HARQ Buffer Reset During LTE Transmission Mode Changes
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Solution Overview
Problem
Current LTE specifications do not adequately address data loss and reception failures during transmission mode changes in HARQ operations, particularly due to unclear activation times and buffer handling procedures, leading to potential data loss or failure in UE reception.
Innovation Solution
The proposed solution involves flushing all downlink HARQ buffers at the UE during transmission mode changes and adjusting buffer handling procedures to ensure that the next transmission is considered as the first transmission for each HARQ process, regardless of whether it is a new or retransmitted data block, and using specific DCI formats to ensure reliable data transmission during uncertainty windows.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If transmission mode changes are implemented to enable multiple simultaneous transport blocks, then transmission capacity and productivity are improved, but data loss and reception failures occur during reconfiguration
Solution Approach 1:
The patent applies preliminary action by flushing HARQ buffers before the actual transmission mode change occurs. The eNB signals the UE to flush buffers in advance, ensuring that any pending soft combining operations are cleared before the new transmission mode activates. This prevents data loss that would otherwise occur during the transition period when the UE might be in an inconsistent state between old and new transmission modes.
2Reliability
If HARQ buffers are flushed during transmission mode changes, then data loss is reduced, but transmission time and reconfiguration duration increase
Solution Approach 1:
The buffer flushing is performed as a preliminary action before the transmission mode change, allowing the UE to prepare cleanly for the new mode without delaying the actual mode transition. The eNB coordinates the flushing timing so that it completes before the new transmission mode becomes active, minimizing the impact on overall reconfiguration duration.
Solution Approach 2:
The patent introduces an intermediary mechanism using DCI format 1A as a bridge during the transition period. When the UE is in the process of reconfiguring, the eNB uses DCI format 1A (a simplified DCI format) to ensure reliable downlink transmission until the UE has fully completed buffer flushing and is ready for the new transmission mode. This intermediary approach ensures data integrity during the transition without requiring extended reconfiguration time.
3Productivity
If the eNB applies new transmission mode earlier than UE reconfiguration completion, then transmission efficiency is improved, but reception failures occur due to buffer inconsistency
Solution Approach 1:
The patent applies preliminary action by having the UE flush its HARQ buffers before the eNB actually applies the new transmission mode. This ensures that the UE is in a consistent, clean state when the new mode activates, preventing reception failures that would occur if buffers contained inconsistent data from the old mode.
Solution Approach 2:
The patent uses feedback mechanisms where the UE signals to the eNB when buffer flushing is complete, and the eNB confirms when the new transmission mode is successfully applied. This feedback loop ensures that the eNB and UE are synchronized in their understanding of the current transmission mode, preventing reception failures caused by mismatched expectations.
Data Source
AI summary
A method and device for handling hybrid automatic repeat request (‘HARQ’) operations during transmission mode changes, the method detecting a transmission mode change; and manipulating an HARQ process buffer based on the detecting. Further, a method and network element for handling hybrid automatic repeat request (‘HARQ’) operations during transmission mode changes, the method checking when a user equipment is in a transmission mode uncertainty window; and blocking communications to the user equipment or utilizing a downlink control information format 1A for communications to the user equipment.