eem496 communication systems laboratory - report4 - digitally modulated signals using matlab, pam...
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Instructor : Ass. Prof. Nuray AT
TA : Res. Assistant. Zafer Hüseyin ERGAN
ANADOLU UNIVERSITYDEPARTMENT OF ELECTRICAL AND ELECTRONICS
ENGINEERING
EEM 496
Communication Systems
Laboratory
Experiment 4
DIGITALLY MODULATED SIGNALS USING MATLAB:
PAM (ASK), PSK, AND QAM
Date: 11.03.2010
16169230356 OSMAN GÜLERCAN
1) Purpose
The aim of this experiment is to study digitally modulated signals which are
PAM (ASK), PSK, and QAM, also construct their constellation diagrams,
baseband and passband forms using MATLAB.
2) Lab Work
The MATLAB codes, which are given in the experiment file, were
implemented by changing the modulation types; also, plotting the
waveforms, the results were observed.
In the MATLAB codes, we first set the M-ary modulation parameter ‘M’ to 8
and the number of symbol intervals ‘n’ to 2. By doing this, we observed 9
figures that show us some of waveforms of PAM(ASK), PSK, and QAM
signals.
For each modulation types, we compared the modulation constellations, input
signals as M-ary levels, also both baseband and passband signals.
Then we changed the number of symbol intervals ‘n’ to 4 and 8. We studied
the differences of signals that Matlab generated. When the M-ary modulation
parameter M=8, we also changed the carrier frequency ‘fc’ to 36 and
sampling rate of the modulated signal ‘fs’ to 10e4.
In this code, sampling rate of the message signal was constantly 1, we
couldn’t change it because some of the vector’s length had already assigned
to 1.
Lastly, we set the the M-ary modulation parameter to 16, and the number of
symbol intervals ‘n’ to 4. Then we run it and observed the modulation
waveforms again.
3) Results
m=8, n=2
m=8, n=4
m=8, n=8
m=16, n=4
m=8, n=4, fc=36
m=8, n=4, fs=10e4
4) Matlab Code
% This program shows the illustration of PAM (ASK), PSK, and QAM signals.
% Both bandpass and passband signals are shown. Keep the n, Fs , and fc settings.
clear; clc; close all
n = 4; % Number of symbol intervals
M = 16; % Use M-ary modulation
Fd = 1; % Sampling rate of the message signal
Fs = 100; % Sampling rate of the modulated signal
fc = 18; % Carrier frequency
x = randint(n,1,M); % Random multilevel message signal (from zero to M-1)
xt = reshape(repmat(x,1,Fs)',1,n*Fs); t = 1:1:n*Fs; % Arrange time axis
% PAM (ASK) Signals
% A) Baseband ASK
sask = real(dmodce(x,Fd,Fs,'ask',M)); modmap('ask',M); set(gcf,'Color',[1 1 1])
pause
subplot(2,1,1); plot(t,xt); title('Input signal x(t) as M-ary levels')
axis ([min(t) max(t) -0.1 max(x)*1.1])
set(gca,'XTick',[50 100 150 200 250 300 350 400])
set(gca,'XTickLabel',{'T/2';'T';'3T/2';'2T';'5T/2';'3T';'10T/2';'4T'},'FontWeight','bold');
subplot(2,1,2); plot(t,sask); title('ASK baseband signal - s_m(t)'); xlabel('Time Axis')
axis ([min(t) max(t) -1.1 1.1])
set(gca,'XTick',[50 100 150 200 250 300 350 400])
set(gca,'XTickLabel',{'T/2';'T';'3T/2';'2T';'5T/2';'3T';'10T/2';'4T'},'FontWeight','bold');
pause; clf reset
% B) Bandpass PAM (ASK)
uask = dmod(x,fc,Fd,Fs,'ask',M);
subplot(2,1,1); plot(t,sask); set(gcf,'Color',[1 1 1])
title('ASK baseband signal - s_m(t)')
axis ([min(t) max(t) -1.1 1.1])
set(gca,'XTick',[50 100 150 200 250 300 350 400])
set(gca,'XTickLabel',{'T/2';'T';'3T/2';'2T';'5T/2';'3T';'10T/2';'4T'},'FontWeight','bold');
subplot(2,1,2); plot(t,uask); title('ASK bandpass signal - u_m(t)'); xlabel('Time Axis')
axis ([min(t) max(t) -1.1 1.1])
set(gca,'XTick',[50 100 150 200 250 300 350 400])
set(gca,'XTickLabel',{'T/2';'T';'3T/2';'2T';'5T/2';'3T';'10T/2';'4T'},'FontWeight','bold');
pause
% PSK Signals
% A) Baseband PSK
spsk = dmodce(x,Fd,Fs,'psk',M); figure; modmap('psk',M);set(gcf,'Color',[1 1 1])
pause
subplot(2,1,1); plot(t,xt); title('Input signal x(t) as M-ary levels')
axis ([min(t) max(t) -0.1 max(x)*1.1])
