Radio Link Monitoring Reference Signal Detection in Unlicensed Spectrum
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Solution Overview
Problem
In existing radio link monitoring (RLM) systems, the physical layer of user equipment (UE) faces challenges in evaluating channel quality on unlicensed frequency bands due to intermittent channel availability and variable power, leading to inaccurate link quality assessment and delayed detection of link failures or recoveries.
Innovation Solution
The UE determines whether a reference signal from the base station is received in any subframe and performs RLM only if the signal is available, allowing for accurate link state assessment and timely detection of link failures or recoveries by distinguishing between effective and ineffective reference signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE performs RLM based on CRS in each frame on unlicensed frequency bands, then the channel quality can be continuously monitored, but the link quality assessment becomes inaccurate due to intermittent channel availability and variable power
Solution Approach 1:
The base station performs preliminary action by determining in advance whether to transmit the reference signal in each subframe and notifying the UE of this decision. This allows the UE to prepare appropriately for RLM - either performing measurement when signal is transmitted or skipping when not transmitted - thereby ensuring accurate link quality assessment only when valid reference signals are available, resolving the contradiction between continuous monitoring and measurement accuracy
Solution Approach 2:
The system introduces dynamic adaptability by making the reference signal transmission optional and controllable on a per-subframe basis. The base station can dynamically adjust whether to transmit CRS for RLM depending on channel conditions and scheduling decisions, and the UE dynamically adapts its RLM behavior accordingly. This dynamic mechanism ensures that RLM is performed only when meaningful measurements can be obtained, maintaining both reliability and measurement precision
2Loss of time
If the UE continuously monitors channel quality on unlicensed frequency bands, then link failures can be detected earlier, but false detections occur due to intermittent reference signal transmission
Solution Approach 1:
The base station provides feedback to the UE by notifying whether a reference signal will be transmitted in each subframe. The UE uses this feedback to determine whether to perform RLM in that subframe. This feedback mechanism prevents the UE from attempting measurements when no reference signal is transmitted (avoiding false out-of-sync detections) while enabling timely detections when signals are transmitted, thus resolving the contradiction between early detection and detection accuracy
Solution Approach 2:
The base station performs preliminary notification about reference signal transmission status before the UE needs to make measurement decisions. This preliminary information allows the UE to optimize its monitoring behavior - actively monitoring when signals are expected and conserving resources when signals will not be transmitted - thereby achieving both timely link failure detection and high detection accuracy without false positives
3Area of stationary object
If the UE performs RLM on all subframes, then monitoring coverage is maximized, but system resources are wasted on subframes where reference signals are not transmitted
Solution Approach 1:
The system implements dynamic RLM operation where the UE adjusts its monitoring activity based on base station notifications. When reference signals are transmitted, the UE performs RLM to maintain monitoring coverage; when reference signals are not transmitted, the UE skips RLM to conserve energy. This dynamic adaptation resolves the contradiction by making monitoring coverage conditional on actual signal availability rather than attempting uniform monitoring across all subframes
Solution Approach 2:
The base station provides preliminary information about reference signal transmission plans, enabling the UE to proactively adjust its monitoring behavior. The UE can prepare to monitor when signals are coming and skip monitoring when signals will not be transmitted, maximizing effective monitoring coverage while minimizing energy consumption on subframes where monitoring would be futile
Data Source
AI summary
The present disclosure provides a method for RLM and a corresponding UE. The method comprises the steps of: determining, by a UE and on a carrier used for RLM, whether a reference signal transmitted by a base station for RLM is received in any subframe; performing RLM based on the reference signal if the reference signal transmitted by the base station is received in any subframe; and, determining, according to a result of RLM, whether link failure is detected. With the solutions, a link state capable of accurately reflecting the actual link quality can be acquired, so that a higher layer of a UE can timely make a decision on link failure or link recovery.