# Tag Info

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 ...

3

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 ...

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

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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