RRC Connection Recovery via Context Forwarding
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Solution Overview
Problem
In LTE mobile communication networks, radio link failures (RLF) and handover failures (HOF) lead to prolonged outage times and data loss due to inefficient connection recovery processes, especially in heterogeneous networks where imprecise cell measurements and inadequate handover times are common.
Innovation Solution
The implementation of a fast NAS recovery process, where a NAS service request is triggered during RRC reestablishment to quickly obtain UE context information from an MME via the S1 interface, reducing outage time and data loss by enabling quicker restoration of RRC connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional RRC reestablishment procedure is used after radio link failure or handover failure, then connection recovery is attempted, but outage time is prolonged and data loss occurs
Solution Approach 1:
The source eNB forwards UE context information to the target eNB before the UE actually performs RRC reestablishment. This preliminary action ensures that when the UE initiates reestablishment, the target eNB already has the necessary context, eliminating the need for time-consuming context retrieval during the recovery process and thus reducing outage time while ensuring reliable connection restoration
Solution Approach 2:
The source eNB acts as an intermediary by caching and forwarding UE context information to the target eNB. This intermediary action allows the target eNB to obtain context information quickly without directly querying the MME, thereby reducing outage time while maintaining connection recovery reliability
2Reliability
If traditional RRC reestablishment procedure is used, then connection recovery is attempted, but data loss occurs during the recovery process
Solution Approach 1:
The source eNB forwards UE context information including buffered data to the target eNB before handover or before RRC reestablishment is needed. This preliminary action ensures that data is already available at the target eNB, preventing data loss during the transition and eliminating the need for data retransmission after connection recovery
Solution Approach 2:
The source eNB serves as an intermediary that caches and transfers UE context and buffered data to the target eNB. This intermediary mechanism ensures seamless data transfer during handover or connection recovery, preventing data loss by ensuring the target eNB has all necessary data before the UE reconnects
3Ease of operation
If UE performs cell selection and RRC reestablishment without pre-forwarded context, then connection recovery is attempted, but target eNB lacks UE context information
Solution Approach 1:
The source eNB proactively forwards UE context information to the target eNB before the UE needs to perform RRC reestablishment. This preliminary action ensures that when the UE selects the target cell and initiates reestablishment, the target eNB already possesses all necessary UE context information, making the reestablishment process smooth and eliminating information gaps
Solution Approach 2:
The source eNB acts as an intermediary that caches and forwards UE context information to the target eNB. This intermediary mechanism ensures that the target eNB receives complete UE context information in advance, eliminating the need for complex context retrieval procedures and simplifying the RRC reestablishment process
Data Source
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AI summary
An enhanced connection recovery upon lost RRC connection due to radio link failure (RLF) or handover failure (HOF) is proposed. A UE first establishes an RRC connection in a source cell in a mobile communication network. Later on, the UE detects a failure event and starts an RRC reestablishment procedure in a target cell to restore the RRC connection. In a first novel aspect, a fast NAS recovery process is applied to reduce the outage time in the target cell. In a second novel aspect, context fetching is used to reduce the outage time in the target cell. In a third novel aspect, a loss-less reestablishment procedure is proposed to reduce data loss during the connection recovery.