LTE Handover PDCP-SDU Sequence Number Reporting
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Solution Overview
Problem
In the LTE system, redundant re-transmissions of Packet Data Convergence Protocol-Service Data Units (PDCP-SDUs) during cell handover lead to a waste of precious radio resources due to the lack of accurate acknowledgment and sequence number reporting between the Source Evolved Node B (S_eNB) and the User Equipment (UE).
Innovation Solution
The method involves the S_eNB sending a PDCP-SDU Sequence Number (SN) report to the Target Evolved Node B (T_eNB), which then informs the UE of the received SNs, allowing the UE to discard and avoid re-transmitting PDCP-SDUs that have been successfully received by the S_eNB, thereby reducing redundant re-transmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE re-transmits PDCP-SDUs based on ACK reception status, then data reliability is improved, but radio resources are wasted due to redundant re-transmissions
Solution Approach 1:
The patent implements a feedback mechanism where the S_eNB sends ACKs to the UE for successfully received PDCP-SDUs. The UE uses this feedback information to determine whether to re-transmit data, thereby avoiding redundant re-transmissions while maintaining data reliability.
Solution Approach 2:
The patent applies preliminary action by having the S_eNB send ACKs in advance for successfully received PDCP-SDUs before the handover is complete. This allows the UE to prepare the re-transmission list accurately, excluding already successfully transmitted data, thus preventing radio resource waste.
2Reliability
If the S_eNB forwards all received PDCP-SDUs to the T eNB, then data completeness is improved, but redundant data causes resource waste
Solution Approach 1:
The patent extracts the ACK information from the overall data transmission process. The S eNB separates the successfully received PDCP-SDUs (for which ACKs are sent) from those that need re-transmission, and this extracted information is used to construct an accurate re-transmission list, preventing redundant data forwarding.
Solution Approach 2:
The patent introduces ACKs as an intermediary mechanism between the S eNB and UE. These ACKs serve as a mediator that carries information about successfully received data, enabling the UE to accurately identify which data should be re-transmitted and which should be excluded, thus preventing radio resource waste.
3Reliability
If the UE transmits all unacknowledged PDCP-SDUs during handover, then data reliability is improved, but transmission efficiency deteriorates
Solution Approach 1:
The patent applies partial action by having the UE transmit only the necessary PDCP-SDUs that truly need re-transmission. The UE uses the ACK information to partially filter the re-transmission list, excluding already successfully transmitted data, thereby improving transmission efficiency while maintaining reliability.
Solution Approach 2:
The patent uses feedback from ACKs to optimize the re-transmission process. The UE receives feedback about successfully received data and adjusts its re-transmission behavior accordingly, transmitting only the necessary data and avoiding redundant transmissions, thus improving transmission efficiency.
Data Source
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AI summary
A method and device for indicating data re-transmission when area switching in LTE system, wherein the method comprises the following steps: S_eNB sends PDCP-SDU CN report to T_eNB in order to announce PDCP-SDU SN received, and T_eNB announces PDCP-SDU SN received by S_eNB to UE. Thereby, UE would not re-transmit PDCP-SDU corresponding to received SN, which avoids re-transmission of useless PDCP-SDU, and saves radio resources comparing with prior solutions.