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5G NR Dual Active Protocol Stack (DAPS) Handover

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1. 5G NR Handover Basics:

In 5G networks, handovers are essential for maintaining continuous communication as a user moves between different cells. A handover involves transferring the connection from one base station (eNodeB in LTE or gNB in 5G NR) to another. The handover process aims to ensure seamless connectivity, minimal disruption, and optimal resource utilization.

2. Dual-Active Protocol Stack:

Dual-active protocol stack refers to the capability of having two independent protocol stacks simultaneously active in a device. This is often employed to enable smooth transitions between different network generations or technologies.

3. Overview of 5G NR Architecture:

  • gNB (New Radio Base Station): The gNB is the radio access network component in a 5G network. It communicates with user equipment (UE) and coordinates with the core network (5G Core or 5GC).
  • 5G Core (5GC): The 5G Core network handles the control and management of user traffic, providing services like session management, authentication, and mobility management.

4. Handover Process in 5G NR:

a. Mobility Management:

  • UE Measurement: The UE continuously measures the signal quality from neighboring cells.
  • Event Trigger: Based on predefined thresholds, an event is triggered, indicating a need for handover.

b. Handover Decision:

  • Measurement Report: The UE sends a measurement report to the source gNB.
  • Target Cell Selection: The source gNB evaluates the report and selects a suitable target cell for handover.

c. Dual-Active Protocol Stack Handover:

  • Preparation: The dual-active protocol stack ensures that both the source and target gNBs are ready for the handover.
  • Data Forwarding: Both gNBs are capable of forwarding data during the handover process.
  • Control Signaling: Control signaling facilitates the transfer of the UE context and necessary parameters between the source and target gNBs.

d. Handover Execution:

  • Switching the Connection: The UE's connection is switched from the source to the target gNB.
  • Radio Resource Configuration: The target gNB configures radio resources to continue the communication.
  • Data Path Continuity: Data forwarding is maintained to minimize disruption.

5. Key Considerations:

  • Latency: Minimizing handover latency is crucial to maintain a seamless user experience.
  • Dual Connectivity: Dual connectivity involves simultaneous connection to multiple cells, enhancing data rates and reliability.