is it possible to define global title on figures?

Yes this is possible by creating a new axes which takes up much of the figure. Then a title for this axes. Turning the axes Visible property 'off' will make the axes "disappear", but the title will inherit this property and you will need to turn the Visible property for the title back 'on'.

x = 0:0.001:2*pi;
y1 = cos(x);
y2 = sin(x);
f = figure;
subplot(2,1,1)
plot(x,y1)
subplot(2,1,2)
plot(x,y2)
a = axes;
t1 = title('Global Title');
a.Visible = 'off'; % set(a,'Visible','off');