CU-DU Split Data Retransmission for Seamless Handover

Solution Overview

Problem

In wireless communication systems with a split central unit (CU) and distributed unit (DU), data loss occurs when a user equipment (UE) changes DUs due to mobility, as the source DU cannot retransmit lost data to the UE without an interface with the target DU.

Innovation Solution

A method where the CU sends a message to the source DU to stop transmitting data to the UE, and the source DU provides information on unsuccessfully transmitted data to the CU, which then retransmits it to the target DU, ensuring seamless data transfer during DU changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the source DU continues transmitting data to the UE during mobility, then data transmission is maintained, but data loss occurs when the UE changes DUs

Engineering Contradiction:

Improvedata transmission reliabilityVSAvoiddata loss

Core Design Contradiction:

ReliabilityVSLoss of information

Solution Approach 1:

The source DU stops transmitting data to the UE before the UE actually changes DUs. The CU notifies the source DU to stop transmission in advance, and the source DU provides information on unsuccessfully transmitted data to the CU, which then retransmits it to the target DU. This preliminary action prevents data loss by ensuring data is transferred before the mobility event occurs.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The CU acts as an intermediary between the source DU and target DU during UE mobility. Instead of the source DU directly retransmitting data to the target DU (which would require an interface between DUs), the CU receives lost data information from the source DU and forwards it to the target DU, enabling seamless data transfer without direct DU-to-DU retransmission.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Loss of information

If the source DU stops transmitting data to the UE during mobility, then data loss is prevented, but transmission interruption occurs

Engineering Contradiction:

Improvedata loss preventionVSAvoidtransmission interruption time

Core Design Contradiction:

Loss of informationVSLoss of time

Solution Approach 1:

The source DU stops transmitting data to the UE before the UE actually changes DUs. The CU notifies the source DU to stop transmission in advance, and the source DU provides information on unsuccessfully transmitted data to the CU, which then retransmits it to the target DU. This preliminary action prevents data loss by ensuring data is transferred before the mobility event occurs.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The data transmission process is made continuous through coordinated action between source DU, CU, and target DU. The source DU provides information on lost data to the CU, which immediately retransmits it to the target DU, ensuring that data transmission continues without interruption despite the UE's mobility.

Inventive Principle:

Principle #20Continuity of useful action

3Loss of information

If the source DU retransmits lost data directly to the target DU, then data loss is recovered, but interface complexity between DUs is required

Engineering Contradiction:

Improvedata recoveryVSAvoidinterface complexity

Core Design Contradiction:

Loss of informationVSDevice complexity

Solution Approach 1:

The CU acts as an intermediary between the source DU and target DU during UE mobility. Instead of the source DU directly retransmitting data to the target DU (which would require an interface between DUs), the CU receives lost data information from the source DU and forwards it to the target DU, enabling seamless data transfer without direct DU-to-DU retransmission.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The functions of data loss recovery and data forwarding are merged into the CU's operation. The CU handles both the notification from the source DU and the retransmission to the target DU as a single coordinated action, eliminating the need for separate DU-to-DU interfaces and simplifying the overall system architecture.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS11323929B2Method and apparatus for transmitting data in CU-DU split scenario

Publication Date: 2022.05.03 LG ELECTRONICS INC

AI summary

Provided are a method in which a source distribution unit (DU) of a base station stops transmitting data to a user equipment (UE) in a wireless communication system, and an apparatus supporting the method. The method may include: receiving, from a central unit (CU) of the base station, a message indicating to stop transmitting data to the UE; and stopping transmitting data to the UE, upon receiving the message from the CU of the base station.