LTE Handover Secondary Link Interruption Mitigation
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Solution Overview
Problem
Current LTE handover processes in LTE-WLAN aggregation (LWA) scenarios often result in interruptions to data transmission on the secondary link during handover, as the connection to the PDCP layer is re-established, leading to disruptions in both uplink and downlink communications.
Innovation Solution
The method involves maintaining an existing connection between the UE and the WLAN access point during handover by using a logical node called WLAN Termination (WT) to manage the forwarding of uplink PDUs from the source BS to the target BS, and employing specific ciphering keys to minimize disruption on the secondary link.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LTE handover is performed in LWA scenario by re-establishing PDCP layer connection, then handover completion is achieved, but data transmission on secondary link is interrupted
Solution Approach 1:
The patent segments the handover process into two independent parts: primary link handover (WWAN) and secondary link data transmission (WLAN). By decoupling these functions and allowing them to proceed independently, the PDCP layer re-establishment for handover no longer interrupts WLAN data transmission, thus resolving the contradiction between handover completion and data transmission continuity.
Solution Approach 2:
The patent introduces an intermediary mechanism where the source eNB forwards downlink PDCP PDUs to the target eNB before handover execution. This intermediary data forwarding path ensures that data transmission continues seamlessly during the PDCP layer re-establishment process, preventing interruption on the secondary link while handover is completed.
2Reliability
If PDCP layer connection is re-established during handover, then handover procedure is completed, but uplink and downlink communications are disrupted
Solution Approach 1:
The patent implements preliminary data forwarding from source eNB to target eNB before the handover is executed. By preparing the data path in advance, the system eliminates communication disruption during PDCP layer re-establishment, as data can immediately flow through the new path without waiting for handover completion.
Solution Approach 2:
The patent maintains continuous data transmission by establishing a forwarding path that operates throughout the handover process. The source eNB continues forwarding PDCP PDUs to the target eNB during the entire PDCP re-establishment period, ensuring uninterrupted uplink and downlink communications while handover proceeds.
3Reliability
If reassociation with WLAN is performed during LTE handover, then connection is maintained, but handover efficiency is reduced
Solution Approach 1:
The patent enables the WLAN connection to maintain itself independently during LTE handover through the established data forwarding mechanism. The UE does not need to perform reassociation with WLAN because the data path is automatically maintained through eNB forwarding, allowing the connection to serve itself without additional handover procedures and thus improving handover efficiency.
Data Source
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AI summary
Techniques for minimizing interruption for UL and/or DL transmission via a secondary link during a handover on a primary link. In response to a handover indication, a UE, source BS and target BS may take one or more actions to maintain an existing connection between the UE and a secondary link. For example, the UE, source BS, and target BS may take one or more actions to maintain a connection between the UE and a WLAN AP (e. g., using the Sequence Number, SN, of the last PDCP packet forwarded to the WLAN-AP, or the highest received SN, HRW, and using the ciphering key of the source or target BS, or a permanent ciphering key of the WLAN-AP).