PDCP Window Management for HFN Synchronization in Split Bearers
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Solution Overview
Problem
In dual connectivity communication systems, particularly with packet data convergence protocol (PDCP) in unacknowledged mode (UM), there is a challenge in maintaining hyper-frame number (HFN) synchronization due to lack of acknowledgement, leading to potential HFN desynchronization and packet misinterpretation, especially in scenarios with packet duplication and varying transmission delays across multiple paths.
Innovation Solution
A pulled window mechanism is introduced to manage HFN, where packets received outside the receiving window are considered new, and feedback is provided to the transmitter to adjust the window size based on statistical information, ensuring that only PDCP PDUs within the transmission window are sent, and timers are used to track the oldest PDUs for accurate transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If packet duplication is used across multiple RLC entities in UM mode, then reliability is improved, but HFN desynchronization occurs due to lack of acknowledgement
Solution Approach 1:
The patent implements a feedback mechanism where the receiving PDCP entity monitors the transmission window size and provides feedback to the transmitting PDCP entity. This feedback enables the transmitter to adjust its window size dynamically, ensuring that duplicate packets are properly tracked and acknowledged even in UM mode, thereby preventing HFN desynchronization while maintaining reliability
Solution Approach 2:
The patent introduces a dynamic transmission window size adjustment mechanism. Instead of using a fixed window size, the window size is adapted based on the reception status of packets across multiple RLC entities. This dynamic adjustment allows the system to maintain proper HFN synchronization while supporting packet duplication for reliability
2Reliability
If multiple transmission paths are used for packet duplication, then reliability is improved, but transmission delay varies across paths
Solution Approach 1:
The patent implements preliminary actions by starting timers for each duplicated PDCP PDU when it is submitted to the lower layer for transmission. These timers track the expected delivery time of packets through different RLC entities, allowing the system to proactively manage timing issues before they cause HFN desynchronization or packet loss
3Productivity
If transmission window size is increased to accommodate multiple paths, then packet delivery is improved, but HFN desynchronization risk increases
Solution Approach 1:
The patent implements dynamic window size adjustment where the transmission window size is not fixed but adapts based on the actual reception status of packets. The window size is increased when packets are successfully received and decreased or held when there are timing concerns, thereby allowing high throughput while preventing HFN desynchronization
Solution Approach 2:
The receiving PDCP entity provides feedback to the transmitting entity about the reception status of packets. This feedback mechanism allows the transmitter to adjust its transmission window size dynamically, ensuring that the window is large enough to accommodate multiple transmission paths for high throughput, but not so large as to cause HFN desynchronization
Data Source
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AI summary
Various communication systems may benefit from the appropriate control of the timing of communication. For example, certain wireless communication systems may benefit from packet data convergence protocol windows, for example in the case of split bearers being in use. A method can include transmitting a plurality of protocol data units over a bearer mapped to a plurality of logical channels. The protocol data units can be transmitted in a radio link control unacknowledged mode. The method can also include managing at least one transmission characteristic of the transmitted plurality of protocol data units.