5G Architecture and Functional Components
NG-RAN: Radio Access Network
- gNB Functions: Handles radio scheduling, coding, MIMO, HARQ, and QoS enforcement.
- CU/DU Split: The gNB is divided into a Centralized Unit (CU) for non-real-time tasks and a Distributed Unit (DU) for real-time tasks via the F1 interface.
- Connectivity: Connects to the 5G Core via the NG interface and to other gNBs via the Xn interface for handovers.
5G Core: Service-Based Architecture
- AMF: Manages mobility, connections, and authentication.
- SMF: Handles session management, IP assignment, and QoS policies.
- UPF: Manages user plane data forwarding; the primary node for user traffic.
- AUSF: Authentication server.
- NSSF: Network Slice Selection Function for UE slice assignment.
- UDM: Unified Data Management (subscriber database).
5G Flexibility Features
- CP/UP Split: Control and User planes scale independently.
- Network Slicing: Multiple virtual networks on shared hardware.
- Dynamic TDD: Slot-by-slot UL/DL allocation based on traffic.
- Scalable OFDM: Architecture supporting sub-GHz to mmWave.
Comparison: 4G EPC vs. 5G Core
| Feature | 4G EPC | 5G Core |
|---|---|---|
| Architecture | Rigid physical nodes | Service-Based (cloud-native) |
| Mobility | MME | AMF |
| Session Mgmt | SGW + PGW | SMF + UPF |
| Auth | HSS | AUSF + UDM |
| CP/UP Split | Partial | Strict |
| Network Slicing | Not supported | Native |
| Scalability | Node-based | Independent CP/UP |
| Deployment | Hardware | Containers/VMs |
Dynamic TDD Configurations
TDD uses the same frequency for UL and DL, separated by time:
- Static TDD: Fixed UL/DL pattern; simple but inefficient for asymmetric traffic.
- Semi-static TDD: Configured per-UE via RRC; allows receiver power-saving.
- Dynamic TDD: Scheduler assigns UL/DL per slot via DCI; highly flexible.
Signaling and Challenges
- DCI Scheduling: UE monitors slots for transmission instructions.
- Slot Format Indicator (SFI): Broadcasts patterns for radio preparation.
- Interference: Requires coordination to prevent cross-link interference between neighbor cells.
5G Transmission Scheme
- Waveform: OFDMA for downlink; DFT-spread OFDM for power-limited uplink.
- Scalable Numerology: Supports µ=0 (15 kHz) to µ=4 (240 kHz) for varied latency needs.
- Structure: 10 ms frames, 1 ms subframes, and 14-symbol slots.
Initial Beam Management
- Beam Sweeping: gNB transmits synchronization signals (SSB) in multiple directions.
- UE Measurement: UE measures RSRP to identify the best beam.
- RACH: UE initiates access via the strongest beam.
- Maintenance: Continuous monitoring and recovery if a beam is blocked.
SDN in 5G Management
- Separation: Decouples control plane intelligence from data plane forwarding.
- Centralization: Enables global network visibility and automated routing.
- Efficiency: Facilitates network slicing and reduces reliance on proprietary hardware.
Functional Split Criteria
- RAN vs. Core: RAN handles real-time radio functions; Core handles non-real-time session and authentication tasks.
- CU vs. DU: CU (Centralized Unit) manages non-real-time protocols (RRC/PDCP); DU (Distributed Unit) manages real-time protocols (RLC/MAC/PHY).
Network Slice Controller
The orchestrator maps SLA requirements (latency, throughput) to virtual resources, monitors slice performance in real-time, and manages the lifecycle of virtual network functions.