# Questions tagged [ofdm]

OFDM stands for Orthogonal, Frequency-Division Multiplexing.

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### OFDM channel estimation using the transmitted signal multiplied with a matrix

I have OFDM system, where the modulated signal $x$ with length $N$, and $N$ is the number of subcarriers in OFDM symbol. $x$ is multiplied with a well-known unitary matrix $G \in N \times N$ before ...
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### Problem using MMSE estimation of channel frequency response

I need to model the minimum mean square error (MMSE) performance in estimating channel frequency response. I have channel's power delay profile (PDP) as a table with tap delays and powers. The ...
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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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### Understanding the In-band Emission limit in TS 38101-1 Table 6.4.2.3-1?

I am sharing the IBE table 6.4.2.3-1 on TS 38101-1 For General emission requirement, there are three parts.The third part is (-57 dBm+10*log10(scs/15kHz))-P_RB. Where, P_RB is the average transmitted ...
441 views

### 802.11a OFDM Long Preamble Cyclic Prefix

im currently looking at an implementation of the preamble for OFDM in the 802.11a standard, as shown in the pic below What I dont understand is the cyclic prefix (labelled GI2). Based on this picture ...
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### 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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### Blind coarse OFDM frequency estimation

Is it possible to blindly estimate a coarse carrier frequency offset of an OFDM signal where $\lvert f_{\rm off}\rvert > \frac{\Delta f}2$, where $\Delta f$ = subcarrier spacing? Blind is defined ...
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### Ricean Multipath channel model implementation

I'm trying to implement a multipath ricean channel model. I had found several resources but I'm kind of lost with too much information. What I have from now is the following step: ...
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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 ...
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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### 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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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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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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### 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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### 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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### 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 =...
1 vote
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### How can I perform semi-blind non-orthogonal successive interference cancellation (SIC) / source-separation with SISO in 4G/5G Downlink?

Semi-blind non-orthogonal successive interference cancellation in the single antenna case with 4G/5G signals (applies generally though). This is very similar to NOMA in 5G, except that I have no ...
1 vote
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### How to calculate received signal power for a Multi-User MIMO OFDM system?

I have a Multi-User MIMO system where there are 2 users served by a base station. The base station consists of 64 transmit elements and the users are equipped with linear antenna array consisting of 3 ...
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### In OFDM, does the parameter time offset is important if there is only one mobile in the cell?

I am learning about OFDM, and in my reading, I have noticed that (mentioned everywhere) synchronization is a very critical aspect of OFDM. Here, I am writing in the context of time synchronization (...
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### Why does carrier frequency offset (CFO) cause carrier phase error (CPE)?

I've already asked 2 questions on this but there is one discrepancy I cannot reconcile and is the crux of the problem: \begin{align} \newcommand{\prefix}{\frac1N\sum\limits_{n=0}^{N-1}} R_l &= \...
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### On the performance of DCT-based OFDM

I am trying to understand the OFDM based on DCT instead of DFT in order to compare between their performance. In case of AWGN, the performance is logic, but when I perform channel equalization in DCT-...
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### 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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### 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. ...
1 vote
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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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### 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
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### 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 ...
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### Beamforming with NDP frames

During beamforming, the Tx first sends NDP Announcement (which is a broadcast frame) thereby reaching all Rx in its area. And then it follows by sending NDP. Is the 2nd frame (NDP) is also a ...
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### How to model fading channels in MATLAB?

I am asked to write a MATLAB program for the simulation of the end-to-end transmission of a JPG file through a fading channel by using OFDM technique for one of my courses' term project. I wrote my ...
1 vote
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### Ideal channel in OFDM simulation

I am trying to simulate an OFDM based system in MATLAB where the estimated channel in the reciever is fed back to transmitter. As a proof of concept I wanted to return the ideal channel. I used the ...
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### Correct scaling for AWGN noise in OFDM system after adding Preambles

I have a two-part question: Question 1 I wonder if anyone can explain about the scaling factor that is used for AWGN noise in OFDM system. For example I know about the scaling factor for normal OFDM ...
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### OFDM in multipath channel simulation in it++

I am trying to simulate OFDM for an multi-path channel. I am using it++ for simulation. ...
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Why do we need 2N-FFT at the receiver when we want to demodulate ZP-OFDM signal ?
1 vote
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### Spectrum of OFDM with raised cosine window(overlap and add)

I'm having trouble observing OFDM with a raised cosine (RC) window in Matlab. I know how to generate an OFDM signal with a raised cosine (RC) window, I just don't understand when the last W samples ...
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### How to calculate energy of an OFDM signal?

What is the difference between power and energy of OFDM signal. How to calculate energy of an OFDM signal, if we consider OFDM symbol size is 64, and QPSK is used as modulation scheme?
1 vote
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### how to determine a length of a channel? ( given path, delay)

Given a channel matrices for each subcarrier of a frequency selective channel (OFDM): i.i.d.. channel =(randn(ntx,nrx, N)+1i*randn(ntx,nrx, N))/sqrt(2); simulated ...
1 vote
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### 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 ...
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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 ...
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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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### 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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### 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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### 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,...