Reference Signal Transmission in Unlicensed 5G NR
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Solution Overview
Problem
In 5G New Radio (NR) communications, reference signal (RS) transmissions in unlicensed bands face challenges due to Listen-Before-Talk (LBT) failures, leading to delayed measurements and degraded system performance, as RSs may not be transmitted when the channel is occupied, causing incorrect channel quality assessments and potential loss of time/frequency tracking.
Innovation Solution
Implementing a method where a wireless transmit/receive unit (WTRU) configures and uses candidate RS resources based on LBT failures, allowing RS transmissions to occur in alternative resources when the primary channel is occupied, thereby ensuring continuous RS availability and accurate channel measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LBT is performed before RS transmission in unlicensed bands, then channel access is controlled to avoid collisions, but RS transmission may be delayed or blocked when channel is occupied, leading to measurement delays and degraded system performance
Solution Approach 1:
The gNB performs LBT preparation and channel assessment in advance before the scheduled RS transmission time. If the channel is found to be occupied during this preliminary assessment, the gNB proactively selects an alternative RS resource from pre-configured candidate resources, avoiding the need to wait for channel availability at the original transmission time and thus reducing transmission delay while maintaining reliable channel access control.
2Reliability
If RS transmission is blocked due to LBT failure, then channel collision is avoided, but channel quality assessment becomes incorrect and time/frequency tracking is lost
Solution Approach 1:
The patent introduces candidate RS resources as intermediary alternatives to the primary RS resource. When LBT failure occurs and the primary RS transmission is blocked, the gNB switches to transmitting RS in the candidate resource instead. This intermediary mechanism ensures that RS transmission can still proceed (maintaining measurement accuracy) while the LBT protocol continues to prevent channel collisions in the unlicensed spectrum.
Solution Approach 2:
The system changes the transmission parameter from the original RS resource to an alternative candidate RS resource when LBT fails. This parameter change allows the gNB to maintain RS transmission capability and measurement accuracy while adhering to LBT requirements for collision avoidance in unlicensed bands.
3Reliability
If alternative RS resources are configured for LBT failure cases, then continuous RS availability is maintained, but system complexity increases due to additional configuration and selection mechanisms
Solution Approach 1:
The gNB pre-configures and pre-selects candidate RS resources along with their associated parameters (time, frequency, beam) before actual transmission occurs. This preliminary preparation of alternative resources eliminates the need for complex real-time decision-making and resource allocation when LBT fails, as the gNB only needs to switch between pre-defined options rather than dynamically configuring new resources.
Solution Approach 2:
The system dynamically switches between primary and candidate RS resources based on LBT outcomes. The gNB monitors channel conditions and automatically selects appropriate alternative resources when needed, providing adaptive RS transmission that maintains continuity without requiring complex manual intervention or reconfiguration.
Data Source
AI summary
Methods, apparatuses, systems, and/or procedures for reference signal (RS) transmissions and receptions in wireless communications (e.g., 5G NR) are disclosed. For example, a method implemented by a wireless transmit/receive unit (WTRU) includes receiving configuration information indicating a set of RS resources, a set of candidate RS resources, and a threshold; receiving a first RS in an RS resource of the set of RS resources; selecting a candidate RS resource from the set of candidate RS resources, based on a determination that a measurement result of the received first RS is less than or equal to the threshold; and receiving a second RS in the selected candidate RS resource.