Focus: Handover, RAT, SA/NSA, QoS, eSIM, Security
1. Radio Access Technology (RAT)
- Refers to wireless access methods such as LTE (4G), NR (5G), Wi-Fi (802.11 series).
- TCU must support multi-RAT handovers (e.g., 3G ↔ 4G ↔ 5G ↔ Wi-Fi).
- Prioritization (e.g., LTE for eCall) is essential for safety and reliability.
2. SA vs NSA Architectures
- SA (Standalone): Full 5G system with native 5G core; supports ultra-low latency and network slicing.
- NSA (Non-Standalone): Combines LTE control plane with 5G user plane; common for current deployments.
- TCU Implication: NSA is standard today, but SA compatibility is important for future-proofing.
3. 5G Frequency Bands – FR1 vs FR2
| Band Type | Characteristics | TCU Relevance |
|---|---|---|
| FR1 (Sub-6GHz) | Wide coverage, stable connection (e.g., n78/3.5GHz) | Preferred for in-vehicle use |
| FR2 (mmWave) | Ultra-high speed, low latency but short range | Suitable for V2X or HD map downloads |
4. Handover Types & Specifications
3GPP-Defined Handover Types
| Type | Description | Spec Reference |
|---|---|---|
| Intra-RAT HO | Within same RAT (e.g., LTE→LTE) | TS 36.331 / 38.331 |
| Inter-RAT HO | Across RATs (e.g., LTE→5G) | TS 23.401 / 23.502 |
| Inter-System HO | Across systems (e.g., 5G → Wi-Fi) | ATSSS (Rel-16/17) |
| Vertical HO | Wi-Fi ⇄ Cellular transition | IEEE 802.11r/k/v + ATSSS |
Implementation Challenges
- TCU requires seamless handover with minimal packet loss during transitions.
- Wi-Fi ⇄ Cellular handover depends on:
- 802.11r (Fast Transition)
- 802.11e (QoS Policy)
- EAP-SIM / EAP-AKA for seamless auth.
- 3GPP Rel-16/17 enables Multipath TCP / QUIC for parallel session continuity.
5. 5G Use Case Categories
| Category | Description | TCU Usage |
|---|---|---|
| eMBB | Enhanced Mobile Broadband | Streaming, OTA updates |
| URLLC | Ultra-Reliable Low Latency Communication | eCall, remote control, V2X |
| mMTC | Massive Machine-Type Communication | Fleet data, sensor telemetry |
6. QoS & Network Slicing
- QoS ensures differentiated priority and bandwidth:
- High priority: safety services (eCall)
- Low priority: infotainment data
- Network Slicing allows logical separation:
- Safety Slice – eCall, V2X
- Infotainment Slice – media & app downloads
- Diagnostics Slice – telemetry, OTA, logging
7. SIM Architecture (eSIM / DSDA / Remote Provisioning)
- eSIM + Remote Provisioning allows post-shipment carrier profile switching.
- Multi-IMSI or DSDA (Dual SIM Dual Active) enables redundancy:
- One SIM for emergency
- One SIM for general communication
- Essential for global SKU support and carrier failover.
8. Security Protocols and Network Protections
- End-to-End Encryption: IPSec / TLS
- Secure Boot & Verified Boot: Validate TCU at startup
- 5G SEPP (Security Edge Protection Proxy): Inter-PLMN security and firewalling