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The necessity of null subcarrier in OFDM?

In looking to LTE specifications, with the subcarrier spacing $\Delta f = 15 \textrm{kHz}$, for bandwidth $10 \textrm{MHz}$, fft size $N_{fft} = 1024$ that needs a sampling rate $F_s \geq 1024 \times ...
AlexTP's user avatar
  • 6,595
3 votes
2 answers
293 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). ...
Md. Hasan Rahman's user avatar
3 votes
2 answers
8k views

System Frame Number in LTE Specifications

What exactly is System Frame Number in LTE specifications? What is the use of it? I have read that it is a 10 bit number and used for synchronization purposes. But it's not clear how it helps for ...
spectre's user avatar
  • 575
3 votes
3 answers
2k views

Why is LTE either FDD or TDD?

In LTE systems, up- and downlink are duplexed either using FDD or TDD. Why has this not been designed to utilize the same multiplexing technique as used for the downlink (OFDMA)? Resource blocks could ...
The Bernard's user avatar
2 votes
1 answer
503 views

SC-FDMA in LTE system

I am trying to understand how SC-FDMA is used in LTE system. Every description I found so far refers to DFT and IDFT. However, when I checked 3GPP TS 36.211 chapter 5.4 (SC-FDMA baseband signal ...
faust1002's user avatar
2 votes
0 answers
144 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 ...
Md. Hasan Rahman's user avatar
1 vote
1 answer
8k views

What is the difference between Antenna port and Physical Antenna in LTE?

I have just started working on the 5G NR physical layer and I have difficulty understanding the concept of Antenna Port at the downlink. In release 10 there supposedly 15-22 antenna ports for CSIRS (...
Mayank's user avatar
  • 23
1 vote
1 answer
640 views

am I recording LTE uplink signals?

I have this app in my phone which tells me the LTE UL frequency and power: so I went with my SDR and measured the received signal at that frequency: Now, how can I be sure this is the transmitted ...
Natalia Molinero Mingorance's user avatar
1 vote
1 answer
2k views

SC-FDMA disadvantages

I understand the advantages of SC-FDMA over OFDM and I also understand the disadvantage of additional complexity (FFT block), are there another disadvantages? Also, if $N$ has to be bigger than $M$ ($...
Gabizon's user avatar
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1 vote
1 answer
66 views

LTE PSS Channel Estimation for coarse SSS Equalization

In LTE the Primary Synchronisation Signal (PSS) can be detected by taking a correlation with the known 3 zadoff chu sequences (roots: 25,29,34). Once the peak has been detected the receiver knows ...
Sonny Wandel's user avatar
1 vote
1 answer
750 views

IFFT and DAC relationship in OFDM Transmitter

Say, for LTE BW 20 MHz, I have total 2048 SubCarrier at IFFT Input leading to 2048 Output (Complex) at IFFT Output, and in 1 OFDM Symbol (useful symbol length) of time 66.67 usec, the sampling rate ...
Reddi Suresh's user avatar
1 vote
1 answer
246 views

LTE Channel Estimation

I am trying understand LTE channel estimation. I have multiple questions: How much phase shift does a typical LTE channel have? Can all that be corrected using pilots? Where do we typically implement ...
Sampath's user avatar
  • 15
1 vote
1 answer
251 views

For a 20 MHz channel, with 1200 usable subcarriers(18 MHz occupied), what should be the size of the FFT on the transmitter before IFFT is applied?

I am trying to simulate the SC-FDMA transmission and I read H Myung's paper and research on the topic but I am not sure exactly on what should be the size of FFT at the transmitter. For a 20 MHz ...
samz12's user avatar
  • 37
1 vote
1 answer
125 views

Doesn't use of Duplexer in FDD system limits it's capability?

I read FDD has separate Rx and TX frequency to operate on, so it can work simultaneously and do Receive and Transmission. When I use Duplexer ( I read Duplexer needed if we want a single antenna to do ...
Reddi Suresh's user avatar
1 vote
1 answer
364 views

What is role of BW and frequency in internet speeds?

