LEO NR-NTN Cell Reselection With Predictive Satellite Assistance
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Solution Overview
Problem
The frequent and unpredictable cell reselection due to high-speed movement of LEO satellites in NTN networks leads to challenges in maintaining stable wireless communication, as traditional RSRP and RSRQ measurements are inadequate for predicting signal degradation and coverage holes.
Innovation Solution
LEO NTN systems provide satellite assistance information, including ephemeris data and orbital parameters, to help UEs predict candidate cells along the satellite's trajectory, prioritize TN cells over NTN cells, and differentiate between earth-fixed and earth-moving beams for improved cell reselection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional RSRP and RSRQ measurements are used for cell reselection in LEO satellite networks, then the cell reselection process follows conventional terrestrial network procedures, but the high-speed movement of LEO satellites causes frequent and unpredictable cell reselection, leading to unstable wireless communication
Solution Approach 1:
The network provides satellite assistance information including ephemeris data and orbital parameters to UEs in advance. This allows UEs to predict future satellite positions and pre-determine candidate cells along the satellite trajectory, performing cell reselection proactively before signal degradation occurs rather than reactively after measurement thresholds are breached.
Solution Approach 2:
Satellite assistance information acts as an intermediary between the satellite's high-speed movement and the UE's cell reselection process. The ephemeris data and orbital parameters serve as predictive models that bridge the gap between terrestrial measurement-based reselection and satellite-based predictive reselection, enabling the UE to anticipate cell changes.
2Productivity
If UEs perform continuous cell reselection measurements based on signal strength thresholds, then the cell reselection mechanism can adapt to changing signal conditions, but in LEO satellite networks this results in excessive measurement overhead and unnecessary searches due to predictable satellite motion patterns
Solution Approach 1:
The network provides satellite assistance information including ephemeris data and orbital parameters to UEs in advance. This allows UEs to predict future satellite positions and pre-determine candidate cells along the satellite trajectory, performing cell reselection proactively before signal degradation occurs rather than reactively after measurement thresholds are breached.
Solution Approach 2:
The invention changes the fundamental parameter basis for cell reselection from real-time signal strength measurements (RSRP/RSRQ) to predictive orbital parameters (ephemeris data, position, velocity). This parameter transformation allows the system to exploit the deterministic nature of satellite motion to reduce measurement overhead while maintaining reselection accuracy.
3Reliability
If the network prioritizes TN cells over NTN cells during cell reselection, then UEs can maintain better coverage by selecting terrestrial cells when available, but this requires additional complexity in cell prioritization and selection logic
Solution Approach 1:
The network configures different priority levels for different cell types (TN vs. NTN) based on local coverage conditions. UEs apply these priority configurations when performing cell reselection, allowing terrestrial cells to be preferred in areas with good TN coverage while maintaining the ability to select NTN cells when appropriate. This localized prioritization approach maintains coverage quality without requiring complex global selection logic.
Data Source
AI summary
Methods for a New Radio (NR)-based, Low Earth Orbit (LEO) Non-Terrestrial Networks (NTN) are proposed to improve cell selection and reselection by using satellite assistance information. Different from traditional 5G New Radio systems, the LEO NTN can provide the next cell information along the satellite trajectory using System Information Broadcast (SIB). The assistance information can include satellite's long term ephemeris in the format of Position Velocity (PV) information or details of satellite's other orbital parameters. During TN-NTN join coverage, as TN cells are expected to have a better coverage then NTN cells, the network can assign higher priority to the TN cells over NTN cells. Similarly, for a mobility involving earth-fixed and earth-moving beams (cells), earth-fixed cells can be prioritized over earth-moving beams for cell reselection.