PDCP Sequence Number Reconfiguration for Lossless HFN Synchronization
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Solution Overview
Problem
Current communication systems face challenges in lossless bearer reconfiguration, particularly when transitioning from a longer to a shorter sequence number in PDCP, leading to potential HFN desynchronization issues due to incorrect inference of packet data units and integrity verification.
Innovation Solution
Implementing specific actions at both data-receiving and data-transmitting PDCP entities to adjust state variables and reconfigure sequence number lengths, including resetting count values and discarding or buffering SDUs, to ensure correct HFN inference and ordered delivery during the reconfiguration process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the PDCP sequence number length is reconfigured to a shorter value to reduce header size and improve transmission efficiency, then transmission efficiency is improved, but HFN desynchronization problems occur due to more than half of the SN space being in flight
Solution Approach 1:
The patent applies preliminary action by performing a mass-discard of service data units (SDUs) at the transmitting PDCP entity before or during the reconfiguration to ensure that no more than half of the new shorter SN space will be in flight. This proactive clearing of buffers prevents HFN desynchronization from occurring in the first place, allowing the shorter SN length to be adopted without compromising reliability.
Solution Approach 2:
The patent changes the PDCP sequence number length parameter from a longer value to a shorter value during reconfiguration. This parameter change reduces the header size and improves transmission efficiency, but is accompanied by controlled actions (mass-discard) to maintain HFN synchronization reliability during the transition.
2Quantity of substance
If more than half of the newly adopted shorter SN space is allowed in flight to maximize utilization, then transmission capacity is improved, but the data-receiving entity cannot correctly infer HFN values
Solution Approach 1:
The receiving PDCP entity performs preliminary actions by determining whether more than half of the shorter SN space would be in flight and, if so, discarding received SDUs with higher count values. This ensures that the HFN can be correctly inferred from the shorter SN without ambiguity, maintaining measurement precision while allowing maximum safe utilization of the SN space.
Solution Approach 2:
The patent implements feedback mechanisms where the receiving entity monitors the count values and SN space utilization, and when thresholds are exceeded, triggers discarding actions. This feedback loop ensures that HFN inference accuracy is maintained while maximizing the use of available SN space for data transmission.
3Reliability
If SDUs are discarded to prevent HFN desynchronization during reconfiguration, then HFN synchronization is maintained, but data loss occurs
Solution Approach 1:
The patent applies preliminary action by performing the mass-discard of SDUs as a controlled, coordinated operation during the reconfiguration process. Rather than discarding SDUs due to errors or failures, the system proactively manages the discard timing and scope to maintain HFN synchronization while minimizing unnecessary data loss. The discard is performed only when necessary to prevent desynchronization.
Solution Approach 2:
The reconfiguration event itself, which changes the SN length parameter, triggers the controlled discard operation. This parameter change necessitates the discard to maintain synchronization, but the patent manages this transition to minimize data loss by coordinating the discard with the reconfiguration timing and ensuring only necessary SDUs are discarded.
4Device complexity
If the PDCP entity refrains from retransmitting SDUs during reconfiguration to avoid complexity, then device complexity is reduced, but data delivery reliability deteriorates
Solution Approach 1:
The patent applies preliminary action by completing the mass-discard of SDUs before or during the reconfiguration, ensuring that the transmitting entity's buffer is cleared of SDUs that could cause HFN desynchronization. This preliminary clearing eliminates the need for complex retransmission control logic during reconfiguration, as there are no conflicting SDUs to manage, thereby maintaining data delivery reliability without increasing device complexity.
Data Source
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AI summary
Various communication systems may benefit from appropriate handling of reconfiguration. For example, certain wireless communication systems may benefit from lossless bearer reconfiguration when handling a transition from the user of a longer sequence number to a shorter sequence number. A method can include determining, by a protocol entity, if a next expected highest count value among count values associated with protocol data units received is more than a pre-defined limit ahead of a lowest count value among count values associated with protocol data units expected to be received. The method can also include resetting the next expected highest count value to a new value corresponding to a predefined upper limit, conditional on the determination.