Parallel WIRELESS

5G NR LOGICAL ARCHITECTURE AND ITS FUNCTIONAL SPLITS

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

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