RRC Establishment Cause Override for NR-to-LTE Voice Fallback
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Solution Overview
Problem
The existing LTE and NR technologies face challenges in minimizing call setup delay and reducing the likelihood of call setup failures during voice call fallback, particularly in NR to LTE voice fallback scenarios, which affect user experience and network resource efficiency.
Innovation Solution
A method and apparatus for a UE to identify the need for EPS or inter-RAT fallback for a voice call, override the establishment cause to indicate a mobile-originated voice call, and perform an access barring check based on this override, thereby optimizing the RRC connection process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE follows the standard RRC connection establishment procedure with establishment cause from NAS layer, then the access barring check may block voice calls due to incorrect cause indication, but this increases call setup delay and call setup failure likelihood
Solution Approach 1:
The UE performs preliminary identification that an RRC connection is being established for EPS fallback or inter-RAT fallback for voice call before the access barring check. This preliminary action allows the UE to override the establishment cause with the correct cause value (e.g., mo-voiceCall) in advance, ensuring the access barring check uses the proper criteria and prevents unnecessary blocking, thereby reducing call setup delay while maintaining high success rate
Solution Approach 2:
The invention changes the establishment cause parameter from its default NAS-layer provided value to a corrected value that accurately reflects the voice call fallback scenario. By modifying this parameter before the access barring check, the system ensures proper evaluation of access conditions, preventing false rejections and reducing call setup failures without increasing delay
2Reliability
If the UE performs access barring check with incorrect establishment cause, then call setup failures increase, but performing additional checks increases processing complexity
Solution Approach 1:
The UE performs preliminary identification of the fallback scenario before the access barring check, determining that the RRC connection is for EPS fallback or inter-RAT fallback. This preliminary action enables the UE to override the establishment cause with the correct value, ensuring accurate access barring evaluation without requiring complex additional checks during the connection establishment process
Solution Approach 2:
The invention modifies the establishment cause parameter to accurately reflect the voice call fallback scenario. This parameter change simplifies the access barring check by providing the correct cause value upfront, eliminating the need for complex conditional logic or multiple verification steps, thereby maintaining low device complexity while improving check accuracy
Data Source
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AI summary
Various aspects of the present disclosure generally relate to wireless communication. In some aspects, a user equipment (UE) may identify that a radio resource control connection is to be established for evolved packet system fallback or inter radio access technology fallback from New Radio for a voice call. The UE may determine that an establishment cause received from a network access stratum (NAS) layer does not indicate high priority access. The UE may override the establishment cause such that the establishment cause indicates a mobile originated (MO) voice call based at least in part on determining that the establishment cause received from the NAS layer does not indicate high priority access. The UE may perform an access barring check of an MO voice call based at least in part on overriding the establishment cause such that the establishment cause indicates an MO voice call. Numerous other aspects are provided.