Questions tagged [ofdm]
OFDM stands for Orthogonal, Frequency-Division Multiplexing.
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Do we need a transmit and a receive filter in a OFDM transceiver system?
can anyone specify in brief what are the filters that can be used as a transmit and receive filter in OFDM. Any material to start with will be very much appreciated. Thank you!
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The use of FDM for a single message signal
Suppose I have a single message signal, m(t), that is subjected to AWGN upon transmission.
Is there any way that FDM (or any multiplexing strategy) can be used to ultimately improve the SNR of the ...
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17 views
Channel Capacity of OFDM with Index Modulation
I am trying to figure out the channel capacity of OFDM with index modulation (OFDM-IM). One of the article reports that the conditional channel capacity of OFDM-IM is $\mathcal{C}_{\mathrm{OFDM-IM}}(\...
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34 views
Effect of Adding the cyclic prefix on the toeplitz matrix in OFDM
Assuming we have $N$ symbols to transmit encoded in block $k$,
Performing $N$−iFFT at the transmitter, we now have
The resulted signal $x(k)$ has length of $N$. inserting a cyclic prefix $CP$ ...
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92 views
Frequency domain samples to time domain without knowing the sampling rate?
I have some frequency response data from 802.11a OFDM communication in channel 8 of the 5 GHz band, and I would like to inverse transform this to produce the corresponding time domain response. That ...
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Can anyone tell what is the general BER obtained when using a DUC and a DDC in the system?
I am trying to build a wideband frequency hopping OFDM system on Simulink and later on hardware. My OFDM system, along with subcarrier interleaving works fine otherwise. The problem arises when I ...
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1answer
18 views
Carrier Frequency Offset Correction Limitations
I know that carrier frequency offset is typically detected and corrected in OFDM systems. I was wondering if there is a way to determine the theoretical limit to how much offset can be successfully "...
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47 views
Can we use discrete cosine transform with imaginary part
I have been reading about the difference between the use of iFFT and iDCT with OFDM.
What I understood that iDCT can only be used with one phase modulated symbol which is PAM/BPSK modulation.
It ...
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39 views
Is MMSE equalizer necessary?
For observation $y$, channel coefficient $h$ and gaussian noise $w \sim \mathcal{CN}(0,\sigma^2)$,
$$y = hx + w \tag{1}$$
Note that for OFDM system, (1) is assumed channel input-ouput equation on ...
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2answers
38 views
Preamble length and channel estimation
For OFDM we select the known gold sequence as the preamble or pilots. We can correctly estimate the channel(10 to 20taps).
Is there any relationship between the length of preamble and the number of ...
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7 views
Power of ICI in OFDM System
I am studying the effect of time offset in OFDM system, I am interested in calculating the power of the ICI on each subcarrier, I am a bit confused about how to do it in Matlab, so how can I measure ...
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20 views
Frequency domain channel coefficients in OFDM
I want to find frequency domain channel coefficients in OFDM in matlab. The channel is multipath rayleigh in nature. I had tried the following code but not getting the results.
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36 views
What is the forward error correction in 802.11a?
I am trying to put together a baseband-equivalent simulation of 802.11a signals, which according to Wikipedia has a variable encoding (PSK, QAM, etc.) that have differing coding rates (1/2, 2/3, 3/4) ...
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34 views
Strange signals in wifi channel
I am currently working with a USRP B200 mini-i to receive 802.11 signals from various usb wifi devices. When sending packets with the USB device over a channel, lets say 2.412GHz, i can't really see ...
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34 views
Demodulating an oversampled OFDM signal
I'm trying to simulate an OFDM signal that has been captured with a receiver that has a much larger bandwidth than the OFDM signal. I tried the following MATLAB code to simulate an OFDM signal that's ...
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49 views
How to Emulate Sample Frequency Offset for OFDM in Matlab?
I am studying the effect of sampling frequency offset on OFDM, and in order to emulate SFO, I have to slightly change the sampling rate of the signal. In order to have a +5ppm offset, I have to change ...
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1answer
133 views
What is the difference between (Sample Timing Offset), (Carrier Frequency offset), and (Sampling Frequency Offset)?
Briefly, can anyone explain to me what is the difference between (Sample Timing Offset), (Carrier Frequency offset), and (Sampling Frequency Offset)?
and is Sampling Frequency Offset (SFO) like STO ...
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16 views
(Frequency Offset): Relationship between Normalized Carrier Frequency Offset (normalized CFO) & ppm in OFDM system
How can I change a normalized carrier frequency offset (CFO) to ppm? And If the DAC sampling rate is 30GS/s, and the clock frequency is 15GHz, then should I use 30G or 15G when I calculate ppm? ...
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88 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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12 views
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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46 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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90 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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80 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
88 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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42 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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19 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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26 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
28 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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2answers
87 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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57 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
54 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
86 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
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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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70 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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48 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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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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1answer
48 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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109 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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24 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
47 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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44 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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201 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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47 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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238 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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2answers
454 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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76 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
132 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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1answer
63 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 ...
