OFDM stands for Orthogonal, Frequency-Division Multiplexing.
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OFDM in Time domain
This tutorial shows the idea of analog time domain OFDM. My question is if we can sample the analog signal and use time-domain OFDM in a similar fashion. Why do we need to apply IFFT/FFT to the signal ...
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18 views
what are the hot area of searching in FMBC and Massive MIMO
I'd like to ask about Massive MIMO, and FBMC .. what are the hot areas of searching in these two topics ?
I mean for example in OFDM, it's needed to check the ISI, ICI and channel estimation and so ...
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40 views
OFDM RF signal waveform
From the Wikipedia article:
"An inverse FFT is computed on each set of symbols, giving a set of complex time-domain samples. These samples are then quadrature-mixed to passband in the standard way. ...
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18 views
Common Cyclic prefix for a set of cascaded OFDM symbols
I've seen research papers / baseband systems that deal with synchronization using a common CP(Cyclic Prefix).
The transmission structure comprises , a family of complex orthogonal sequences, with ...
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54 views
Why Convolution between signal and channel is not done directly in SIMO channel
In OFDM system, I need to transmit a signal $x$ in SIMO channel $H$ with one $Tx$ antenna and 4 $Rx$ receiver's antennas. The initial equation for that convolution is $r=Hx+n$ where $n$ is the noise. $...
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How multiple HT-LTF in 802.11n (MIMO-OFDM) standard is used to estimate the CSI
In the 802.11n preamble, the number of HT-LTF (High Throughput- Long Training Field) is equal to the number of spatial streams. Therefore, for a 2 by 2 MIMO system, there will be 2 HT-LTFs. These HT-...
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45 views
Use of Long Training Field (LTF) of 802.11 standard
In 802.11a/n the preamble part has L-LTF(Legacy-Long Training Field) and HT-LTF(High Throughput-Long Training Field). I want to clarify my understanding of these two fields:
Are the only difference ...
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50 views
What's the difference between SISO and SIMO in using matched Filters
Suppose we are transmitting a signal $x$ in $OFDM$ with $N$ subcarriers, After performing Parallel/Serial conversion and then N-points
FFT, we suppose to have signal $s = IFFT^Hx$, Then adding the ...
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35 views
OFDM Short Training Field clarification
I want to clarify my understanding of OFDM training fields. Please correct me if I am wrong as I am getting 2 different information from online resources.
For 802.11a standard the preamble contains ...
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43 views
How to determine the original size of the FFT used in unknown OFDM symbol
Given an unknown OFDM symbol consisting of 9144 samples, interested to know the size of the FFT used in the TX/Number of bins.
Down-sampling to 512,256,128,64,32 yields the following.
Do not see how ...
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49 views
Is sparse signal in time domain is sparse in Frequency domain
In OFDM system, if we have a multi-path environment, we supposed to have a sparse received signal in time domain, then $FFT$ is performed to convert it into frequency domain.
My question, does the ...
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21 views
Effect Guard interval in OFDM
In an OFDM system, if guard interval is left empty(zero padding is used), why does the orthogonality of subcarriers no longer holds?
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Peculiar OFDM Constellation
Currently testing blind demodulation methods on recorded OFDM signal.
The recordings were done with coax cables.
While the estimated Frequency and Time shifts were not accurate enough for ...
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30 views
Is the Channel shortening similar to Time domain Equalizer (TEQ)
I used to read about Time domain equalizer (TEQ) in many lectures, i.e here , But in many other papers, that's called Channel shortening i.e here .
However, in the a two above links, the cost ...
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74 views
What is about the circular convolution in OFDM
In an OFDM system, serial-to-parallel conversion for data is done, then the DFT is performed and then adding the cyclic prefix (CP).
My question is related to that step of adding a CP. As I know, ...
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30 views
how to set Equalizer's coefficient using generalized eigenvector.
In that paper https://jwcn-eurasipjournals.springeropen.com/articles/10.1186/1687-1499-2012-72 .. Equation 3,
$J(w) = w^HBw/w^HCw$ ..
