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8

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 would be easier for you. Everything in my answer is for 36.211 v8.7.0. The section 5.6 SC-FDMA baseband signal generation and 6.12 OFDM baseband signal ...


7

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 synchronization (frequency carrier, DFT starting frame, pilots, ...) because it is the information obtained after the waveform synchronization. It is decoded in Master ...


6

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 both FDD and TDD are defined. Historically, people want to utilize efficiently the precious spectrum. FDD needs two bands while TDD needs only one. ...


5

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 processing method in the band. Currently, MIMO in LTE uses frequency between sub-carriers and space diversity (SFBC, spatial multiplexing and beamforming) and ...


4

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 defined such that the channel over which a symbol on the antenna port is conveyed can be inferred from the channel over which another symbol on the same antenna ...


3

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 that helps! Can your RTL-Dongle actually receive at 1.72 GHz? So, first the bitter pill: There's a lot of sellers out there that offer RTL dongles and claim ...


3

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 used for two purposes: The null subcarriers along the edges are used to allow for easily-realizable anti-aliasing filters. Given a sample rate of 15.36 MHz (...


3

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 for channel estimation in uplink Application of non-linear MIMO detection algorithms is harder (i.e. more complex), because you essentially have coupled MxM ...


2

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, because OFDM converts a high-speed data channel into a number of parallel lower-speed channels. Also: MIMO-OFDM is a particularly powerful combination ...


2

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 figure below. Note that this is just one of possible implementations of SC-FDMA which is called DFT spread OFDM. The another is time domain approach. Check ...


2

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 subcarriers are mapped with data and other with pilots. Pilots have known defined values (usually scrambled BPSK symbols). The sampling frequency offset results in ...


2

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 Inverse FFT, you are creating the time domain waveform that would represent all of those constellations being broadcast in parallel on closely spaced carriers each ...


2

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 viewed as the Fourier Transform of a complex signal with positive and negative frequencies as the baseband spectrum centered about $f=0$ is identical to that ...


2

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 to Nyquist would be 20 MHz (and we would do something larger than this for practical reasons). So there is no issue here with the 30.72 MHz sampling rate ...


1

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. Typically, SNRs would be calculated in the digital domain. However, these answers won't help you and you'll need to delve into the theory more deeply. If you ...


1

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 trig identity). The IQ inphase and quadrature modulators produce the sine and cosine in the appropriate ratios to produce the transmit phase as needed. This ...


1

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, you can map a complex number onto an RF carrier by multiplying the real part by $\cos \omega t$, and the imaginary part by $\sin \omega t$. This is I/Q ...


1

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 15khz gap (say SubCarrier are N), now we get our OFDM Signal and we can send it. In short: no. You can't generate an OFDM system just by placing carriers in a ...


1

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 searching around for information, you probably want to include "diplexer" in your search. The problem with frequency-division or code-division multiplexing ...


1

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 network to combine multiple component carriers for you. So, all in all, not a signal processing, but a system and spectrum utilization as well as a financial ...


1

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). As received signal power increases, the Signal to Noise Ratio (SNR), $\gamma$, increases, since SNR is the ratio of signal power to the noise power. If $\...


1

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 quite small. The power you can radiate from a small aperture is limited as well so overall our power budget suffers. The only way out is directivity (cf. Friis ...


1

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 simultaneously. We need to talk about different meanings of the word "Bandwidth". In networks technology, that often means "number of bits per second that this system ...


1

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 hardware accelerators as below. FPGA is wasteful of area and too power hungry which cannot be afforded in modem (low power device) The LTE channel estimation is done ...


1

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: Assemble all the data symbols along the subcarriers (can contain data for multiple users, as you said). Compute DFT (via FFT, typically) Add cyclic prefix (...


1

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 what is known as the DCI, in the downlink control channel. Each user will decode data only on the subcarriers on which it has a grant allocated by the base ...


1

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 different and for the receiver unknown, multiple antenna precoding will experience different radio channels even if the MIMO antennas are located at the same site. ...


1

Operating frequency of an antenna is not related to whether it's a single antenna or in MIMO configuration. Operating frequency is related to the geometry of the antenna. The antenna is designed to be optimal in delivering and radiating power in that frequency. MIMO is a mathematical method to put the signal of interest on the antennas in such a way that ...


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