c1(i+1);

end

end

subplot(4,1,4) %For Plotting The Modulated wave

plot(t,mm)

xlabel('Time')

ylabel('Amplitude')

title('Modulated Wave')

The following INPUTS GIVEN TO GENERATE FSK MODULATED WAVE:

Enter the freq of 1st Sine Wave carrier:10

Enter the freq of 2nd Sine Wave carrier:30

Enter the freq of Periodic Binary pulse (Message):5

Enter the amplitude (For Both Carrier & Binary Pulse Message):4

Wave Forms:

Result:

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

02

Time

Am

plitu

de Carrier 1 Wave

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

02

Time

Am

plitu

de Carrier 2 Wave

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

24

Time

Am

plitu

de Binary Message Pulses

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

02

Time

Am

plitu

de Modulated Wave

Page 32



PSK Modulation & Demodulation

AIM:

To perform the simulation of PSK modulation and demodulation using MATLAB.

EQUIPMENTS REQUIRED:

1. Operating system:Windows XP

2. Software:MATLAB

THEORY:

The simplest PSK technique is called binary phase-shift keying (BPSK). It uses two opposite

signal phases (0 and 180 degrees). The digital signal is broken up timewise into individual bits

(binary digits). The state of each bit is determined according to the state of the preceding bit. If

the phase of the wave does not change, then the signal state stays the same (0 or 1). If the phase

of the wave changes by 180 degrees -- that is, if the phase reverses -- then the signal state

changes (from 0 to 1, or from 1 to 0). Because there are two possible wave phases, BPSK is

sometimes called biphase modulation.

MATLAB is a programming language developed by MathWorks. It started out as a matrix

programming language where linear algebra programming was simple. It can be run both under

interactive sessions and as a batch job. Alternatives to MATLAB exist including open source

software packages.

MATLAB is interesting in that it is dynamically compiled. In other words, when you're using it,

you won't run all your code through a compiler, generate an executable, and then run the

executable file to obtain a result. Instead, MATLAB simply goes line by line and performs the

calculations without the need for an executable. Partly because of this, it is possible to do

calculations one line at a time at the command line using the same syntax as would be used in a

file. It's even possible to write loops and branches at the command line if you want to. Of course

this would often lead to a lot of wasted efforts, so doing anything beyond very simple

calculations, testing to see if a certain function, syntax, etc. works, or calling a function you put

into an .m file should be done within an .m file.

PROGRAM:

clc;

clearall;

closeall;

n=100;

Page 33

EXPT. NO-11



x=[ones(1,20) zeros(1,20) ones(1,20) zeros(1,20) ones(1,20)];

subplot(4,1,1);

plot(x);

title('input signal');

xlabel('number of samples');

ylabel('amplitude');

f=1*10^6;

fs=10*10^6;

for i=0:n-1

d(i+1)=sin(2*pi*(f/fs)*i);

end

subplot(4,1,2);

plot(d);

title('carrier signal');



for i=0:n-1

if(x(i+1)==0)

x(i+1)=sin(2*pi*(f/fs)*i);

else

x(i+1)=sin(2*pi*(f/fs)*i+pi);

end

end

subplot(4,1,3);

plot(x);

title('PSK Signal');



Page 34



for i=0:n-1

if(x(i+1)==sin(2*pi*(f/fs)*i))

x(i+1)=0;

else

x(i+1)=1;

end

end

subplot(4,1,4);

plot(x);

title('PSK Signal');



OUTPUT:

RESULT:

Page 35



Differential Phase Shift Keying

Aim: To write a MATLAB program for Differential Phase Shift Keying and to observe the output

wave forms.

