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NR-UL Handover Preparation Transfer

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The NR-UL (New Radio Uplink) Handover Preparation Transfer is a technical procedure in 5G networks that deals with the preparation and transfer of uplink data and signaling when a handover from one cell to another is required. This procedure ensures that ongoing communication from the User Equipment (UE) is smoothly handed over from the source cell to the target cell. Below is a detailed technical explanation of the NR-UL Handover Preparation Transfer:

Handover Trigger:

  • The NR-UL Handover Preparation Transfer is initiated when specific conditions indicate that a handover from the source cell to the target cell is necessary. These conditions can include factors like signal quality, cell load, or network policies.

UE and Network Roles:

  • The UE is the mobile device (e.g., smartphone, IoT device), while the network includes both the source gNodeB (5G base station) and the target gNodeB, along with core network elements.

Initial Handover Decision:

  • Before the handover preparation begins, the network may determine that a handover is necessary based on measurements and evaluations of the radio environment.
  • The decision to initiate a handover is typically made by the source cell (source gNodeB).

Resource Allocation:

  • The source cell allocates resources for the UE's uplink transmission during the handover preparation phase.
  • These resources may include time slots, frequency bands, and power levels.

Measurement and Evaluation:

  • The UE may perform measurements on both the source and target cells to assess their signal quality, interference levels, and other relevant parameters.
  • The UE evaluates whether the target cell offers better radio link quality or improved network conditions compared to the source cell.

Handover Decision Confirmation:

  • If the UE determines that the target cell is a better candidate for handover, it communicates this decision to the source cell through an appropriate signaling message.

Handover Command Message:

  • The source cell (source gNodeB) sends a Handover Command message to the UE, instructing it to prepare for the handover to the target cell.
  • This message includes information about the target cell, handover parameters, and timing information.

UE Preparation:

  • Upon receiving the Handover Command message, the UE prepares for the handover by configuring its uplink transmission parameters to match those of the target cell.
  • The UE may also synchronize its timing with the target cell and set up new radio bearers.

Data Buffering and Retransmission:

  • To ensure data continuity during the handover, the UE may buffer uplink data that was transmitted but not acknowledged by the source cell.
  • If necessary, the UE may retransmit this data after the handover is complete.

Measurement Gap Configuration:

  • In some cases, the network may configure a measurement gap to allow the UE to perform measurements on neighboring cells during the handover preparation process.
  • These measurements help the UE determine if the handover to the target cell is indeed the best choice.

Handover Confirmation:

  • After completing the handover preparations, the UE sends a Handover Complete or Handover Request message to the source cell, indicating its readiness to hand over to the target cell.

Handover Execution:

  • The actual handover execution, where the UE transitions its communication from the source cell to the target cell, follows the handover preparation transfer.

Service Resumption:

  • After the handover is complete, the UE can resume its active services, including data sessions, voice calls, or other communication, using the target cell.

Continuous Monitoring:

  • Both the UE and the network continue to monitor the quality of the radio link in the target cell to ensure its stability and make further adjustments if needed.

In summary, the NR-UL Handover Preparation Transfer is a technical procedure in 5G networks that ensures the smooth transition of uplink communication from the source cell to the target cell during a handover. This procedure involves measurements, handover decision-making, handover command messages, UE preparation, data buffering, and retransmission. The goal is to minimize service interruption and maintain high-quality communication as the UE moves between cells in the network.