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5g nsa handover

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5G NSA (Non-Standalone) refers to a deployment scenario where 5G networks are deployed on top of existing LTE (4G) infrastructure. This means that the 5G radio access network (RAN) is connected to the LTE core network for signaling and management purposes. When a user device moves between LTE and 5G coverage areas, a handover procedure is required to ensure seamless connectivity and user experience.

Here's a technical breakdown of the 5G NSA handover process:

  1. Initial Connection:
    • When a user device (e.g., smartphone) initially connects to the network, it might start in LTE mode if it's within an LTE coverage area.
    • As the device moves or as conditions change, it may need to connect to a 5G cell for better performance or coverage.
  2. Measurement and Triggering:
    • The device continuously monitors the signal strength and quality of nearby cells, both LTE and 5G.
    • Based on predefined thresholds (like signal strength or interference levels), the device decides when to initiate a handover.
  3. Handover Decision:
    • Once the device determines that the 5G network offers better conditions than the current LTE connection (or if there's a need for a 5G connection due to specific service requirements), it triggers the handover process.
  4. RAN Handover Preparation:
    • The device sends a handover request to the LTE eNodeB (base station). This request indicates the desire to move the connection to a 5G cell.
    • The LTE eNodeB then initiates a process to prepare for the handover. This includes allocating resources on the 5G side and signaling to the 5G gNB (Next-Generation NodeB) about the impending handover.
  5. Data Path Switch:
    • Before the actual handover occurs, the data path for the user's traffic is set up between the LTE eNodeB and the 5G gNB.
    • This ensures that when the handover is executed, there's minimal interruption to the user's ongoing sessions or applications.
  6. Handover Execution:
    • Once everything is prepared, the handover is executed. This involves the device disconnecting from the LTE cell and connecting to the 5G cell.
    • The 5G gNB then establishes the necessary radio resources and configurations to continue the user's session uninterrupted.
  7. Verification and Cleanup:
    • After the handover, both the LTE eNodeB and the 5G gNB verify the successful transfer of the user's data session.
    • If everything is successful, the resources on the LTE side are released, ensuring efficient use of network resources.
  8. Core Network Updates:
    • Although the RAN (Radio Access Network) handles the radio-related aspects of the handover, the core network also plays a role.
    • After the RAN handover, the core network updates its routing and session management information to ensure that user data continues to flow correctly.

The 5G NSA handover process in a dual-connectivity scenario involves continuous monitoring by the user device, decision-making based on signal conditions, preparation by both LTE and 5G radio access networks, and efficient transfer of the user's data session from LTE to 5G to ensure seamless connectivity and user experience.