ifft integer matlab cyclic prefix

x=ifft(modData).*sqrt(64); x1 = [x(:,end-Ncp+1:end) ,x];

i get this error :Subscript indices must either be real positive integers or logicals.

[Adam]

So make sure the subscript indices are real positive integers or logicals! You haven't given any indication as to what most of the things are in that expression for us to know, but using the debugger you should be able to fix this very quickly.

[best16 programmer]

the modData is modulated with qpsk, so it gives complex values,i want to add the cyclic prefix using the x1.it still given me the same error