# Daily Report day 5
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26/07/2021
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## 1. Aspects : Baseband Technology (5G NR Physical Layer Design)

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### A. 5G NR Physical Layer Design
#### Introduction
To realize the vision of 5G vision, the PHY system is designed and it is referred as New Radio.
The key technology components of the NR physical layer are:
1. Waveform
2. modulation
3. Multiantenna transmission (MIMO)
4. Channel coding

#### Modulation
- 5G still use OFDM-based modulation as in LTE
- OFDMA
- CP-OFDMA
- SC-FDMA
- NR supports QPSK, 16 QAM, 64 QAM and 256 QAM modulation formats for both uplink and downlink, as in LTE.
- 256QAM : is used to support higher data rate transmission
- π/2-BPSK : standard BPSK signal by multiplying the symbol sequence with a rotating phasor with phase increments per symbol period of π/2
- To reduce peak-to-average power ratio
- To enhanced power amplifier efficiency at lower data rates, which is important for mMTC services.

#### 5G NR Modulation and Coding Scheme (MCS) Characteristics
- Modulation and Coding Scheme (MCS) defines the numbers of useful bits per symbols
- MCS selection is done based on radio condition and BLER
- MCS is change by gNB based on link adaptation algorithm
- MCS information is provided to UE using DCI
- There are about 32 MCS Indexes (0-31) are defined and MCS Index 29,30 and 31 are reserved and used for re-transmission
- 3GPP Specification 38.214 has given three tables for PDSCH MCS namely 64 QAM Table, 256 QAM Table and Low Spectral Efficiency 64 QAM Table

#### Waveform
- NR has a scalable OFDM numerology to enable diverse services on a wide range of frequencies and deployments.
- The subcarrier spacing is scalable and specified as 15 × 2μ kHz, where μ is an integer and 15 kHz is the subcarrier spacing used in LTE.

#### Numerology
- The very simple definition of Numerology would be 'subcarrier spacing type'.
- In LTE, we don't need any specific terminology to indicate the subcarrier spacing since there is only one subcarrier spacing,
- in NR there are several different types of subcarrier spacing as summarized in the following table.

NR should cover very wide range of operating frequency (e.g, sub 3 Ghz, sub 6 Ghz and mmWave(over 25 Ghz).
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### B. MIMO in 5G
Massive MIMO is the extension of traditional MIMO technology to antenna arrays having a large number of controllable antennas. Transmission signals from the antennas are adaptable by the physical layer via gain or phase control.
- Enhance Coverage
- Enhance Capacity
Why do we need Massive MIMO?
- Capacity Requirements
- Most Macro Networks will become congested
- Spectrum < 3GHz and base sites will run out of capacity by 2020
- Coverage Requirements
- Below 6GHz: desire to deploy LTE/NR on site grids sized for lower carrier frequencies
- Above 6GHz: Large Bandwidths but poor path loss conditions
- Technology Capability
- Active Antennas are becoming technically and commercially feasible
- Massive MIMO requires Active Antenna technology
- 3GPP Spec Support
- 3GPP supports Massive MIMO in Rel-13/14 for LTE and Rel-15 for NR/5G
- 3GPP-New-Radio will be a “beam-based” air interface
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### C. Channel Coding
- 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
- 3GPP has adopted Polar Coding for 5G/NR Uplink/Downlink control channel for eMBB.
- Polar codes can asymptotically (for code length going to infinity) achieve the capacity of any binary input symmetric memoryless channel with encoding and decoding complexity of the order O(N log N), where N is the code length.
- At present they are the only class of channel codes that are provably capacity achieving with an explicit construction.
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### D. OFDM System
#### 1. OFDM System Block Diagram

#### 2. Channel Encoder
The channel encoder method uses convolution with a polynomial generator.

#### 3. Modulator
There are several types of modulation that can be done in the OFDM system:
- BPSK
- QPSK
- QAM-16
- QAM-64

#### 4. Fourier (IFFT / FFT)
- It 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

#### 5. Cyclic Prefix
- CP is added to the symbol data with the aim of overcoming the effects of inter symbol interference, because of multipath fading
- The CP insertion process is carried out by duplicating the back of the symbol to the front

In an OFDM transmission, we know that the transmission of cyclic prefix does not carry 'extra' information in Additive White Gaussian Noise channel.

#### 6. OFDM Review
- OFDM transmission typically defined by IEEE 802.11a standard specification
- We have understood that the minimum frequency separation for two sinusoidal with arbitrary phases to be orthogonal is 1/T, where T is the symbol period

#### 7. Frequency Spread
- 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.

#### 8. Energy in OFDM
Combining the two aspects mentioned before, the relation between symbol energy and the bit energy is as follows:
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## 2. Summary
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A physical layer forms the backbone of any wireless technology. The NR physical layer has a flexible and scalable design to support diverse use cases with extreme (and sometimes contradictory) requirements, as well as a wide range of frequencies and deployment options.
The key technology components of the NR physical layer are modulation schemes, waveform, frame structure, reference signals, multi-antenna transmission and channel coding.
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## 3. Comment
5G NR (new radio) is a new radio access technology (RAT) applied to 5G networks. This access radio is very important because it is a data transmission on 5G.

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# <center>Discussion with Team</center>
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