PDCP Reordering for LTE Handover Efficiency
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Solution Overview
Problem
In mobile communication systems, especially in LTE, handover of ARQ entities is frequent, leading to inefficiencies in communication due to accumulative retransmissions and potential data packet loss or repeated transmission during handover, which complicates the process and reduces efficiency.
Innovation Solution
A method and apparatus that involve transmitting correctly received PDCP PDUs with a special indication for reordering, buffering out-of-sequence PDUs, and selectively retransmitting missing packets to ensure in-sequence delivery, thereby improving communication efficiency during handover by managing the reordering and retransmission of packets between cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If accumulative retransmission is performed in target cell during handover, then complexity of higher layer entity is reduced, but data packets already transmitted in source cell are retransmitted causing communication inefficiency
Solution Approach 1:
The patent segments the retransmission process by introducing a PDCP reordering entity that separates in-sequence delivery from actual packet transmission. This entity buffers out-of-sequence packets and releases them in order, preventing unnecessary retransmissions while maintaining simplicity in the higher layer entity.
Solution Approach 2:
The PDCP reordering entity acts as an intermediary between the RLC layer and higher layers. It receives packets from the RLC layer, reorders them based on PDCP sequence numbers, and delivers them in sequence to higher layers, thereby eliminating the need for accumulative retransmission complexity in the higher layer entity.
2Adaptability or versatility
If ARQ entity is re-established frequently in handover as in LTE, then communication path establishment is improved, but data packet loss or repeated transmission occurs reducing efficiency
Solution Approach 1:
The patent applies preliminary action by having the source eNodeB transmit downlink data packets to the target eNodeB before handover completion. The PDCP reordering entity in the target eNodeB is prepared in advance to handle these packets, ensuring no data loss occurs during the frequent handovers characteristic of LTE.
Solution Approach 2:
The patent ensures continuity of useful action by maintaining the PDCP reordering entity across handovers. This entity continuously buffers and reorders packets, ensuring uninterrupted in-sequence delivery to the UE even as ARQ entities are frequently re-established during LTE handovers.
3Speed
If out-of-sequence packets are immediately delivered to higher layer, then processing speed is improved, but in-sequence delivery requirement is violated causing data integrity issues
Solution Approach 1:
The patent applies dynamics by making the packet delivery process adaptive. The PDCP reordering entity dynamically decides when to release buffered packets based on the arrival of subsequent packets. Once all packets up to a certain sequence number are received, they are released in sequence, optimizing both speed and integrity.
Solution Approach 2:
The patent uses preliminary action by pre-buffering out-of-sequence packets in the PDCP reordering entity. This allows the system to quickly release packets in sequence once they are all received, maintaining high processing speed while ensuring data integrity through in-sequence delivery.
Data Source
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AI summary
Improving communication efficiency in handover re-establishing an ARQ entity in a mobile communication system is disclosed. The method includes transmitting first Packet Data Convergence Protocol (PDCP) Packet Data Units (PDUs) correctly received from the source cell, together with a special indication requiring reordering of the first POCP PDUs, from a Radio Link Control (RLC) receiving buffer to a POCP receiving entity when a handover command message from a source cell to a target cell is received; buffering the first POCP PDUs in a POCP PDU reordering buffer by the POCP receiving entity in response to the special indication; and when a second PDCP PDU is received from the target cell through a new RLC receiving entity for the target cell, outputting third PDCP PDUs up to a PDCP PDU before a first missing PDCP PDU having a sequence number higher than that of the second PDCP PDU from the PDCP reordering buffer. In the method, a POCP entity performs reordering, thereby improving efficiency of communication.