Thank you RBB. That was very helpfully.
I wrote a code now, but Im still not sure, if that is right, because its still not working.
Maybe you can have a quick look at my code?!
PI_r=z(1:4:512).'; %%Pilots at the right position at the receiver
PI_t=ones(128,1)+j*ones(128,1); %%Pilots i generated at the transmitter
PI=PI_r./PI_t; %%thats my H=Y/X
X=ifft([PI].',128 ); %%note: changed my amount of Pilots in 128
Y=fft(X,512); %%make 512 datas with my 128 point.
b=z./Y; %%thats my channel correction now. but its not working. z=my received datas after fft
I hope you could help me... would be so urgent.
thank you so much.