## 5G NR Physical Layer Design
Day 6: July 26th, 2021

###### tags: `PNJ` `5G O-RAN` `ITB NTUST 5G course`

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### 3 Most Important Aspects
1. 5G NR Physical Layer
2. 5G NR Terminologies
3. Tutorial of OFDM System
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### Summary
1. 5G NR Physical Layer
The key technology components of the NR physical layer are: Waveform, Modulation, Multiantenna transmission (MIMO), Channel coding. 5G still use OFDM-based modulation as in LTE such as OFDMA, CP-OFDMA, SC-FDMA. NR supports QPSK, 16 QAM, 64 QAM and 256 QAM. 256QAM is used to support higher data rate transmission. π/2-BPSK to reduce peak-to-average power ratio & to enhanced power amplifier efficiency at lower data rates, which is important for mMTC services. Massive MIMO is base station with hundreds of antennas multiple users and low power antennas. The characteristics in MIMO are more antennas than number of users, multiplexing gain, small low power antennas, very directive signals. little interference leakage. Massive MIMO benefits are high spectral efficiency, array gain, high energy efficiency, high data rate, user tracking, low power consumption, less fading, low latency, more reliability. Flexible channel coding scheme is one of the fundamental components of the NR access technology, to meet higher data rates and more diverse requirements of typical NR scenarios: eMBB, mMTC, and URLLC. Candidate schemes: CC, Turbo Coding, LDPC, Polar Coding.

2. 5G NR Terminologies
5G NR Terminologies consist subcarrier spacing, frame-subframe, slot, and symbol. The very simple definition of Numerology would be 'subcarrier spacing type’. In NR there are several different types of subcarrier spacing that is from 0 – 4. 5G several numerologies, because NR should cover very wide range of operating frequency (e.g, sub 3 Ghz, sub 6 Ghz and mmWave(over 25 Ghz). Due to physics, it is hard (almost impossible) to come up with single numerology (subcarrier space) that can cover the whole of these range without sacrificing too much of efficiency or performance. In 5G, Downlink and uplink transmissions are organized into frames with 10ms duration, each consisting of ten subframes of 1ms. Each frame is divided into two equally-sized half-frames of five subframes each with half-frame 0 consisting of subframes 0 – 4 and half-frame 1 consisting of subframes 5 – 9. In Total, there are 10 subframes in one frame. Number of slot per subframe in 5G variates with carrier spacing. There can be 1, 2, 4, 8, or 16 slots subframe.

3. OFDM System
There are several types of modulation that can be done in the OFDM system: BPSK, QPSK, QAM-16, QAM-64. Fourier (IFFT / FFT) is the main part of OFDM system for multicarrier modulation-demodulation process, Convert data to time domain and vice versa, Transmitter -> IFFT & Receiver -> FFT, Fourier specifications: 256 parallel data. Cyclic Prefix is added to the symbol data with the aim of overcoming the effects of inter symbol interference, because of multipath fading. Cyclic Prefix insertion process is carried out by duplicating the back of the symbol to the front. OFDM transmission typically defined by IEEE 802.11a standard specification. In OFDM transmission, all the available subcarriers from the DFT is not used for data transmission. Typically, some subcarriers at the edge are left unused to ensure spectrum roll off.
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### Comment
The main different between 4G and 5G is about subcarrier spacing type. In LTE, subcarrier spacing is fixed 15 kHz. LTE don’t need any specific terminology to indicate subcarrier spacing because LTE not have many use cases. In 5G, subcarrier spacing type is define as Numerology. 5G has five numerology ( 0 – 4).
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### Discussion Team
1. Discuss about OFDM assignment
2. Dividing the sub-topic for every member to dig into details (actually in Saturday, 24th July 2021)
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