# Tag Info

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Maybe 8 years late on this one. But it appears that topics related to OFDM involving 'IFFT' is not even really physical OFDM as such. The issue seems to be with the complete lack of information about the topic of 'OFDM' involving IFFT. At first, we expect (or get the impression) that taking an IFFT of complex number sequences is going to help physically ...

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You're right, the DC carrier is usually left out (for technical reasons – you need very good receiver hardware to be able to receive that one with a good SINR). That means you simply can't use all 64 bins of your FFT! For example, IEEE 802.11a uses, if I remember correctly, only 52 of 64 carriers; the rest is filled with nulls around DC or at the band edges.

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The answer to your question lies in the following - We have QAM Complex Symbols that is required to be communicated over a certain bandwidth. We have decided that we would be using OFDM for this purpose i.e. we want to divide the available bandwidth into $N$ equally-spaced equal-width parallel non-interfering sub-channels and load each sub-channel with one ...

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I understand what you mean - possibly due to the complete lack of information out there that attempts to explain the situation properly. I think it is more along the lines like the following. Consider a sequence of vectors (on paper) in the 'frequency domain'. It's really just a 'virtual' frequency domain. This set of vectors can be complex numbers that ...

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This is just a nice way to rewrite Equation (2). Using Block matrix interpretation: \begin{align} \underline{H}^H\underline{H}=\begin{bmatrix}H_{R\times T}^H&\sigma I_T\end{bmatrix}\begin{bmatrix}H_{R\times T}\\\sigma I_T\end{bmatrix}=H_{R\times T}^HH_{R\times T}+\sigma^2I_T \tag{a} \end{align} \begin{align} \underline{H}^H\underline{y}=\begin{bmatrix}H_{...

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