HARQ-ACK Response Windows for Unlicensed Carrier LBT
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Solution Overview
Problem
In wireless communication systems, particularly in LTE TDD and LAA configurations, HARQ-ACK feedback transmissions on unlicensed carriers face challenges due to unpredictable channel access and poorer channel quality, leading to reduced DL throughput performance when LBT fails, as they are not transmitted on the LAA secondary cell uplink.
Innovation Solution
Implementing a response window with multiple subframes for HARQ-ACK feedback opportunities, allowing multiple attempts for transmission after successful LBT, and using techniques like time or spatial bundling to compress multiple HARQ-ACKs, enhancing transmission chances and improving DL throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If HARQ-ACK feedback is transmitted on unlicensed carriers, then DL throughput can be improved through additional transmission capacity, but transmission reliability deteriorates due to unpredictable channel access and LBT failures
Solution Approach 1:
The patent implements a dynamic response window mechanism that adapts to LBT outcomes. When LBT succeeds, the response window is activated for HARQ-ACK transmission; when LBT fails, the window is deferred to subsequent subframes. This dynamic adaptation allows the system to exploit unlicensed carrier opportunities when available while maintaining reliability through fallback options.
Solution Approach 2:
The patent establishes a pre-configured response window structure with multiple subframes before HARQ-ACK transmission is actually attempted. This preliminary setup includes defining the window parameters, identifying candidate subframes, and preparing the transmission opportunity in advance, allowing the system to quickly react when LBT succeeds without delaying the feedback timing.
2Measurement precision
If multiple HARQ-ACK feedback bits are transmitted separately, then acknowledgment accuracy is improved, but transmission overhead increases and reliability decreases due to multiple LBT attempts required
Solution Approach 1:
The patent applies bundling techniques that combine multiple HARQ-ACK feedback bits into a single transmission unit. Time-domain bundling aggregates ACK/NACK information across multiple subframes, while spatial bundling combines feedback from multiple antenna ports. This merging reduces the number of separate LBT attempts needed while preserving the essential acknowledgment information.
Solution Approach 2:
The patent changes the parameter of HARQ-ACK feedback granularity by introducing bundling options. Instead of transmitting individual ACK/NACK bits separately, the system transforms multiple bits into bundled feedback units, altering the information structure to reduce transmission overhead and improve reliability through fewer LBT attempts.
3Adaptability or versatility
If HARQ-ACK feedback timing follows standard LTE timing, then system compatibility is maintained, but transmission opportunities are lost when LBT fails in the scheduled subframe
Solution Approach 1:
The patent implements dynamic timing adjustment that maintains compatibility with standard LTE HARQ timing while adapting to unlicensed carrier conditions. The response window mechanism allows the system to shift HARQ-ACK transmission to alternative subframes within the window when the originally scheduled subframe's LBT fails, thereby preserving throughput without breaking system compatibility.
Data Source
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AI summary
Apparatuses, methods, and systems are disclosed for data acknowledgment. One apparatus includes a transmitter that transmits data to a device. The apparatus may include a processor that determines a response window having multiple subframes for receiving an acknowledgement corresponding to the data. The apparatus may include a receiver that receives the acknowledgement within the response window.