8
votes
Accepted
SC-FDMA in LTE system
First of all, in refering to standard specification, please mention the version because the numeration between versions can be different.
My answer should be only a comment but I think with images it ...
- 6,725
8
votes
Accepted
System Frame Number in LTE Specifications
System Frame Number (SFN) is essentially a counter. As its name suggests, it indicates the index of a system frame modulo 1024, with the index ranging from 0 to 1023 (10 bits).
SFN does not aid in ...
- 6,725
7
votes
Why is LTE either FDD or TDD?
You are mixing two things modulation and multiple access. SC-FDMA has been chosen because it is battery-friendly modulation. SC-FDMA is used in both FDD and TDD modes.
There are several reasons why ...
- 6,725
5
votes
What is the transmission frequency of mimo antennas?
If you are refering to "E-UTRA operating bands" defined by 3GPP standands (section 5.5), the answer is NO.
In LTE access network, an operating band is assigned to a physical cell and MIMO is a signal ...
- 6,725
4
votes
Accepted
The necessity of null subcarrier in OFDM?
The only portion of the spectrum that is "occupied" or "transmitted" are the subcarriers that are actually used (i.e. 10 MHz instead of 15 MHz). The null subcarriers referenced in your question are ...
- 24.8k
4
votes
Accepted
What is the difference between Antenna port and Physical Antenna in LTE?
This answer is for LTE standard, not 5G NR. However I do believe that the basic concept does not change since.
(Logical) Antenna port is defined formally as in 3GPP 36.211
An antenna port is ...
- 6,725
4
votes
What type of LO lekage Correction algorithm is used in 5GNR?
In direct conversion transceivers, the LO leakage is pretty much a given. Some systems, mainly OFDM systems like Wifi, deal with that by simply leaving the DC carriers unused. And that's it. No ...
- 32.5k
4
votes
What type of LO lekage Correction algorithm is used in 5GNR?
Just want to provide some details to complement Marcus's answer.
(1) 5G NR does not avoid DC carrier, (2) it is possible to use it to modulate data (accepting degradation), and (3) 3GPP does not ...
- 6,725
3
votes
Accepted
am I recording LTE uplink signals?
There's a lot of different domains of knowledge coming together here, so I'll split my answer into multiple sections, each answering an implicit question that you raise in your explicit question. Hope ...
- 32.5k
3
votes
Accepted
SC-FDMA disadvantages
Some more disadvantages:
Channel estimation using pilots is harder, because you do not have orthogonal data on each frequency bin, compared to OFDM. That's why e.g. LTE uplink resorts to a midamble ...
- 6,238
2
votes
Why OFDM is more appropriate with MIMO than other multiple access method?
One possible answer is given at the beginning of the text:
Raleigh suggested and later proved that the processing required by
MIMO at higher speeds would be most manageable using OFDM modulation,
...
- 378
2
votes
Accepted
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?
We perform M point FFT on each Q block, then map the FFT results to intended positions of 1200 available subcarriers (subcarrier mapping), which are finally the input of a 2048-iFFT operation. See the ...
- 6,725
2
votes
Accepted
LTE Channel Estimation
FPGA is only user to verify the initial RTL which is specifically written to do each of the task listed below. Once the verification is done there is a tape out and everything is implemented in ...
- 2,655
2
votes
Accepted
How to determine Carrier Aggregation Class
what are the criteria to decide contiguous carriers?
the amount of spectrum that a mobile network operator owns, the amount of data you want to transmit, and a commercially-motivated decision by the ...
- 32.5k
2
votes
Accepted
What's practical interpretation of showing DC Offset in frequency domain?
A DC offset in the frequency domain will be an impulse at $f=0$. The interpretation of this is a single tone interference: "DC" is no different spectrally than any other frequency when ...
- 55k
2
votes
Accepted
OFDM SubCarrier and its relationship with IFFT in context of Real and Complex
When you map data to subcarrier symbols in OFDM, that IS a complex mapping. Each "constellation symbol" becomes the magnitude and phase for an FFT bin, so ultimately when you take the ...
- 55k
2
votes
IFFT and DAC relationship in OFDM Transmitter
The sampling rate of 30.72 MHz refers to a complex sampling rate of the baseband signal. For a bandwidth of 20 MHz, the single sided bandwidth would be 10 MHz and the minimum sampling rate according ...
- 55k
2
votes
A question on communication system without modulation
The specific experiment you describe is not particularly difficult as these things go, but it's far from trivial!
I would start by brushing up on DSP concepts with a book such as "SDR for ...
- 15.4k
2
votes
What is use of Quadrature Converter in OFDM?
In OFDM, the output of DAC after IFFT is a complex analog signal. In order to transmit this complex signal, two orthogonal RF channels are needed, one to transmit the real part, another one to ...
- 292
2
votes
Accepted
LTE PSS Channel Estimation for coarse SSS Equalization
Every 5 ms it is sent an OFDM Symbol which carries a PSS. So by using the block based channel estimation it might be possible to interpolate these PSS channel responses over time to get a $ h_{x_u}(f,...
- 6,725
1
vote
How is SNR Calculated in OFDM Reciever?
Your questions are quite broad and hence difficult to answer. If the communication system can afford the bandwidth for a pilot signal, then a pilot can be used. Yes, channel estimation would be needed....
1
vote
Doesn't use of Duplexer in FDD system limits it's capability?
What that article is calling a "duplexer" is normally (according to Wikipedia, and to my experience with radio installations in the 1990's) called a "diplexer". So if you're ...
- 13.3k
1
vote
OFDM Query : Why In Phase and Quadrature Phase RF Conversion is needed?
Each IFFT complex result bin represents an amplitude and a phase for some frequency. You can use the sum of the a sine and a cosine in the appropriate ratios to produce a sinusoid of any phase (see ...
- 35.7k
1
vote
Accepted
OFDM Query : Why In Phase and Quadrature Phase RF Conversion is needed?
Because the output of the IFFT operation is a vector of complex numbers. An RF signal is a real thing, so you can't just multiply a sine wave by a complex number and get something sensible.
However, ...
- 13.3k
1
vote
NR PUSCH non-codebook based precoding
See the book entitled "5G NR The next generation of wireless access technology" by Erik Dahlman. On page 165, Chapter 9, says "There is also a possibility for the network to operate ...
- 11
1
vote
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 ...
- 32.5k
1
vote
How does higher received signal power enable higher data rates?
The answer is Shannon's limit, which is given by:.
$C = B log_2 (1 + γ)$
where $C$ is the “capacity,” or maximum error-free data rate, $B$ is the bandwidth of the
channel, and $γ$ is the SNR (or SINR)....
- 95
1
vote
Why do we need >= 95% throughput for LTE Sensitivity measurement according to 3GPP
It's a definition. There's probably no specific reason
other than "the committee agreed on it".
Point is: this is for comparability of other tests. So, the actual number 95% is less ...
- 32.5k
1
vote
Accepted
Why is beamforming needed in 5G?
One reason is that higher frequencies are envisioned. With higher frequencies, the path loss grows (cf. Friis equation). Also, the wavelength is reduced and thus, $\lambda/2$ radiators start becoming ...
- 2,463
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