EPS Fallback Redirection for Failed 5G SA Voice Handover
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Solution Overview
Problem
Existing 5G standalone (SA) networks face issues with Evolved Packet System Fallback (EPSFB) procedures failing due to uncertainty in B1 measurement reports, leading to unsuccessful voice calls when transitioning from 5G to 4G, especially when B1 measurements are delayed, not received, or when the UE is stuck in race conditions or other procedures.
Innovation Solution
A method and system that dynamically manage communication channels by configuring UE with event measurements, receiving measurement reports, and using neighbor relation tables to redirect the UE to release connections with the 5G network and reselect a 4G frequency band when B1 measurements fail or handover procedures fail, ensuring seamless transition to LTE.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the gNB 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 B1 measurement is delayed or not received before wait timer expiry
Solution Approach 1:
The gNB configures the UE with A3 event measurement and neighbour relation table (NRT) in advance, before the EPSFB procedure is triggered. This preliminary configuration ensures that when EPSFB needs to be initiated, the UE already has the necessary measurement parameters and neighbour cell information ready, eliminating delays caused by waiting for B1 measurement reports.
Solution Approach 2:
The patent introduces A3 event measurement as an intermediary mechanism. Instead of directly relying on B1 measurement reports which may be delayed, the system uses A3 event measurements (which trigger when neighbour cell becomes offset better than serving cell) as an intermediate step to identify suitable target cells for EPSFB, ensuring more reliable and timely handover decisions.
2Productivity
If the gNB initiates IRAT handover after receiving B1 measurement report, then the UE can be handed over to a suitable LTE cell, but the procedure fails when the reported LTE cell is not available in the NR to LTE neighbour list
Solution Approach 1:
The gNB pre-configures the UE with a neighbour relation table (NRT) containing valid LTE neighbour cells before the EPSFB procedure. This preliminary action ensures that when the UE reports measurement results, the gNB can immediately identify valid target cells from the pre-configured NRT without encountering issues of unavailability or needing to query additional neighbour information during the critical handover execution phase.
3Reliability
If the gNB triggers EPSFB procedure, then voice call can be established on LTE network, but the procedure fails when UE is stuck in race condition or other procedures
Solution Approach 1:
The patent uses A3 event measurement as an intermediary trigger mechanism that is less prone to race conditions. Instead of directly triggering EPSFB based on complex B1 measurement reporting timelines that can conflict with other procedures, the system waits for A3 event measurements which naturally trigger when neighbour cell quality exceeds serving cell by a configured offset, providing a more robust and race-condition-resistant trigger point.
4Loss of time
If the gNB configures UE with B1 measurements and sets wait timer, then the system can wait for measurement report, but the procedure fails when UE fails to send B1 measurement before timer expiry
Solution Approach 1:
The gNB performs preliminary configuration of A3 event measurements and NRT before the EPSFB procedure is needed. This advance preparation eliminates the need for time-critical B1 measurement reporting during the procedure execution, as the UE already has the measurement configuration and neighbour information ready, significantly reducing timing-related failures.
Data Source
AI summary
The present disclosure relates to a method for performing an evolved packet system fallback (EPSFB). 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) 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 get redirected on reported frequency with best measurement when handover failed.