HARQ Feedback Adaptation via CBG Segmentation
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Solution Overview
Problem
Current wireless communication systems face challenges in efficiently managing receiver feedback for hybrid automatic repeat request (HARQ) processes, particularly in determining the optimal format, content, type, and timing of feedback, which affects the reliability and efficiency of codeblock group (CBG) and transport block (TB) based HARQ operations.
Innovation Solution
The system determines receiver feedback based on the HARQ processing state, including the sequence, link quality, demodulation performance, and number of successfully decoded codeblocks, and configures wireless transmit/receive units (WTRUs) to adaptively allocate resources for HARQ feedback, using minislots for retransmissions and varying CB-to-CBG mapping strategies to minimize retransmissions and optimize feedback reporting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If TB-based HARQ feedback is used, then feedback overhead is reduced, but retransmission efficiency deteriorates
Solution Approach 1:
The transport block is divided into multiple code block groups (CBGs), and HARQ feedback is provided at the CBG level rather than the entire TB level. This segmentation allows selective retransmission of only the failed CBGs, reducing feedback overhead while improving retransmission efficiency by avoiding retransmission of successfully decoded portions.
Solution Approach 2:
Different feedback strategies are applied to different CBGs based on their decoding status. Successfully decoded CBGs are acknowledged with ACK, while failed CBGs receive NACK and are scheduled for retransmission. This localized quality approach optimizes resource utilization by focusing retransmission efforts only where needed.
2Productivity
If CBG-based HARQ feedback is used, then retransmission efficiency is improved, but feedback complexity increases
Solution Approach 1:
The feedback mechanism is segmented into CBG-level acknowledgments, where each CBG receives individual ACK/NACK feedback. This segmentation improves retransmission efficiency by enabling selective retransmission while managing complexity through standardized feedback formats and procedures for each CBG group.
Solution Approach 2:
The system dynamically adapts the number of CBGs and their sizes based on transport block size, code rate, and channel conditions. This dynamic configuration allows the system to optimize between feedback granularity and complexity, adjusting the CBG structure to match current transmission requirements and reduce unnecessary feedback overhead.
3Productivity
If adaptive resource allocation is used, then resource utilization is optimized, but scheduling complexity increases
Solution Approach 1:
The system employs dynamic resource allocation where the number and size of CBGs are adapted based on transport block size, code rate, and channel conditions. This dynamic approach optimizes resource utilization by matching feedback granularity to actual transmission needs, while base station coordination manages the scheduling complexity through centralized decision-making.
Solution Approach 2:
The system changes key parameters such as the number of CBGs, CBG size, and feedback timing based on channel conditions and traffic requirements. These parameter adjustments enable optimized resource utilization across varying network conditions while maintaining manageable complexity through standardized parameter sets and configuration procedures.
4Loss of time
If minislots are used for retransmission, then latency is reduced, but synchronization complexity increases
Solution Approach 1:
The retransmission process is segmented into minislot-based opportunities, allowing rapid retransmission of failed CBGs without waiting for full slot boundaries. This segmentation reduces latency by enabling faster feedback and retransmission cycles, while standardized minislot structures manage synchronization complexity through predefined timing relationships.
Data Source
AI summary
Systems, methods, and instrumentalities are disclosed for receiver feedback in wireless systems. Receiver feedback format, content, type and/or timing may be determined as a function of, for example, at least one of a type of soft-combining processing to apply in a HARQ process, a HARQ operating point for the HARQ process, one or more reference transmissions for controlling a type of HARQ feedback for the HARQ process, and a feedback suppression parameter for one or more transmissions in a sequence associated with the HARQ process or a transport block (TB). Uniform and non-uniform CB-to-CBG mapping may be provided (e.g., by a WTRU) based on, for example, one or more parameters, interference and channel conditions and/or a probability of or actual pre-empting transmissions. A CB to CBG mapping indication may be provided, for example, in support of selecting a CB to CBG mapping from multiple CB to CBG mappings. Intra- and inter-WTRU interference/preemption indications may be provided.