fmcw.m

Mtlab toolbox containing useful m files to generate LPI signals

%******************************************************************************
% fmcw.m
%
% Use:  Code to generated triangular FMCW signals
%
% Inputs:       Amplitude of the carrier signal
%		        Carrier signal frequency - f (Hz)
%               Sampling frequency - fs (HZ)
%               Desired SNR in dB
%               Modulation bandwidth (deltaF)
%               Modulation period (tm)
%               Number of triangles in the signal 
%               
%
%Output:        In-phase (I) and Quadarture (Q) components of the signal
%               with 4 triangular periods.
%******************************************************************************

clc;clear all;
disp('*******************************************');
disp('******************* FMCW ********************');
disp('**********************************************');

%	DEFAULT VARIABLES 
A  = 1;						            %Amplitude
f0 =1e3;                                %Carrier signal frequency -  (Hz)
fs = 7e3;   	    	                %Sampling frequency
SNR_dB  = 0;					        %Desired SNR in dB
deltaF = 250;				            %Modulation bandwidth
tm = 20;	    				        %Modulation period
triangles=5;                            %No of triangles to be generated 
sigma=1;                            

% NEW INPUT 
newvar = 1;
while newvar == 1;
    disp(' ')
    disp('WHICH PARAMETER DO YOU WANT TO SET ?  ')
    disp(' ')
    fprintf('1. Amplitude of the carrier signal - A= %g.\n', A) 
    fprintf('2. Carrier frequency - f0 (Hz)= %g.\n', f0)    
    fprintf('3. Sampling frequency - fs (Hz)=%g.\n',fs)  
    fprintf('4. Signal to noise ratio - SNR_dB (dB)= %g.\n', SNR_dB)   
    fprintf('5. Modulation bandwidth - deltaF (Hz)= %g.\n', deltaF)
    fprintf('6. Modulation period - tm (milli-seconds)= %g.\n',tm)
    fprintf('7. No changes\n')
    disp(' ')
    option= input('Select a option: ');
    switch option
    case 1
        A=input('New Amplitude = ');        
    case 2
        f0=input('Carrier frequency (Hz)=');
    case 3
        fs=input('New Sampling frequency (Hz)= ');
    case 4        
        SNR_dB=input('New Signal to noise ratio (dB)= '); 
    case 5        
        deltaF=input('New modulation bandwidth (Hz)= ');
    case 6
        tm=input('New modulation period (milli-seconds)= ');
    case 7
        newvar = 0;
    end
    clc;
end

tm=tm/1000;

if SNR_dB ~= -inf
   SNR = 10^(SNR_dB/20);			%20log since we're dealing with voltage
   sigma = A/(sqrt(2)*SNR);		    %Std. Dev. of noise required to achieve input SNR
else 
   SNR = 0;						             %For noise only, SNR = 0
   sigma = 1;					              %If user wants noise only, let Std Dev = 1
end

ts = 1/fs;    	                               %Sample Period
time = (0:ts:(tm-ts))';	%Vector of sample times

%Build the pure sin & cos waveforms
I_carrier = cos(2*pi*f0.*time); % Carrier signals
Q_carrier = sin(2*pi*f0.*time); % Carrier signals

  
%sI1 is the In-Phase (I) transmitted signal for the up-ramp (without noise)
%sI2 is the In-Phase (I) transmitted signal for the down-ramp (without noise)
if SNR ~= 0
   sI1 = A*cos(2*pi*((f0-deltaF/2).*time + deltaF/(2*tm).*time.^2));
   sI2 = A*cos(2*pi*((f0+deltaF/2).*time - deltaF/(2*tm).*time.^2));
else
   sI1 = zeros(length(time),1);		%If noise only, Signal = 0
   sI2 = zeros(length(time),1);
end

%Next two lines add req'd noise level to up & down ramps (I channel).
%Used to plot time sequence & PSD for each ramp
sI1_noisy = sI1 + sigma*randn(length(sI1),1);
sI2_noisy = sI2 + sigma*randn(length(sI2),1);


%Creates the I-channel time sequence of four up&down ramp pairs (NO noise)
I = [sI1;sI2;sI1;sI2;sI1;sI2;sI1;sI2];

%Adds the required noise to the time sequence

[a,b]=size(I);
SNR=10^(SNR_dB/10);
power=10*log10(A^2/(2*SNR));%calculate SNR in dB for WGN function
noise=wgn(a,b,power);%calculate noise at specified SNR
IwN=I+noise;               %add noise to I with P4 phase shift


%sQ1 is the Quadrature (Q) transmitted signal for the up-ramp (without noise)
%sQ2 is the Quadrature (Q) transmitted signal for the down-ramp (without noise)
if SNR ~= 0
   sQ1 = A*sin(2*pi*((f0-deltaF/2).*time + deltaF/(2*tm).*time.^2));
   sQ2 = A*sin(2*pi*((f0+deltaF/2).*time - deltaF/(2*tm).*time.^2));
else
   sQ1 = zeros(length(time),1);		%If noise only, Signal = 0
   sQ2 = zeros(length(time),1);
end

%Next two lines add req'd noise level to up & down ramps (Q channel).
%Used to plot time sequence & PSD for each ramp
sQ1_noisy = sQ1 + sigma*randn(length(sQ1),1);
sQ2_noisy = sQ2 + sigma*randn(length(sQ2),1);



