Multi-Grant Scheduling for HARQ and Random Access in 5G NR-U
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Solution Overview
Problem
In wireless communication systems, especially in shared radio frequency spectrum, the listen-before-talk (LBT) procedure can lead to delayed success, causing puncturing of data transmissions, which degrades decoding performance and increases interference in 5G NR-U networks, affecting the reliability and efficiency of random access and HARQ processes.
Innovation Solution
Implementing multiple transmission occasions and repetition rules for random access and HARQ processes, allowing UEs to repeat transmissions based on LBT outcomes, and associating each transmission occasion with specific HARQ processes to minimize interference and ensure successful decoding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LBT procedure is performed before scheduled transmission, then channel access is ensured, but transmission delay increases and data puncturing occurs
Solution Approach 1:
The base station performs LBT procedure in advance to acquire channel occupancy time (COT) before scheduling uplink transmissions. This preliminary channel acquisition allows the BS to allocate multiple transmission occasions within the reserved COT period, enabling UEs to transmit without performing their own LBT procedures, thus eliminating transmission delays while ensuring reliable channel access.
Solution Approach 2:
The uplink transmission opportunity is segmented into multiple transmission occasions within the BS's COT period. Each transmission occasion can be independently allocated to different UEs or HARQ processes. This segmentation allows efficient utilization of the pre-acquired channel while providing flexibility to handle multiple transmissions without requiring repeated LBT procedures.
2Reliability
If multiple transmission occasions are allocated, then transmission reliability improves, but resource allocation complexity increases
Solution Approach 1:
Multiple transmission occasions are combined into a single uplink grant message sent from the base station to the UE. The grant includes information about multiple transmission occasions within the BS's COT, allowing the UE to transmit multiple times without receiving separate grants for each occasion. This merging approach improves transmission reliability while minimizing scheduling complexity at both the BS and UE.
Solution Approach 2:
The base station's pre-acquired channel occupancy time serves as a self-service mechanism that automatically reserves multiple transmission occasions for uplink transmissions. Once the BS performs LBT and acquires COT, the channel is effectively reserved for its scheduled UEs without requiring additional LBT procedures or complex coordination, simplifying the overall resource allocation process.
3Productivity
If puncturing is applied to fit transmission in remaining time, then transmission occurs, but decoding performance degrades
Solution Approach 1:
The base station performs LBT and acquires channel occupancy time in advance before scheduling uplink transmissions. This preliminary action ensures that the channel is reserved and available for the entire scheduled transmission period, eliminating the need for puncturing. UEs can transmit complete data blocks without time constraints, maintaining full decoding performance while ensuring transmission execution.
Data Source
AI summary
Wireless communications systems and methods related to multi-grant scheduling are provided. A user equipment (UE) receives, from a base station (BS), an uplink (UL) scheduling grant indicating one or more transmission occasions. The UE performs a category 2 (CAT2) listen-before-talk (LBT) based on the one or more transmission occasions being within a channel occupancy time (COT) of the BS. The UE transmits one or more UL transmissions during the one or more transmissions occasions based on the CAT2 LBT.