# Questions tagged [ofdm]

OFDM stands for Orthogonal, Frequency-Division Multiplexing.

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### Spectral efficiency of OFDM

For OFDM we know that: $R_b^{OFDM} = N \cdot R_s \cdot \log_2(M)$ Where N is the number of subcarriers, $R_s = 1/T_s$ is the subcarrier bit rate and $\log_2(M) = \ell$ is the number of bits per ...
1 vote
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### What is the Wrap-Around Phenomenon in FFT?

If I take FFT of a finite sequence and take longer length of IFFT of the frequency domain data by padding zeros with it, how will the wrap around of DFT effect the procedure? It would be great if ...
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### How to insert the pilot data in CDMA system with time varied channel

Generally, when using the OFDM system with time-varied channel, the pilot data is placed in such subcarriers of every symbol before informing the IFFT process. Then after the FFT process at the ...
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### What are the differences between linear convolution and circular convolution?

While studying OFDM, I saw that the convolution between transmitted symbols and channel tap coefficients are converted into circular convolution by using cyclic prefix. But why circular convolution is ...
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### How circular convolution achieves the single-tap equalization in OFDM?

I was wondering how circular convolution achieved using cyclic prefix in OFDM helps to achieve single-tap equalization on frequency domain in the receiver, but without cyclic prefix why this property ...
32 views

### 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 ...
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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 ...
35 views

### 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 ...
1 vote
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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 ...
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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?
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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 ...
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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 ...
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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 ...
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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 ...
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1 vote
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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 ...
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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 ...
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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 ...
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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 ...
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1 vote
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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 ...
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1 vote
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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 ...
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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 ...
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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,...
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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 ...
119 views

### 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.
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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?
1 vote
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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 ...
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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 ...
1 vote
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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 ...
1 vote
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### 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. ...
114 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 ...
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1 vote
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### 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 ...
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1 vote
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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=...
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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 ...
1 vote
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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 ...
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1 vote
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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 ...
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1 vote
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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1 vote
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### 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 ...
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1 vote
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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 ...
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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 ...
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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 ...
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### 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 ...
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### 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 ...
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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 ...
1 vote
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### 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. ...
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### 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 ...
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