HARQ ACK+ Feedback for 5G Sidelink Outer Loop Adaptation
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Solution Overview
Problem
Current 5G wireless systems face challenges in efficiently implementing hybrid automatic repeat requests (HARQ) for outer loop adaptation in new radio sidelink communication, particularly due to the high cost and resource consumption associated with CSI feedback, which complicates scheduling and degrades sidelink performance.
Innovation Solution
The introduction of a smart HARQ feedback mechanism, including a new state called 'ACK+', which allows user equipment (UE) to indicate support for more aggressive modulation and coding schemes, enabling finer granularity in link adaptation and reducing the need for extensive CSI feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional CSI feedback is used for link adaptation, then link quality can be monitored, but resource consumption and system complexity increase significantly
Solution Approach 1:
The patent extracts the essential feedback information needed for link adaptation from the complex CSI feedback mechanism. Instead of using full CSI feedback, the invention uses only HARQ acknowledgments (ACK/NACK) which are already part of the standard protocol, thereby removing unnecessary complexity while retaining the core functionality of link quality monitoring.
Solution Approach 2:
The system uses existing HARQ feedback mechanisms to serve the dual purpose of error correction and link adaptation. The HARQ ACK/NACK signals, originally designed for retransmission control, are repurposed to provide link quality information for outer loop adaptation, eliminating the need for separate CSI feedback channels.
2Measurement precision
If extensive CSI feedback is implemented, then link adaptation accuracy improves, but spectrum efficiency decreases due to resource consumption
Solution Approach 1:
The patent implements a feedback-based outer loop adaptation mechanism that uses HARQ acknowledgments to adjust the target block error rate (BLER). The system continuously monitors HARQ feedback and dynamically adjusts the modulation and coding scheme (MCS) to maintain optimal link adaptation without requiring extensive CSI feedback, thereby preserving spectrum efficiency.
Solution Approach 2:
The invention changes the adaptation parameter from CSI-based to HARQ-based feedback. By using the presence or absence of HARQ acknowledgments as the adaptation signal, the system achieves link adaptation accuracy while minimizing resource consumption and maintaining high spectrum efficiency.
3Productivity
If HARQ feedback is used for outer loop adaptation, then resource consumption is reduced, but link adaptation granularity becomes coarser
Solution Approach 1:
The patent implements a dynamic outer loop adaptation mechanism that adjusts the target BLER based on HARQ feedback patterns. The system dynamically modifies the MCS selection to compensate for the coarser granularity of HARQ-based feedback, thereby achieving fine-tuned link adaptation while maintaining resource efficiency.
Solution Approach 2:
The system performs preliminary MCS selection based on channel conditions and then refines the selection using HARQ feedback from previous transmissions. This two-stage approach allows the system to achieve fine link adaptation granularity by combining preliminary estimation with feedback-driven refinement, without requiring extensive real-time CSI feedback.
Data Source
AI summary
Intelligent hybrid automatic repeat request (HARQ) feedback can better support link adaption. Thus, in addition to the traditional HARQ feedback, which is to relay acknowledgement (ACK) and negative acknowledgement (NAK) data based on a decoding result, a new state for the HARQ feedback can be represented as “ACK+”. Consequently, ACK+ can be used to indicate to the network that a modulation and coding scheme (MCS) of a current data packet is too conservative, and the user equipment (UE) is capable of supporting a more aggressive MCS.