csdr/grc_tests/psk31_sigmodel.m

#!/usr/bin/octave

global Tb=20

function g=gbb(t) %impulse response of pulse shaping filter
	global Tb
	g=t;
	for i = 1:size(t)(2)
		if (t(i)>1*Tb || t(i)<=-1*Tb)
			g(i) = 0;
		else
			g(i) = 0.5+cos((t(i)/(Tb*1))*pi)/2; %this is not RRC, rather a sinusoidal pulse shape
		end
	end
end

global padding=[-2 2];

function [toreturny, plotrange]=y(s)
	global Tb
    global padding
	slen=size(s)(2)
	plotrange=((padding(1)-1)*Tb):(slen+padding(2))*Tb-1;
	plotlen=size(plotrange)(2)
	toreturny=zeros(1,plotlen);
	for i=1:slen %sum of (symbol[i] * filter impulse response) for all symbols
		toreturny+=s(i)*gbb(plotrange.-(i-1)*Tb); 
	end
    plotrange=plotrange/Tb
end

function fmtplot(h)
    FN = findall(h,'-property','FontName');
    set(FN,'FontName','/usr/share/fonts/truetype/ttf-dejavu/DejaVuSerifCondensed.ttf');
    set(FN,'FontName','times');
    FS = findall(h,'-property','FontSize');
    set(FS,'FontSize',18);
    set(FS,'FontSize',18);
end

h=figure(1);
subplot(2, 1, 1);
[a b]=y([1]);
plot(b, a, 'linewidth', 2)
title(sprintf("Impulse response of pulse shaping filter"))
xlabel('t/Ts')
ylabel('h(t)')

subplot(2, 1, 2);
[a b]=y([1 1 -1 -1 1 1 1 -1 1 -1 1 1]);
plot(b, a, 'linewidth', 2)
title("Baseband signal for modulator input\nbit sequence: 110011101011") %assuming that differential encoding has already been performed
xlabel('t/Ts')
ylabel('s(t)')
xbounds = xlim;
set(gca,'XTick',xbounds(1):xbounds(2));
fmtplot(h);
pause
exit

%fourier analisys of baseband signal
h2=figure(2);
padding=[-1 1]
plot(y([1]))
h3=figure(3);
fftvals=abs(fft(y([1])));
sizefftvals=size(fftvals)(2)
fftvals=[fftvals(sizefftvals/2:sizefftvals) fftvals(2:sizefftvals/2)]
plot(fftvals, "-")
pause