I want to transmit a number of symbols with QPSK-modulation over a channel by using OFDM.(adsbygoogle = window.adsbygoogle || []).push({});

I have never used cyclic prefix before so I'm not so sure about this. In my lab instructions they seem to say that I add the cyclic prefix directly from the IFFT:ed version of the bit-stream and append it to the original IFFT sequence.

b bits----QPSK-----> s(k)

z = IFFT(s[k])

z_cyclic = z[N-Ncp]...z[N-1], z(0], z[1]...z[N-1]

y = z_cyclic + noise

s_out = FFT(y) ---> bhat

However, when I do this I get the wrong bits out.

If i send 5 zeros: [0 0 0 0 0] and add a cyclic prefix after the IFFT then i should get a output bhat in the form of:

cyclic + 0 0 0 0 0

where cyclic is additional ones an zeros due to the fact that i made the time-signal longer (appended the cyclic prefix).

But in my case I get both ones and zeros in my output.

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# Add cyclic prefix to OFDM system

Can you offer guidance or do you also need help?

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