Questions tagged [ofdm]
OFDM stands for Orthogonal, Frequency-Division Multiplexing.
-1
votes
0answers
16 views
Quantizing a time domain complex signal to fixed point
I am encoding every element of an OFDM time domain signal(complex double) using "uencode" from matlab and also another function to a specified no. of bits say 16.
quant_OFDM = q_uencode(OFDM_original,...
0
votes
0answers
36 views
Working principal of MIMO(2 by 2)-OFDM (802.11n)
I have gained basic knowledge on MIMO-OFDM from online sources and in process of building 802.11n standard in GnuRadio+USRP B210. My goal is to analyze the channel state information and play with it ...
0
votes
2answers
43 views
Understanding FFT size in OFDM modulation
I know that the FFT size is the the number of subcarriers OFDM system have. But I also know that the FFT has to be $ 2^N $ big (in order to process N samples from time domain to frequency domain).
...
0
votes
0answers
23 views
OFDM system with cyclic prefix
I have:
Bit rate $ R_b = 25.6 [Mbit/s]$
Sampling frequency at the input of the receiver: $ f_p = 8 [MHz]$
Protective spacing between successive OFDM symbols: $ τ = 16 [µs] $
The combined length of ...
0
votes
0answers
9 views
Calculating the Channel state information for localization
I want to build a localization system using 4G LTE for a project. Intuitively, I can get the position measuring the time a signal leaves the Base Station to the User Equipment. Knowing that these ...
0
votes
0answers
51 views
OFDM modulator: Transmission time calculation
I have a problem with a certain task.
The frequency of the signal sampling at the OFDM modulator output is
20 MHz. The length of the protection period is 2 microseconds and it is
20% of the ...
0
votes
1answer
39 views
In OFDM, what is the length of the cyclic suffix that is added before windowing?
I searched for length of cyclic suffix but all I can find information about is the cyclic prefix, I want to know also if there is short guard interval and long guard interval does it affect the length ...
0
votes
0answers
23 views
Why do we need two Long training sequences for Channel Estimation in 802.11a and 802.11p systems?
I am working on 802.11p and was wondering about the channel estimation part.
At physical layer (PPDU), The preamble contains 10 Short Training Sequence and two Long training same sequences.
Why do ...
0
votes
1answer
35 views
What is fft input size for ofdm?
From the Transmitter comes a block of size N+L (where N is the number of subcarriers and L is the cyclic prefix length). Then the block goes through a Channel which adds delay and AWGN, so this ...
1
vote
1answer
30 views
Quantized error in scatter plots for a hamming windowed LTE signal
I have a time domain signal based on LTE standards.
Carrier spacing = 15KHz, Symbols per slot = 6, extended Cyclic Prefix = 512 samples
FFT size = 2048, No. of sub carriers = 1200, channel BW = 20MHz, ...
0
votes
0answers
39 views
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 ...
0
votes
0answers
57 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 ...
0
votes
1answer
49 views
How to filter an OFDM signal? [closed]
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 ...
0
votes
2answers
43 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 ...
0
votes
0answers
42 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 ...
1
vote
0answers
66 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., ...
0
votes
1answer
23 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 ...
-1
votes
1answer
20 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 ...
0
votes
1answer
44 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 ...
1
vote
1answer
37 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 ...
0
votes
1answer
43 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 ...
0
votes
1answer
84 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-...
0
votes
1answer
71 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 ...
1
vote
1answer
49 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 ...
1
vote
1answer
73 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
...
0
votes
1answer
98 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 ...
-1
votes
1answer
46 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 ...
0
votes
1answer
96 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. ...
1
vote
2answers
91 views
Why Convolution between Signal and a 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. $...
0
votes
1answer
125 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 ...
0
votes
1answer
64 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 ...
0
votes
1answer
83 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 ...
0
votes
2answers
94 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 ...
1
vote
1answer
74 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 ...
0
votes
1answer
40 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 ...
2
votes
1answer
121 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, ...
0
votes
1answer
43 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 ...
0
votes
1answer
124 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 ...
1
vote
0answers
66 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 ...
1
vote
1answer
112 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 ...
0
votes
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 $NN=0$....
1
vote
1answer
37 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 ...
2
votes
4answers
63 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 ...
0
votes
0answers
72 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 ...
1
vote
0answers
71 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 ...
0
votes
1answer
76 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 ...
2
votes
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 ...
1
vote
1answer
57 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 ...
0
votes
1answer
105 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?
...
1
vote
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 ...
