Wireless Terminal Intersystem Handover via Routing Area Update
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Solution Overview
Problem
Current inter-RAT handover processes, particularly during intra-cell changes between E-UTRAN and GERAN networks, face issues with unsynchronized state information and lack of specific procedures to handle asynchronous contexts, leading to CCO-to-GERAN failures when ISR is active and the routing area is not changed.
Innovation Solution
The wireless terminal triggers a routing area update or deactivates the ISR function, allowing for successful intersystem changes by initiating a Cell Change Order (CCO) procedure and ensuring successful handover completion, even without pending uplink data or requests, thus overcoming the lack of triggers for access to the target GERAN cell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the wireless terminal remains in connected mode with ISR active during inter-RAT handover, then power consumption is reduced and signaling is minimized, but handover completion fails when routing area is not changed and no uplink data is pending
Solution Approach 1:
The wireless terminal performs a routing area update procedure before the inter-RAT handover is considered complete. This preliminary action ensures that the target cell is properly registered and the handover can be completed successfully, even when the routing area remains unchanged and no uplink data is pending. The RA update procedure is triggered as part of the handover completion process to prevent handover failures.
2Reliability
If the wireless terminal triggers routing area update during inter-RAT handover, then handover completion is ensured, but signaling overhead and procedure complexity increase
Solution Approach 1:
The routing area update procedure is triggered as a preliminary step during the inter-RAT handover process. By performing the RA update before final handover completion, the system ensures that all necessary registration and synchronization steps are completed in advance, preventing potential handover failures and reducing the need for re-attempts.
Solution Approach 2:
The handover process maintains continuous useful action by seamlessly integrating the routing area update procedure into the handover workflow. The terminal continues the handover process without interruption, triggering the RA update as part of the continuous handover sequence, which ensures smooth transition and completion.
3Reliability
If the wireless terminal deactivates ISR function during inter-RAT handover, then handover failures are prevented, but power consumption increases and signaling overhead increases
Solution Approach 1:
The wireless terminal deactivates the ISR function as a preliminary action before completing the inter-RAT handover. This ensures that the handover process can proceed without the constraints of ISR, allowing proper registration and completion even when routing area is not changed. The ISR function is deactivated temporarily during the critical handover phase to prevent failures.
Data Source
AI summary
A wireless terminal can communicate with two radio access networks (RAN) (304, 306) of different types. The wireless terminal can register simultaneously with a RAN of the first type and a RAN of the second type and can wirelessly connect to a RAN of either the first type or the second type in a connected state. The wireless terminal when registered with both a first RAN and a second RAN and when wirelessly connected to the first RAN in the connected state, receives a mobility signal via the first RAN indicating a RAN of the second type and, in response to receiving the mobility signal and in response to being so registered with the first RAN and second RAN, transmits an access trigger signal (417). The access trigger signal indicates that the wireless terminal is to be connected to the second RAN in the connected state.