PDCP SDU Cache Management via Early Deletion

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Solution Overview

Problem

In the LTE protocol, PDCP SDUs mapped to RLC Unacknowledged Mode (UM) or Transparent Mode (TM) are discarded when the discard timer expires, leading to unnecessary occupation of cache space in User Equipment (UE) as they are not retained for re-establishment procedures.

Innovation Solution

A method and apparatus that delete PDCP SDUs and corresponding PDU when the discard timer does not expire and additional preset conditions are met, such as delivery to the RLC layer or confirmation of association with an RLC PDU, reducing cache space occupation by ensuring timely deletion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If PDCP SDU is retained in the PDCP layer until the discard timer expires or successful delivery is confirmed, then the reliability of data transmission is improved, but the cache space occupied by PDCP SDU increases

Engineering Contradiction:

Improvedata transmission reliabilityVSAvoidcache space occupied by PDCP SDU

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The PDCP layer performs preliminary deletion of PDCP SDU when the PDCP PDU is delivered to the RLC layer or when association with an RLC PDU is confirmed, before the discard timer expires. This preliminary action reduces cache space occupation while maintaining transmission reliability through early deletion based on delivery status.

Inventive Principle:

Principle #10Preliminary action

2Device complexity

If PDCP SDU mapped to RLC UM or TM is discarded only when the discard timer expires, then the simplicity of the protocol is maintained, but the cache space occupation increases unnecessarily

Engineering Contradiction:

Improveprotocol complexityVSAvoidcache space occupied by PDCP SDU

Core Design Contradiction:

Device complexityVSQuantity of substance

Solution Approach 1:

The deletion condition for PDCP SDU is made dynamic by introducing an additional condition: deletion occurs when either the discard timer expires OR when the PDCP PDU is delivered to the RLC layer/association with RLC PDU is confirmed. This dynamic condition allows flexible deletion based on delivery status without significantly increasing protocol complexity.

Inventive Principle:

Principle #15Dynamics

3Reliability

If PDCP SDU is retained for potential re-establishment procedures, then the reliability of data transmission during re-establishment is improved, but the cache space occupation increases

Engineering Contradiction:

Improvedata transmission reliability during re-establishmentVSAvoidcache space occupied by PDCP SDU

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

Different retention policies are applied to different types of PDCP SDUs: PDCP SDUs mapped to RLC AM are retained for re-establishment procedures, while PDCP SDUs mapped to RLC UM or TM are deleted earlier when delivery conditions are met. This local quality differentiation maintains reliability where needed while reducing cache space occupation where possible.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS11558494B2Method and apparatus for processing data, user equipment and computer-readable storage medium

Publication Date: 2023.01.17 BEIJING XIAOMI MOBILE SOFTWARE CO LTD

AI summary

A method of processing data includes: receiving, by a Packet Data Convergence Protocol (PDCP) layer, a PDCP Service Data Unit (SDU) from an upper layer; and deleting the PDCP SDU and a PDCP Packet Data Unit (PDU) corresponding to the PDCP SDU upon determining that a discard timer corresponding to the PDCP SDU is not expired and a preset condition is satisfied. The PDCP SDU is mapped to an Unacknowledged Mode (UM) or a Transparent Mode (TM) of a Radio Link Control (RLC) layer. Thus, the PDCP SDU will not reside in a UE cache, thereby reducing cache space occupied by the PDCP SDU.