Questions tagged [ofdm]
OFDM stands for Orthogonal, Frequency-Division Multiplexing.
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Precoding algorithm for OFDM
I working on an implementation of a linear precoding algorithm for MIMO OFDM system and I have an issue with symbol estimation part.
Let me briefly explain what I am doing:
H- channel matrix ...
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1answer
51 views
Large spike at beginning of signal after applying Bandpass filter
Foreword: I am a PhD student and fairly unexperienced with many signal processing and engineering concepts, please be gentle.
I am attempting to filter out a frequency range of 1Hz to 2Hz from a 2....
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Transmit beamsteering algorithm for OFDM signal [closed]
I want to steer my transmit signal at a specific signal. Suppose the OFDM modulated signal for a SISO system is x(t). Now for a 4-antenna system in want to steer this signal to a specific angle $\...
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Is there any commodity WiFi device supports dynamic OFDM subcarriers selection in demodulation?
For example, given an OFDM symbol with $N$ subcarriers, the WiFi device only demodulates subcarriers $1$ to $N_{1}$, and ignore subcarriers $N_{1} + 1$ to $N$, where $1 < N_{1} < N$?
Is there ...
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32 views
OFDM synchronisation Schmidl and Cox method - question
If somebody has good knowledge about the synchronisation method (related to the OFDM topic) developed by Schmidl and Cox, then you will probably be able to help me with my question about their ...
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73 views
Implementation OFDM system in Matlab
I am working on the OFDM transmission system. A channel is given, MR x MT; input data MT x S, and length of a cyclic prefix (CP)....
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1answer
53 views
Doppler effect in underwater acoustic channel
I got my BER vs SNR graph as shown. I was trying to show the difference in BER with OFDM signal transmission under Doppler effect and without Doppler effect. However, based on my understanding, the ...
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2answers
62 views
Is it possible the difference between OFDM-CP and OFDM-ZP about 10dB
I'm building basic matlab code for ofdm, but when I change the CP OFDM into ZP-OFDM with sme parameters, I get the performance is worse by up to 10 dB!! Is that right ? or there is some thing wrong in ...
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36 views
Underwater acoustic channel is giving me a flat BER vs SNR curve
I need to do OFDM and GFDM signal transmission in underwater acoustic channel. I have my underwater acoustic channel as follow.
...
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18 views
Adding Symmetric alpha stable noise to channel
I am doing GFDM in underwater acoustic channel with symmetric alpha stable noise. My GFDM signals is in frequency domain. I generate a symmetric alpha stable noise wish to add in to the channel. I am ...
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1answer
19 views
Modulation with Maximum Likelihood decoder and capacity
My question comes from the high spectrum efficiency claim of OFDM. This seems not correct IMHO, at least theoretically.
For me, we lose energy in using cyclic prefix, hence OFDM should be a waste of ...
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1answer
20 views
Simulate BER curves for OFDM with convolutional coding
I am tasked with generating performance curves for an OFDM transmitter/receiver, and I am unsure how to calculate the appropriate AWGN power, and where exactly the apply it.
The transmitted packets ...
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32 views
Difference between OFDM and FDM
In Frequency Division Multiplexing we provide one channel to one user.
Example like BandWidth of user1's voice is 200Khz. I provide one channel of 200KHz in FDM for uplink as shown in the figure.
...
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1answer
42 views
What is the difference between the V-OFDM and OSDM
I am trying to understand the difference(s) between V-OFDM (Vector Orthogonal Frequency Division Multiplexing) and OSDM (Orthogonal Signal Division Multiplexing) which are used as a multicarrier ...
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1answer
37 views
Demodulation of OFDM symbol in LTE for multi-user case
I was trying to understand what exactly happens when you try to modulate an ofdm symbol in the downlink in LTE for multi-user case.
When we modulate, usually we allocate different sets of RBs for ...
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1answer
80 views
On the signal recovery in OFDM after estimation
Given a modulated signal X which is transmitted based on OFDM with N = 256 sub-carriers through channel ...
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1answer
32 views
I need to insert an underwater acoustic channel model to an existing code that compared between OFDM and GFDM
The acoustic channel model that I have will output the channel impulse response. However, my signal is modulated in frequency domain (by doing fft). Hence, I want to obtain a frequency response of the ...
