NACK Triggered Optimization for URLLC Retransmission Reliability
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Solution Overview
Problem
Wireless communication networks, particularly in URLLC-U, face challenges in maintaining high retransmission success rates due to interference and congestion, which are exacerbated by stringent latency and reliability requirements.
Innovation Solution
The method involves a user equipment (UE) determining a failed transmission and transmitting a negative acknowledgment (NACK) in a previously allocated acknowledgement resource, triggering actions such as NACK triggered CSI reporting, switching to a different bandwidth part, or triggering SRS transmission to improve retransmission success rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional transmission methods are used in URLLC-U, then the system can maintain simple operation, but the retransmission reliability deteriorates due to interference and congestion
Solution Approach 1:
The system performs preliminary actions by pre-configuring multiple bandwidth parts (BWPs) and resource allocation patterns before transmission failures occur. When a NACK is received, the UE and gNB automatically switch to pre-configured alternative BWPs or resource patterns, eliminating the need for complex real-time negotiation and reducing overall system complexity while improving retransmission reliability.
Solution Approach 2:
The system dynamically adapts transmission parameters based on real-time feedback. Upon receiving a NACK, the UE triggers dynamic resource reallocation and the gNB dynamically adjusts downlink grants, switching between multiple configured BWPs. This dynamic adaptation enables the system to maintain high retransmission reliability by responding flexibly to interference conditions without requiring overly complex procedural overhead.
2Reliability
If more resources are allocated for retransmission, then the retransmission success rate improves, but the network congestion and interference increase
Solution Approach 1:
The system segments the available bandwidth into multiple distinct bandwidth parts (BWPs), each with its own resource allocation characteristics. When retransmission is needed, the system selects from these segmented portions rather than expanding the total resource pool. This segmentation allows the network to maintain high retransmission success rates by utilizing diverse spatial-frequency resources while avoiding the congestion and interference that would result from uniformly expanding all resources.
Solution Approach 2:
The system changes transmission parameters such as bandwidth part selection, resource block allocation, and modulation schemes based on the specific failure conditions indicated by NACK feedback. By adapting parameters dynamically rather than simply increasing resource allocation, the system achieves improved retransmission success rates while minimizing the harmful effects of network congestion and interference through parameter optimization rather than brute-force resource expansion.
3Speed
If the UE waits for explicit gNB instructions for retransmission, then the protocol simplicity is maintained, but the latency increases
Solution Approach 1:
The UE performs self-service by autonomously triggering retransmission actions upon receiving a NACK, without waiting for explicit gNB instructions. The UE automatically switches to alternative pre-configured BWPs and initiates resource reallocation procedures independently. This self-service capability dramatically reduces latency by eliminating the round-trip time for gNB instructions while the autonomous actions are managed through pre-established configurations that prevent excessive complexity.
Solution Approach 2:
The system performs preliminary configuration of multiple bandwidth parts and retransmission procedures before actual failures occur. When a NACK is received, the UE can immediately execute pre-planned retransmission actions without waiting for gNB instructions. This preliminary action approach reduces latency significantly while the structured pre-configuration ensures that autonomous UE actions remain manageable and do not introduce excessive protocol complexity.
4Measurement precision
If channel state information is reported more frequently, then the adaptation accuracy improves, but the overhead and processing complexity increase
Solution Approach 1:
The system implements targeted feedback mechanisms where the UE reports channel state information and transmission outcomes specifically in response to NACK events and at configured intervals. This feedback approach provides sufficient channel state information accuracy for effective adaptation while avoiding continuous high-frequency reporting that would increase processing complexity and overhead. The feedback is triggered selectively based on transmission conditions rather than continuously.
Solution Approach 2:
The system employs periodic channel state information reporting at optimally configured intervals rather than continuous reporting. The UE transmits CSI periodically based on pre-configured schedules that balance measurement precision needs with processing complexity constraints. This periodic action allows the network to maintain adequate adaptation accuracy while significantly reducing the overhead and processing requirements compared to continuous or event-driven frequent reporting.
Data Source
AI summary
A method of wireless communication includes determining, by a user equipment (UE) in response to a failed transmission to the UE by a base station, to transmit a negative acknowledgment (NACK). The method additionally includes transmitting, by the UE to the base station, the NACK in an acknowledgement (ACK) resource previously allocated by the base station, and triggering at least one action, by the UE in response to at least one of the determination to transmit the NACK or the transmission of the NACK. The at least one action improves retransmission success rate. In another aspect, a method of wireless communication includes receiving, by a base station from a UE, a NACK in an ACK resource previously allocated by the base station, and triggering at least one action, by the base station in response to the receipt of the NACK. The at least one action improves retransmission success rate.