Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [ofdm]

OFDM stands for Orthogonal, Frequency-Division Multiplexing.

0
votes
0answers
31 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 ...
0
votes
0answers
50 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 ...
0
votes
1answer
38 views

How to filter an OFDM signal? [on hold]

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 ...
0
votes
2answers
38 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 ...
0
votes
0answers
19 views

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 ...
1
vote
0answers
57 views

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., ...
-1
votes
0answers
16 views

How to filter an OFDM signal for reducing Out of Band emissions and how to decide the filter length?

I have an OFDM time domain signal (Based on LTE stds) with cyclic prefix of length 512 samples. Each FFT/IFFT bin is 2048. I need to apply different filters (window based, equiripple etc) to it to ...
0
votes
1answer
21 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 ...
-1
votes
0answers
19 views

For an extended cyclic prefixed symbol what should be the FFT size?

I'm running an OFDM simulation based on LTE stds. Im simulating for 6 symbols in 1 slot of a subframe. I have appended an extended cyclic prefix (512 samples) to each symbol thus making each symbol ...
-1
votes
1answer
18 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 ...
0
votes
1answer
38 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 ...
1
vote
1answer
28 views

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 ...
0
votes
1answer
36 views

Is CMA equalization applicable for OFDM

I have a question regarding the constant modulus algorithm (CMA), as you know it's one of the known algorithms used for blind equalization. The cost function of the CMA is build blindly, it means ...
-1
votes
0answers
28 views

How symbol synchronization is achieved in 802.11n standard

According to the 802.11n standard, packet detection and synchronization is done with the preamble part of the frame. A packet is detected with the correlation method, that is comparing the short ...
0
votes
1answer
54 views

What is the index modulation in OFDM and Subcarrier Index modulation?

I'm new here, I'd like to ask about the OFDM-IM (OFDM - Index modulation), what is it and how it works? Is it the same as SIM-OFDM? I checked white papers, I see it's using the index of sub-...
0
votes
1answer
62 views

Ambiguity in the IFFT process in OFDM

I am still trying to iron out some ambiguities in my understanding of the IFFT component of OFDM modulation schemes. So here we have a QAM symbol $s_0$ being multiplied with the subcarrier for that ...
1
vote
1answer
45 views

Visualising OFDM subcarriers in the frequency domain

Im struggling to understand why in some images the frequency domain shows clear bars with amplitude and phase and with 0 frequency variation (it is clear that the frequency of the waves does not ...
1
vote
1answer
62 views

OFDM Simulation process

I'm trying to understand OFDM by making a simulation. Are these steps correct? generate M random complex QAM symbols. example: (1+j,1-j,-1-j,1-j....) Split my M samples into a N 2048 sized arrays ...
0
votes
1answer
76 views

What is the mixed numerology in OFDM

In order to meet the user requirements in the next generation radio access technology, the ongoing standardization within 3rd Generation Partnership Project (3GPP) offers flexibility in terms of ...
-1
votes
1answer
43 views

OFDM in Time domain

This tutorial shows the idea of analog time domain OFDM. My question is if we can sample the analog signal and use time-domain OFDM in a similar fashion. Why do we need to apply IFFT/FFT to the signal ...
0
votes
1answer
79 views

OFDM RF signal waveform

From the Wikipedia article: "An inverse FFT is computed on each set of symbols, giving a set of complex time-domain samples. These samples are then quadrature-mixed to passband in the standard way. ...
0
votes
0answers
20 views

Common Cyclic prefix for a set of cascaded OFDM symbols

I've seen research papers / baseband systems that deal with synchronization using a common CP(Cyclic Prefix). The transmission structure comprises , a family of complex orthogonal sequences, with ...
0
votes
1answer
74 views

Why Convolution between signal and channel is not done directly in SIMO channel

In OFDM system, I need to transmit a signal $x$ in SIMO channel $H$ with one $Tx$ antenna and 4 $Rx$ receiver's antennas. The initial equation for that convolution is $r=Hx+n$ where $n$ is the noise. $...
0
votes
1answer
61 views

Use of Long Training Field (LTF) of 802.11 standard

In 802.11a/n the preamble part has L-LTF(Legacy-Long Training Field) and HT-LTF(High Throughput-Long Training Field). I want to clarify my understanding of these two fields: Are the only difference ...
0
votes
1answer
62 views

What's the difference between SISO and SIMO in using matched Filters

Suppose we are transmitting a signal $x$ in $OFDM$ with $N$ subcarriers, After performing Parallel/Serial conversion and then N-points FFT, we suppose to have signal $s = IFFT^Hx$, Then adding the ...
0
votes
1answer
64 views

OFDM Short Training Field clarification

I want to clarify my understanding of OFDM training fields. Please correct me if I am wrong as I am getting 2 different information from online resources. For 802.11a standard the preamble contains ...
0
votes
2answers
71 views

How to determine the original size of the FFT used in unknown OFDM symbol

Given an unknown OFDM symbol consisting of 9144 samples, interested to know the size of the FFT used in the TX/Number of bins. Down-sampling to 512,256,128,64,32 yields the following. Do not see how ...
1
vote
1answer
59 views

Is sparse signal in time domain is sparse in Frequency domain

In OFDM system, if we have a multi-path environment, we supposed to have a sparse received signal in time domain, then $FFT$ is performed to convert it into frequency domain. My question, does the ...
0
votes
1answer
36 views

Is the Channel shortening similar to Time domain Equalizer (TEQ)

I used to read about Time domain equalizer (TEQ) in many lectures, i.e here , But in many other papers, that's called Channel shortening i.e here . However, in the a two above links, the cost ...
2
votes
1answer
106 views

What is about the circular convolution in OFDM

In an OFDM system, serial-to-parallel conversion for data is done, then the DFT is performed and then adding the cyclic prefix (CP). My question is related to that step of adding a CP. As I know, ...
0
votes
1answer
42 views

how to set Equalizer's coefficient using generalized eigenvector.

