HARQ Feedback Segmentation for NACK DTX Ambiguity Resolution
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Solution Overview
Problem
In wireless communication systems with Carrier Aggregation, the ambiguity in NACK/DTX feedbacks leads to uncertainty for Base Stations, affecting HARQ retransmissions and PDCCH Link Adaptation, resulting in throughput degradation and improper outer-loop adjustments.
Innovation Solution
A method and apparatus for performing HARQ transmission in a downlink from a Base Station to User Equipment, where ambiguous NACK/DTX feedbacks are resolved by setting them as NACK or DTX based on the number of HARQ transmissions, allowing for proper DL assignment and outer-loop adjustment of PDCCH, and achieving Incremental Redundancy combining gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If Carrier Aggregation is implemented to increase throughput, then data transmission rate is improved, but feedback ambiguity between NACK and DTX occurs making it impossible to distinguish the two states
Solution Approach 1:
The feedback bit is segmented into multiple parts: a first feedback bit indicating ACK/NACK status and a second feedback bit indicating DTX status. This segmentation allows the UE to provide differentiated feedback for different reception states, enabling the eNB to accurately distinguish between NACK and DTX without ambiguity.
Solution Approach 2:
The feedback mechanism transitions from a single-dimensional bit (0 or 1) to a two-dimensional feedback space using two separate bits. This dimensional expansion provides additional states to represent different feedback conditions (ACK, NACK, DTX) independently, resolving the ambiguity that existed in the single-bit feedback system.
2Device complexity
If NACK/DTX feedbacks are bundled for multiple codewords to simplify processing, then processing complexity is reduced, but accuracy of HARQ retransmission and Link Adaptation adjustment deteriorates
Solution Approach 1:
The feedback for multiple codewords is segmented into separate feedback bits for each codeword rather than bundled into a single combined feedback. This allows the eNB to receive individual ACK/NACK/DTX information for each codeword, maintaining measurement precision while managing complexity through systematic bit allocation.
Solution Approach 2:
The patent introduces an intermediate feedback mechanism where the UE provides detailed per-codeword feedback that acts as an intermediary between the complex multi-codeword transmission state and the eNB's processing requirements. This intermediary feedback structure preserves accuracy while enabling systematic processing.
3Reliability
If ambiguous NACK/DTX feedbacks are treated as NACK for HARQ retransmission, then retransmission reliability is improved, but system throughput deteriorates due to unnecessary retransmissions
Solution Approach 1:
The feedback is segmented into distinct ACK, NACK, and DTX indicators using separate bits. This allows the eNB to reliably identify when a NACK is truly needed versus when DTX occurred, enabling accurate retransmission decisions that maintain reliability while avoiding unnecessary retransmissions that would reduce throughput.
Solution Approach 2:
Instead of treating all non-ACK feedbacks as NACK (the conventional approach), the patent inverts the logic by explicitly identifying DTX states separate from NACK states. This inversion allows the system to differentiate between cases requiring retransmission (NACK) and cases where no transmission occurred (DTX), optimizing throughput while maintaining reliability.
Data Source
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AI summary
Methods, apparatuses and a user equipment for performing a Hybrid Automatic Repeat Request (HARQ) transmission in a downlink from a base station to at least one user equipment are provided. An exemplary method comprises receiving a HARQ feedback to a HARQ transmission performed with respect to a transport block. The method further comprises determining whether the HARQ feedback is an ambiguous HARQ feedback with respect to a negative acknowledgement or a discontinuous transmission. The method additionally comprises setting (S206) the ambiguous HARQ feedback as the negative acknowledgement or the discontinuous transmission based on the number of HARQ transmissions having been performed and the corresponding received HARQ feedbacks within a target number of HARQ transmissions counting from a first HARQ transmission. With the methods and apparatuses, the ambiguity of the HARQ feedback can be overcome and communication efficiency may be improved.