Variable SCell Activation Delay for Unlicensed Spectrum
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Solution Overview
Problem
In LTE systems, especially in Licensed Assisted Access (LAA) and standalone unlicensed spectrum operations, the activation of secondary cells (SCells) is delayed due to the Listen-Before-Talk (LBT) procedure, which affects synchronization and timely activation, leading to non-deterministic SCell activation delays and potential failure in meeting activation requirements.
Innovation Solution
A variable SCell activation delay method is introduced, where the UE activates an SCell on an unlicensed carrier within a time period (T0) based on the number of missed DRS occasions due to LBT failures, allowing activation even when DRS signals are not contiguously transmitted, and the network node adapts LBT to minimize DRS transmission losses during activation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LBT procedure is applied to SCell activation in unlicensed spectrum, then channel access compliance is improved, but activation delay becomes non-deterministic and may fail to meet requirements
Solution Approach 1:
The patent makes the SCell activation delay dynamic by tying it to the actual LBT procedure completion time rather than using a fixed predetermined delay. The UE determines the activation delay based on when the LBT procedure successfully completes, allowing the system to adapt to varying channel conditions while ensuring compliance with LBT requirements.
Solution Approach 2:
The patent changes the activation delay parameter from a fixed value to a variable that depends on LBT procedure outcomes. The network configures a maximum delay parameter, but the actual delay is determined by when LBT succeeds, transforming a static parameter into a dynamic one that reflects real-time channel access conditions.
2Adaptability or versatility
If DRS transmission is subject to LBT procedure, then unlicensed spectrum sharing fairness is improved, but DRS signal availability for synchronization becomes non-deterministic
Solution Approach 1:
The patent provides beforehand cushioning by configuring a maximum activation delay parameter that accounts for potential LBT failures. This pre-configured parameter ensures that even if DRS transmissions are delayed due to LBT, the UE has sufficient time to complete synchronization and activation within the maximum allowed delay, maintaining reliability despite non-deterministic signal availability.
Solution Approach 2:
The patent implements feedback mechanisms where the UE monitors DRS signal availability and reports synchronization status to the network. The network uses this feedback to adjust activation timing and ensure that SCell activation completes successfully even when DRS transmissions are interrupted by LBT procedures.
Data Source
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AI summary
The disclosure relates to a method performed in a wireless device served by a network node of a radio communications system. The wireless device is capable of carrier aggregation and is configured by the network node with a primary cell, PCell, and a first secondary cell, SCell. The method comprises receiving (910) an activation command for activating the first SCell. The method also comprises performing (920) a first activation procedure for activating the first SCell in response to the activation command, over a variable time period increasing with a number of times that a discovery reference signal occasion of the first SCell is not available at the wireless device during the first activation procedure. The disclosure also relates to the corresponding method in the network node as well as the wireless device and the network node.