HARQ-ACK Transmission Order Verification in 5G NR
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Solution Overview
Problem
In 5G NR networks, the scheduling of HARQ-ACK based PDSCH transmissions is disrupted due to multiple DL assignments, particularly for PDSCHs configured for downlink semi-persistent scheduling, leading to out-of-order (OOO) issues when PUCCH repetitions collide with DL symbols or SSB symbols, causing delays and invalid transmissions.
Innovation Solution
The user equipment (UE) determines an earliest available slot for PUCCH transmission when the initial slot is unavailable, and verifies that the resource assigned for the second PDSCH's HARQ-ACK transmission does not end before the first PDSCH's resource, ensuring that the order of HARQ-ACK transmissions is maintained by using the resource assigned for the first PDSCH's transmission, even if the second slot is used for the first HARQ-ACK.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PUCCH repetitions are used for HARQ-ACK transmission, then transmission reliability is improved, but out-of-order transmission issues occur when collisions with DL symbols or SSB symbols cause slot unavailability
Solution Approach 1:
The network performs preliminary checking of PUCCH slot availability before assigning resources, verifying that the slot does not collide with DL symbols or SSB symbols. This preventive approach avoids out-of-order transmission issues by ensuring selected slots are valid for PUCCH transmission from the outset.
Solution Approach 2:
The system implements feedback mechanisms where the UE reports slot availability status and collision information to the network. This feedback enables the network to adjust PUCCH slot assignments dynamically, maintaining transmission order while preserving the reliability benefits of PUCCH repetitions.
2Productivity
If multiple DL assignments are scheduled, then network resource utilization is improved, but scheduling order verification becomes complex and error-prone
Solution Approach 1:
The scheduling verification process is segmented into distinct stages: initial slot assignment verification, collision detection with DL/SSB symbols, and sequential ordering validation. This segmentation breaks down the complex multi-assignment verification into manageable steps, reducing errors while maintaining high resource utilization.
Solution Approach 2:
The network performs preliminary verification of scheduling order and slot availability before finalizing multiple DL assignments. By checking resource conflicts and transmission ordering in advance, the system avoids complex post-scheduling corrections while maximizing resource utilization across multiple assignments.
Data Source
AI summary
A user equipment (UE) may generate first HARQ-ACK information bits based on a first PDSCH and second HARQ-ACK information bits based on a second PDSCH. The UE may determine a first slot for an expected PUCCH transmission with the first HARQ-ACK information bits. When the UE is configured for deferring HARQ-ACK for the first PDSCH and when the first slot is unavailable for the expected PUCCH transmission, the UE may determine an earliest second slot that is available. The UE may also determine a third slot for an expected PUCCH transmission with the second HARQ-ACK information bits assigned for the second PDSCH. The resource assigned for transmission of the first HARQ-ACK information bits is used to verify the order for the first and second HARQ-ACK transmissions regardless of whether the first slot is unavailable and the second earliest slot is used for transmission of the first HARQ-ACK information bits.