PDCP Reordering Mechanism for Dual Connectivity Packet Gaps
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Solution Overview
Problem
In dual connectivity wireless communication systems, PDCP packets experience out-of-order delivery due to differences in data transmission speeds between network points, leading to sequence number gaps, which complicates in-order delivery to upper layers, especially during radio link degradation or data loss.
Innovation Solution
A method is introduced to detect and manage sequence number gaps by triggering a reordering process and using timers to ensure PDCP SDUs are delivered in ascending order, utilizing COUNT numbers for reordering and timer-based delivery mechanisms to handle gaps and data loss scenarios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If packets are multiplexed onto two different radio links in dual connectivity, then data transmission speed and system performance are improved, but packet delivery order is compromised due to different transmission speeds
Solution Approach 1:
The patent introduces a reordering buffer as an intermediary component between the PDCP layer and upper layers. This buffer receives out-of-order packets from the RLC layer and systematically reorders them before delivery to upper layers, thereby resolving the contradiction between high-speed multiplexed transmission and reliable in-order delivery.
Solution Approach 2:
The patent implements preliminary reordering actions by detecting sequence number gaps at the PDCP layer and triggering reordering processes before packets are delivered to upper layers. This anticipatory approach ensures that even though packets arrive out-of-order due to dual connectivity, they are reordered in advance to maintain correct sequence.
2Stability of the object's composition
If reordering is performed in RLC layer, then in-sequence delivery of RLC SDUs is guaranteed, but PDCP SDU reordering is still needed due to sequence number gaps from multiple HARQ processes
Solution Approach 1:
The patent extracts the reordering function from the RLC layer and relocates it to the PDCP layer. By implementing reordering at the PDCP layer rather than relying solely on RLC layer reordering, the system can handle sequence number gaps caused by multiple HARQ processes more effectively, while simplifying the overall protocol structure.
Solution Approach 2:
The patent employs feedback mechanisms where the PDCP layer monitors sequence number gaps and triggers reordering processes based on detected anomalies. This feedback-driven approach allows the system to dynamically adjust reordering operations based on actual packet arrival patterns, reducing unnecessary reordering complexity.
3Productivity
If X2 flow control is used to send RLC PDUs in batches, then transmission efficiency is improved, but sequence number gaps are created causing out-of-order delivery
Solution Approach 1:
The patent introduces the reordering buffer as an intermediary that receives batched RLC PDUs from the RLC layer and systematically reorders them based on sequence numbers before delivering to upper layers. This mediator component allows batched transmission to maintain efficiency while ensuring sequence number continuity is restored at the PDCP layer.
Solution Approach 2:
The patent implements preliminary detection and correction actions by monitoring sequence number gaps at the PDCP layer and triggering reordering processes before packets are delivered to upper layers. This anticipatory approach compensates for the sequence disruptions introduced by X2 flow control batching.
Data Source
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AI summary
Apparatus and methods are provided to reorder PDCP SDUs. In one novel aspect, a timer-based PDCP reordering process is triggered upon detecting a PDCP gap existing condition, which indicates an SN gap between the PDCP SDUs of two parallel RLC entities larger than zero. The PDCP gap-closing condition is detected when the last-delivered SDU COUNT number plus one equals to the next-expected SDU COUNT number. In one embodiment, all the stored PDCP SDUs with consecutive COUNT numbers starting from the received SDU COUNT number are delivered upon detecting the PDCP gap-closing condition. In another novel aspect, a reordering timer is started upon detecting the PDCP gap condition. In one embodiment, the expiration of the reordering timer triggers the delivery of SDUs to upper layers. In one embodiment, the UE is configured with dual connectivity and the reordering SDU COUNT numbers and the reordering timers are associated with different connectivity configured.