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22 views
On the use of OMP for sparse channel estimation based on pilots
Given an OFDM frame whose length is 256 sub-carriers, the length of guard interval CP is 64, and the transmitted known pilots 'in red' are 64 too as below:
where the received signal is suppose to ...
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1answer
48 views
Block by block CCDF and PAPR analysis in MATLAB
There are few signals (OFDM-like modulation scheme with uniformly distributed data source) generated by my script. I need to compare scheme performance in sense of CCDF (Complementary Cumulative ...
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Why are guard bands employed in FBMC even though the prototype filter has near perfect leakage performance?
FBMC employs prototype filter which has a good performance in reducing the spectrum leakage to almost zero but there are a few implementations online where they have still used guard bands on either ...
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1answer
39 views
For a 20 MHz channel, with 1200 usable subcarriers(18 MHz occupied), what should be the size of the FFT on the transmitter before IFFT is applied?
I am trying to simulate the SC-FDMA transmission and I read H Myung's paper and research on the topic but I am not sure exactly on what should be the size of FFT at the transmitter.
For a 20 MHz ...
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54 views
Channel state information from non-HT packets: is that possible?
I read several papers about CSI data, but one thing is not clear.
I would like to extract csi from legacy rate packets. I read some forums related to existing CSI tools and they only state that CSI ...
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41 views
Understanding the concept of semi-blind receivers
In the book "Signals and Images: Advances and Results in Speech, Estimation, Compression... ", an overview of using tensor analysis in signal processing is given. On page 243 it is explained that an ...
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Can you explain me in a easy way what the use of Cyclic Prefix in OFDM is? [duplicate]
I cannot understand why cyclic prefix is used. I know that it mitigates the effect of ICI but I can't see how. Can you explain please? Formulas and mathematics is well accepted. Thanks.
I read this ...
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3answers
74 views
Explanation a flat fading channel in case MIMO OFDM
I am trying to understand flat fading and frequency selective channels.
As I understood, in the case of flat fading channels MIMO channel elements, $h_{i,j}$, are random variables.
Which assumption ...
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19 views
Derive the LFSR sequence from demodulated bitstream
I'm new here and hope to have good feedback from you.
I'm trying to blindly demodulate an RF signal and managed to get a sequence of bits for a preamble. After some research, I'm in fact exactly in ...
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1answer
27 views
qam demapper why are soft-outputs used?
I'm starting to learn about OFDM QAM demapping, and a lot of documentation points to using "soft-output" algorithms that calculate Log-Likelihood Ratios (LLRs).
Why is this method advantageous?
My ...
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35 views
what should the the output of an FIR filter (root raised cosine) look like?
I am implementing a filter that is FIR on verilog HDL ,, I understand what happen in the filter well, I mean the delay, multiply and sum, the problem that I can't imagine how can I get the desired ...
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159 views
How is DJI OcuSync wireless link physical layer implemented?
I'm looking for documentation on the wireless command link of the DJI OcuSync. I found this website (in Chinese). It seems like an OFDM link that uses Alamouti codes?
I'm specifically interested in ...
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33 views
How to relate power spectral density with the number of resource blocks in LTE?
I am running a simulation with 100 Resource blocks for LTE OFDM and I plotted a PSD for it. Now I am able to bring down the out of band emissions when I perform an algorithm on it. Based on the ...
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172 views
Why does power spectral density of OFDM signal changes with number of zero subcarriers
I am trying to plot the power spectral density (PSD) of an OFDM signal with $N_{dsc}$ subcarriers and $N_{zeros} = N_{fft}-N_{dsc}$ zero subcarriers.
I am using the matlab function pwelch() to plot ...
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21 views
getting channel matrix from rayleighch matlab object
If I use "rayleighchan" of the communication toolbox, and I set the Doppler frequency, number of paths, path gain, etc . How can I extract the channel response to use it in MMSE channel estimation?
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132 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 ...
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2answers
309 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).
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65 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 ...
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14 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 ...
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66 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 ...
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1answer
104 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 ...
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74 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 ...
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1answer
57 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 ...
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1answer
46 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, ...
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61 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 ...
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66 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
247 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 ...
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2answers
58 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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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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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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1answer
45 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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1answer
39 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
116 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 ...
