HARQ Buffer Handling During LTE Transmission Mode Changes
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Solution Overview
Problem
Current LTE technologies face issues with data loss and reception failures during transmission mode changes due to the lack of clear procedures for HARQ process reconfiguration and buffer management, particularly when transitioning between different numbers of transport blocks per subframe.
Innovation Solution
The proposed solution involves flushing all downlink HARQ buffers at the UE during transmission mode changes, especially when the number of transport blocks per HARQ process changes, and using specific DCI formats to ensure reliable data transmission during uncertainty windows, along with buffer repartitioning and retention strategies to maintain data integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If transmission mode changes are implemented to support multiple transport blocks, then data transmission capacity is improved, but data loss occurs during mode transitions due to HARQ buffer management issues
Solution Approach 1:
The patent applies preliminary action by flushing HARQ buffers before transmission mode changes occur. The UE receives a transmission mode change indication and proactively flushes all downlink HARQ buffers in advance, ensuring that stale data is cleared before the mode transition, thereby preventing data loss while enabling the productivity improvement of multiple transport blocks
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the state of HARQ buffers based on transmission mode. When transitioning to a mode supporting multiple transport blocks, the system changes the buffer state from retaining data to flushing data, and uses DCI format parameters (such as NDI toggling) to indicate whether to flush or retain buffers, thereby resolving the reliability issue while maintaining productivity gains
2Reliability
If HARQ buffers are flushed during transmission mode changes, then data loss is minimized, but retransmission efficiency decreases due to loss of soft combined data
Solution Approach 1:
The patent applies partial action by selectively flushing only those HARQ buffers that contain stale data associated with the old transmission mode, while retaining buffers that contain valid data needed for retransmissions. This partial flushing approach maintains data integrity for necessary retransmissions while clearing out obsolete data, thereby balancing reliability improvement with productivity preservation
Solution Approach 2:
The patent uses feedback mechanisms through DCI formats to communicate with the UE about buffer flushing decisions. The eNB sends DCI indications that provide feedback on whether the UE should flush or retain HARQ buffers, allowing the system to optimize the balance between data integrity and retransmission efficiency based on current transmission conditions and mode transition requirements
3Reliability
If DCI formats are used to indicate buffer flushing during transmission mode changes, then data transmission reliability is improved, but system complexity increases due to additional signaling
Solution Approach 1:
The patent applies universality by using existing DCI formats for multiple purposes: they continue to indicate transport block assignments and modulation schemes while also indicating HARQ buffer flushing decisions. This multi-functionality allows the system to improve data transmission reliability through explicit buffer management signaling without adding separate dedicated signaling channels, thereby limiting the increase in system complexity
Solution Approach 2:
The patent uses DCI formats as an intermediary mechanism between the eNB and UE to coordinate buffer management during mode transitions. The DCI serves as a mediator that carries implicit or explicit buffer flushing indications, enabling reliable data transmission coordination without requiring direct complex negotiation protocols between the eNB and UE, thus managing signaling complexity while improving reliability
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.