First the bandwidth (BW): It is the amount of data that can be transferred simultaneously.just like more no. of highway lanes so that many cars can travel side by side simultaneously. Frequency It ...
Shashank 's user avatar
1 vote
1 answer
137 views

Demodulation of OFDM symbol in LTE for multi-user case

I was trying to understand what exactly happens when you try to modulate an ofdm symbol in the downlink in LTE for multi-user case. When we modulate, usually we allocate different sets of RBs for ...
wanderer's user avatar
  • 151
1 vote
0 answers
51 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
  • 151
1 vote
0 answers
26 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 =...
Md. Hasan Rahman's user avatar
1 vote
0 answers
177 views

Mapping from Antenna ports to Antenna Elements 5G NR

I have a question related to CSI-RS channel estimation. Let us assume that the base station has 64 antennas and we decide to use 32 antenna ports for CSI-RS transmission. Also, UE has 4 antennas. My ...
gkami's user avatar
  • 11
1 vote
0 answers
121 views

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 ...
joemelsha's user avatar
1 vote
0 answers
32 views

Why do adjacent cells use different channels?

In chapter 15 of the book Wireless Communications by Andrea Goldsmith, Goldsmith gives a formula for an estimate of the signal-to-interference-ratio for the node on the edge of a cell in a cellular ...
awelkie's user avatar
  • 153
1 vote
0 answers
41 views

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 (...
Aragorn's user avatar
  • 135
1 vote
0 answers
43 views

Preamble generation of narrowband signals

I have to generate a complex sine wave with a sampling frequency of 1.92MHz and subcarrier spacing of 3.75kHz. The number of FFT points is 512. The narrowband frequency is 180kHz. I also have to ...
StarStrider's user avatar
1 vote
1 answer
114 views

Quantized error in scatter plots for a hamming windowed LTE signal

I have a time domain signal based on LTE standards. Carrier spacing = 15KHz, Symbols per slot = 6, extended Cyclic Prefix = 512 samples FFT size = 2048, No. of sub carriers = 1200, channel BW = 20MHz, ...
samz12's user avatar
  • 37
1 vote
0 answers
205 views

How often do a LTE eNodeB scheduler schedule?

Scheduler schedules the resource for each UE. How often do a LTE eNodeB scheduler schedule? Is the time between each scheduling fixed? any idea/reference will be great help on this regard. Thanks.
pikapika00's user avatar
0 votes
2 answers
106 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
0 votes
3 answers
1k views

OFDM SubCarrier and its relationship with IFFT in context of Real and Complex

In the process of OFDM Signal generation. We take symbols (constellation symbols) and map it to a sub-carrier (real analog time domain) harmonics of 15khz, add different sub-carriers separated by ...
Reddi Suresh's user avatar
0 votes
1 answer
63 views

A question on communication system without modulation

I know that these sort of platforms are strict and you need to have an idea of what you are doing before asking a question. I am not really that knowledgeable about signal processing though I have an ...
Tshepang's user avatar
0 votes
1 answer
1k views

What's practical interpretation of showing DC Offset in frequency domain?

In homodyne reciever, we read about LO Leakage causing DC Offset. Say my output at downconversion is in analog voltage range +5 and -2, and there is a DC offset of 1 unit So, it can be added right? To ...
Reddi Suresh's user avatar
0 votes
2 answers
251 views

OFDM Query : Why In Phase and Quadrature Phase RF Conversion is needed? [duplicate]

OFDM Basic Query- x[n] produced at output of IFFT is in discrete time, so we can use DAC and then RF Upconversion (multiply it with LO Frequency say f) and send it, why are we doing RF up conversion ...
Reddi Suresh's user avatar
0 votes
1 answer
279 views

4G LTE Sampling Frequency Offset

Could someone please explain how the 4G LTE OFDM measures and corrects the sampling frequency offset? I can see a number of algorithms proposed in the literature, but I am trying narrow it down to the ...
Sampath's user avatar
  • 15
0 votes
1 answer
105 views

Why OFDM is more appropriate with MIMO than other multiple access method?

As read from MIMO-OFDM wikipidia page says Research conducted during the mid-1990s showed that while MIMO can be used with other popular air interfaces such as time-division multiple access (TDMA) ...
Charles Hou's user avatar
0 votes
1 answer
149 views

CFO limit for correct LTE Zadoff-Chu Synchronization

I am working with Zadoff-Chu sequences in a Python simulation of an LTE-like communication system and need to understand the effects of carrier frequency offset (CFO) on these sequences. Specifically, ...
Sonny Wandel's user avatar
0 votes
1 answer
81 views

Raw BER or Uncoded BER in LTE/5G

Could you please tell me what would be the benefit of using Raw BER (or uncoded BER) in comparison to BER? Thanks
Aragorn's user avatar
  • 135
0 votes
3 answers
378 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
0 votes
1 answer
136 views

Why don't we have LTE EARFCN for frequency in decimal to second place?

