# Questions tagged [ofdm]

OFDM stands for Orthogonal Frequency Division Multiplexing. It is a communications transmission technique that breaks the carrier into multiple sub-carriers (hence, the multiplexing in frequency).

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### Symbol-level frequency-selective channel model representation (in OFDM)

The general symbol-level representation for a frequency-selective channel is: $$y[k] = \sum_{l=0}^{L-1} s[k-l]h_{l} + z[k]$$ where $s[k-l]$ is transmitted symbols, $z[k]$ is noise, $L$ is the ...
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I'm fairly new to GNU Radio and was looking for a way to communicate using OFDM without using packet headers. I am trying to implement a simple version of OFDM with fixed length frames. I have ...
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### Can I reconstruct the channel impulse response from OFDM least square channel estimation?

I'm working on a successive interference cancellation (SIC) project for an OFDM system. I used pilots and least square channel estimation to estimate the channel frequency response (CFR.) It works ...
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### What is the relation between symbol duration and subcarrier frequency spacing in OFDM?

What is the exact relation between symbol duration and frequency spacing? You may know in WiFi6, about 11ax band, there are more sub-carriers compared to WiFi5 because of using shorter frequency ...
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### Why the does channel capacity not increase as the number of subcarriers increases?

We usually consider multi-carrier (interchangeably multi-channel) communications. By using the multi-carrier system, instead of one-broadband system, we can obtain many advantages, for example, able ...
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### MU-MIMO - do all antennas stream in different frequencies?

I have few questions on how MU-MIMO in WiFi works. Do all antennas stream in different frequencies or stream in same channel but different sub carriers(OFDMA?) Do MIMO antennas always work in OFDM ...
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### OFDM IDFT implementation

i have some doubts with the implementation of the IDFT in OFDM systems. The question concerns the expression of the IDFT of the OFDM signal. During the symbols period $T_s$ we have the following ...
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### How to calculate subcarriers bandwidth and cyclic prefix length in an OFDM using the IFFT

I'm trying to understand how OFDM works thanks also to the Simulink OFDM block. Now, I have understood that the OFDM modulation "convert" a faster bit rate using a certain bandwidth into a ...
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### Why the frequency spectrum of my OFDM output signal has a series of spike?

I'm trying to understand OFDM modulation using Matlab Simulink and I've built the following system I sent to the input of the OFDM block a frame of 15 samples that comes from the 16-QAM modulator. ...
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### How to calculate bit rate (physical layer) in ISDB-T (OFDM system)?

I was looking at OFDM (ISDB -T) specification. I couldn't figure out how they get the bit rate of 16.851 Mbps by having the following information? symbol length: 1.008 ms carrier interval: 0.992 kHz ...
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### what is the architecture of a wireless communication? Please explain patiently [closed]

Orthogonal Frequency Division Multiple Access (OFDMA) and Frequency Shift Keying(FSK). Hey, I'm extremely confused with the gigantic number of modulation schemes out there. Please help. I understand ...
1 vote
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### Minimum data rate for OFDM?

I'm relatively new to electronics, so sorry for my awkward understanding of topics. I'm just trying to wrap my head around some basic concepts here. From my understanding, in OFDM, the information ...
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### How are the neat sinc function shaped carriers produced in OFDM?

I am learning about OFDM and QAM. Every explanation I have read illustrates how the separate carriers are sinc functions that are arranged to overlap in a nice orthogonal way so as to cancel out ...
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### Maximum transmit power allowed for 802.11g

I'm learning about the 802.11 regs. In a book I'm using, "CCNA Wireless 200-355 Official Cert Guide (Certification Guide) 1st Edition by, David Hucaby (Author). Page 53", it has the following clause ...
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### OFDM symbol period and minimum burst durations

I have been reading about cognitive radio using OFDM and literature on technologies like LTE and 802.11 variants. A useful value in the system analysis is the OFDM symbol period $T_u$. Is it ...
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### In actual OFDM trasmitter, is the stepwise waveform after IFFT put on the carrier as it is?

I simulated OFDM on MATLAB,though,the spectrum of it is not white(flat shape). Why? IFFT circuit of actual transmitter uses higher IFFT order than the count of subcarriers? P.S. I simulated with the ...
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### Differences between OFDM, OFDMA and SC-FDMA?

I understand that - multiple user scenarios lead to OFDMA in SD-FDMA at any point of time, all subcarriers carry the same symbol. What I want is to understand on what exactly differentiates them.
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### OFDM numerical example

Am I correct in this example? For example, I have data a data stream like this 101100011100...11001001 .... . Let say a symbol is 64 bits. I will use 16 qam-ofdm. For this, I separate a symbol to 16 ...
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### what is the performance of an OFDM system in one-path channel (Flat response channel),with no multi path propagation?

i work on modelling a OFDM system in a indoor optical wireless channel (LOS channel), since my channel is LOS there is no multi -path propagation , so the delay spread of my channel is much smaller ...
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### VLC - OFDM with RPI3 [closed]

Edited, We want to transfer data in high speed's. we are using RPI3 for all the mathematics calculation. As we know the RPI dose not support ADC with high sample rate so it irrelevant for us. We ...
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