Apparatus:

Operating System: Windows

Software Tools: Matlab

Theory:

Differential phase shift keying (DPSK), a common form of phase modulation conveys data by

changing the phase of carrier wave. In DPSK, there is no absolute carrier phase reference, instead

transmitted signal itself used as phase reference. For example, in differentially encoded BPSK a

binary '1' may be transmitted by adding 180° to the current phase and a binary '0' by adding 0° to

the current phase. For a signal that has been differentially encoded, there is an obvious alternative

method of demodulation. Instead of demodulating as usual and ignoring carrier-phase ambiguity,

the phase between two successive received symbols is compared and used to determine what the

data must have been. When differential encoding is used in this manner, the scheme is known as

differential phase-shift keying (DPSK).

PROGRAM

DPSK transmitter

nS=1000;

nSym=2000; %Number of samples

M=2;

Tb=1e-6; %Bit rate

fc=1e6; %Carrier frequency

s=randi([0 M-1],nSym,1); %Information signal

s_mod=pskmod(s,M,pi); %NRZ Polar encoder

s_mod=rectpulse(s_mod,nS);

h1=scatterplot(s_mod);

t=0:(Tb/nS):nSym*Tb-(Tb/nS); %Time domain

t=transpose(t);

figure(2);plot(t,s_mod)

axis([0 (10*Tb-(Tb/(nS))) -1.2 1.2]); %plot only first 10 bits

title('Input bit stream after NRZ Encoder');

xlabel('Time(seconds)');

Expt No:12

Page 36




s_tx_nn=s_mod.*cos(2*pi*fc*t)

Channel with AWGN Noise

%Additive Channel Noise

att=1;

SNR=1;

s_tx_noise=awgn(s_tx_nn,SNR,'measured');

h2=scatterplot(s_tx_noise,nS,nS/2);

%Additive Channel attenuation(10dB)

s_tx_noise_att=s_tx_noise/att;

DPSK Receiver

s_tx=s_tx_noise_att;

s_rx=s_tx.*cos(2*pi*fc*t);

figure;plot(t,s_rx);

axis([0 (10*Tb-(Tb/(nS))) -2/att 2/att]);

title('Recieved Signal Before Integration')

xlabel('Time(Seconds)') ylabel('Amplitude')

figure;stem(0:nS*nSym-1, s_mod(1 :nS*nSym))

plot(t,s_tx_noise_att,'g')

hold on

plot(t,s_tx_nn/att,'LineWidth',1); %DPSK madulated signal+Noise axis([0

(10*Tb-(Tb/(nS))) -2/att 2/att]);

title('Tx vs. Rx (Normalized)')

xlabel('Time (Seconds) ')

ylabel('Amplitude')

h3=scatterplot(s_rx,nS,nS/2);%Scatter Plot in presence of Noise

y=intdump(s_rx,nS);

y_mod=rectpulse(y,nS);

h4=scatterplot(y_mod, nS, nS/2);%Scatter Plot when Noise is removed

r_mod=pskdemod(y_mod,M,pi);%DPSK Demodulation

figure; plot(t,r_mod)

axis([0 (10*Tb-(Tb/(nS))) -0.2 1.2]);

title('Demodulated output')

xlabel('Time (seconds) ')

ylabel('Amplitude')

Page 37



Page 38



Result:

Page 39

Type your text



QPSK Modulation and Demodulation

AIM: To write a MATLAB program for QPSK Modulation and Demodulation and to observe

the output wave forms.

Requirements: PC and MATLAB software

Description:Quadrature phase shift keying (QPSK) modulators are used to change the

amplitude, frequency, and/or phase of a carrier signal in order to transmit information.

QPSK devices modulate input signals by 0°, 90°, 180°, and 270° phase shifts. QPSK

modulators modulators are used in conjunction with demodulators that extract information

from the modulated, transmitted signal. Some QPSK modulators include an integral

dielectric resonator oscillator. Others are suitable for military or wireless applications.

QPSK modulators with root raised cosine (RRC) and Butterworth filters are also

available.

