PDCP/RLC Handling in DC Split Bearers to Prevent Duplicate Delivery

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Solution Overview

Problem

The Past HFN Duplicate Delivery problem in PDCP layer of DC split bearer in 5G networks leads to degraded TCP performance due to duplicate packet delivery issues when radio link quality fluctuates, especially in high data rate scenarios like 5G mmWave blockage and fallback to LTE.

Innovation Solution

Implementing mechanisms such as increasing PDCP SN space, re-establishing RLC entities, and using new RRC configurations to manage and discard duplicate packets, ensuring half of the PDCP SN space is not in flight and maintaining HFN synchronization.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If PDCP SN space is increased to prevent duplicate delivery, then reliability is improved, but device complexity increases

Engineering Contradiction:

Improveduplicate packet preventionVSAvoidPDCP SN space management

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent changes the PDCP SN space parameter from its conventional size to a larger size (e.g., from 12 bits to 18 bits or more). This parameter change extends the sequence number range, allowing the receiver to distinguish between current and duplicate packets over longer periods and across more packets, thereby preventing duplicate delivery while managing complexity through standardized parameter adjustment

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent extends the PDCP SN space by adding more bits, effectively moving from a lower-dimensional sequence number space to a higher-dimensional one. This dimensional expansion provides a larger addressing space that prevents wraparound issues and duplicate packet confusion without requiring complex external management mechanisms

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Stability of the object's composition

If RLC entities are re-established to manage blockage, then service continuity is improved, but transmission delays increase

Engineering Contradiction:

Improveservice continuityVSAvoidre-establishment delay

Core Design Contradiction:

Stability of the object's compositionVSLoss of time

Solution Approach 1:

The patent performs preliminary actions by maintaining RLC entities in a suspended rather than fully released state during blockage events. This allows for faster recovery since the entities don't need complete re-establishment, reducing the time loss while maintaining service continuity through quick resumption of data transmission

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces dynamic management of RLC entities, where entities can be suspended, resumed, or re-established based on real-time radio conditions. This dynamic approach allows the system to adapt to blockage events by temporarily suspending rather than permanently releasing entities, enabling faster recovery when conditions improve while maintaining service continuity

Inventive Principle:

Principle #15Dynamics

3Reliability

If packets are discarded to prevent duplicates, then reliability is improved, but loss of information increases

Engineering Contradiction:

Improveduplicate packet eliminationVSAvoidvalid packet discarding

Core Design Contradiction:

ReliabilityVSLoss of information

Solution Approach 1:

The patent implements feedback mechanisms where the receiver uses the extended PDCP SN space to provide accurate acknowledgment information back to the transmitter. This feedback allows the transmitter to distinguish between duplicate packets (which should be discarded) and new valid packets (which should be delivered), eliminating duplicates while preserving all valid information without unnecessary discards

Inventive Principle:

Principle #23Feedback

4Reliability

If HFN synchronization is maintained during fallback, then reliability is improved, but device complexity increases

Engineering Contradiction:

ImproveHFN synchronizationVSAvoidsynchronization management

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent makes the HFN synchronization mechanism universal across different radio access technologies (NR and LTE). By designing the synchronization mechanism to work consistently across both NR and LTE networks during fallback scenarios, the system maintains reliability without requiring separate complex synchronization management for each technology, as the same principles apply universally

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentEP3520470B1PDCP, RLC handling in DC split bearer

Publication Date: 2025.07.02 APPLE INC

Figure 1A~1B
Figure 2A~2C
Figure 3A~3C

AI summary

Embodiments of PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control) handling in DC (Dual Connectivity) split bearer are generally described herein. In some embodiments, a UE (user equipment) decodes a configuration, provided via RRC (radio resource control) signals, for identifying a RLC-Rx (radio link control receive) link source of packets. The UE decodes a packet at a first RLC-Rx link. The UE decodes a packet at a second RLC-Rx link. The UE distinguishes, in a PDCP (packet data convergence protocol) entity, the packet decoded at the first RLC-Rx link from the packet decoded at the second RLC-Rx link, based on the configuration and SNs (sequence numbers) of the packets. The UE decodes a distinct packet in the PDCP entity.