Flexible TDD HARQ-ACK Feedback via Cross-Subframe Scheduling
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Solution Overview
Problem
In flexible-TDD systems, the timing coupling between UL grant and DL transmission scheduling causes issues with HARQ-ACK feedback, leading to inefficiencies in resource utilization, particularly in small cells with rapidly changing traffic conditions, as existing methods do not adapt dynamically to instantaneous traffic situations.
Innovation Solution
A signaling method that allocates TDD UL-DL configurations for wireless communication systems, allowing UL subframes to carry HARQ-ACK feedback for multiple DL and special subframes, with UL grants sent on corresponding DL or special subframes within the DL association set, and schedules PDCCH/EPDCCH transmissions only on subframes not after the UL grant, using cross-subframe scheduling to improve timing alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If semi-static UL-DL configuration is used, then system complexity is reduced and compatibility is improved, but resource utilization efficiency deteriorates due to inability to adapt to instantaneous traffic conditions
Solution Approach 1:
The patent implements dynamic TDD UL-DL configuration that can be changed on a radio frame basis, allowing the system to adapt to instantaneous traffic conditions. The eNB can dynamically reconfigure UL-DL subframe assignments based on current traffic demands, moving from static semi-persistent configuration to flexible dynamic configuration that responds to real-time network conditions.
Solution Approach 2:
The patent introduces downlink assignment index (DAI) signaling in advance to inform UEs about the number of downlink subframes requiring HARQ-ACK feedback. This preliminary indication allows UEs to prepare appropriate feedback configurations before the actual feedback transmission, enabling dynamic adaptation while maintaining systematic control.
2Productivity
If dynamic TDD reconfiguration is implemented, then resource utilization efficiency is improved, but HARQ timing synchronization deteriorates due to frequent configuration changes
Solution Approach 1:
The patent applies preliminary action by sending DAI signaling in advance in downlink subframes to indicate the total number of downlink subframes that require HARQ-ACK feedback. This allows the UE to know beforehand how many acknowledgments to prepare, ensuring proper timing synchronization even when TDD configurations change dynamically. The DAI provides forward-looking information that prevents timing conflicts.
Solution Approach 2:
The patent implements enhanced feedback mechanisms where the DAI information is fed back to UEs through downlink control channels, enabling them to adjust their HARQ-ACK feedback timing and content accordingly. This feedback loop ensures that dynamic configuration changes do not disrupt the reliability of HARQ timing synchronization.
3Adaptability or versatility
If cross-subframe scheduling is used, then scheduling flexibility is improved, but timing coupling issues worsen causing HARQ-ACK feedback errors
Solution Approach 1:
The patent applies preliminary action by incorporating DAI signaling that indicates in advance the number of downlink subframes requiring feedback, even when those subframes are scheduled cross-subframe. This preliminary indication allows the UE to correctly associate feedback with the appropriate downlink transmissions despite the temporal separation between scheduling and data transmission, preventing timing coupling errors.
Solution Approach 2:
The DAI acts as an intermediary parameter that bridges the timing gap created by cross-subframe scheduling. It provides a reference count that mediates between the flexible cross-subframe scheduling mechanism and the rigid HARQ-ACK timing requirements, ensuring accurate feedback association without sacrificing scheduling flexibility.
4Ease of operation
If UL grant is sent on the last DL subframe, then timing alignment is simplified, but resource utilization deteriorates due to restricted scheduling options
Solution Approach 1:
The patent applies preliminary action by sending DAI signaling in advance in earlier downlink subframes rather than waiting for the last DL subframe. This allows the UE to prepare HARQ-ACK feedback earlier and enables more flexible scheduling decisions, improving resource utilization while maintaining timing alignment through the predictive information provided by DAI.
Solution Approach 2:
The patent implements dynamic scheduling where UL grants and DAI signaling can be sent at flexible timings rather than being constrained to the last DL subframe. This dynamic approach allows the eNB to optimize resource allocation based on current traffic conditions while the DAI ensures proper timing alignment is maintained through advance notification.
Data Source
AI summary
There is provided methods for use in control signaling in advanced wireless communication systems that support flexible allocation of TDD UL-DL configurations. Where HARQ-ACK bundling is used, PDCCH/EPDCCH transmissions indicating DL SPS release and PDSCH transmissions with corresponding PDCCH/EPDCCH are scheduled only on DL and/or special subframes in a DL association set which are not after the subframe in the DL association set carrying an UL grant. Where HARQ-ACK multiplexing is used, the value of the DL assignment index (VDAIUL) is set to the number of subframes in the DL association set. Cross-subframe scheduling is also used.