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Channel Estimation for OFDM

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susasue

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Hi everybody.
I read some paper about channel estimation, but I still couldn't get the idea, how to use it in my case.... :???:
I have a QPSK signal with 512 signals where 200 of them are pilots.
i transmitted them and after the FFT i get a constellation with 4 points.
but unfortunately at the wrong place. So I guess, that channel estimation will solve my problem.
Can somebody explain me, how to get the channel property?!
Thanks for your help
susasue :smile:
 

RBB

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Since you know the expected pilot values, call it X(w) and you know the received pilot values, call it Y(w), then you know the channel response at that frequency: H(w) = Y(w) / X(w).
So you'll have 200 different channel estimation values of H(w). One for each pilot location.
There are any number of algorithms to apply the channel estimation to the rest of your FFT bins. The simplest being a linear interpolation.
 

susasue

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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.
 
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