EARFCN 3302 means 2675.20 MHz EARFCN 3303 means 2675.30 MHz What about 2675.25 MHz? Why don't we have values defined for decimals with two places.
Reddi Suresh's user avatar
0 votes
1 answer
192 views

How to measure NB-IoT signal quality with GNU Radio?

I need to measure the quality of an NB-IoT signal. Is it possible to obtain RSRP, RSSI RSRQ or SINR using GNU Radio?
Nicolas's user avatar
  • 101
0 votes
1 answer
372 views

How is SNR Calculated in OFDM Reciever? [closed]

Can you please guide me on the information to calculate SNR for OFDM Reciever? Is OFDM Pilots used for it? And do we need to follow channel estimation like steps of interpolation to determine it? I'm ...
Reddi Suresh's user avatar
0 votes
1 answer
609 views

NR PUSCH non-codebook based precoding

While reading 3gpp 38.211, Chapter 6.3.1.5 I noticed For non-codebook-based transmission, the precoding matrix equals the identity matrix. So, I guess, non-codebook-based precoding shall be ...
Dmitriy's user avatar
0 votes
1 answer
32 views

How to determine Carrier Aggregation Class

We see classes defined for Carrier Aggregation. The number of continuous carrier determines which class of CA it is. what are the criteria to decide contiguous carriers? Do the carriers need to stick ...
Reddi Suresh's user avatar
0 votes
1 answer
60 views

How does higher received signal power enable higher data rates?

On page 30, of the book Fundamentals of LTE by Arunabha Ghosh et al. it is written: This allows broadcast signals from different cells to combine over the air to significantly enhance the received ...
Shashank V M's user avatar
0 votes
1 answer
155 views

Why is beamforming needed in 5G?

With the advent of 5G Era, base station density increases, the cell radius decreases, and LOS propagation gets more dominant. So, why do we need for beamforming in 5G NR, although we have smaller ...
ozi2020's user avatar
0 votes
3 answers
489 views

Frequency Domain Correction of Frequency Offset or Doppler Frequency in LTE

We are working on LTE Uplink CFO Correction for 3 MHz band. The time domain CFO correction is easy, which depends on the processing of 3840 samples step by step multiply by $\exp(-j 2\pi f_\text{...
Sagar Salwe's user avatar
0 votes
2 answers
206 views

How multi layer map to different beams in LTE Beamforming

I understand for SU-MIMO Beamforming single layer maps to all antennas with phase shift applied to create beam. Also I understand in this case all beams will be carrying same signal (say s1). But in ...
Albert's user avatar
  • 1
0 votes
0 answers
19 views

Computing Channel Power from file containing RMS measurements from tri-axial spectrum analyzer

I have some files from a spectrum analyzer in RMS mode equipped with a tri-axial antenna. I am supposed to compute the channel power evolution for two distinct LTE channels. I have files containing ...
marco890's user avatar
0 votes
1 answer
47 views

Multipath Propagation Correction for LTE signals

How can I correct multipath propagation for LTE signals generated from different eNodeBs? My end goal is to implement localization of my USRP using LTE or FM signals. Currently I am carrying out a few ...
Ahsan Yousaf's user avatar
  • 1,533
0 votes
0 answers
29 views

How to accomodate feedback bits from Base Station to devices in LTE or 5g?

I am trying to think of a way in which the base station (BS) can send say 100 bits of feedback to devices in my cell. My confusion is what is a good way to send this feedback bits. This is during the ...
wanderer's user avatar
  • 151
0 votes
0 answers
51 views

LTE Standard. Where to begin?

I've started working as a wireless engineer fresh from college. I wanted to learn LTE standard and I don't know where to begin. I was wondering if you could guide me through this process. I found some ...
Jacob's user avatar
  • 121
0 votes
1 answer
159 views

Which are the realictic enviroment will be suitable for TDLC300 channel model?

TR 38.901 Section 7.7.2 mentioned that the TDL-A, TDL-B, and TDL-C channel models are constructed for NLOS scenarios. In TS 38.101-4 Annex B.2.1, in Table B.2.1.1-1 (picture is attached), delay ...
Aragorn's user avatar
  • 135
0 votes
0 answers
37 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 ...
Md. Hasan Rahman's user avatar