Radio Terminal RRC State Transition Control for Interworking
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Solution Overview
Problem
Current state transitions between NR RRC states and E-UTRA RRC states are inefficient, particularly when a UE in the NR RRC_INACTIVE state moves to an E-UTRA cell, as existing methods do not provide explicit conditions for state transitions and may unnecessarily transition to the E-UTRA RRC_IDLE state, even if the E-UTRA cell supports interworking with the 5G system.
Innovation Solution
A radio terminal and base station system that controls state transitions among RRC_CONNECTED, RRC_INACTIVE, and RRC_IDLE states for both NR and E-UTRA RATs, altering the state transition operation based on whether the E-UTRA cell supports interworking with the 5G core network and RAN, allowing transitions to E-UTRA RRC_CONNECTED state if interworking is supported, or E-UTRA RRC_IDLE state if not.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the UE transitions to E-UTRA RRC_IDLE state when moving from NR RRC_INACTIVE state, then the state transition is simple and follows existing procedures, but unnecessary state changes occur even when the E-UTRA cell supports interworking with 5G system
Solution Approach 1:
The patent applies dynamics by making the state transition behavior adaptive rather than static. The UE dynamically adjusts its state transition operation based on real-time detection of interworking support information from the E-UTRA cell. When interworking is supported, the UE transitions to RRC_CONNECTED state; when not supported, it transitions to RRC_IDLE state. This dynamic adaptation eliminates unnecessary state changes and optimizes mobility efficiency while maintaining operational simplicity.
Solution Approach 2:
The patent implements feedback by having the UE detect and respond to interworking support information broadcast by the E-UTRA cell. This feedback mechanism allows the UE to make informed state transition decisions based on the target cell's capabilities. The feedback loop ensures that state transitions are optimized according to actual network conditions and interworking support, preventing unnecessary transitions to RRC_IDLE state when interworking is available.
2Adaptability or versatility
If the UE always transitions to E-UTRA RRC_IDLE state from NR RRC_INACTIVE state, then the procedure is standardized and simple, but mobility performance deteriorates when interworking is supported
Solution Approach 1:
The patent makes the state transition behavior dynamic by conditioning it on the detection of interworking support. Instead of always transitioning to RRC_IDLE state, the UE now adapts its behavior based on the target E-UTRA cell's capabilities. This dynamic approach enhances mobility reliability by maintaining RRC_CONNECTED state when interworking is supported, ensuring more reliable service continuity while still allowing RRC_IDLE transition when interworking is not available.
Solution Approach 2:
The patent uses feedback from the E-UTRA cell's interworking support information to determine the appropriate state transition. This feedback mechanism enables the UE to reliably assess whether the target cell can support interworking with the 5G core network and RAN. Based on this feedback, the UE makes reliable state transition decisions that maintain service continuity when possible, thereby improving mobility reliability without sacrificing adaptability to different network configurations.
3Productivity
If the UE detects interworking support information and alters state transition operation, then mobility efficiency is improved, but device complexity increases
Solution Approach 1:
The patent applies self-service by enabling the UE to autonomously detect interworking support information and independently decide on state transition operations without requiring complex network control or additional signaling. The UE's own capabilities and the broadcast information from the E-UTRA cell are sufficient for the UE to make optimal state transition decisions. This self-service approach improves mobility efficiency while minimizing device complexity, as the enhancement relies on the UE's existing detection and decision-making capabilities rather than adding complex control mechanisms.
Data Source
AI summary
When a radio terminal (2) in a first RAT RRC_INACTIVE state in the first radio access network (RAN) (3) and having a Non-Access Stratum (NAS) connection with a first core network (CN) (4) associated with the first RAT moves to a cell (51) of a second RAN (6), the radio terminal (2) alters an RRC state transition operation of the radio terminal (2) depending on whether the second RAN (6) supports interworking with at least one of the first CN (4) and the first RAN (3).