Program:

clc;

clear all;

close all;

%GENERATE QUADRATURE CARRIER SIGNAL

Tb=1;t=0:(Tb/100):Tb;fc=1;

c1=sqrt(2/Tb)*cos(2*pi*fc*t);

c2=sqrt(2/Tb)*sin(2*pi*fc*t);

%generate message signal

N=8;m=rand(1,N);

t1=0;t2=Tb

for i=1:2:(N-1)

t=[t1:(Tb/100):t2]

if m(i)>0.5

m(i)=1;

m_s=ones(1,length(t));

else

m(i)=0;

m_s=-1*ones(1,length(t));

end

%odd bits modulated signal

odd_sig(i,:)=c1.*m_s;

if m(i+1)>0.5

m(i+1)=1;


else

m(i+1)=0;

m_s=-1*ones(1,length(t));

Page 40

EXPT. NO-13

Type your text



end

%even bits modulated signal

even_sig(i,:)=c2.*m_s;

%qpsk signal

qpsk=odd_sig+even_sig;

%Plot the QPSK modulated signal

subplot(3,2,4);plot(t,qpsk(i,:));

title('QPSK signal');xlabel('t---->');ylabel('s(t)');grid on; hold on;

t1=t1+(Tb+.01); t2=t2+(Tb+.01);

end

hold off

%Plot the binary data bits and carrier signal

subplot(3,2,1);stem(m);

title('binary data bits');xlabel('n---->');ylabel('b(n)');grid on;

subplot(3,2,2);plot(t,c1);

title('carrier signal-1');xlabel('t---->');ylabel('c1(t)');grid on;

subplot(3,2,3);plot(t,c2);

title('carrier signal-2');xlabel('t---->');ylabel('c2(t)');grid on;

% QPSK Demodulation

t1=0;t2=Tb

for i=1:N-1

t=[t1:(Tb/100):t2]

%correlator

x1=sum(c1.*qpsk(i,:));

x2=sum(c2.*qpsk(i,:));

%decision device

if (x1>0&&x2>0)

demod(i)=1;

demod(i+1)=1;

elseif (x1>0&&x2<0)

demod(i)=1;

demod(i+1)=0;

elseif (x1<0&&x2<0)

demod(i)=0;

demod(i+1)=0;

elseif (x1<0&&x2>0)

demod(i)=0;

demod(i+1)=1;

end

t1=t1+(Tb+.01); t2=t2+(Tb+.01);

end

subplot(3,2,5);stem(demod);

title('qpsk demodulated bits');

xlabel('n---->');ylabel('b(n)');grid on;

Page 41



wave forms:

Result:

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5-2

-1

0

1

2QPSK signal

t---->

s(t

)

1 2 3 4 5 6 7 80

0.2

0.4

0.6

0.8

1binary data bits

n---->

b(n

)

3 3.2 3.4 3.6 3.8 4 4.2 4.4-1.5

-1

-0.5

0

0.5

1

1.5carrier signal-1

t---->

c1(t

)

3 3.2 3.4 3.6 3.8 4 4.2 4.4-1.5

-1

-0.5

0

0.5

1

1.5carrier signal-2

t---->

c2(t

)

1 2 3 4 5 6 7 80

0.2

0.4

0.6

0.8

1qpsk demodulated bits

n---->

b(n

)

Page 42



Delta modulation

AIM:To write a MATLAB program for Delta Modulation and to observe the output wave

forms.


Description: A Delta modulation (DM or Δ-modulation) is an analog-to-digital and digital-to-analog

signal conversion technique used for transmission of voice information where quality is not of

primary importance. DM is the simplest form of differential pulse-code modulation (DPCM)

where the difference between successive samples is encoded into n-bit data streams. In delta

modulation, the transmitted data are reduced to a 1-bit data stream.

