HARQ-less Semi-Persistent Scheduling for Satellite Latency
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Solution Overview
Problem
In non-terrestrial networks, the long round trip time for HARQ operations in satellite communications leads to high latency and increased costs for retransmissions, making traditional HARQ methods inefficient for latency-sensitive applications, particularly in scenarios like GEO satellite access where propagation delays are significant.
Innovation Solution
Implementing a HARQ-less operation for semi-persistent scheduling transmissions, where HARQ state feedback is disabled, allowing for blind retransmissions and dynamic configuration through RRC signaling, reducing the need for immediate feedback and optimizing resource usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional HARQ operation is used in satellite communications, then reliability of data transmission is improved through retransmission mechanisms, but latency increases significantly due to long round trip times
Solution Approach 1:
The patent extracts and removes the HARQ feedback mechanism from the transmission system for SPS transmissions. By disabling HARQ state feedback (both ACK and NACK), the system eliminates the round trip time delay associated with feedback and retransmission decisions, while maintaining reliability through alternative means such as blind retransmissions configured via RRC signaling.
Solution Approach 2:
The patent introduces dynamic configuration capability where the network can flexibly enable or disable HARQ operation for SPS transmissions based on current conditions. The gNB can dynamically indicate whether HARQ-less operation should be applied through RRC signaling, allowing the system to adapt between traditional HARQ mode and HARQ-less mode depending on latency requirements and network conditions.
2Reliability
If HARQ state feedback is enabled for SPS transmissions, then transmission reliability is improved, but device complexity increases due to additional feedback processing requirements
Solution Approach 1:
The patent removes the HARQ state feedback processing functionality from the UE for SPS transmissions. By configuring HARQ-less operation, the UE no longer needs to generate, transmit, or process HARQ feedback signals, significantly simplifying the feedback processing complexity while maintaining acceptable reliability through blind retransmission mechanisms.
3Loss of time
If HARQ operation is disabled for latency-sensitive applications, then latency is reduced, but retransmission capability is lost
Solution Approach 1:
The patent implements blind retransmission mechanisms where the UE autonomously determines when retransmission is needed without waiting for HARQ feedback. The UE uses configured parameters (such as transmission count limits and timing information) to self-manage the retransmission process, enabling reliability maintenance while operating without HARQ feedback.
Data Source
AI summary
A method for a UE for performing a HARQ feedback operation for an SPS transmission is disclosed. The method comprises receiving a transmission configuration for a scheduled transmission, the transmission configuration indicating a first number of HARQ processes used for the scheduled transmission; receiving an SPS transmission configuration for an SPS transmission, the SPS transmission configuration indicating a second number of HARQ processes used for the SPS transmission; receiving scheduling signaling including a reserved HARQ process number for indicating that a HARQ state feedback operation for the scheduled transmission is disabled; determining a first HARQ process number corresponding to the SPS transmission, the first HARQ process number being selected according to the second number of HARQ processes and being equivalent to the reserved HARQ process number; and transmitting a HARQ state feedback for the SPS transmission with a second HARQ process number derived according to the first HARQ process number.