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Normally OFDM is demodulated using FFTs. …

OFDM (sub)carriers are only exactly orthogonal over a certain IFFT block length (and integer multiples). …

The sinusoidal basis vectors of an FFT are only purely orthogonal over the whole length of the FFT. And orthogonality is required to be able to contain independent data bits that can be separated by …

A silent guard interval would likely increase PAPR (peak to average power), which requires a sender capable of more dynamic range (without clipping or generating power supply noise, etc.) A long eno …

You forgot to mix or heterodyn the complex FFT output up to the carrier frequency. Then the negative index FFT bins will be below the carrier in frequency. FingerIO appears to use a very high audio …

OFDM does both, using many different frequency carriers that are orthogonal over certain time windows, and within each frequency, using the fact that the sine and cosine functions are orthogonal over that … Note that the trick is that the the I and Q data must stay constant within that time window for OFDM to work. Else orthogonality is broken. …

The “O” in OFDM stands for orthogonal. …

Your 2nd paragraph ends incorrectly. Each IFFT input is "shredded" across the all values in the time domain, but only effects one subcarrier in the frequency domain. Just as adding a single pure sin …

LTE uses OFDM. OFDM with a long enough cyclic prefix turns multipath distortion into a large number of flat fading channels at slightly different frequencies. … An OFDM system can either dynamically re-assign channels that have faded below some allowed S/N, or use some sort of redundancy (an ECC or error correcting code) across channels. …

Assuming frequency lock, OFDM does not need any per sample fine time synchronization or any per sample interpolation. … Instead the receiver can either synchronize to the entire OFDM frame, or determine the frame time to sample time offset (which may include a smaller-than-time-interval-between-samples component) after …

You may be confusing to O in OFDM as orthogonality in the mathematical sense with orthogonality in the engineering sense. … Thus, legal OFDM is not orthogonal (mathematically), but is (enough to work). …

For instance, each subcarrier in an OFDM system can have a different size of QAM constellation. …

Each IFFT complex result bin represents an amplitude and a phase for some frequency. You can use the sum of the a sine and a cosine in the appropriate ratios to produce a sinusoid of any phase (see t …

I think of it as 2 sets of guard bands, one set in the frequency domain (unused spectrum), and one set in the time domain (OFDM cyclic prefix). …