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IRAT Handover From UTRAN Preparation Failure

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An Inter-Radio Access Technology (IRAT) Handover From UTRAN (UMTS Terrestrial Radio Access Network) Preparation Failure is a technical scenario that occurs when the network attempts to initiate an IRAT handover (e.g., from UTRAN to LTE or 5G), but the preparation phase of the handover is unsuccessful. This could happen due to various reasons, and resolving the failure is crucial to ensure the seamless mobility of the User Equipment (UE) between different radio access technologies. Here's a detailed technical explanation of IRAT Handover From UTRAN Preparation Failure:

1. Handover Trigger and Preparation:

  • The IRAT Handover From UTRAN Preparation Failure scenario begins when the network decides to initiate an IRAT handover. This decision can be triggered by factors such as UE mobility, network optimization, or quality of service considerations.
  • The network initiates preparations for the handover, which include selecting a target cell in the target RAT (e.g., LTE or 5G) and allocating resources for the upcoming handover.

2. UE Handover Preparation:

  • Simultaneously, the UE also prepares for the handover. It tunes its radio interface parameters to match those of the target cell in the target RAT.
  • The UE may also perform measurements on neighboring cells to assess the suitability of the target cell for handover.

3. Handover Request and Configuration:

  • Once the preparations are complete, the network generates an "IRAT Handover From UTRAN Command" message, which contains instructions for the UE to initiate the handover.
  • This message includes information about the target RAT, target cell identifiers, handover type, radio resource configuration details, and security parameters.

4. Transmission to the UE:

  • The "IRAT Handover From UTRAN Command" message is transmitted from the network (UMTS Radio Network Controller, or U-RNC) to the targeted UE over the UTRAN interface.

5. UE Reception and Processing:

  • The UE receives the "IRAT Handover From UTRAN Command" message and processes the instructions contained in the message.
  • It performs any necessary configuration changes to prepare for the handover.

6. UE Handover Preparation Attempt:

  • The UE attempts to prepare for the handover based on the instructions received from the network.
  • This includes configuring its radio parameters, such as frequency, timing, and power levels, to align with the target cell in the target RAT.

7. Handover Preparation Failure Detection:

  • During the preparation phase, if any issues prevent the UE from successfully preparing for the handover, both the UE and the network detect the failure.
  • Failure detection can occur due to various reasons, such as signal quality issues, incompatible frequencies, or resource unavailability in the target RAT.

8. Failure Cause Analysis:

  • The UE and the network analyze the cause of the handover preparation failure to determine why the preparation phase was unsuccessful.
  • This analysis helps identify the specific issues that need to be addressed to resolve the failure.

9. Handover Failure Handling:

  • Depending on the cause of the preparation failure, the network and the UE may take specific actions to address the issue:
  • Reconfiguration: The network may reconfigure the handover parameters or choose a different target cell in the target RAT.
  • UE Instructions: The UE may receive updated instructions from the network to address the specific failure cause.
  • Reporting: The UE may send measurement reports to the network to provide feedback on the failure and the conditions in the current cell.

10. Service Continuity and Recovery: - During and after the handover preparation failure recovery attempts, the UE continues to use the UTRAN network for communication. - Service continuity is maintained in UTRAN until the preparation issues are resolved and the handover can be successfully completed.

11. Procedure Continuation or Abandonment: - The IRAT Handover From UTRAN Preparation Failure procedure can continue with additional attempts to prepare for the handover, reconfiguration, or alternative actions. - If the issue cannot be resolved, the network may choose to abandon the handover attempt and keep the UE connected to UTRAN.

12. Procedure Completion or Handover: - The IRAT Handover From UTRAN Preparation Failure scenario is considered complete when one of the following conditions is met: - The handover is successfully prepared for, and the UE transitions to the target RAT. - The network and the UE determine that the handover cannot be prepared for successfully, and alternative actions are taken (e.g., instructing the UE to remain in UTRAN, initiating a different handover).

Resolving preparation failures in IRAT handovers is essential for ensuring uninterrupted service for the UE as it moves between different radio access technologies. It allows for efficient network resource management and optimization while maintaining the quality of service for the user.