PDCP Status Report for DAPS Handover Packet Duplication

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Solution Overview

Problem

During Dual Active Protocol Stack (DAPS) handovers in wireless communication networks, packet duplication occurs because the target access node is not aware of downlink packets received by the UE from the source access node after the handover, leading to delays and resource inefficiencies.

Innovation Solution

The UE transmits a PDCP status report to the target access node after releasing the radio connection with the source access node, indicating the Sequence Numbers (SNs) of missing PDCP Service Data Units (SDUs). This allows the target access node to discard duplicated packets and avoid forwarding them to the UE.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the target access node forwards all downlink packets to the UE after handover, then packet loss is avoided, but packet duplication occurs and downlink resources are wasted

Engineering Contradiction:

Improvepacket delivery completenessVSAvoiddownlink resource efficiency

Core Design Contradiction:

ReliabilityVSLoss of substance

Solution Approach 1:

The UE sends a PDCP status report to the target access node, providing feedback information about which packets have been successfully received. This feedback mechanism enables the target access node to identify and discard duplicate packets, resolving the contradiction between ensuring complete packet delivery and avoiding resource waste from duplicate transmissions.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The PDCP status report is transmitted in advance before the target access node forwards downlink packets. This preliminary action allows the target access node to have advance knowledge of received packets and make informed decisions about packet forwarding, preventing duplicate transmissions and optimizing resource usage.

Inventive Principle:

Principle #10Preliminary action

2Loss of substance

If the target access node waits for PDCP status report before forwarding packets, then duplication is avoided, but transmission delays increase

Engineering Contradiction:

Improvedownlink resource efficiencyVSAvoidpacket transmission delay

Core Design Contradiction:

Loss of substanceVSLoss of time

Solution Approach 1:

The target access node forwards packets partially in advance based on available information, rather than waiting completely for the PDCP status report. This partial action reduces transmission delay while the subsequent status report allows for correction of any potential duplications, balancing speed and accuracy.

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The PDCP status report mechanism is prepared and transmitted in advance, allowing the target access node to process the information and adjust packet forwarding decisions proactively. This preliminary preparation minimizes the impact on transmission timing while ensuring duplication avoidance.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If the UE maintains connection with source access node longer, then packet loss is reduced, but handover completion time increases

Engineering Contradiction:

Improvepacket delivery reliabilityVSAvoidhandover duration

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The PDCP status report provides critical feedback information that allows the UE to confidently disconnect from the source access node. By informing the target access node of successfully received packets, the status report enables faster connection release without risking packet loss, thus resolving the contradiction between reliability and speed.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The handover process utilizes changes in PDCP sequence numbers and status report parameters to determine when it is safe to transition from source to target connection. These parameter changes provide objective criteria for timing the connection release, optimizing both reliability and speed of handover completion.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS20250151162A1User Equipment, Target Access Node and Methods in a Wireless Communications Network for Handling Packet Data Convergence Protocol (Pdcp) Service Data Units (Sdu) When Performing a Dual Active Protocol Stack (DAPS) Handover

Publication Date: 2025.05.08 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

The present disclosure relates to telecommunications. In one of its aspects, the disclosure concerns a method performed by a User Equipment for handling Packet Data Convergence Protocol (PDCP) Service Data Units (SDUs) when performing a Dual Active Protocol Stack (DAPS) handover of at least one radio bearer from a source access node to a target access node in a wireless communications network. The method comprises obtaining a trigger to perform the handover and establishing a radio connection for the at least one radio bearer with the target access node. An uplink transmission of PDCP SDUs is switched from the source to the target access node over the established radio connection. A radio connection with the source access node is released and a PDCP status report is transmitted to the target access node for each configured radio bearer. The respective PDCP status report indicates PDCP Sequence Numbers (SNs) of missing PDCP SDUs.