UE Random Access Window Positioning for Long-RTT NTN Uplinks
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Solution Overview
Problem
In non-terrestrial networks (NTNs), the extremely long round trip time (RTT) between satellite and user equipment (UE) limits communication performance and reliability, particularly in unlicensed spectrum usage, leading to increased latency and difficulty in adapting suitable offset values for uplink transmissions.
Innovation Solution
The UE and base station determine and configure time durations and positions for random access procedures, including window and transmission positions, to adapt suitable offset values and durations, enhancing communication performance and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE uses LBT procedure to access unlicensed spectrum in NTN, then channel access fairness is improved, but transmission latency increases due to channel sensing requirements
Solution Approach 1:
The base station performs channel sensing and acquires channel occupancy time in advance before the UE needs to transmit. The BS then shares this pre-acquired channel access opportunity with the UE, allowing the UE to transmit without performing its own LBT procedure. This preliminary action by the BS eliminates the time-consuming channel sensing step for the UE while maintaining fair channel access through BS-controlled sharing.
Solution Approach 2:
The base station acts as an intermediary between the unlicensed channel and the UE. Instead of the UE directly accessing the channel through LBT, the BS mediates by sensing the channel first and then allocating the channel occupancy time to the UE. This intermediary role allows the BS to manage channel access fairness while reducing UE transmission latency.
2Reliability
If the UE performs channel sensing before transmission in unlicensed spectrum, then channel access reliability is improved, but transmission throughput decreases due to MCOT limitations
Solution Approach 1:
The base station performs channel sensing and acquires maximum channel occupancy time (MCOT) in advance before the UE needs to transmit data. By sharing this pre-acquired MCOT with the UE, the system ensures reliable channel access (since the BS has already verified channel availability) while enabling the UE to transmit with greater throughput potential, as the MCOT duration is determined by the BS based on overall system needs rather than being limited by individual UE sensing results.
3Speed
If the UE determines random access transmission position autonomously, then access speed is improved, but communication performance deteriorates due to long RTT in NTN
Solution Approach 1:
The base station provides feedback to the UE regarding the determined transmission position for random access. Instead of the UE autonomously determining the position without knowledge of network conditions, the BS uses its awareness of the long RTT characteristics and current channel state to provide guidance or confirmation to the UE. This feedback mechanism ensures that the UE's transmission timing is optimized for the actual network conditions, improving communication performance while maintaining reasonable access speed.
Solution Approach 2:
The random access transmission position is made dynamic rather than fixed or purely autonomous. The system adapts the transmission position based on the long RTT characteristics of NTN and current network conditions. The BS can adjust the transmission position information provided to the UE dynamically, allowing the system to optimize performance for varying conditions while accounting for the inherent latency of satellite communication.
Data Source
AI summary
A user equipment (UE), a base station, and an information transmission method are provided. The information transmission method includes determining, by a user equipment (UE), a first time duration and/or a second time duration; and determining, by the UE, a first position using the first time duration and/or a second position using the second time duration for a random access procedure, wherein the first position comprises a position of a first window and the second position comprises a position of a first transmission. This can solve issues in the prior art, adapt a suitable offset value and/or duration for the subsequent transmission, provide a good communication performance, and/or provide high reliability.