Cell Reselection Using Expected Serving Time in NTN
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Solution Overview
Problem
Current cell reselection processes in non-terrestrial networks (NTN) are inefficient due to the dynamic nature of satellite beams and the lack of consideration for the remaining service time (Tservice) of a cell, leading to suboptimal handovers and connectivity issues.
Innovation Solution
Incorporating Tservice into the cell reselection criteria, where the UE performs intra-frequency measurements when Tservice is low or near the serving cell edge, and scaling down the serving cell signal power to trigger reselection, while also considering location-based conditions to prioritize cell ranking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE performs cell reselection based on traditional signal quality criteria (RSRP/RSRQ) without considering Tservice, then the cell reselection process is simple and fast, but the connectivity reliability deteriorates in NTN environments where satellite beams are dynamic and have limited service time
Solution Approach 1:
The network provides Tservice information to the UE in advance through system information blocks or dedicated signaling. This allows the UE to proactively plan cell reselection before the satellite beam moves out of coverage, rather than reacting after connectivity is lost. The UE uses this preliminary information to trigger measurements and prepare handover to target cells while still in time.
Solution Approach 2:
The cell reselection criteria are made dynamic by incorporating Tservice as a time-dependent parameter. The evaluation metrics change based on the remaining service time of the current satellite beam, allowing the system to adapt to the dynamic nature of NTN where satellite positions and beam coverage continuously change.
2Loss of time
If the UE waits for signal quality to degrade before performing cell reselection, then energy consumption is reduced, but the handover timing becomes suboptimal in NTN where satellite beams have limited and predictable service duration
Solution Approach 1:
Instead of waiting for signal degradation, the UE performs measurements preliminarily based on Tservice thresholds. When Tservice drops below a configured threshold, the UE proactively initiates cell reselection measurements and evaluations, ensuring handover occurs at the optimal time before the satellite beam exits coverage, rather than reacting to signal quality degradation.
3Reliability
If the UE performs frequent cell reselection measurements to maintain optimal connectivity in NTN, then the connectivity reliability improves, but the device complexity and processing overhead increase
Solution Approach 1:
The measurement frequency and criteria are dynamically adjusted based on Tservice. When Tservice is high, the UE can reduce measurement activity. When Tservice approaches critical thresholds, the UE increases measurement frequency and performs more comprehensive cell evaluations, optimizing the balance between reliability and complexity.
Data Source
AI summary
According to some embodiments, a method performed by a wireless device for cell selection or reselection in a non-terrestrial network (NTN) comprises determining whether to perform one or more cell selection or reselection measurements based on a cell selection or reselection criteria. The cell selection or reselection criteria is based on a signal quality of a serving cell and a relationship between the wireless device and a satellite or spot beam of the NTN. Upon determining that the cell selection or reselection criteria for performing measurements is satisfied, performing the one or more cell selection or reselection measurements.