In that paper https://jwcn-eurasipjournals.springeropen.com/articles/10.1186/1687-1499-2012-72 .. Equation 3, $J(w) = w^HBw/w^HCw$ .. $B$ and $C$ are matrices, $w$ the filter coefficients vector ...
0
votes
1answer
110 views

How I can perform SIMO channel convolution in MATLAB

In OFDM system, I need to transmit a signal $x$ in SIMO channel $H$ of single Tx antenna and $4$ Rx antennas. The initial equation for that convolution is $r = Hx + n$ where $n$ is the noise. As ...
1
vote
0answers
45 views

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
1answer
85 views

OFDM: How to do the carrier recovery of the quadrature(I/Q) demodulation

For an OFDM system, after the OFDM modulation, the quadrature modulation is used to move the signal from the baseband to the pass-band. But when it comes to the receivers, I can't find any way to make ...
0
votes
1answer
46 views

In OFDM, does $N N^H$ equal $I$?

I'm still new in OFDM and reading about it, but I have a question. In OFDM system, when having $N$ data symbol assigned to sub-carriers, $N$ should be orthogonal with each others, which means $NN=0$....
1
vote
1answer
32 views

Sharp sample transition in OFDM signal

I am implementing OFDM PHY for Visible Light Communication in FPGA. (I am quite new to communication system and signal processing, so please understand my lack of background knowledge.) The FFT size ...
2
votes
4answers
48 views

Bandlimiting and OFDM spectrum - what is considered “bandlimited”?

I have been reading about OFDM modulation, it's not clear to me how you can have band-limited OFDM but given its prevalence in wireless communication there must be some designation of approximately ...
0
votes
0answers
59 views

What is the relationship between FFT size and demodulation in OFDM

As I mentioned in the title of the question, how can we demodulate the data in order to get the same number of subcarriers with different FFT size. For example, 10 MHz LTE can be sampled with 15.36 ...
1
vote
0answers
56 views

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 ...
0
votes
1answer
61 views

OFDM. Cyclic Prefix and ISI

Sorry that I created a new question about OFDM, but I donät have enough reputation to comment on other questions. I have read all the topics here and I have some doubts. 1) I found in the book that ...
2
votes
1answer
39 views

issue in DFT of OFDM by blocks and N-by-N

I'm trying to study and understand the OFDM, and during coding the OFDM in MATLAB, I faced this issue: suppose we have the Numsymbol = 256, and dataqpsk our used data, The issue which I face that ...
1
vote
1answer
55 views

What is the impulse response of SIMO channel and its equivalent in oversampling?

1- According to the below paragraph : Could someone explain, What mean M here? I mean when saying with Order M ? 2- On the other hand, When performing Fractional sampling, for example sampling ...
0
votes
1answer
78 views

What's the relation between the sampling rate and FFT size in OFDM

In OFDM system, Is there relationship between Sampling rate and FFT size? For example, if we downsample or oversample the received signal, Should we decrease or increase the FFT size accordingly? ...
1
vote
1answer
39 views

Is it possible to recover QAM constellation of an undersampled OFDM signal?

The OFDM signal I'm interested in is rated for a 204.8MHz sampling rate! I'm limited to sampling at 20MHz to give me just enough resolution into the range of subcarriers I'm interested in, but I just ...
0
votes
0answers
46 views

bits to an OFDM symbol

I have been trying to get a hang of OFDM but it's in vain. This is my understanding so far. Let's say I have a stream of bits 010101010.... and so forth. We then group the bits depending on the ...
0
votes
0answers
25 views

find power of recieved signal of usrp b200 in gnu radio companion

how to find power of recieved signal of usrp b200 in gnu radio companion from frequency sink block (the frequency plot) or any other block available in gnu radio. I am transmitting and receiving ofdm ...
0
votes
0answers
231 views

Why does my OFDM demod in GNU Radio not return anything?

This is the flowgraph I used: Output after mod: Output after demod: I've read that it might be a synchronization problem but since I'm not actually transmitting anything over a medium, that shouldn'...
0
votes
1answer
239 views

Cyclic prefix length in baseband OFDM with ZF equalizer

My question is about baseband OFDM. I try to plot the BER according to the SNR. I noticed that changing cyclic prefix length does not affect the performances. I.e., following the code below, ...
0
votes
1answer
97 views

Rake Receiver vs OFDM and multi-path channel

My Question is, Can we use the Rake Receiver with OFDM modulation? As you know, Rake receiver is usually used with DSSS modulation, so can we use it with OFDM? in other words, Does the Rake Receiver ...
0
votes
0answers
141 views

Phase Noise in OFDM simulation

I am trying to simulate phase noise in OFDM and in search of a mathematically tractable model. So far, I have managed to get phase noise by multiplicating $e^{j\phi(n)}$ in frequency domain where $\...