PDCP Synchronization After RRC Re-establishment

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Solution Overview

Problem

In LTE systems, the synchronization of Packet Data Convergence Protocol (PDCP) operations after RRC connection re-establishment is not clearly specified, leading to issues such as missing PDCP Service Data Units (SDUs), header decompression failures, inefficient key usage, and incorrect ciphering key application during handovers between eNodeBs.

Innovation Solution

The method involves performing an RRC Reconfiguration procedure to resume all radio bearers except the signaling radio bearer 1 (SRB1), re-transmitting PDCP SDUs with a reset header compression/decompression protocol, generating a new base-key (KeNB) for ciphering/deciphering, and utilizing this new key to ensure correct PDCP operations after RRC connection re-establishment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If RRC connection re-establishment is performed during handover, then connection continuity is maintained, but PDCP operation synchronization fails causing data transmission errors

Engineering Contradiction:

Improveconnection continuityVSAvoidPDCP operation synchronization

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by resetting the header compression context and initializing PDCP state variables before resuming data transmission after RRC re-establishment. This preparatory synchronization ensures that both transmitter and receiver are in a consistent state before actual data transfer resumes, preventing the decomposition failures that would otherwise occur during handover.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes critical PDCP parameters including resetting the header compression context, reinitializing sequence numbers, and updating ciphering key states. These parameter changes are systematically applied to both transmitting and receiving PDCP entities to ensure they operate from a synchronized baseline state after connection re-establishment.

Inventive Principle:

Principle #35Parameter changes

2Speed

If header compression protocol is not reset after RRC re-establishment, then data transmission speed is maintained, but header decompression fails due to context mismatch

Engineering Contradiction:

Improvedata transmission speedVSAvoidheader decompression accuracy

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent performs preliminary resetting of the header compression context before resuming data transmission. By clearing and reinitializing the compression context at the transmitter and the decompression context at the receiver before actual data flow resumes, the system ensures both ends have synchronized state information, enabling successful header decomposition without compromising transmission speed.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent ensures that the header compression context is properly copied and synchronized between transmitting and receiving PDCP entities after re-establishment. By maintaining identical context states at both ends through systematic reset and reinitialization, the system enables accurate header decomposition while preserving efficient compressed data transmission.

Inventive Principle:

Principle #26Copying

3Device complexity

If ciphering key is not updated after RRC re-establishment, then processing overhead is reduced, but security is compromised due to key desynchronization

Engineering Contradiction:

Improveprocessing overheadVSAvoidciphering key synchronization

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent systematically updates ciphering key parameters including the base key (KeNB), derived keys (K_RRCenc, K_UPenc), and associated state variables (HFN, COUNT) after RRC re-establishment. This comprehensive key parameter refresh ensures both transmitter and receiver use synchronized, secure keys while maintaining efficient processing through structured key management.

Inventive Principle:

Principle #35Parameter changes

4Productivity

If PDCP state variables are not reinitialized after RRC re-establishment, then operational efficiency is improved, but data integrity is lost due to missing PDCP SDUs

Engineering Contradiction:

Improveoperational efficiencyVSAvoiddata integrity

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent applies preliminary reinitialization of PDCP state variables including sequence numbers (TX_SN, RX_SN), next PDCP SDU counters, and delivery status indicators before resuming data transmission. This preparatory state reset ensures both transmitting and receiving entities have synchronized, accurate state information, preventing SDU loss and ensuring complete data integrity while maintaining operational efficiency through systematic state management.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9191982B2Method for synchronizing PDCP operations after RRC connection re-establishment in a wireless communication system and related apparatus thereof

Publication Date: 2015.11.17 HTC CORP

AI summary

A method used in an E-UTRAN for synchronizing PDCP operations after a RRC connection re-establishment procedure with a user equipment (UE) is provided. The method includes: initiating an RRC reconfiguration procedure to resume all radio bearers other than a signaling radio bearer 1 (SRB1) when an RRC connection is re-established; re-transmitting a designated group of PDCP Service Data Units (SDUs) to the UE when a data radio bearer (DRB) mapped on Radio Link Control (RLC) Acknowledged Mode (AM) is resumed.