Triangle Pulse with fourier transformation - matlab

Question

I have a basic exercise for telecommunications with matlab, and i must plot a triangle pulse with (-c,0) to (c,0) with c = 6 and Amplitude = 1 in a for loop for M pulses and approach the periodic pulse using N Fourier series terms. I can't find something on the internet that can help me so far.
A similar code for rect pulse that I made and works is this:
a = 1;
b = 3;
N = 1000;
t = linspace(a-2*a,b+2*b,N);
A = 1;
y = rect_pulse(A,a,b,t);
plot(t,y);
grid on
axis([a-2*a b+2*b 0 2*A]);
M = 5;
T=7;
t_new = linspace(a-2*a,b+(M-1)*T+2*b,N);
y_new = zeros(1,N);
for index = 1:1:M
temp_y = rect_pulse(A,a+(index-1)*T,b+(index-1)*T,t_new);
y_new = y_new + temp_y;
end
figure;
plot(t_new,y_new);
grid on;
axis([a-2*a b+(M-1)*T+2*b 0 2*A]);
Where rect_pulse is this:
function y = rect_pulse (A,a,b,t)
N=length(t);
y = zeros(1,N);
for index = 1:1:N
if(t(1,index)>=a) && (t(1,index)<=b)
y(1,index) = A;
end
end
And fourier series is this:
function y_fourier = fourier_series_rect_pulse(a,b,To,N,t)
y_fourier = 0;
wo = (2*pi)/To;
for n = -N:1:N
f_real = #(x) cos(n*wo*x);
f_imag = #(x) sin(n*wo*x);
cn = (1/To)*(quad(f_real,a,b)) - j*quad(f_imag,a,b));
y_fourier = y_fourier + cn*exp(j*n*wo*t);
end
y_fourier = real(y_fourier);
Any ideas how to make this in to triangle pulse?

Answer 1

This probably deviates significantly from your approach but if you're curious here is a script I came up with to generate a triangular pulse train that can be adjusted. This method, unfortunately, uses the fft() function which may or may not be off-limits in your case. Most of the script uses indexing and manipulating vectors. Additional spectral components may be seen due to the DC offset of the alternating triangular wave and the limited number of cycles available in the vector representation of the triangular wave.
Triangular Pulses and Fourier Transforms:
Triangular Pulse with Duty-Off Period:
Higher frequency spectral components present due to the abrupt corners that occur at the transition states of the triangle pulse and duty-off period.
%******************************************************%
%PROPERTIES THAT CAN BE CHANGED%
%******************************************************%
Plotting_Interval = 0.01; %0.01 seconds%
Pulse_Width = 1/20; %6 seconds%
Period = 1/20; %10 seconds (should be at least the pulse width)%
Start_Time = 0;
End_Time = Pulse_Width*1000; %(1000 pulses)%
%******************************************************%
if(Period < Pulse_Width)
Period = Pulse_Width;
end
Time_Vector = (Start_Time: Plotting_Interval: End_Time);
Points_Per_Unit_Time = 1/Plotting_Interval;
Half_Pulse = Pulse_Width/2;
Number_Of_Points = Pulse_Width/Plotting_Interval;
Rising_Slope = linspace(0,1,floor(Number_Of_Points/2) + 1);
Falling_Slope = 1 - Rising_Slope;
Triangular_Pulse = [Rising_Slope Falling_Slope(2:end)];
t = (0: Plotting_Interval: Pulse_Width);
Periodic_Triangular_Pulse = zeros(1,length(Time_Vector));
for Cycle = 1: +Period/Plotting_Interval: End_Time/Plotting_Interval
Periodic_Triangular_Pulse(1,Cycle:Cycle+length(Triangular_Pulse)-1) = Triangular_Pulse(1,1:end);
end
Periodic_Triangular_Pulse = Periodic_Triangular_Pulse(1,1:length(Time_Vector));
subplot(1,2,1); plot(Time_Vector,Periodic_Triangular_Pulse);
Triangle_Frequency = 1/Period;
title("Triangular Pulse Train " + num2str(Triangle_Frequency) + "Hz (first 10 cycles)");
axis([0 Period*10 0 1]);
xlabel("Time (s)"); ylabel("Amplitude");
Signal_Length = length(Periodic_Triangular_Pulse);
Fourier_Transform = fft(Periodic_Triangular_Pulse);
Fs = 1/Plotting_Interval;
P2 = abs(Fourier_Transform/Signal_Length);
P1 = P2(1:floor(Signal_Length/2)+1);
P1(2:end-1) = 2*P1(2:end-1);
f = Fs*(0:(Signal_Length/2))/Signal_Length;
subplot(1,2,2); plot(f,P1)
title("Single-Sided Fourier Transform");
xlabel("Frequency (Hz)"); ylabel("Magnitude");
Ran using MATLAB R2019b