Cell Selection Using Expected Service Time in Non-Terrestrial Networks
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Solution Overview
Problem
In Non-Terrestrial Networks (NTNs), the rapid movement of satellites creates challenges for cell selection and handover processes, leading to increased energy consumption and potential page misses due to frequent cell reselections, especially in RRC_IDLE and RRC_INACTIVE states, where synchronization and measurement processes are inefficient and battery-draining.
Innovation Solution
The introduction of 'expected time to be served' as a criterion for cell selection and reselection, where wireless devices calculate or estimate how long a cell will provide sufficient channel quality, allowing them to choose cells with the longest expected coverage time, thereby reducing unnecessary reselections and conserving energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional cell selection and reselection criteria are used in NTN, then devices can maintain basic connectivity, but frequent cell reselections occur due to satellite movement, increasing energy consumption and causing page misses
Solution Approach 1:
The patent applies preliminary action by calculating the expected time to be served for each candidate cell before performing cell reselection. Devices use satellite ephemeris data and geometric relationships to predict how long a cell will remain suitable for service, allowing them to proactively select cells with longer expected service duration and avoid frequent reselections
Solution Approach 2:
The patent changes the cell selection parameter from traditional signal strength metrics alone to include the expected time to be served. By introducing this new parameter based on satellite position, device position, and cell geometry, the system optimizes cell selection to reduce reselection frequency while maintaining connection reliability
2Loss of information
If frequent cell reselections are performed to track satellite movement, then up-to-date cell information is maintained, but synchronization and measurement processes become inefficient and drain battery
Solution Approach 1:
The system performs preliminary calculations of expected service time using satellite ephemeris and geometric data before actual cell reselection. This allows devices to predict which cells will remain suitable for longer periods, reducing the need for frequent synchronization and measurement operations
Solution Approach 2:
The patent enables self-service by allowing devices to autonomously calculate expected service duration using broadcast satellite ephemeris data and their own position information. Devices can independently determine optimal cell selection without continuous network assistance, reducing signaling overhead and processing time
3Ease of operation
If devices select cells based on current signal quality alone, then immediate connectivity is established, but cells may become unsuitable quickly due to satellite motion, requiring reselection
Solution Approach 1:
The patent extends the cell selection criterion from static signal quality metrics to include dynamic parameters such as satellite position, device position, and calculated expected service time. This allows devices to select cells that will remain suitable for longer durations while maintaining straightforward selection procedures
Solution Approach 2:
The system performs preliminary assessment of cell suitability by calculating expected service duration before final cell selection. Devices evaluate multiple parameters in advance to identify cells that will provide sustained service, reducing the likelihood of rapid cell becomes unsuitable
Data Source
AI summary
A method performed by a wireless device for cell selection in a Non-Terrestrial Network (NTN) includes obtaining information indicating an expected time for the wireless device to be served in at least one cell and determining whether to perform a cell selection or reselection procedure based at least in part on the information indicating the expected time for the wireless device to be served in the at least one cell.