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# Tag Info

## Hot answers tagged ofdm

Accepted

### Flat fading criterion of OFDM subcarrier spacing

Your mathematical derivation is correct, your $H[k]$ is the single-tap equalizer (i.e. one tap for each subcarrier, and the subcarriers do not mix with each other. That's the orthogonal in OFDM). ...
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### Coherence bandwidth/delay spread in OFDM

Indeed, the constraint $T_s(N+N_{cp}) \gg T_m$ should be derived as $T_s(N+N_{cp}) \gg T_s N_{cp} \geq T_m$. The first inequality to make sure that the CP overhead is as small as possible. The second ...
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### OFDM time vs. frequency domain channel estimation/equalization

Traditionally, OFDM became popular in WiFi and LTE because the channel model consisted of multi-path. That is, the radio signal transmitted in 1-6GHz frequencies bounced from various obstacles (walls, ...
• 2,293
Accepted

### The necessity of null subcarrier in OFDM?

The only portion of the spectrum that is "occupied" or "transmitted" are the subcarriers that are actually used (i.e. 10 MHz instead of 15 MHz). The null subcarriers referenced in your question are ...
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### Difference between Fine and Coarse Frequency Offset in OFDM

If in doubt, read the original Schmidl&Cox Paper Robust Frequency and Timing Synchronization for OFDM. It's actually a good read, and a good paper with respect to demonstration of state of the art,...
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### Why Convolution between Signal and a Channel Is Not Done Directly in SIMO Channel

I've said, in another comment, convolution using the function conv "i.e in MATLAB" and convolution using the Toeplitx matrix must give the same results. That's ok. Now, according to your code, the ...
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Accepted

### What is the forward error correction in 802.11a?

From the official standard, IEEE Std 802.11a-1999, Part 11, section 17.3.5.5 Convolutional encoder, see the rate 1/2 code: The resulting two streams A and B are interleaved bit-alternatingly. The ...
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### Setting Parity Check Matrix for LDPC channel coding

As specified in documentation, using 'ParityCheckMatrix' you can configure the Parity Check Matrix (PCM) during the constructions of the encoder/decoder objects. ...
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### Spectral efficiency of with OFDM vs without OFDM?

The spectral efficiency of OFDM is strictly worse than that of a pulse-shaped QAM signal with the same rate. OFDM requires a guard interval, on which no useful information is transmitted. It is ...
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Accepted

### Intercarrier Interference (ICI) with OFDM signals

As Marcus mentioned in the comments under the original question, this is complicated with lots to understand. Thankfully, the framework is already here with other posts to at least pursue Marcus' ...
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Accepted

### Can an OFDM waveform be spread (DSSS)?

You can do a lot of things. Some are sensible! Remember why you're using OFDM (frequency-domain equalization) and remember that the temporal structure of the OFDM symbol (as the IDFT of the data ...
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Accepted

### Frequency-domain vs Time-domain OFDM oversampling

Your first method is just not using the subcarriers at the band edges (the ones that you zero-pad). It is hence equivalent to a sinc-interpolation in the time domain. Finally, a cyclic prefix (or ZP, ...
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### What type of LO lekage Correction algorithm is used in 5GNR?

In direct conversion transceivers, the LO leakage is pretty much a given. Some systems, mainly OFDM systems like Wifi, deal with that by simply leaving the DC carriers unused. And that's it. No ...
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### What type of LO lekage Correction algorithm is used in 5GNR?

Just want to provide some details to complement Marcus's answer. (1) 5G NR does not avoid DC carrier, (2) it is possible to use it to modulate data (accepting degradation), and (3) 3GPP does not ...
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Accepted

### VOFDM (Vector OFDM) advantages and disadvantages

Referring to VOFDM as described in this reference, some thoughts on that (I wrote this summary some years ago, due to an issue in my own research). We can understand VOFDM as quite similar to ...
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Accepted

Some more disadvantages: Channel estimation using pilots is harder, because you do not have orthogonal data on each frequency bin, compared to OFDM. That's why e.g. LTE uplink resorts to a midamble ...
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