User Terminal LBT Compliance and Resource Utilization in Unlicensed Bands
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Solution Overview
Problem
In future radio communication systems, such as 5G, 5G+, NR, and Rel. 15 or later versions, there is a risk of inappropriate communication in the unlicensed band due to unclear operation procedures, which can lead to non-compliance with LBT regulations and reduced radio resource utilization efficiency.
Innovation Solution
A user terminal is equipped with a receiving section that receives synchronization signal blocks and reference signals for measurement within a given frequency domain duration, and a control section that manages the reception of physical downlink channels based on the transmission candidate positions of these signals, ensuring appropriate communication in the unlicensed band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If listening (LBT) is performed before transmission in the unlicensed band, then compliance with LBT regulations is achieved, but radio resource utilization efficiency is reduced due to uncertain transmission opportunities
Solution Approach 1:
The base station performs listening (LBT) in advance before transmitting synchronization signal blocks and reference signals in the unlicensed band. This preliminary channel access procedure ensures that transmission only occurs when the channel is clear, maintaining LBT regulation compliance while enabling subsequent data transmissions without repeated listening requirements.
Solution Approach 2:
The transmission procedure is divided into distinct phases: first performing LBT to acquire channel access, then transmitting synchronization signal blocks and reference signals, and finally transmitting physical downlink channels. This segmentation allows each function to be performed optimally - LBT ensures compliance, while the structured transmission phases maximize resource utilization within the acquired channel access window.
2Reliability
If synchronization signal blocks and reference signals are transmitted in the unlicensed band, then user terminal can perform synchronization and measurement, but transmission may be interrupted due to LBT failures
Solution Approach 1:
The base station performs LBT and transmits synchronization signal blocks and reference signals before transmitting physical downlink channels. This preliminary transmission of essential synchronization and measurement signals ensures that user terminals can establish synchronization and perform measurements even if subsequent data transmissions are interrupted by LBT failures in later time slots.
Solution Approach 2:
By transmitting synchronization signal blocks and reference signals in advance during the initial channel access opportunity, the system cushions against potential future transmission interruptions. User terminals are equipped with necessary synchronization and channel state information before potential LBT failures may occur, maintaining service stability despite transmission discontinuities.
3Productivity
If physical downlink channels are transmitted without considering SSB transmission timing, then transmission efficiency is improved, but reception accuracy deteriorates due to potential signal overlap
Solution Approach 1:
The base station dynamically adjusts the timing of physical downlink channel transmissions based on the actual transmission timing of synchronization signal blocks. By making the physical channel transmission timing dependent on the SSB transmission outcome, the system adapts to channel conditions and LBT results, maintaining both transmission efficiency and reception accuracy through flexible timing coordination.
Solution Approach 2:
The transmission timing of physical downlink channels is determined based on feedback from the SSB transmission process. The base station uses information about SSB transmission success and timing to adjust subsequent physical channel transmissions, ensuring that resources are properly coordinated and avoiding signal overlap while maintaining efficient resource utilization.
Data Source
Figure 1A~1B
Figure 2
Figure 3A~3B
AI summary
In order to perform appropriate communication in an unlicensed band, a user terminal according to one aspect of the present disclosure includes a receiving section that receives at least one of a synchronization signal block and a reference signal for measurement in a given duration of a frequency domain to which listening is applied, and a control section that controls reception of a physical downlink channel based on a transmission candidate position of at least one of the synchronization signal block and the reference signal for measurement when the physical downlink channel is received in the given duration.