## Parallel WIRELESS

## 5G NR LOGICAL ARCHITECTURE AND ITS FUNCTIONAL SPLITS

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## 5G ENABLERS AND PRINCIPLES

### Novel Concepts That Were Not Envisioned by the Previous Generation Architectures

### - Modularization

- Previous networks: monolithic network functions corresponding to physical network elements
- 5G networks: modular network functions (NFs) for both control plane (CP) and user plane (UP) for both access network (AN) and core network (CN)

### - Network Slicing

- NFs to provides specific network capabilities for service verticals
- Resource abstractions by utilizing software-based NFs

- “Network programmability” by extending SDN to all control and data layers
- In network slices supporting URLLC, virtual NFs deployed closely to the users → reduced latency
- Multi-Access Edge Computing (MEC)
- Native support of MEC → reduced E2E latency and increased network efficiency

## 5G NR RADIO ACCESS NETWORK

### Basic Architecture

- The gNB is responsible for all radio-related functions in one or several cells
- RRM and admission control and
- Routing of user-plane (UP) data to UPF through N3
- Routing control-plane (CP) information to AMF through N2
- 3GPP considered the split concept (DU and CU) for NR from the beginning

## WHERE DID THE SPLIT CONCEPT START? It Started with C-RAN

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## EVOLUTION TO OPENRAN

### Distributed and Central Units

- 3GPP introduced the DU and CU concept as the evolution path toward vRAN
- Introduction of midhaul provides more flexibility for transport options

## 5G RAN FUNCTIONAL SPLITS

### Native Support for Various Functional Splits Along Two Dimensions

- Control Plane/User Plane split (Vertical split)
  - First step for introduction of SDN in the RAN
  - Allows separate optimization of CP and UP
  - Consistent CP in multi-vendor networks
  - More challenges for lower layer splits

### Central Unit/Distributed Unit split (Horizontal split)
- Obtain centralization gain, both in terms of performance gains and economy of scale
- Shift functionalities to deferent locations based on morphologies and transport availabilities
- Make overall RAN more future proof and less costly for future generation upgrades

## HIERARCHICAL RRM

### 5G CU/DU Split and Hierarchical RRM

- Central RRM located at CU coordinates the lower layer functions across multiple DUs
- The general functionalities of central RRM are:
  - Radio resource allocation
  - Call admission
  - Call selection
  - Load balancing
  - Inter-Cell Coordination
  - Context Awareness
  - HARQ Manager

- MAC dynamic scheduler is the most important part of RRM
- Dynamic scheduler needs context information for the users under its control to fulfill the user QoS
- Variable TTI size scheduling

# SPLITS TRADE-OFFS

- Not a single split is going to fit all
- Only a software-based RAN can support dynamic and fluid split options
- Different morphologies require different splits
- Control plane splits (vertical) are as important as user plane splits (horizontal)

# PARALLEL WIRELESS SPLIT ARCHITECTURE

## Split Architecture for All Gs

**RRH DU/CU Aggregator/Controller**

| **Open RAN** | **Fronthaul** | **Backhaul** | | | | 
|---|---|---|---|---|---|---| 
| | | | | | S6a | | 
| • Virtual Radio Unit vBBU: COTS server to act as a CU/DU | RRH | | | S1-MME | | | 
| • Open RAN Controller: full software based All G | | | | MME | HSS | 
| SON and orchestrator | Option 7.2 Split | | | | | | | 
| | | S11 | | | | 
| • Split 7.2 for efficiency and fronthaul scalability | COTS vBBU (DU/CU) | | S1-U | S5/S8 | SGi |

Internet **RRH** **vBBU** Option 7.2 Split MAC

| | | **RF PreCoding/Beam Forming** | **PDCP** | **RLC** | **RRC** | | 
|---|---|---|---|---|---|---|---|
| | | | | | | | | 
| RRH | CU/DU | Open RAN Controller | Low-PHY RRH | FEC¹ High-PHY vRU | Demodulation | Data | RAN Controller | 
| RF + Low-PHY | High-Phy/MAC | | | | | | |

Fronthaul Backhaul

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