%Creates the Q-channel time sequence of four up&down ramp pairs (NO noise)
Q = [sQ1;sQ2;sQ1;sQ2;sQ1;sQ2;sQ1;sQ2];

%Adds the required noise to the time sequence

QwN=Q+noise;  

%*******************************************************
%PLOTS
%******************************************************
[uu,cc]=size(time);
disp(' ')
plt = input('Do you want to generate plots of the signal (Y/y or N/n) ?','s');
disp(' ')
if (plt == 'Y') | (plt =='y')
    disp(' ')
    %Plots time sequence & PSDs of In-Phase (cos) waveform
    figure; 
    subplot(2,1,1);
    plot(time(1:uu),I_carrier(1:uu)); grid;
    title('Pure In-Phase Sinusoidal Carrier');
    xlabel('Time (s)'); ylabel('Cos(2*pi*f_0*t)');
    subplot(2,1,2);
    psd(I_carrier,[],fs);
    title('Power Spectral Density of Pure In-Phase Carrier');   
    
    %Plots time sequence & PSDs of Quadrature (sin) waveform
    figure; 
    subplot(2,1,1);
    plot(time(1:uu),Q_carrier(1:uu)); grid;
    title('Pure Quadrature Sinusoidal Carrier');
    xlabel('Time (s)'); ylabel('-Sin(2*pi*f_0*t)');
    subplot(2,1,2);
    psd(Q_carrier,[],fs);
    title('Power Spectral Density of Pure Quadrature Carrier');   
    
    %Plots the triangular modulating waveform
%     figure;
%     plot(elapsed_time,f); grid;
%     title('Triangular Modulating Signal')
%     xlabel('Time (us)'); ylabel('Frequency (MHz)');
    
    %Plots time sequence & PSD for I-channel up ramp

    figure;
    subplot(2,1,1);
    plot(time, sI1_noisy); grid;
    title(['In-Phase, Up-Ramp Transmitted Signal - SNR = ', num2str(SNR_dB), ' dB'])
    xlabel('Time (s)'); ylabel('Signal');
    subplot(2,1,2);
    psd(sI1_noisy,[],fs);
    title('Power Spectral Density of In-Phase, Up-Ramp Segment');
    
    
     %Plots time sequence & PSD for I-channel down ramp
    figure;
    subplot(2,1,1);
    plot(time, sI2_noisy); grid
    title(['In-Phase, Down-Ramp Transmitted Signal- SNR = ', num2str(SNR_dB), ' dB'])
    xlabel('Time (s)'); ylabel('Signal');
    subplot(2,1,2);
    psd(sI2_noisy,[],fs);
    title('Power Spectral Density of In-Phase, Down-Ramp Segment');
    
    
    %Plots time sequence & PSD for Q-channel up ramp
    figure;
    subplot(2,1,1);
    plot(time, sQ1_noisy);grid;
    title(['Quadrature, Up-Ramp Transmitted Signal - SNR = ', num2str(SNR_dB), ' dB'])
    xlabel('Time (s)'); ylabel('Signal');
    title(['Quadrature, Up-Ramp Transmitted Signal (Near End) - SNR = ', num2str(SNR_dB), 'dB'])
    xlabel('Time (s)'); ylabel('Signal');
    subplot(2,1,2);
    psd(sQ1_noisy,[],fs);
    title('Power Spectral Density of Quadrature, Up-Ramp Segment');
    
    
    %Plots time sequence & PSD for Q-channel down ramp
    figure;
    subplot(2,1,1);
    plot(time, sQ2_noisy); grid;
    title(['Quadrature, Down-Ramp Transmitted Signal - SNR = ', num2str(SNR_dB), 'dB'])
    xlabel('Time (s)'); ylabel('Signal');
    subplot(2,1,2);
    psd(sQ2_noisy,[],fs);
    title('Power Spectral Density of Quadrature, Down-Ramp Segment');
    
else
    disp('Signal not plotted')
    fprintf('\n\n')
end


%Saves the I & Q vectors in a .mat file for processing by the receiver folks
disp(' ')
saveresult = input('Do you want to save the new signal (Y/y or N/n) ?','s');
if (saveresult == 'Y') | (saveresult =='y') 
    I2=I; Q2=Q;
    I=IwN; Q=QwN;
    ff=floor(f0/1e3);
    ffs=floor(fs/1e3);
    save(['F_', num2str(ff), '_', num2str(ffs), '_', num2str(deltaF), '_', num2str(tm*1000), '_',num2str(SNR_dB)],'I','Q');
    I=I2;
    Q=Q2;
    save(['F_' num2str(ff) '_' num2str(ffs) '_' num2str(deltaF) '_' num2str(tm*1000) '_s'],'I','Q');
    disp(' ');
    disp(['Signal and noise save as :  F_' num2str(ff) '_' num2str(ffs) '_' num2str(deltaF) '_' num2str(tm*1000) '_' num2str(SNR_dB)]);
    disp(['Signal only save as :         F_' num2str(ff) '_' num2str(ffs) '_' num2str(deltaF) '_' num2str(tm*1000) '_s']);
    disp(['Directory:                       ' num2str(cd)]); 
else
    disp(' ')
    disp('Signal not saved')
    fprintf('\n\n')
end