# Questions tagged [ofdm]

OFDM stands for Orthogonal, Frequency-Division Multiplexing.

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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
26 views

### 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 ...
1 vote
32 views

### 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 ...
1 vote
32 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 ...
17 views

### 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 ...
107 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 ...
61 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 ...
43 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 ...
1 vote
76 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 ...
1 vote
61 views

### 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 ...
41 views

### 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 ...
168 views

### 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 ...
41 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 ...
94 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 ...
37 views

### 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
125 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. ...
91 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 ...
46 views

### Why is the gnu radio FFT block in dvbt_rx_8k.grc but not in debt_tx_8k.grc? I don't understand

I am a beginner who is learning about DVB-T. I noticed a difference in the examples provided by the official source and I am confused about it. This is dvbt_tx_8k This is dvbt_rx_8k What is the ...
10 views

### How is received power distributed in partially used channel?

I want to learn how the RSSI is distributed in received signal in an OFDM block. When a UE transmits a signal, assume it allocates certain number of resource blocks (RBs), for instance 10 RBs in 20 ...
45 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 ...
25 views

### How to get prior channel knowledge for estimation the channel using MMSE?

I have implemented an OFDM communication system in Matlab. I use the 802.11ac preamble for estimating the channel using the least square estimator. However I would like to implement the MMSE too. I ...
160 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 ...
73 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 ...
1 vote
20 views

### 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 =...
315 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 ...
55 views

### How does carrier size / bandwidth effect propagation

I'm working with software-defined coded orthogonal frequency division multiplexing radios. They have a choice of bandwidth, 1,2,3-20MHz. Of course, as you increase your bandwidth (carrier size), you ...
46 views

### 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 ...
31 views

### Noise Applied to OFDM Subcarriers

Assume we have an OFDM signal received with AWGN + phase noise. Then, we extracted some subcarriers after the demodulation. Now each subcarrier $Y_l[k]$ includes a noise component $Z_l[k]$ according ...
37 views

### Oversampling of OFDM post-IFFT frame

I would like to build IQ radio waveform - first part - synchronisation sequence (ZC) and second part, OFDM frame with Cyclic Prefix(after IFFT). I want to to oversample ZC sequence at transmitter, and ...
1 vote
252 views

### Sampling Time Offset estimation for OFDM signal

I have a signal constituted by known OFDM symbols, and my goal is precisely estimate the Sampling Time Offset (STO). However, while the STO in the context of a single-carrier modulation is pretty ...
66 views

### Cross correlation of OFDM short preamble produces two peaks

I am trying to cross correlate the short preamble of an OFDM transmission. This is the preamble I am using: ...
89 views

### Phase Measurements of OFDM Signal with USRP

I am doing some analysis on a received OFDM signal using USRP N210 with GNURadio. Figure OFDM RX shows the OFDM receiver (please refer to GNURdaio workshop slides) . The transmitted OFDM signal is ...
1 vote
144 views

### Why does OFDM need cyclic prefix?

As I understand, by using multiple carriers, OFDM can mitigate the effects of multi-path delay as the symbol duration is larger than the delay. In this case, why do we still need to add cyclic prefix ...
30 views

### Is there any phase or frequency impairements caused by different sampling frequency at transmitter and receiver?

I have an OFDM Tx Rx chain with different sampling rates at the Transmitter and Receiver with the same center frequency used for transmission and reception. I understand that different center ...
48 views

### Diversity gain in MIMO-OFDM system

What is the diversity gain in $4\times2$ vs $2 \times 2$ MIMO system. Is it $10 \log \left( N_{t} - N_{r} \right)$?
42 views

95 views

### What is the reason of the getting a clipped signal at the receiving end when using experimental tests

I am using a sine wave signal (for test) with the following scenario: Computer #1 --> AWG --> DC bias (2.2 Voltage) --> light source --> lens *** wireless channel 2 meters *** --> lens -...
44 views

### What is the meaning of the small power of the signal at the receiving end

I experimentally transmit an OFDM signal through 2 meters channel. When I estimate the channel at the receiving end, I find the channel coefficients very small. An example of the channel I find is: <...
79 views

### 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 ...
30 views

### Can I use FIR interpolator while modeling a DAC (Digital-to-Analogue converter) in 5G NR transmitter?

Problem statement: I am explaining my concept on The DAC implementation in 5G NR using an example. For a CBW=20 MHz, SCS=15 KHz, the sampling frequency= 30.72 MHz. After the time domain signal ...
170 views

### Pulse shaping filter (e.g. RRC) implementation in OFDM transmission?

I am a bit confused regarding the implementation of Pulse shaping filter in OFDM (Both CP-OFDM & SC-FDMA) system. I am explaining my concept in the following, The difference between CP-OFDM and ...
35 views

### slot size intuition question in 5G NR

from the 5G NR manual shown bellow. there is a diagram i have attache. is there some intuitive explanation regarding why as the carrier spacing goes high then the slot time goes low. how are these two ...
41 views

### Concept clarification on baseband system model of LO leakage impairments in 5G NR?

I am trying to generate a baseband (BB) system model with LO leakage impairments and correction. The channel bandwidth $BW = 20$ MHz, Subcarrier Spacing $= 15$ kHz, oversampling rate = $4$ (just ...
152 views

### What type of LO lekage Correction algorithm is used in 5GNR?

I have done a base-band modeling of a 5G NR OFDM (CP-OFDM/ DFT-s-OFDM) transmission system. And I have added a DC leakage as an RF impairment and transmitted the signal through a PA (Power Amplifier). ...
88 views

### OFDM system capacity if we double the subcarriers

Suppose we have two OFDM based systems A & B. System A has $N$ subcarriers and bandwidth $W$, and the number of samples in the CP is 10% of $N$. System B has $2N$ subcarriers, $2W$ bandwidth and ...
189 views

### How to estimate the average distance between peaks (maxima) of the magnitude of an OFDM signal?

Given an arbitrary configuration of carriers having bandwidths that belong to the 3GPP standard (5, 10, 15, 20, 25, 30, 35, 40, 50, ..., 100 MHz), is there a method/rule-of-thumb to estimate the ...
1 vote
331 views

### Does the data rate of ofdm depends on number of subcarriers

I am trying to investigate the performance of OFDM system practically, I am using sampling rate $1 GSps$ giving bandwidth $B = 0.5 GHz$. What I find is when setting the number of subcarriers $N = 64$ ...