PDCP Sequence Number Length Adaptation in LTE Handovers

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Solution Overview

Problem

The current LTE-Advanced scheme faces challenges in handover processes between cells using different PDCP sequence number lengths, leading to increased load on the C-Plane and handover delay when changing the PDCP-SN from 'Shorter-SN' to 'Longer-SN' or vice versa during handovers between macrocells and femtocells.

Innovation Solution

A radio base station and mobile station system that notifies and changes the PDCP sequence number length during handovers, allowing seamless communication by using a transmission unit to inform the mobile station of the sequence number length change, thereby reducing the need for pre-handover setup and minimizing C-Plane load and delay.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the PDCP sequence number length is changed from Shorter-SN to Longer-SN during handover, then the tolerance to packet loss is improved, but the overhead becomes large and handover delay increases

Engineering Contradiction:

Improvetolerance to packet lossVSAvoidhandover delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The target base station notifies the mobile station in advance of the PDCP sequence number length change before the handover is completed. This preliminary notification allows the mobile station to prepare for the change, avoiding delays and reducing handover time while ensuring reliable packet loss tolerance in the target cell.

Inventive Principle:

Principle #10Preliminary action

2Adaptability or versatility

If the PDCP sequence number length is changed during handover, then the adaptability to different cell types is improved, but the load on C-Plane increases

Engineering Contradiction:

Improveadaptability to different cell typesVSAvoidload on C-Plane

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The mobile station autonomously determines the PDCP sequence number length based on notifications from the target base station during handover. This self-service approach eliminates the need for complex C-Plane coordination and manual configuration, reducing C-Plane load while maintaining adaptability to different cell types.

Inventive Principle:

Principle #25Self-service

3Ease of manufacture

If the PDCP sequence number length is changed after handover, then the simplicity of the procedure is improved, but the communication efficiency deteriorates

Engineering Contradiction:

Improvesimplicity of procedureVSAvoidcommunication efficiency

Core Design Contradiction:

Ease of manufactureVSProductivity

Solution Approach 1:

The target base station notifies the mobile station of the PDCP sequence number length change before handover completion. This preliminary action ensures that the mobile station is already configured correctly when handover begins, eliminating communication delays and maintaining high communication efficiency while keeping the procedure simple.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentEP2793508B1Wireless base station and mobile station

Publication Date: 2017.11.29 NTT DOCOMO INC

Figure 1(a)~1(b)
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Figure 3

AI summary

Provided is a radio base station and a mobile station capable of reducing a handover delay while avoiding an increase of a load on the C-Plane even in a case where the kind of the PDCP-SN used within a cell after the handover is changed. A radio base station eNB #1 according to the present invention includes a transmission unit 11 configured to notify a mobile station UE that the length of the PDCP-SN used in communication within the cell #11 (or the cell #1) is changed in a case where the mobile station UE performs a handover from the cell #1 to the cell #11 (or in a case where the mobile station UE performs a handover from the cell #11 to the cell #1).