Sidelink HARQ Codebook Construction Using SAI-Based Feedback
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Solution Overview
Problem
Existing wireless communication systems face challenges in efficiently constructing Hybrid Automatic Repeat reQuest (HARQ) codebooks for Sidelink (SL) transmissions, particularly in scenarios where HARQ-ACK feedback is not received from all receiving UEs, leading to uncertainties in resource allocation and scheduling decisions by the Base Station.
Innovation Solution
A method and apparatus for constructing HARQ codebooks by a User Equipment (UE) that involves receiving SL PDCCH scheduling information, obtaining a SL Assignment Indicator (SAI) field, and consolidating HARQ-ACK bits based on SAI values and PSFCH resource indices to ensure accurate feedback to the Base Station, even in cases of incomplete HARQ-ACK feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If HARQ codebook construction uses traditional methods without SAI field, then the structure is simpler, but the reliability of scheduling decisions deteriorates due to uncertain resource allocation when HARQ-ACK feedback is incomplete
Solution Approach 1:
The SAI field performs preliminary counting and tracking of received PDCCHs before the HARQ codebook is fully constructed. This advance preparation ensures that even when HARQ-ACK feedback is incomplete, the Base Station has already established the correct codebook size and structure through the SAI field's accumulation counter, eliminating scheduling uncertainties.
Solution Approach 2:
The SAI field establishes a feedback mechanism where the UE reports the accumulative number of received PDCCHs to the Base Station. This feedback loop allows the Base Station to dynamically adjust the HARQ codebook construction based on actual reception status, ensuring reliable scheduling decisions even when not all HARQ-ACK feedback is received.
2Measurement precision
If the UE waits for complete HARQ-ACK feedback before constructing the codebook, then the codebook accuracy is improved, but the time delay increases
Solution Approach 1:
The SAI field performs preliminary counting of received PDCCHs and provides this information to the UE before the HARQ codebook construction is complete. This allows the UE to construct an accurate codebook based on the SAI field's accumulation counter rather than waiting for all HARQ-ACK feedback, significantly reducing time delay while maintaining codebook accuracy.
Solution Approach 2:
The SAI field acts as an intermediary between the Base Station's scheduling decisions and the UE's codebook construction. It provides intermediate information (the accumulative count of received PDCCHs) that enables the UE to accurately construct the codebook without waiting for complete HARQ-ACK feedback, thus bridging the time gap while maintaining precision.
3Speed
If the Base Station schedules resources without accurate HARQ-ACK feedback, then the scheduling speed is improved, but the resource allocation efficiency deteriorates
Solution Approach 1:
The SAI field creates a feedback mechanism that provides the Base Station with information about how many PDCCHs were successfully received. This feedback enables the Base Station to schedule resources more efficiently by adjusting the codebook size based on actual reception status, maintaining both high scheduling speed and resource allocation efficiency even when not all HARQ-ACK feedback is received.
Solution Approach 2:
The HARQ codebook construction becomes dynamic through the SAI field, allowing the codebook size to adapt based on the number of received PDCCHs. This dynamic adjustment enables the Base Station to optimize resource allocation efficiency in real-time while maintaining fast scheduling speed, as the codebook automatically adjusts to the actual transmission state rather than using a fixed size.
Data Source
AI summary
A method, performed by a UE, includes receiving a first Sidelink (SL) Physical Downlink Control Channel (PDCCH) from a Base Station (BS), wherein the first SL PDCCH provides scheduling information for at least one SL transmission; obtaining a value of a SL Assignment Indicator (SAI) field from the first SL PDCCH, wherein the value of the SAI field indicates an accumulative number of a first received SL PDCCHs up to the first SL PDCCH; and constructing a Hybrid Automatic Repeat reQuest (HARQ) codebook for a first quantity of SL transmission (s) scheduled by a second quantity of a second received SL PDCCHs; wherein the HARQ codebook is transmitted to the BS from the UE, the first quantity of the SL transmission (s) includes the at least one SL transmission, the second received SL PDCCHs include the first received SL PDCCHs, and the first received SL PDCCHs include the first SL PDCCH.