Missing Reference Signal Handling in Unlicensed Wireless Systems
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Solution Overview
Problem
In wireless communication systems, particularly on unlicensed frequencies, the absence of reference signals (RLM-RS) leads to delayed radio link failure (RLF) declarations due to the inability to receive Out-of-Sync (OOS) or In-Sync (IS) indications, causing unnecessary delays in declaring RLF or initiating recovery procedures.
Innovation Solution
A method and apparatus where the wireless device configures a correlation window or timer to consider the missing reference signal indication as either OOS or IS, allowing for timely declaration of RLF and preventing unnecessary delays by increasing counters related to these indications, thus enabling prompt recovery procedures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If LBT is applied on unlicensed frequency, then fair spectrum sharing with other unlicensed systems is achieved, but reference signal transmission may be blocked causing delayed RLF declaration
Solution Approach 1:
The patent applies preliminary action by configuring a correlation window timer in advance before reference signal transmission occurs. When the timer expires without detecting expected reference signals, the device proactively triggers RLF declaration, preventing delays that would occur while waiting for normal signal-based detection mechanisms.
Solution Approach 2:
The patent introduces an intermediary mechanism by using a correlation window timer as a mediator between the LBT channel access mechanism and the RLF detection system. This timer bridges the gap caused by LBT blocking reference signals, providing an alternative timing-based method to detect link failure without requiring actual reference signal reception.
2Productivity
If RLM-RS transmission is blocked due to busy channel, then channel access for other systems is maintained, but OOS/IS indications cannot be received causing monitoring delays
Solution Approach 1:
The patent implements feedback by establishing a correlation window that continuously monitors for the absence of reference signals. When the window expires without detecting expected signals, this feedback mechanism triggers RLF declaration, creating a closed-loop system that detects failures through absence detection rather than requiring active signal reception.
Solution Approach 2:
The patent applies preliminary anti-action by pre-configuring the correlation window timer to counteract the potential delay caused by blocked reference signals. This timer runs in advance and provides a predetermined timeout mechanism that prevents the system from waiting indefinitely for reference signals that may be blocked by LBT.
3Reliability
If consecutive OOS/IS indications are required for RLF declaration, then false RLF declarations are reduced, but RLF detection is significantly delayed when reference signals are missing
Solution Approach 1:
The patent applies dynamics by making the RLF detection mechanism adaptive to different conditions. The correlation window timer provides a dynamic timeout-based detection method that operates independently of the static consecutive indication requirement. This creates a flexible system that can declare RLF based on either multiple indications or timer expiration, depending on which mechanism triggers first.
Data Source
AI summary
A method and apparatus for handling of missing reference signal on unlicensed frequency in a wireless communication system is provided. The upper layer of the wireless device receives, from a lower layer of the wireless device, a first indication related to a first reference signal from a network, wherein the first indication is one of In-Sync (IS) indication or Out-of-Sync (OOS) indication. The upper layer of the wireless device starts a timer. The upper layer of the wireless device receives, from the lower layer of the wireless device, a second indication while the timer is running, wherein the second indication informs that a second reference signal from the network is missing. The upper layer of the wireless device increases a counter related to the first indication upon receiving the second indication.