PDCP Sequence Gap Detection to Reduce RLC Retransmissions
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Solution Overview
Problem
In wireless communication systems, the process of PDCP reordering can lead to unnecessary RLC retransmissions due to missing PDU sequence numbers, causing deciphering failures and inefficient bandwidth usage.
Innovation Solution
The PDCP layer identifies sequence gaps and triggering conditions, such as reordering timer expiration or memory limits, to update the RLC reception buffer, skipping missing PDUs and reducing the need for HARQ retransmissions by indicating the last received PDU's sequence number to the RLC layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the RLC layer requests retransmission of missing PDUs during PDCP reordering, then data completeness is improved, but unnecessary retransmissions increase causing bandwidth waste and power consumption
Solution Approach 1:
The PDCP layer provides feedback information (indication) to the RLC layer about the reception buffer status and sequence gaps. This feedback mechanism allows the RLC layer to understand which PDUs are actually needed, preventing unnecessary retransmissions while ensuring data completeness.
Solution Approach 2:
The PDCP layer acts as an intermediary between the RLC layer and upper layers. It receives PDUs from the RLC layer, performs reordering, and manages the reception buffer. This intermediary role allows it to filter out unnecessary retransmission requests by informing the RLC layer about sequence gaps and buffer status.
2Reliability
If the RLC reception buffer is updated continuously to track missing PDUs, then data integrity is improved, but system complexity increases
Solution Approach 1:
The RLC layer updates its reception buffer autonomously based on the indication from the PDCP layer. When the PDCP layer detects a sequence gap, it provides an indication to the RLC layer, which then self-updates its reception buffer to reflect the last successfully received PDU, reducing the need for continuous complex coordination.
Solution Approach 2:
The reception buffer is updated by changing its parameter (the sequence number of the last received PDU) based on triggering conditions such as sequence gap detection or timer expiration. This parameter change approach simplifies the buffer management while maintaining data integrity.
3Reliability
If the RLC layer maintains a reception buffer to track received PDUs, then data completeness is improved, but memory usage increases
Solution Approach 1:
The RLC reception buffer is updated to discard entries for PDUs that are no longer needed. When the PDCP layer provides an indication of the last received PDU, the RLC layer can discard buffer entries beyond this point, freeing memory while maintaining completeness of necessary data through selective retention.
Data Source
AI summary
Methods, systems, and devices for wireless communications are described. A receiving device may receive, at a first operational layer of the receiving device, one or more protocol data units (PDUs) within a set of PDUs. The receiving device may identify, at a second operational layer of the receiving device, a sequence gap associated with a missing PDU from the set of PDUs, the first operational layer being a lower operational layer of the receiving device than the second operational layer. The receiving device may determine, at the second operational layer, that a triggering condition associated with the missing PDU has occurred. The receiving device may provide, by the second operational layer and based at least in part on the triggering condition occurring, an indication to update a reception buffer of the first operational layer to a last received protocol data unit of the set of PDUs.