$B$ and $C$ are matrices, $w$ the filter coefficients vector ...
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91 views
How I can perform SIMO channel convolution in MATLAB
In OFDM system, I need to transmit a signal $x$ in SIMO channel $H$ of single Tx antenna and $4$ Rx antennas. The initial equation for that convolution is $r = Hx + n$ where $n$ is the noise.
As ...
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28 views
ADC sampling rate in OFDM baseband processor
I have optical OFDM baseband TX and RX implemented in FPGA. The design is tested using one FPGA board in loopback connection from DAC to ADC via coaxial cable. It works fine, the BER is about 1.10^-8 ...
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57 views
OFDM: How to do the carrier recovery of the quadrature(I/Q) demodulation
For an OFDM system, after the OFDM modulation, the quadrature modulation is used to move the signal from the baseband to the pass-band.
But when it comes to the receivers, I can't find any way to make ...
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45 views
In OFDM, does $N N^H$ equal $I$?
I'm still new in OFDM and reading about it, but I have a question.
In OFDM system, when having $N$ data symbol assigned to sub-carriers, $N$ should be orthogonal with each others, which means $NN=0$....
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21 views
Sharp sample transition in OFDM signal
I am implementing OFDM PHY for Visible Light Communication in FPGA. (I am quite new to communication system and signal processing, so please understand my lack of background knowledge.)
The FFT size ...
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42 views
Bandlimiting and OFDM spectrum - what is considered “bandlimited”?
I have been reading about OFDM modulation, it's not clear to me how you can have band-limited OFDM but given its prevalence in wireless communication there must be some designation of approximately ...
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51 views
What is the relationship between FFT size and demodulation in OFDM
As I mentioned in the title of the question, how can we demodulate the data in order to get the same number of subcarriers with different FFT size.
For example,
10 MHz LTE can be sampled with 15.36 ...
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36 views
How can I oversample OFDM received signal in MATLAB
I need to oversample a received signal in OFDM by MATLAB, according to the below diagram, but when I oversample, I finally get the same number of samples however that should be double. !! The ...
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38 views
OFDM. Cyclic Prefix and ISI
Sorry that I created a new question about OFDM, but I donät have enough reputation to comment on other questions.
I have read all the topics here and I have some doubts.
1) I found in the book that ...
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36 views
issue in DFT of OFDM by blocks and N-by-N
I'm trying to study and understand the OFDM, and during coding the OFDM in MATLAB, I faced this issue:
suppose we have the Numsymbol = 256, and dataqpsk our used data, The issue which I face that ...
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51 views
What is the impulse response of SIMO channel and its equivalent in oversampling?
1- According to the below paragraph :
Could someone explain, What mean M here? I mean when saying with Order M ?
2- On the other hand, When performing Fractional sampling, for example sampling ...
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60 views
What's the relation between the sampling rate and FFT size in OFDM
In OFDM system,
Is there relationship between Sampling rate and FFT size? For example, if we downsample or oversample the received signal, Should we decrease or increase the FFT size accordingly?
...
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37 views
Is it possible to recover QAM constellation of an undersampled OFDM signal?
The OFDM signal I'm interested in is rated for a 204.8MHz sampling rate!
I'm limited to sampling at 20MHz to give me just enough resolution into the range of subcarriers I'm interested in, but I just ...
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40 views
bits to an OFDM symbol
I have been trying to get a hang of OFDM but it's in vain.
This is my understanding so far.
Let's say I have a stream of bits 010101010.... and so forth.
We then group the bits depending on the ...
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find power of recieved signal of usrp b200 in gnu radio companion
how to find power of recieved signal of usrp b200 in gnu radio companion from frequency sink block (the frequency plot) or any other block available in gnu radio. I am transmitting and receiving ofdm ...
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132 views
Why does my OFDM demod in GNU Radio not return anything?
This is the flowgraph I used:
Output after mod:
Output after demod:
I've read that it might be a synchronization problem but since I'm not actually transmitting anything over a medium, that shouldn'...