set(gca,'XTick',[50 100 150 200 250 300 350 400])
set(gca,'XTickLabel',{'T/2';'T';'3T/2';'2T';'5T/2';'3T';'10T/2';'4T'},'FontWeight','bold');
s1psk = reshape(spsk,Fs/2,2*n);smtpsk = [];
for i = 1:2:2*n-1
s3 = [real(s1psk(:,i));imag(s1psk(:,i+1))];
smtpsk = [smtpsk;s3];
end
subplot(2,1,2); plot(t,smtpsk); title('PSK baseband signal - s_m(t)'); xlabel('Time Axis')
axis ([min(t) max(t) -1.1 1.1])
set(gca,'XTick',[50 100 150 200 250 300 350 400])
set(gca,'XTickLabel',{'T/2';'T';'3T/2';'2T';'5T/2';'3T';'10T/2';'4T'},'FontWeight','bold');
pause;clf reset
% B) Bandpass PSK
upsk = dmod(x,fc,Fd,Fs,'psk',M);
subplot(2,1,1); plot(t,smtpsk); set(gcf,'Color',[1 1 1])
title('PSK baseband signal - s_m(t)')
axis ([min(t) max(t) -1.1 1.1])
set(gca,'XTick',[50 100 150 200 250 300 350 400])
set(gca,'XTickLabel',{'T/2';'T';'3T/2';'2T';'5T/2';'3T';'10T/2';'4T'},'FontWeight','bold');
subplot(2,1,2); plot(t,upsk); title('PSK bandpass signal - u_m(t)'); xlabel('Time Axis')
axis ([min(t) max(t) -1.1 1.1])
set(gca,'XTick',[50 100 150 200 250 300 350 400])
set(gca,'XTickLabel',{'T/2';'T';'3T/2';'2T';'5T/2';'3T';'10T/2';'4T'},'FontWeight','bold');
pause
% QAM Signals
% A) Baseband QAM
sqam = dmodce(x,Fd,Fs,'qask',M); figure; modmap('qask',M); set(gcf,'Color',[1 1 1])
pause
subplot(2,1,1); plot(t,xt); title('Input signal x(t) as M-ary levels')
axis ([min(t) max(t) -0.1 max(x)*1.1])
set(gca,'XTick',[50 100 150 200 250 300 350 400])
set(gca,'XTickLabel',{'T/2';'T';'3T/2';'2T';'5T/2';'3T';'10T/2';'4T'},'FontWeight','bold');
s1qam = reshape(sqam,Fs/2,2*n); smtqam = [];
for i = 1:2:2*n-1
s3 = [real(s1qam(:,i));imag(s1qam(:,i+1))];
smtqam = [smtqam;s3];
end
subplot(2,1,2); plot(t,smtqam); title('QAM baseband signal - s_m(t)'); xlabel('Time Axis')
axis ([min(t) max(t) -M*0.9/2 M*0.9/2])
set(gca,'XTick',[50 100 150 200 250 300 350 400])
set(gca,'XTickLabel',{'T/2';'T';'3T/2';'2T';'5T/2';'3T';'10T/2';'4T'},'FontWeight','bold');
pause; clf reset
% B) Bandpass QAM
uqam = dmod(x,fc,Fd,Fs,'qask',M);
subplot(2,1,1); plot(t,smtqam); set(gcf,'Color',[1 1 1])
title('QAM baseband signal - s_m(t)')
axis ([min(t) max(t) -M*0.9/2 M*0.9/2])
set(gca,'XTick',[50 100 150 200 250 300 350 400])
set(gca,'XTickLabel',{'T/2';'T';'3T/2';'2T';'5T/2';'3T';'10T/2';'4T'},'FontWeight','bold');
subplot(2,1,2); plot(t,uqam); title('QAM bandpass signal - u_m(t)'); xlabel('Time Axis')
axis ([min(t) max(t) -1.1 1.1])
set(gca,'XTick',[50 100 150 200 250 300 350 400])
set(gca,'XTickLabel',{'T/2';'T';'3T/2';'2T';'5T/2';'3T';'10T/2';'4T'},'FontWeight','bold');
5) Conclusion
In this experiment, we have studied digitally modulated signals PAM (ASK),
PSK, and QAM with their constellation diagrams, including baseband and
passband forms. The message signals described as digitally with changing
amplitudes so that we could easily see the M-ary levels step-up or step-down
on the figures by the values of n>2. We tested the signals when n=2, 4 and 8.
At the ASK modulation, we saw that the amplitude was changed according to
ASK baseband signal which was related to M-ary level. We can say that the
amplitude of carier frequency was changed by a digital input signal to
generate ASK. Similarly, the phase of carier signal changed at the output of
bandpass signal in order to generate PSK. When the baseband signal’s
amplitude changed, the phase of bandpass signal also changed with constant
amplitude. Lastly, we tested QAM that is a combination of ASK and PSK
and they are out of phase with each other by 90°. We also changed sampling
rate of the modulated signal to 10e4 and the carrier frequency to 36. As the fd
was increased, baseband and passband signals seemed more flat, and as the fc
was increased the passband signals seemed more fluctuated. To sum up,
some of digitally modulated signals PAM(ASK), PSK, and QAM were
analyzed using MATLAB.
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