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IRAT Handover From UTRAN Request

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The IRAT (Inter-Radio Access Technology) Handover From UTRAN (UMTS Terrestrial Radio Access Network) Request is a technical procedure in mobile telecommunications networks, especially in the context of transitioning from UMTS (Universal Mobile Telecommunications System) to other radio access technologies like LTE (Long-Term Evolution) or 5G. This procedure is initiated when a user equipment (UE) needs to perform a handover from a UTRAN cell to a cell in a different radio access technology. Here's a detailed technical explanation of the IRAT Handover From UTRAN Request procedure:

1. UTRAN-to-Non-UTRAN Handover Trigger:

  • UE Movement and Network Assessment: The need for an IRAT handover arises when the UE, which is currently connected to a UTRAN cell, moves out of the UTRAN coverage area and into an area covered by a different radio access technology (e.g., LTE or 5G). The network assesses the need for handover based on factors like signal quality and available resources.

2. Handover Preparation:

  • Target Radio Access Technology Selection: The network selects the target cell in the non-UTRAN radio access technology (e.g., LTE) to which the UE should hand over its connection. This selection is based on criteria such as signal strength, cell load, and quality of service.
  • Resource Allocation: Resources in the target cell are allocated to accommodate the incoming UE's connection.

3. Handover Request:

  • UE Initiates Handover Request: The UE realizes it needs to switch to a different radio access technology and initiates an IRAT Handover From UTRAN Request message. This message is typically sent to the serving UTRAN cell's radio network controller (RNC).

4. RNC Processing:

  • Message Handling: The serving RNC receives the IRAT Handover From UTRAN Request message from the UE and processes it.
  • Verification: The RNC verifies the request's validity and ensures that the UE is allowed to perform an IRAT handover.

5. IRAT Handover Preparation Transfer Request:

  • Message Generation: If the handover is approved, the RNC generates an IRAT Handover Preparation Transfer Request message. This message contains information about the handover, including the target cell's identity and radio parameters.
  • Message Signaling: The IRAT Handover Preparation Transfer Request is sent to the UE, instructing it to prepare for the handover.

6. UE Processing:

  • Message Reception: The UE receives the IRAT Handover Preparation Transfer Request message and processes it.
  • Context Configuration: The UE configures its radio parameters, including power levels and modulation schemes, based on the information provided in the message.

7. IRAT Handover Preparation Transfer Acknowledge:

  • UE Response: After configuring its radio parameters, the UE generates an IRAT Handover Preparation Transfer Acknowledge message to acknowledge that it has prepared for the handover.
  • Message Signaling: The acknowledgment is sent to the RNC.

8. RNC Handling:

  • Message Reception: The RNC receives the IRAT Handover Preparation Transfer Acknowledge message from the UE.

9. Handover Decision:

  • Decision in RNC: Based on the UE's acknowledgment and its own assessment, the RNC makes the final decision to proceed with the IRAT handover.

10. IRAT Handover Execution:

  • Handover Execution: If the handover is approved, the UE switches its connection from the UTRAN cell to the target cell in the non-UTRAN radio access technology (e.g., LTE).
  • Service Continuation: The UE can continue sending and receiving data, voice, or other communications in the new radio access technology.

The IRAT Handover From UTRAN Request procedure is crucial for maintaining a continuous and efficient connection as the UE moves between different radio access technologies within the network. It ensures that the UE remains connected to the best available cell and radio technology for seamless communication.