signal modulation

% MATLAB Script for a Binary ASK with two Amplitude Levels

format long;

% Clear all variables and close all figures
clear all;
close all;
clc;

% The number of bits to send - Frame Length
N = 8;

% Generate the bit stream
str = input ("Give me some text: ", "s");
bit_stream = (dec2bin (uint8 (str), N) - "0").'(:).';

% Enter the two Amplitudes
% Amplitude for 0 bit
A1 = 2;

% Amplitude for 1 bit
A2 = 5;

% Frequency of Modulating Signal
f = 10e3;

% Sampling rate - This will define the resoultion
fs = 5e6;

% Time for one bit
t = [0 : 1/fs : 2/f];

% This time variable is just for plot
time = [];

ASK_signal = [];
Digital_signal = [];

for ii = 1: 1: length(bit_stream)

    % The Original Digital Signal
    Digital_signal = [Digital_signal (bit_stream(ii)==0) * zeros(1,length(t)) + (bit_stream(ii)==1)*ones(1,length(t))];

    % The ASK Signal
    ASK_signal = [ASK_signal (bit_stream(ii)==0)*A1*sin(2*pi*f*t) + (bit_stream(ii)==1)*A2*sin(2*pi*f*t)];

    time = [time t];
    t =  t + 2e-4;
end

% Plot the Original Digital Signal
subplot(3,1,1);
plot(time,Digital_signal,'r','LineWidth',2);
xlabel('Time (bit period)');
ylabel('Amplitude');
title('Original Digital Signal');
axis tight;
grid on;

% Plot the ASK Signal
subplot(3,1,2);
plot(time,ASK_signal,'LineWidth',1);
xlabel('Time (bit period)');
ylabel('Amplitude');
title('ASK Signal with two Amplitudes');
axis tight;
grid  on;

% Plot the ASK Spectrum
Nsamps = length(ASK_signal);
%t1 = (1/fs)*(1:Nsamps);       %Prepare time data for plot

%Do Fourier Transform
y_fft = abs(fft(ASK_signal));  %Retain Magnitude
y_fft = y_fft(1:Nsamps/2);     %Discard Half of Points
f1 = fs*(0:Nsamps/2-1)/Nsamps; %Prepare freq data for plot

%Plot ASK in Frequency Domain
subplot(3,1,3);
plot(f1, y_fft, 'linewidth', 2, 'r');
xlim([0 20e3]);
xlabel('Frequency (Hz)');
ylabel('Amplitude');
title('Spectrum plot for ASK modulated Signal');
grid on;