AM DSB SC.zip_AM_SC_am dsb_dsb_dsb modulation

% MATLAB script for Illustrative Problem 3.4. % Demonstration script for LSSB-AM modulation. The message signal % is +1 for 0 < t < t0/3, -2 for t0/3 < t < 2t0/3, and zero otherwise. clear echo on t0=.15; % signal duration ts=0.001; % sampling interval fc=250; % carrier frequency snr=10; % SNR in dB (logarithmic) fs=1/ts; % sampling frequency df=0.25; % desired freq. resolution t=[0:ts:t0]; % time vector snr_lin=10^(snr/10); % SNR % the message vector m=[ones(1,t0/(3*ts)),-2*ones(1,t0/(3*ts)),zeros(1,t0/(3*ts)+1)]; c=cos(2*pi*fc.*t); % carrier vector udsb=m.*c; % DSB modulated signal [UDSB,udssb,df1]=fftseq(udsb,ts,df); % Fourier transform UDSB=UDSB/fs; % scaling f=[0:df1:df1*(length(udssb)-1)]-fs/2; % frequency vector n2=ceil(fc/df1); % location of carrier in freq. vector % Remove the upper sideband from DSB. UDSB(n2:length(UDSB)-n2)=zeros(size(UDSB(n2:length(UDSB)-n2))); ULSSB=UDSB; % Generate LSSB-AM spectrum. [M,m,df1]=fftseq(m,ts,df); % Fourier transform M=M/fs; % scaling u=real(ifft(ULSSB))*fs; % Generate LSSB signal from spectrum. signal_power=spower(udsb(1:length(t)))/2; % % Compute signal power. noise_power=signal_power/snr_lin; % Compute noise power. noise_std=sqrt(noise_power); % Compute noise standard deviation. noise=noise_std*randn(1,length(u)); % Generate noise vector. r=u+noise; % Add the signal to noise. [R,r,df1]=fftseq(r,ts,df); % Fourier transform R=R/fs; % scaling pause % Press a key to show the modulated signal power. signal_power pause % Press any key to see a plot of the message signal. clf subplot(2,1,1) plot(t,m(1:length(t))) axis([0,0.15,-2.1,2.1]) xlabel('Time') title('The message signal') pause % Press any key to see a plot of the carrier. subplot(2,1,2) plot(t,c(1:length(t))) xlabel('Time') title('The carrier') pause % Press any key to see a plot of the modulated signal and its spectrum. clf subplot(2,1,1) plot([0:ts:ts*(length(u)-1)/8],u(1:length(u)/8)) xlabel('Time') title('The LSSB-AM modulated signal') subplot(2,1,2) plot(f,abs(fftshift(ULSSB))) xlabel('Frequency') title('Spectrum of the LSSB-AM modulated signal') pause % Press any key to see the spectra of the message and the modulated signals. clf subplot(2,1,1) plot(f,abs(fftshift(M))) xlabel('Frequency') title('Spectrum of the message signal') subplot(2,1,2) plot(f,abs(fftshift(ULSSB))) xlabel('Frequency') title('Spectrum of the LSSB-AM modulated signal') pause % Press any key to see a noise sample. subplot(2,1,1) plot(t,noise(1:length(t))) title('Noise sample') xlabel('Time') pause % Press a key to see the modulated signal and noise. subplot(2,1,2) plot(t,r(1:length(t))) title('Modulated signal and noise') xlabel('Time') subplot(2,1,1) pause % Press any key to see the spectrum of the modulated signal. plot(f,abs(fftshift(ULSSB))) title('Modulated signal spectrum') xlabel('Frequency') subplot(2,1,2) pause % Press a key to see the modulated signal noise in freq. domain. plot(f,abs(fftshift(R))) title('Modulated signal noise spectrum') xlabel('Frequency')