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Questions tagged [ofdm]

OFDM stands for Orthogonal, Frequency-Division Multiplexing.

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Time-domain channel estimation using identical guard interval vectors

Assuming we have the received signal $y = h * x $ where $*$ is circular convolution, $x$ is the transmitted signal, $y$ is the received signal and $h$ is frequency selective channel. The signal $x$ is ...
Sajjad's user avatar
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How single-tap equalization can be performed in OFDM for perfect channel estimation?

If I have for example IFFT length of 3 with cyclic prefix length of 2 and 3 channel taps, how can I illustrate the frequency domain equalization in OFDM? For example as far as I know, it's elementwise ...
Amitabha Bhattacharjee's user avatar
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Free space path loss and Rician fading

Let a be a qam symbols vector , they pass through ofdm modulator by applying ifft and adding cyclic prefix and I apply comm.RicianChannel function for modeling rician fading I want to introduce also ...
ahmed bennani's user avatar
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Channel impulse response (CIR) and OFDM relationship

In Chapter 3 of the [Goldsmith book] (https://faee.sut.ac.ir/Downloads/AcademicStaff/1/Courses/7/Andrea%20Goldsmith-Wireless%20Communications-Cambridge%20University%20Press%20(2005).pdf) we can see ...
rick87's user avatar
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Are there any DC offset compensation algorithm for 5G NR? [duplicate]

Unlike LTE, DC subcarrier is used in 5G-NR. DC subcarrier may suffer from local oscillator leakage. Local oscillator leakage gives rise to DC offset. Are there any DC offset compensation algorithms ...
user71467's user avatar
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Free space path loss and ofdm

I want to apply the Friis equation of free space path loss on OFDM signal. Do I multiply signal by $\frac{c}{4\pi f_cd}$ before IFFT or after?
ahmed bennani's user avatar
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OFDM: From DFT to time-continuous signal

I try to write down the equations that show how constellation symbols (PSK, QAM etc.) are modulated into a time-continuous signal. I read the articles referenced at the end. However, I am still stuck ...
Cornelius's user avatar
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How to detect when signals overlap in OFDM?

If you are in an environment with multiple transmitters of similar signal strengths, before band selection has taken place, how do receivers parse out overlapping OFDM signals from multiple ...
FourierFlux's user avatar
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Do you have to receive a whole OFDM signal to be able to demodulate?

An OFDM signal is made of subcarriers that are orthogonal to each other. This terminology makes me think that if one is only interested in information on a specific subcarrier, only that subcarrier ...
Eind997's user avatar
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In wireless communication, is pulse shaping applied to each BPSK signal before OFDM is used, or not?

I have read a number of posts that seem to ask this question but have not been able to find a definitive answer. Here goes... I understand that BPSK with NO pulse shaping would produce a signal in ...
Drummy's user avatar
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spectral density of Modulated ofdm signal

I have formed my OFDM symbol his length is 88 (Nsubcarrier=72,Ncp=16) with Fs=1080000 Hz we call this symbol as Signal_from_baseband I want to modulate the OFDM symbol with Fc carrier=2.1 GHz and plot ...
ahmed bennani's user avatar
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Channel Estimate for OFDM shows distortion for first last order samples

The Channel Gain Estimation was obtained using Least Square method as follows: Hk= mean(Rx_LTS ./ Tx_LTS, 2); k= -26 to 26 Where Rx_LTS is the received long training sequence (52 samples after ...
Walkürie's user avatar
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How to measure the performance of OFDM System using Error Vector Magnitude

I have used BER vs. Tx-Gain in dB curve as one tool to measure my ofdm system's performance. Besides, I would like to measure the performance using the EVM. How I can implement this EVM measurement in ...
Walkürie's user avatar
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Channel Estimation of OFDM using Long training Sequences

Based on IEEE 802.11a Standards, I am using two Training Sequence-Preamble for Synchronization and Channel estimation. I have read in some papers that the channel estimation is performed by taking the ...
Walkürie's user avatar
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OFDM samples after fft show Amplitude Compression

I transmit OFDM signal with bandwidth 20 MHz via ADALM-Pluto SDR device. To study the effect of the wireless channel, I used the same device for transmission and reception. The maximum bandwidth of my ...
Walkürie's user avatar
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How to calculate Coarse & Fine Carrier freqeuncy Offset using Short and Long training Preamble respectively! Equations not understood

I am transmitting an OFDM signal. According to 802.11a Standards, I am using Short and long training Preamble each has length of 160 samples for time and frequency synchronization. According to Essam ...
Walkürie's user avatar
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OFDM Problem with Simulink IFFT

I'm studying OFDM modulation and trying to implement the Tx system on Simulink. I did what is shown in the picture. I was expecting to see subcarriers but I got "nothing". What am I doing ...
Fabio Andrei Cardos's user avatar
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OFDM interpretation data

I'm studying OFDM modulation. I understand that a bit stream comes in and you get the modulated signals (for example QPSK). Let's say we have 4 subcarriers. At the entrance to the P/S I have [1+j,1-1j,...
Fabio Cardos's user avatar
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How to do MIMO precoding for OFDM?

