Questions tagged [ofdm]
OFDM stands for Orthogonal, Frequency-Division Multiplexing.
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AWGN interpretation of bit error rate in time domain
I'll consider a 20 MHz bandwidth between 1.99-2.01 GHz. The carrier has been modulated by an OFDM signal (I/Q modulation) and is passed through a narrowband filter at the receiver.
The noise that is ...
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50 views
Digital Communications block diagram question
I am new to digital communications and trying to understand the basic underlying concepts of digital comm systems. So far , studying the course , I have some questions which if anyone can answer would ...
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1answer
38 views
How to filter an OFDM signal? [on hold]
Across the channel bandwidth there shoudd be 100 RBs (central 1200 sub carriers in a 2048 bin). Max power normalized to 0dB, the first OOB lobe should be -34dB. This 1st lobe on either side is at 5 ...
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2answers
38 views
What should be the cut off frequency of a Filter operating on an OFDM signal?
I have a time domain OFDM signal and to this I need to apply different linear filter however I am not sure on the cut off frequency. I am simulating for multiple symbols where each symbol has 1200 ...
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19 views
No. of Cyclic prefix for 5G NR signal with 100Mhz bandwidth different subcarrier spacing?
I want to generate a 100Mhz bandwidth 5G NR signal with different subcarrier spacing(15,30,60,120Khz) in matlab. What is the no. of CP to be added for 1st OFDM symbol and the other symbols and also ...
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57 views
Applying DFT to OFDM signals above Nyquist rate
Consider an OFDM signal which has $N=8$ subcarriers and is band-limited to $[-B/2,B/2]$, $\sum_k x_k e^{j2\pi kf_0t}$ where $f_0=\frac{B}{N}$. For this case the Nyquist rate is $2\times B/2=B$, i.e., ...
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How to filter an OFDM signal for reducing Out of Band emissions and how to decide the filter length?
I have an OFDM time domain signal (Based on LTE stds) with cyclic prefix of length 512 samples. Each FFT/IFFT bin is 2048. I need to apply different filters (window based, equiripple etc) to it to ...
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1answer
21 views
How to window a time domain signal for 6 symbols with cyclic prefix length of 512 samples?
Based on LTE stds. I am running a simulation for 6 symbols (each having 1200 central subcarriers) each in a 2048 FFT/IFFT bin. To these symbols are appended 512 samples as cyclic prefixes. I have to ...
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19 views
For an extended cyclic prefixed symbol what should be the FFT size?
I'm running an OFDM simulation based on LTE stds. Im simulating for 6 symbols in 1 slot of a subframe. I have appended an extended cyclic prefix (512 samples) to each symbol thus making each symbol ...
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1answer
18 views
Applying window function to reduce out of band emission for a symbol in LTE simulation?
I have to apply a window to an IFFT'ed signal (based on LTE standards, simulated for 1 symbol - 100 resource blocks - 1200 subcarriers). I have a signal which I have simulated till the IFFT. Now I ...
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1answer
38 views
Sampling Frequency in a OFDM technique:
I am a new learner of OFDM. One source I refer explained OFDM in this way:
Consider 4 symbols $X_0$, $X_1$, $X_2$, $X_3$ $\in \mathbb C$. They are modulated using Multi-Carrier Modulation. The time ...
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1answer
28 views
Modulating ofdm in audio spectrum
Trying to modulate audio with OFDM data.
My fs = 44.1khz, i'm using 64 sub-carriers, but i'm only using 5 sub-carriers for data, so my bandwidth is about 3.445khz. I'm not sure how to properly write ...
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1answer
36 views
Is CMA equalization applicable for OFDM
I have a question regarding the constant modulus algorithm (CMA), as you know it's one of the known algorithms used for blind equalization. The cost function of the CMA is build blindly, it means ...
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28 views
How symbol synchronization is achieved in 802.11n standard
According to the 802.11n standard, packet detection and synchronization is done with the preamble part of the frame. A packet is detected with the correlation method, that is comparing the short ...
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1answer
54 views
What is the index modulation in OFDM and Subcarrier Index modulation?
I'm new here, I'd like to ask about the OFDM-IM (OFDM - Index modulation), what is it and how it works? Is it the same as SIM-OFDM?
I checked white papers, I see it's using the index of sub-...
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1answer
62 views
Ambiguity in the IFFT process in OFDM
I am still trying to iron out some ambiguities in my understanding of the IFFT component of OFDM modulation schemes.
So here we have a QAM symbol $s_0$ being multiplied with the subcarrier for that ...
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1answer
45 views
Visualising OFDM subcarriers in the frequency domain
Im struggling to understand why in some images the frequency domain shows clear bars with amplitude and phase and with 0 frequency variation (it is clear that the frequency of the waves does not ...
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1answer
62 views
OFDM Simulation process
I'm trying to understand OFDM by making a simulation. Are these steps correct?
generate M random complex QAM symbols. example: (1+j,1-j,-1-j,1-j....)
Split my M samples into a N 2048 sized arrays
...
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1answer
76 views
What is the mixed numerology in OFDM
In order to meet the user requirements in the next
generation radio access technology, the ongoing standardization within 3rd Generation Partnership Project (3GPP) offers flexibility in terms of ...
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1answer
43 views
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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1answer
79 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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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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1answer
74 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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1answer
61 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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1answer
62 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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1answer
64 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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2answers
71 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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1answer
59 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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1answer
36 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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1answer
106 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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42 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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1answer
110 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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45 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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85 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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1answer
46 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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1answer
32 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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4answers
48 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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59 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
56 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
61 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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1answer
39 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
55 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
78 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
39 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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46 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
25 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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231 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
239 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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1answer
97 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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141 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 $\...