Program:

clc;

clear all;

close all;

a=2;

t=0:2*pi/50:2*pi;

x=a*sin(t);

l=length(x);

plot(x,'r');

delta=0.2;

hold on

xn=0;

for i=1:l;

if x(i)>xn(i)

d(i)=1;

xn(i+1)=xn(i)+delta;

else

d(i)=0; xn(i+1)=xn(i)-delta;

end

end

stairs(xn)

hold on

for i=1:d

if d(i)>xn(i)

d(i)=0;

xn(i+1)=xn(i)-delta;

else

Page 43

EXPT. NO-14

https://en.wikipedia.org/wiki/Digital_signal

https://en.wikipedia.org/wiki/Analog_signal

https://en.wikipedia.org/wiki/Analog_signal

https://en.wikipedia.org/wiki/Differential_pulse-code_modulation



d(i)=1; xn(i+1)=xn(i)+delta;

end

end

plot(xn,'c');

legend('Analog signal','Delta modulation','Demodulation')

title('DELTA MODULATION / DEMODULATION ')

output:

Result:

0 10 20 30 40 50 60-2

-1.5

-1

-0.5

0

0.5

1

1.5

2DELTA MODULATION / DEMODULATION

Analog signal

Delta modulation

Demodulation

Page 44



AMPLITUDE SHIFT KEYING

Aim: To generate and demodulate amplitude shift keyed (ASK) signal using MATLAB

Theory

Generation of ASK

Amplitude shift keying - ASK - is a modulation process, which imparts to a sinusoid two or

more discrete amplitude levels. These are related to the number of levels adopted by the digital

message. For a binary message sequence there are two levels, one of which is typically zero.

The data rate is a sub-multiple of the carrier frequency. Thus the modulated waveform consists

of bursts of a sinusoid. One of the disadvantages of ASK, compared with FSK and PSK, for

example, is that it has not got a constant envelope. This makes its processing (eg, power

amplification) more difficult, since linearity becomes an important factor. However, it does

make for ease of demodulation with an envelope detector.

Demodulation

ASK signal has a well defined envelope. Thus it is amenable to demodulation by an envelope

detector. Some sort of decision-making circuitry is necessary for detecting the message. The

signal is recovered by using a correlator and decision making circuitry is used to recover the

binary sequence.

Program

%ASK Modulation

clc;

clear all;

close all;

%GENERATE CARRIER SIGNAL

Tb=1; fc=10;

t=0:Tb/100:1;

c=sqrt(2/Tb)*sin(2*pi*fc*t);

%generate message signal

N=8;

m=rand(1,N);

t1=0;t2=Tb

Page 45

Expt no:15



for i=1:N

t=[t1:.01:t2]

if m(i)>0.5

m(i)=1;


else

m(i)=0;

m_s=zeros(1,length(t));

end

message(i,:)=m_s;

%product of carrier and message

ask_sig(i,:)=c.*m_s;

t1=t1+(Tb+.01);

t2=t2+(Tb+.01);

%plot the message and ASK signal

subplot(5,1,2);axis([0 N -2 2]);plot(t,message(i,:),'r');

title('message signal');xlabel('t--->');ylabel('m(t)');grid on

hold on

subplot(5,1,4);plot(t,ask_sig(i,:));

title('ASK signal');xlabel('t--->');ylabel('s(t)');grid on

hold on

end

hold off

%Plot the carrier signal and input binary data

subplot(5,1,3);plot(t,c);

title('carrier signal');xlabel('t--->');ylabel('c(t)');grid on

subplot(5,1,1);stem(m);

title('binary data bits');xlabel('n--->');ylabel('b(n)');grid on

% ASK Demodulation

t1=0;t2=Tb

for i=1:N

t=[t1:Tb/100:t2]

%correlator

x=sum(c.*ask_sig(i,:));

%decision device

if x>0

demod(i)=1;

else

demod(i)=0;

end

Page 46



t1=t1+(Tb+.01);

t2=t2+(Tb+.01);

end

%plot demodulated binary data bits

subplot(5,1,5);stem(demod);

title('ASK demodulated signal'); xlabel('n--->');ylabel('b(n)');grid on

Waveforms:

Result:

Page 47

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