Dual-Protocol Stack Handover for Near-Zero Mobility Interruption
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Solution Overview
Problem
Current LTE systems experience high mobility interruption times during handover, exceeding the required latency for seamless transitions in NR networks, and existing solutions like RACH-less handover and make-before-break procedures are insufficient.
Innovation Solution
Implementing a dual-protocol stack handover with zero or near-zero mobility interruption by configuring UE with protocols for both source and target gNBs, using robust header compression (ROHC) and integrity protection, and managing PDCP data units to maintain continuous communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional handover procedures are used in LTE systems, then handover execution can be completed, but mobility interruption time is high (nearly 50 milliseconds)
Solution Approach 1:
The patent applies preliminary action by performing handover preparation in advance through dual-protocol stack configuration. The UE is configured with both source and target gNB protocol stacks before handover execution, allowing the target gNB to be pre-synchronized and ready. This preliminary setup enables the UE to switch protocols seamlessly during handover, reducing mobility interruption time from 50ms to near-zero while maintaining reliable handover completion.
2Loss of time
If RACH-less handover is implemented, then handover latency is reduced, but it cannot meet the strict latency requirements for NR systems
Solution Approach 1:
The patent extends RACH-less handover concepts by implementing dual-protocol stack configuration where the UE maintains both source and target protocol stacks simultaneously. The target gNB is pre-synchronized with the source gNB before handover, and the UE is pre-configured with target protocol parameters. This preliminary action reduces handover latency further and makes the system adaptable to strict NR latency requirements by enabling seamless protocol switching without random access procedures.
Solution Approach 2:
The patent applies parameter changes by dynamically switching protocol stack parameters between source and target gNBs. The UE configures PDCP, RLC, MAC, and PHY layer parameters for both source and target gNBs, and can switch between them based on handover needs. This parameter flexibility allows the system to adapt to different latency requirements and network conditions, meeting the strict latency demands of NR systems.
3Loss of time
If make-before-break procedures are used, then some mobility interruption is reduced, but the procedures are still insufficient for NR latency requirements
Solution Approach 1:
The patent enhances make-before-break by implementing full dual-protocol stack configuration where the UE maintains both source and target protocol stacks in parallel. The target gNB is pre-synchronized with source gNB, and the UE is pre-configured with target protocol parameters before actual data transmission begins. This comprehensive preliminary action reduces mobility interruption to near-zero while managing complexity through systematic protocol layer configuration and coordination between source and target gNBs.
4Reliability
If dual-stack protocol is implemented for zero mobility interruption, then handover seamlessness is achieved, but protocol stack complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the protocol stack into distinct source and target components at each layer (PDCP, RLC, MAC, PHY). The UE maintains separate protocol entities for source and target gNBs, allowing independent configuration and management of each stack. This segmentation enables seamless handover by allowing the UE to switch between source and target stacks without interference, while managing complexity through modular, layer-by-layer protocol architecture.
Solution Approach 2:
The patent applies universality by designing the dual-protocol stack architecture to handle multiple functions simultaneously. The same protocol stack structure serves both source and target gNBs, and the UE can use either stack for data transmission depending on handover state. This multi-functional design reduces overall complexity by reusing protocol configurations and procedures across both stacks rather than implementing separate specialized procedures for each gNB.
Data Source
AI summary
Apparatus and methods are provided for mobility interruption reduction. In novel aspect, dual-protocol stack handover is performed with zero or close to zero mobility interruption. In one embodiment, the UE receives PDCP SDU from upper layers for UL transmission and is configured with a protocol stack associated with a source gNB and a target gNB for handover. The UE associates a COUNT value corresponding to TX_NEXT to the PDCP SDU, selects an UL gNB as a destination gNB for UL transmission, performs header compression with a robust header compression (ROHC) profile based on the UL gNB. In one embodiment, the UE selects the UL gNB when an UL grant is received from the selected gNB. In another embodiment, corresponding ROHC profiles are configured by the wireless network. In one embodiment, the ROHC profile for the UL gNB is configured by the selected UL gNB.