LTE Handover Assessment Preventing Partial RAB Admission
Solution Overview
Problem
Current handover procedures in LTE networks allow for successful handovers even if not all mandatory Radio Access Bearers (RABs) are admitted by the target cell, leading to partial handovers and potential service failures, particularly affecting VoLTE services where essential bearers like QCI 1 and QCI 5 are not fully admitted, resulting in dropped calls due to incomplete admission control.
Innovation Solution
The source eNB is configured to only perform handovers to target cells that confirm admission of all mandatory RABs needed to support associated Quality of Service Class Identifiers (QCIs), and if these conditions are not met, it attempts handovers to alternative cells or uses Single Radio Voice Call Continuity (SRVCC) to ensure uninterrupted service.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the source eNB allows handover to target cells that do not admit all mandatory RABs, then handover completion rate is improved, but service retainability deteriorates due to partial handovers causing dropped calls
Solution Approach 1:
The source eNB performs preliminary admission control verification by checking whether the target cell can admit all mandatory RABs before executing the handover. This advance verification prevents partial handovers that would lead to service failure, ensuring that handovers are only completed when full service continuity can be guaranteed.
Solution Approach 2:
The patent segments RABs into mandatory and non-mandatory categories based on their association with QCIs. Mandatory RABs (those associated with active QCIs) must be admitted for handover to proceed, while non-mandatory RABs can be optionally admitted. This segmentation enables selective admission control that prioritizes service-critical bearers.
2Reliability
If the source eNB requires admission of all mandatory RABs before handover, then service retainability is improved, but handover completion rate deteriorates due to rejected handovers when target cell resources are insufficient
Solution Approach 1:
The patent applies different admission control requirements to different types of RABs. Mandatory RABs (associated with active QCIs) require strict admission control to ensure service continuity, while non-mandatory RABs have flexible admission requirements. This local quality differentiation allows the system to maintain high service retainability for critical services while permitting handovers to proceed even when resources for non-critical services are unavailable.
3Reliability
If the network performs strict admission control for all RABs during handover, then service quality is improved, but handover complexity increases due to additional signaling and processing
Solution Approach 1:
The patent segments the admission control process into two stages: (1) verification of mandatory RAB admission capability using QCI-based classification, and (2) optional admission of non-mandatory RABs. This segmentation reduces handover complexity by focusing strict control only on service-critical bearers while simplifying handling of non-critical bearers.
Solution Approach 2:
The patent implements partial admission control by requiring admission verification only for mandatory RABs (those associated with active QCIs) rather than all RABs. This partial action approach maintains service quality for critical services while reducing the signaling overhead and processing complexity compared to controlling all bearers.
Data Source
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Figure 3
Figure 4~5
AI summary
A system (115) and method (133, 165) to sustain an on-going voice call or other service during a handover, HO, by preventing the handover to a target cell that fails to admit all the mandatory Radio Access Bearers, RABs, as part of supporting one or more Quality of Service Class Identifiers, QCIs, associated with the ongoing service. When the source evolved Node B, eNB, (122) prevents the HO to the best target cell (123), it may attempt the HO to the next best target cell (124). If the next best cell fails to admit all the mandatory RABs and if there are no other intra-LTE or inter-LTE cells available for HO, the source eNB may perform an inter-Radio Access Technology, RAT, HO using the Single Radio Voice Call Continuity, SRVCC, procedure. By preventing "partial" handovers, the retainability of an ongoing service is significantly improved. The target cells causing failure of particular RABs can be tracked using new counters.