PDCP Buffer Segmentation for RLC Flow Control
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Solution Overview
Problem
In communication systems, particularly in LTE, the flow control between the PDCP and RLC layers is inefficient, leading to packet loss due to overflow in the RLC buffer, and the 1:1 transmission of ACK signals degrades efficiency when multiple PDUs need acknowledgment.
Innovation Solution
A method and apparatus that separate a partial area of the PDCP buffer to store SDUs for the RLC layer, using threshold-based feedback to control PDU transfer, allowing for efficient storage and acknowledgment of PDUs, thereby reducing packet loss and improving transmission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the PDCP buffer stores SDUs for all sectors, then the PDCP buffer size must be large to accommodate all traffic, but this does not prevent packet loss when RLC buffer overflows temporarily
Solution Approach 1:
The invention segments the PDCP buffer into a first buffer for storing SDUs for handover/RRC reconfiguration and a second buffer for storing SDUs to be transferred to the RLC layer. This segmentation allows independent management of different traffic types, enabling the second buffer to be optimized for RLC buffer overflow prevention while the first buffer handles mobility-related traffic, thus improving packet loss prevention without unnecessarily increasing overall buffer size.
Solution Approach 2:
The invention dynamically adjusts the amount of data stored in the second PDCP buffer based on the current RLC buffer status. When the RLC buffer is full, the PDCP layer stops transferring data to the RLC layer and retains SDUs in the second buffer. When the RLC buffer has available space, data transfer resumes. This dynamic adjustment prevents packet loss due to RLC buffer overflow while optimizing PDCP buffer utilization.
2Adaptability or versatility
If the PDCP layer stores SDUs in the PDCP buffer for handover or RRC reconfiguration, then forwarding capability is improved, but the buffer cannot be used to prevent RLC buffer overflow
Solution Approach 1:
The invention divides the PDCP buffer into two separate buffers: the first buffer dedicated to storing SDUs for handover or RRC reconfiguration, and the second buffer dedicated to storing SDUs for transfer to the RLC layer. This segmentation allows the first buffer to maintain handover forwarding capability while the second buffer can be dynamically managed to prevent RLC buffer overflow, thus resolving the conflict between adaptability and reliability.
3Measurement precision
If the lower layer transmits 1:1 ACK or NACK signals for each received PDU, then acknowledgment accuracy is maintained, but transmission efficiency degrades when multiple PDUs need acknowledgment
Solution Approach 1:
The invention merges multiple individual ACK/NACK signals into a single feedback message that contains acknowledgment information for multiple PDUs. Instead of transmitting separate ACK/NACK signals for each received PDU, the lower layer combines the acknowledgment status of multiple PDUs into one message, thereby maintaining accurate acknowledgment information while significantly improving transmission efficiency when multiple PDUs need acknowledgment.
Data Source
AI summary
An apparatus and a method for flow control between a Packet Data Convergence Protocol (PDCP) layer and a Radio Link Control (RLC) layer in a communication system are provided. The method includes storing Service Data Units (SDUs) to be transferred to the RLC layer, receiving information on a capacity that is currently unused in a buffer of the RLC layer from the RLC layer, and generating Packet Data Units (PDUs) from SDUs, a capacity of which corresponds to the information, among packets stored in a buffer of the PDCP layer, and then transferring the generated PDUs to the RLC layer.