I studied OFDM, MIMO, and MU-MIMO, but I'm not sure how it works when MIMO and OFDM are combined. I can't find good literature that talks about MIMO-OFDM. I want to understand how to use eigenmode ...
Ryo Onishi's user avatar
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Understanding FFT size in OFDM

The number of subcarriers = the size of the FFT? The size may be the same or different depending on the document.
Ryo Onishi's user avatar
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Is OFDM equalization performed every 14 symbols?

The number of symbols and slot in a subframe differs depending on the subcarrier spacing Is equalization processing performed for each slot? Or per subframe?
Ryo Onishi's user avatar
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Can the number of subcarriers/user be greater than 12 in 5G?

In 5G, I think 1 resource block (RB) carrier is 12 subcarriers. So one user uses 12 subcarriers. But in some research, 612 subcarriers are used for channel estimation research. Is it okay to use more ...
Ryo Onishi's user avatar
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How are subcarrier symbols modulated into an analog OFDM signal?

I am currently researching about OFDM models (formulae) that show how the individual data symbols (eg., QAM symbols) are converted to OFDM symbols and how the OFDM symbols are turned into an analog ...
Cornelius's user avatar
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simulation models unique to each researcher? Or use a specific common model?

Are the simulation models used by researchers at each university unique to each university? Or use a specific common model? I started working on OFDM research at university, but I'm at a loss as to ...
Ryo Onishi's user avatar
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1 answer
161 views

5G strandard pilot allocation, channel estimation method

I'm trying to create an OFDM simulation, but I don't know the 5G standard pilot allocation estimation method. Is this simulation good? One transmission unit has $64$ subcarriers and $14$ OFDM symbols. ...
Ryo Onishi's user avatar
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108 views

Need to write a simple code in matlab of training sequence or zadoff Chu sequence for my OFDM signal-synchronization

I have written a complete code, in matlab, for my ofdm signal for the transmitter and receiver. Now I want to transmit my ofdm signal via wireless channel using SDR. Now, I need to combine a simple ...
Walkürie's user avatar
1 vote
1 answer
108 views

Complex samples in OFDM signal, after fft-block at the receiver, have rotating amplitude towards zero even after phase correction

First of all, please consider my lack of experience/background in real time transmission using SDR especially if my explanation was expressed technically well.enter image description here I have ...
Walkürie's user avatar
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OFDM complex symbols have dynamic phase shift after the fft-block & before the BPSK demodulator at the receiver ,

I have transmitted and received an OFDM-signal using the same ADALM-Pluto-SDR's Tx/Rx Antenna. I have used BPSK baseband modulation with symbol freq=312.5 KHz, L (length of ifft)=64, fsampling=fsym*L=...
Walkürie's user avatar
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IQ time domain data to Constellation regeneration for a OFDM 16 QAM signal at different power levels to obtain EVM vs Pout information

16 QAM OFDM signal at output of Power amplifier at fixed frequency and different input power levels are received as a IQ data (time domain) by Spectrum analyzer, I would like to generate 16 QAM ...
kecbackbencher's user avatar
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Analyzing the OFDM out-of-band effect when using different guard interval

I am trying to understand the concept of out-of-band (OOB) which occur with OFDM, I have tried to read about it, but I couldn’t understand how I can illustrate that effect with MATLB. This is the ...
Sajjad's user avatar
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Correct OFDM oversampling method

I need to oversample my OFDM signal, however I have issues understanding which OFDM oversampling method is the recommended one. First method : Before taking the IFFT, the OFDM subcarriers are padded ...
Nicolate's user avatar
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56 views

OFDM design considerations for choosing the number of subarriers $N$

I was trying to think of all possible constraints or factors that needs to be taken into consideration while designing an OFDM-based wireless communication system (For example, LTE, 5G technologies ...
wanderer's user avatar
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OFDM parameters vs channel parameters

I would like to understand the relation between OFDM parameters and channel parameters. I know the following: length of cyclic prefix > delay spread ofdm symbol time > coherence time of the ...
user3005720's user avatar
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3 answers
472 views

OFDM Signal and IQ Paths

I understand that we have analog complex signal after it passes DAC after coming out of IFFT in OFDM Transmitter. After that we do orthogonal upconversion on it and send it. I've question now for OFDM ...
Reddi Suresh's user avatar
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2 answers
112 views

What is use of Quadrature Converter in OFDM?