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130 views
Cyclic prefix length in baseband OFDM with ZF equalizer
My question is about baseband OFDM. I try to plot the BER according to the SNR. I noticed that changing cyclic prefix length does not affect the performances. I.e., following the code below, ...
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73 views
Rake Receiver vs OFDM and multi-path channel
My Question is, Can we use the Rake Receiver with OFDM modulation? As you know, Rake receiver is usually used with DSSS modulation, so can we use it with OFDM?
in other words, Does the Rake Receiver ...
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85 views
Phase Noise in OFDM simulation
I am trying to simulate phase noise in OFDM and in search of a mathematically tractable model. So far, I have managed to get phase noise by multiplicating $e^{j\phi(n)}$ in frequency domain where $\...
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143 views
OFDM - why do we need IFFT?
This question is really related to - is there any need for IFFT in the first place?
If we want to send a bunch of complex-numbers (vectors), then most OFDM discussions involve presenting those ...
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1answer
53 views
How to decide what subcarrier allocation should I use in OFDM?
For those familiar with the liquid-dsp library, or with OFDM in general, I am hesitating what subcarrier allocation should I use in a particular wireless system.
By subcarrier allocation I am ...
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35 views
A priori spectral efficiency of OFDM scheme
Of course I can compute the spectral efficiency as the ratio of the measured bit-rate (of data bits, no header, no preable, nor redundancy bits included) and the measured spectral bandwidth. This ...
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How bit shifting with in Barker codes works, shifting by 1 bit and shifting by 2 bits
Let's say I have a 7-bit Barker code [1, 1, -1, -1, -1, 1, -1]
This Barker code shifted by 1 bit is the same as above.
The Barker code shifted by 2 bits is ...
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77 views
How to implement an OFDM system in MATLAB
Hi guys,
I am trying to simulate OFDM in MATLAB. I am referring this diagram to model the system. I have used QPSK modulation. My doubts are as below. Kindly go through them and help me. Thanking you ...
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129 views
Spectra of a basic OFDM transmitter
I try to simulate a primary (or very basic) OFDM transmitter. The goal is to have spectra exactly like these:
But through my Matlab code:
...
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33 views
Phase noise in OFDM
I'm calculating carrier frequency offset in an 802.11p using a short preamble as described in this paper. In simulation my CFO is flat during the duration of the short preamble, however in real world ...
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1answer
58 views
OFDM synchronization using training symbols
In OFDM receivers, special OFDM training symbols for which the data content is known, can be used to perform the synchronization process. A correlation operation is performed between the received ...
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1answer
93 views
Baseband OFDM Implementation questions
Signal processing is not my area of expertise so need help with implementing an OFDM system.
EDIT: The cabling and uncontrolled topology already exists and need a system that re-uses existing ...
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54 views
Applying the concept of orthogonality in DFT subcarriers to OFDM
In OFDM, why is IDFT used and not DFT at the transmission end? Why are we considering time domain signals as frequency domain signals and applying IDFT?
How are positive/negative signs in IDFT/DFT ...
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72 views
Frequency synchronization in OFDM
Could you please help me understanding how the null sub-carriers can be used to estimate the carrier frequency offset and thus performing frequency Synchronization at the receiver?
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38 views
Why do optical OFDM systems require Hermitian symmetry? [duplicate]
I am trying to understand the purpose of Hermitian symmetry in optical OFDM systems. As I understand, Hermitian symmetry means $$x(t)=x^*(-t)$$
Is that true?
And why is this property needed in ...
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30 views
What is the acceptable range for bandwidth utilization factor in OFDM systems?
The bandwidth utilization factor is defined by (alpha=bite rate/bandwidth), for OFDM system, what is the acceptable range for alpha?
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41 views
Beamforming with NDP frames
During beamforming, the Tx first sends NDP Announcement (which is a broadcast frame) thereby reaching all Rx in its area. And then it follows by sending NDP.
Is the 2nd frame (NDP) is also a ...
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41 views
Transmission frquency in MIMO-OFDM system
What I understand in MIMO system, the user data is broken down into several chunks and transmitted over the antennas (say 3 Tx antennas) by using same frequency Fc. In order to use the interference as ...
