Split Signalling Radio Bearer for Dual Connectivity Handover
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Solution Overview
Problem
Current LTE DC solutions lack robustness in handover scenarios where the UE loses connection to the MeNB, leading to issues with duplicate RRC message detection and reconfiguration, especially due to changes in PDCP entities and security keys, which disrupt seamless handover processes.
Innovation Solution
Implementing split signalling radio bearers (SRB) with dual connectivity, allowing control plane data to be transmitted while ceasing user plane data, and using timers to manage handover configurations, ensuring reliable handover by maintaining communication with the SeNB even after the MeNB handover.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If split signalling radio bearers are introduced for E-UTRA-NR Dual Connectivity, then robustness for important signalling such as handover commands and measurement reports is improved, but device complexity increases due to multiple schedulers and non-ideal backhaul requirements
Solution Approach 1:
The patent segments the signalling radio bearer into two separate bearers: one for control plane data (RRC messages) and another for user plane data. This segmentation allows independent management of control and user traffic, enabling the control plane to maintain reliability through the SeNB while the user plane utilizes both MeNB and SeNB resources, thus resolving the contradiction between reliability and complexity.
Solution Approach 2:
The patent introduces the Secondary Node (SeNB) as an intermediary for control plane signalling during handover. The SeNB acts as a mediator that can independently transmit handover commands to the UE, bypassing the Master Node (MeNB) when necessary. This intermediary approach ensures reliable signalling delivery while distributing the complexity of dual connectivity management.
2Reliability
If RRC messages are transmitted through multiple links in dual connectivity, then signalling diversity and handover robustness are improved, but loss of information occurs due to duplicate RRC message detection issues
Solution Approach 1:
The patent implements feedback mechanisms at the PDCP layer to detect and manage duplicate RRC messages. The system uses sequence numbers and acknowledgment protocols to identify when a message has already been received, allowing the UE to filter out duplicates while maintaining the robustness of receiving messages through multiple links. This feedback approach prevents information loss while preserving handover robustness.
Solution Approach 2:
The patent performs preliminary actions by configuring the UE with duplicate detection capabilities before handover occurs. The PDCP entity is pre-configured with sequence number tracking and duplicate message identification algorithms, enabling the UE to proactively detect and discard duplicate RRC messages before they cause processing errors, thus preventing information loss while maintaining signalling diversity benefits.
3Adaptability or versatility
If PDCP entities and security keys are changed during handover, then network reconfiguration is enabled, but seamless handover is disrupted due to detection and measurement issues
Solution Approach 1:
The patent performs preliminary key exchange and PDCP reconfiguration actions before the actual handover execution. The SeNB establishes security keys and configures PDCP entities in advance, so that when handover is triggered, the UE can immediately switch to the pre-configured SeNB resources without interruption. This preliminary preparation enables network reconfiguration while maintaining seamless handover experience.
Solution Approach 2:
The patent implements beforehand cushioning by maintaining parallel PDCP entities and security contexts at both MeNB and SeNB before handover occurs. This dual-context preparation acts as a cushion that absorbs the disruption of key changes and PDCP reconfiguration, allowing the handover to proceed seamlessly. The pre-established backup PDCP entity at SeNB ensures continuous operation even during the reconfiguration transition.
4Reliability
If the UE maintains connection to both MeNB and SeNB during handover, then mobility robustness is improved, but loss of time occurs due to extended handover procedures
Solution Approach 1:
The patent segments the handover procedure into independent control plane and user plane operations. The control plane handover to SeNB can be executed quickly using pre-configured resources, while the user plane data continuity is maintained through the PDCP layer. This segmentation allows the UE to maintain connection to both nodes during handover without excessive time delay, as the control plane changes are applied immediately while user data flows continue uninterrupted.
Solution Approach 2:
The patent ensures continuity of useful action by maintaining active data sessions at the SeNB during the handover process. The PDCP entity at the SeNB continues to process and forward user plane data even before the control plane handover is fully completed. This continuous data processing eliminates idle periods during handover, reducing time loss while the UE maintains robust connectivity to both MeNB and SeNB for coordinated operation.
Data Source
AI summary
According to certain embodiments, a method by a first network node operating as a secondary node for a wireless device having dual connectivity to the first network node and a second network node operating as a source master node is performed during a handover of the wireless device from the second network node operating as the master node to a third network node operating as a target master node. The method includes receiving, from the second network node operating as the source master node, an indication that the first network node is to release one or more resources for serving user plane data to the wireless device. In response to the indication, control plane data is transmitted to the wireless device while ceasing to provide user plane data to the wireless device.