I'm learning about OFDM Transmitter and see that output of IFFT Block produces complex digital signal and we need DAC to convert it to analog and then use RF Frequency mixing to send it out of ...
Naresh Upadhyay's user avatar
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2 answers
244 views

Relation between sampling time, subcarrier spacing and number of subcarriers

For OFDM, will the following relation always hold: subcarrier_spacing * sampling_time = 1/N N: number of subcarriers which is the size of IFFT/FFT This will imply that sampling frequency is exactly ...
user3005720's user avatar
1 vote
2 answers
117 views

Perfect channel estimation for OFDM (via H=Y/X) in MATLAB

Despite using the same channel for convolution, each time I get a different estimated channel. Could you please tell me what I'm doing wrong? I want to demonstrate that I can estimate the same channel ...
Zeynep's user avatar
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Is it possible to consider circular convolution in case of appending the guard interval as a suffix instead of a prefix

In OFDM system, the cyclic prefix is added into the head of time-domain signal to enable the circular convolution with the channel, and then perform one-tap frequency-domain equalization at the ...
Sajjad's user avatar
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Modeling an OFDM signal and comparing it with QPSK

I am trying to model an OFDM signal based on original QPSK stream and compare their baseband spectrums. I've used this article as a reference for plotting spectrum and this as a MATLAB OFDM reference ...
lazba's user avatar
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How can I generate a OFDM baseband signal with the output of the ifft?

I have some understanding problems with OFDM. I think I have understood most of the theoretical concept. At the moment, I am trying to write some Python code to simulate the transmitter part. This is ...
Not A Hobbit's user avatar
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52 views

OFDM Channel Equalization Issue when Resampling

Noticing a strange problem when I upsample an OFDM symbol to a "transmit" sampling rate, pass it through a channel, and then downsample it back to its baseband sampling rate. After doing ...
dsp_dsp's user avatar
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375 views

Relationships among OFDM Bandwidth, Sample rate and Symbol period

I am studying OFDM and have some questions to ask. Assuming my WiFi network operating on 5GHz with OFDM channel BW of 20MHz and N = 10 subcarriers: Does the RF spectrum start at 5GHz (frequency ...
Leon Chang's user avatar
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OFDM does not work with USRP

I found the ofdm flowchart in the Gnu radio examples.(ofdm_loopback) Scheme: The spectrum and the received data of the received signal: After that, I connect the USRP Sink and the USRP Source. The ...
Ice Cool's user avatar
1 vote
1 answer
395 views

How does DFT-s-OFDM precoding reduces PAPR?

I would like to understand how does DFT-s-OFDM reduces PAPR compared to CP-OFDM. I am not able to locate any mathematical explanation for this. If anybody can provide an explanation it will be great. ...
user3005720's user avatar
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1 answer
216 views

Complete OFDM transmitter chain

I am looking for complete OFDM transmitter chain with all the details i.e. starting from modulation symbols up to up conversion to carrier. What I have found on the web is Modulation Symbols serial ...
user3005720's user avatar
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65 views

How to measure the PAPR of OFDM signal in practical case

The way of investigating the PAPR for OFDM system using MATLAB is known, but what I am looking for is: can we measure the PAPR effect in real systems? For example, assuming we have a transmitter and a ...
Fatima_Ali's user avatar
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3 answers
396 views

Why do I get the same PAPR effect with all modulation orders in MATLAB

I am using the basic way to calculate the PAPR of OFDM system using MATLAB, the strange thing I noticed that I get almost the same PAPR effect even when increasing the modulation order from 4 to 64. I ...
Fatima_Ali's user avatar
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1 answer
116 views

Are the OFDM DC components subcarriers mandatory even when using real transforms?

In optical OFDM systems, called DCO-OFDM, we usually use the data with its flipped complex conjugate to produce real time-domain signal while the first and $N/2 +1$ subcarriers are kept null, $N$ is ...
Sajjad's user avatar
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How to model Additional EVM (TxEVM) with LTE waveform?

I would like mention my understanding in the following, In an LTE OFDM signal assume, Nfft=8; scs=15 kHz; BW=5MHz; Sampling Rate N=7.68 MHz; We are taking 1msec of sample; Therefore total sample =...
Md. Hasan Rahman's user avatar
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795 views

Constellation Mapping In OFDM

If i am not mistaken, the two following hold : a. In OFDM Conceptualization, the constellation mapping at Tx (or de-mapping at Rx) is done in Frequency domain b. However the basic theory (Including ...
Vinayak Anant Karandikar's user avatar

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