OFDM stands for Orthogonal, Frequency-Division Multiplexing.
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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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0answers
41 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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0answers
30 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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1answer
29 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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0answers
34 views
How can I get the channel response after FFT in OFDM receiver [closed]
I'm wondering if we can extract the channel in frequency domain in OFDM, in other words, is the below correct?
Assuming we have the received signal Y convoluted with channel h in ofdm system as ...
2
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1answer
35 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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1answer
49 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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1answer
54 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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1answer
35 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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0answers
30 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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0answers
16 views
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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0answers
74 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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1answer
94 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, ...
0
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1answer
62 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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0answers
52 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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1answer
82 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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vote
1answer
38 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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1answer
32 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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0answers
19 views
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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0answers
47 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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0answers
87 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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0answers
32 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
50 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
70 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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0answers
43 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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1answer
59 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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35 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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1answer
26 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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0answers
30 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 ...
0
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1answer
36 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 ...
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1answer
53 views
0
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0answers
14 views
How training symbols in OFDM are used to estimate channel state information [duplicate]
I would like to know how the training symbols in HT-LTF preamble field is sent from Tx to Rx and used to calculate CSI (channel state) and create a matrix on the receiver.
0
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1answer
65 views
How channel state information is calculated from Sounding Packet
What I understand is for Explicit Transmit Beamforming scenario, the Transmitter sends an NDP packet(aka HT Sounding) which consist of OFDM training symbols in packet preamble (HT-LTF) which are ...
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0answers
25 views
What happens when there is no data to transmit in OFDMA?
In the downlink of LTE, OFDMA is used to carry data. I was wondering what is actually happening (at the physical layer) when there are no data to transmit on a data resource block ?
I see two options:...
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1answer
246 views
Subcarrier spacing in OFDM
The idea of OFDM is to spread data across multiple overlapping subcarriers. As they are orthogonal it is still possible to demodulate them. That means, all other subcarriers are 0 at the evaluation ...
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0answers
19 views
1 symbol=500 real values. how to take IFFT in OFDM?
in OFDM we take symbols, do serial to parallel conversion and then perform IFFT. Right? here the problem comes...
instead of using 'pskmod' builtin function, i've made a proper code using sinusoids. ...
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1answer
80 views
Filter length in a Filtered-OFDM system
In a filtered-OFDM system, lets say we have the following parameters:
...
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0answers
76 views
Music algorithm for DOA applied on OFDM preamble
I am currently searching for the most appropriate AOA/DOA algorithm, applicable on preamble extracted from an OFDM signal, which can be implemented using USRP.
4 antennas array is planned to be used. ...
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0answers
45 views
How to model fading channels in MATLAB?
I am asked to write a MATLAB program for the simulation of the end-to-end transmission of a JPG file through a fading channel by using OFDM technique for one of my courses' term project.
I wrote my ...
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0answers
99 views
Channel Estimation Interpolation in OFDM Signal
I am currently working on capturing the signal from the PXI Generator by using LTE Signal with 2x1 MISO, 64 QAM, cell-ID = 0. I am trying to decode the signal after capture it until I got the CRC Pass ...
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0answers
117 views
Schmidl & Cox implementation in simulink
I am trying to implement Schmidl & Cox method for frame synchronisation in MATLAB and simulink as a part of ofdm model.
The following is the MATLAB code for "time lagged autocorrelation" and find ...
0
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1answer
337 views
Flat vs frequency selective fading in MC-CDMA?
I am trying to simulate an MC-CDMA system. I have NXK matrix $S$ which consists of subcarriers ($s_n,_k$ represents subcarrier $n$ of user $k$) and KX1 vector $X$ consists of user symbols. So my ...
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1answer
210 views
Plotting frequency spectrum for a signal with 20MHz bandwidth and sampling frequency of 12.5GHz
I am new to Matlab and I am trying to plot the frequency spectrum of an OFDM signal with bandwidth of $20 \text{ MHz}$ and DAC sampling rate of $12.5 \text{ GHz}$. The number of samples is $400,000$. ...
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2answers
164 views
doesn't OFDM inherently deals with ISI? why cyclic prefix is needed?
As far as I can understand, the motivation to OFDM and multi carrier communication in general was alot due to the ISI caused by multi-path which is equivalent to frequency selective channel.
Now, by ...
3
votes
1answer
430 views
Difference between Fine and Coarse Frequency Offset in OFDM
I need to explain for a project the difference between Fine and Coarse Frequency Offset in OFDM signals. I know what the frequency offset is and what it does to the carrier frequencies but I cannot ...
2
votes
1answer
537 views
Upsampling and Downsampling using IFFT and FFT
Assume in OFDM , there are N=64 subcarriers. I would like to upsample my signal by Factor 8 after IFFT and pass it through channel then downsample it by factor 8 before FFT. I can use upsample, ...
2
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3answers
216 views
Sending complex signal over a single wire
The G.hn protocol uses OFDM to transmit data. And it sounds like they are doing it on a single wire. OFDM symbols are a complex number with I and Q components. How are they able to send two separate ...
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1answer
59 views
QPSK Modulated OFDM Symbol after fading channel
I generate QPSK modulated OFDM signal and then send it to a EPA fading channel, after the channel, I can accurately demodulate the real part of QPSK symbol from the received spectrum, but the ...
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1answer
185 views
Implementing OFDM with audio signals
I've read an interesting paper called FingerIO
that transmits audio waves in OFDM,
and I wanted to implement and generate sounds using MATLAB.
(I am quite new to signal processing, so please ...
2
votes
2answers
411 views
Why is LTE either FDD or TDD?
In LTE systems, up- and downlink are duplexed either using FDD or TDD. Why has this not been designed to utilize the same multiplexing technique as used for the downlink (OFDMA)? Resource blocks could ...
