# 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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Accepted

### Purpose of interleaving in OFDM systems

Interleaving is not specific to OFDM. It is an age old technique used for improving error correcting codes. Basically, most error correction coding techniques are good at suppressing bit-wise errors ...
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### OFDM modulator in LTE

Definitely yes. But after IFFT operation data block is CP extended before transmission. Each sample of OFDM symbol from the output of IFFT is weighted sum of all QAM/PSK modulated subcarriers from the ...
• 1,023
Accepted

### OFDM modulator in LTE

Yes. Cyclic Prefix and windows(prefix and postfix for pulse shaping) are added to the OFDM symbol, but windows are only for overlap-and-add for pulse shaping, so the effective length is M+CP_length ...
• 496

### Number of samples in one period of subcarrier after IFFT

You need as many samples as you have subcarriers. If you have 64 carriers, then you need 64 samples.
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### Effect of cyclic prefix and zero-padding in OFDM

The main idea of using Cyclic prefix in OFDM systems is because of 2 reasons, 1) To eliminate ISI from previous symbol. 2) To model linear convolution as circular convolution If an OFDM symbol ...
• 505

### Multipath resistance of spread spectrum systems

The key idea in spread-spectrum communications is to use much more bandwidth than the minimum required for the signal being sent. Multipath effects occur when the sent signal $s(t)$ and a delayed, ...
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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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### 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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### 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, ...
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Accepted

### 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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### OFDM use a pulse shaping filter or not?

The purpose of pulse shaping filters is not to overcome ISI as is implied in the OP's question. The only reason for using a pulse shaping filter is spectral efficiency, and in the process ISI can be ...
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