Msg4 PDSCH Repetition for Reliable NTN Downlink Access
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Solution Overview
Problem
The introduction of non-terrestrial networks (NTN) in wireless communication systems, such as 5G new radio (NR) networks using satellites, faces challenges with coverage and reliability due to long distances and interference, particularly in downlink channels, which are constrained by power flux density limitations, affecting services like voice and low-data rate communications.
Innovation Solution
Enhancements are introduced for Msg4 PDSCH and HARQ-ACK transmissions in NTN, including Msg4 PDSCH repetition and HARQ-ACK repetition, with triggers and signaling mechanisms to improve coverage, using dedicated preambles, RACH occasions, and DCI formats to manage repetitions and ensure reliable communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If Msg4 PDSCH and HARQ-ACK transmissions are performed in NTN environments, then communication coverage is extended to remote areas, but reliability deteriorates due to long propagation delays and power flux density limitations
Solution Approach 1:
The patent introduces Msg4 PDSCH repetition transmissions where the base station pre-schedules multiple redundant transmissions of the same data before the UE can confirm successful reception. This preliminary action ensures that even if some transmissions are lost due to channel conditions, the data is already available for retransmission, thereby improving reliability without requiring immediate feedback
Solution Approach 2:
The patent implements HARQ-ACK repetition where the UE sends multiple redundant acknowledgments (ACK or NACK) for each Msg4 PDSCH transmission. This feedback mechanism allows the base station to reliably determine whether the UE successfully received the data despite long propagation delays and interference, enabling retransmission decisions to be made with high confidence
2Power
If power flux density is increased to overcome propagation losses in NTN, then signal strength at UE is improved, but regulatory limitations are violated
Solution Approach 1:
Instead of transmitting at continuously high power levels that would violate regulatory limits, the patent uses periodic retransmissions of Msg4 PDSCH at compliant power levels. The base station transmits the same data multiple times at regulated power levels, ensuring that the average power flux density remains within regulatory limits while the cumulative effect of multiple transmissions improves the probability of successful reception
Solution Approach 2:
The patent changes the transmission parameter from power level to number of transmissions. Rather than increasing power flux density beyond regulatory limits, the system maintains compliant power levels and compensates for propagation losses by increasing the number of transmission opportunities, thereby achieving reliable communication without violating regulatory constraints
3Reliability
If Msg4 PDSCH repetition is implemented to improve reliability, then transmission success rate increases, but device complexity increases due to additional signaling and processing
Solution Approach 1:
The patent reuses existing DCI format 1_0 structures and HARQ process mechanisms for Msg4 PDSCH repetition, making the same control structures serve multiple functions: indicating repetition assignments, managing HARQ processes, and providing uplink grants for HARQ-ACK feedback. This multi-functionality approach improves reliability through repetition while minimizing the increase in device complexity by leveraging already-deployed protocol elements
Data Source
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AI summary
System and methods for enhancing Msg4 PDSCH transmissions in a non-terrestrial network are disclosed herein. A user equipment (UE) may trigger a network node to apply Msg4 PDSCH repetition. The network node may, based on the UE sent trigger, apply Msg4 PDSCH repetition and transmit the Msg4 PDSCH and one or more Msg4 PDSCH repetitions to the UE. Additionally, the UE may transmit a Msg4 HARQ-ACK in response to the Msg4 PDSCH and the one or more Msg4 HARQ-ACK repetitions.