5G SA EPS Fallback Redirection for Failed B1 Measurement Handover
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Solution Overview
Problem
Existing 5G standalone (SA) networks face issues with voice call failures due to uncertainties in B1 measurement reports, leading to unsuccessful Evolved Packet System Fallback (EPSFB) procedures, especially during handovers or redirections, resulting in poor user experience and network service interruptions.
Innovation Solution
A method and system that allow the gNodeB to proactively manage UE connections by aborting ongoing activities, configuring event measurements, and initiating emergency redirection to a predefined LTE frequency band when B1 measurements are delayed or not received, thereby ensuring seamless transitions to LTE networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the gNodeB waits for B1 measurement report from UE to initiate EPSFB procedure, then the handover decision can be made based on accurate measurement data, but the procedure fails when UE fails to send B1 measurement before wait timer expiry
Solution Approach 1:
The gNodeB pre-configures the UE with measurement parameters and starts a timer before actually needing the measurement report. This preliminary setup ensures the UE is ready to send the report, and if the timer expires without receiving the report, the gNodeB can immediately trigger emergency redirection to LTE without waiting further, thus resolving the reliability issue while maintaining measurement accuracy requirements.
2Productivity
If the gNodeB initiates IRAT handover after receiving B1 measurement report, then the UE can be handed over to LTE network, but the procedure fails when the reported LTE cell is not available in the NR to LTE neighbour list
Solution Approach 1:
The UE autonomously checks whether the measured LTE cell is present in the pre-configured neighbour list before sending the B1 measurement report. If the cell is not found in the neighbour list, the UE does not send the report, preventing the gNodeB from initiating a failed handover. This self-service approach at the UE side eliminates the reliability issue while maintaining fast handover execution when conditions are appropriate.
3Adaptability or versatility
If the gNodeB triggers EPSFB procedure, then voice call can be established on LTE network, but the procedure fails when UE is active with other handover procedure or stuck in race conditions
Solution Approach 1:
The gNodeB monitors the UE's activity state and other ongoing procedures before triggering EPSFB. When the gNodeB receives a PDU session modification request for IMS voice, it checks whether the UE is engaged in other handover procedures or race conditions. Based on this feedback, the gNodeB decides whether to proceed with EPSFB or abort the activity and perform emergency redirection, thus resolving the reliability issue while maintaining procedural flexibility.
4Speed
If the gNodeB performs emergency release with redirection, then the UE can be redirected to LTE network immediately, but ongoing activities are aborted without completion
Solution Approach 1:
Before performing emergency release with redirection, the gNodeB aborts any ongoing handover activities or race conditions that would prevent successful EPSFB. This preliminary anti-action prevents potential failures and ensures the redirection to LTE can proceed immediately without being blocked by conflicting procedures, thus achieving fast execution while preventing time loss from failed procedures.
Data Source
AI summary
The present disclosure automatically allows a user to make voice call on a Long-Term Evolution (LTE) network when a User Equipment (UE) (104, 310, 410, 510) is not capable to make voice call on a 5G Standalone (SA) network via redirection or via Handover. The present disclosure allows the user to release the 5G SA network and redirect to measured Evolved Universal Terrestrial Radio Access (E-UTRA) Absolute Radio Frequency Channel Number (EARFCN) of LTE band to proceed an Evolved Packet System Fallback (EPSFB) call successfully, if there is unprecedented failure during the handover procedure. The present disclosure allows the user to redirect to LTE Radio Access Technology (RAT) on default frequency band configured in gNodeB (gNB) ((320, 420, 520) during an emergency voice call or when B1 measurement delayed or not received, or while the UE (104, 310, 410, 510) is active with other procedure or stuck in race conditions.