# Functional Split and Open Fronthaul Interface
Day 7: July 27th, 2021

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

:::success
### 3 Most Important Aspect
- 5G Standar
- Functional Split
- O-RAN Fronthaul Interface
:::

## *5G Standar*
#### 5G New Radio
3GPP defines NR (New Radio) bands in FR1 and FR2 in 3GPP Rel.15 NR
- FR1 : 450 MHz - 7.125 GHz
- FR2 : 24.25 GHz - 52.6 GHz
Ultra wide bandwidth
- Up to 100MHz in <= 7GHz
- Up to 400MHz in >7GHz

The Impact of Frequency
High Frequency makes:
1. Higher path loss -> smaller coverage
2. Higher bandwidth -> higher data rate
3. Shorter wavelenght -> more antenna/unit area

5G New Radio consists:
1. Scalable numerologies for low latency and Ultra Realibility
2. Beamforming
3. New channel coding (LDPC for data channel and Pola coding for control channel)
4. Flexibel and modular RAN architecture:
split fronthaul, split control and user plane (CUPS)
5. Native end-to-end support for Network Slicing

#### 5G System Architecture

#### 5G Network Architecture

#### 5G Protocol Stacks

## *Functional Split*
in 5G there are have disaggregation between software and hardware, also in Base Station. The purpose of disaggregation is to make it easy for any vendor can work together.
CPRI (Common Public Radio Interface) is a specification for wireless communication networks that defines the key criteria for interfacing transport, connectivity and control communications between Baseband units (BBUs) and remote radio units (RRUs), which are also called remote radio heads (RRHs).

#### Control/User Plane Separation
From picture above, there are two split that is vertical split and horizontal split. Vertical split divide control plane and user plane, while horizontal split divide central unit and distributed unit.
CUPS (Vertical Split)
- First step to introduce SDN to the RAN
- Consistent CP in multi-vendor networks
- More challenges for lower layer splits

Central Unit/Distributed Unit Split (Horizontal split)
- Centralization gain in terms of performance and scale
- Shift functionalities to different locations
- Reduce the cost of RAN

In 5G O-RAN there are several split options

## *O-RAN Frontahul Interface*

Important function for Fronthaul
- Transporting data between DU and RU
- Splits functionality between O-RU and O-DU
- Enables multivendr RU and DU interoperability
- Increase transmission bandwidth through Split Option 7-2x
- Downlink and uplink bits processing

Architecture of O-RAN Fronthaul Interface

From image above, we can se that O-RAN fronthaul interface used split option 7-2x.

#### Split Option 7-2x
- Implements function up to Resource Element (RE) mapping in O-DU.
- Supports an O-RU that implements
digital beamforming (easy to implement): Category A
digital beamforming + precoding: Category B

#### Open Fronthaul Interface
From image above, open fronthaul interface consist C/U-Plane, S-Plane, and M-Plane.
C/U-Plane: transport using eCPRI or Radio Over Ethernet
S-Plane is a synchronization protocol that use Precision Time Protocol (PTP) or SyncE over Etherner
M-Plane is used for configuration in network management. It will be related to O1 interface. M-Plane consist NETCONF protocol over SSH/TCP/IP.

Open Fronthaul Interface Protocol Stacks