Hot answers tagged

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 ...
user avatar
  • 5,760
7 votes
Accepted

System Frame Number in LTE Specifications

System Frame Number (SFN) is really just a counter. As its name, it tells us the index of system frame modulo 1024, the index is from 0 to 1023 (10 bits). SFN does not help the physical ...
user avatar
  • 5,760
6 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 ...
user avatar
  • 5,760
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 ...
user avatar
  • 5,760
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 ...
user avatar
  • 5,760
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 ...
user avatar
3 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 ...
user avatar
  • 23.7k
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 ...
user avatar
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, ...
user avatar
  • 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 ...
user avatar
  • 5,760
2 votes

4G LTE Sampling Frequency Offset

I am not a specialist of the 4G LTE, but worked on other OFDM waveform similar to it. OFDM signal is made of symbols. Each symbol in frequency domain is made of a number of subcarriers. Some of ...
user avatar
  • 141
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 ...
user avatar
  • 37.1k
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 ...
user avatar
  • 37.1k
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 ...
user avatar
  • 13.8k
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 ...
user avatar
  • 37.1k
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....
user avatar
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 ...
user avatar
  • 34k
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, ...
user avatar
  • 8,285
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 ...
user avatar
  • 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 ...
user avatar
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 ...
user avatar
  • 8,285
1 vote
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 ...
user avatar
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)....
user avatar
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 ...
user avatar
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 ...
user avatar
  • 2,288
1 vote

What is role of BW and frequency in internet speeds?

Are my assumptions correct? no, sorry. (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 ...
user avatar
1 vote
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 ...
user avatar
  • 2,552
1 vote

Demodulation of OFDM symbol in LTE for multi-user case

The zero padding (or the cyclic prefix) takes care of inter-symbol interference that occurs due to delay spread. It is hence something you append to your signal in time domain. Hence the order is this:...
user avatar
  • 2,288
1 vote

How multi layer map to different beams in LTE Beamforming

The answer is simply orthogonalization of radio resources. For any given OFDM symbol, exactly one user will be allocated certain sub carriers. This allocation is dynamic and informed to the user in ...
user avatar
  • 2,552
1 vote

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

In 5G NR or 4G LTE, Multiple Input-Multiple Output (MIMO) transmission is a key technology specifically in downlink. Signals transmitted from gNB/eNB via different antennas or signals subjected to ...
user avatar

Only top scored, non community-wiki answers of a minimum length are eligible