WTRU Mobility Suspension During Discontinuous NTN Coverage
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Solution Overview
Problem
Existing mobile communication systems face challenges in managing mobility under discontinuous coverage, particularly in non-terrestrial networks (NTNs) where coverage gaps occur due to satellite movement, leading to issues such as power consumption, unnecessary declaration of link failures, and loss of network synchronization.
Innovation Solution
A wireless transmit/receive unit (WTRU) determines the start and duration of coverage gaps based on satellite assistance information, transmits a coverage gap report, and receives RRC reconfiguration messages to suspend operations during gaps, allowing for power-saving actions and synchronized reconnection to target cells upon resuming coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the WTRU continues normal operations during coverage gaps in NTNs, then network synchronization and link reliability are maintained, but power consumption increases unnecessarily
Solution Approach 1:
The system dynamically adapts mobility procedures based on coverage conditions. The WTRU determines coverage gap characteristics (start time, duration) and selectively suspends or continues operations based on whether it is in-coverage or out-of-coverage, optimizing power consumption while maintaining synchronization when needed
Solution Approach 2:
The suspend indication message changes operational parameters (suspension of uplink transmission, downlink transmission, timers, counters, measurements, radio link monitoring) based on coverage gap detection, allowing the system to switch between active and suspended states to balance reliability and power consumption
2Reliability
If the WTRU performs continuous mobility procedures during coverage gaps, then network synchronization is maintained, but unnecessary link failures are declared
Solution Approach 1:
The system performs preliminary determination of coverage gap characteristics before entering the gap. The WTRU receives assistance information, determines the coverage gap start and duration, and proactively suspends mobility procedures in advance, preventing unnecessary link failure declarations that would occur if normal procedures continued blindly
Solution Approach 2:
The suspend indication mechanism provides feedback from the network to the WTRU about upcoming coverage gaps. The WTRU uses this feedback to adjust its mobility behavior, suspending operations during gaps and resuming when coverage is restored, thereby avoiding false link failure detections
3Use of energy by moving object
If the WTRU suspends all operations during coverage gaps, then power consumption is reduced, but mobility procedures may be interrupted
Solution Approach 1:
The system uses periodic coverage gap reports and suspend/resume indications to rhythmically switch between suspended and active states. The WTRU suspends operations during predicted coverage gaps and resumes normal mobility procedures when coverage is restored, maintaining productivity while reducing power consumption during inevitable outages
Solution Approach 2:
The network provides preliminary suspend indication messages before coverage gaps occur, allowing the WTRU to prepare by suspending operations in advance. This preliminary action ensures that when the WTRU emerges from the coverage gap, it can quickly resume mobility procedures without interruption, maintaining productivity
Data Source
AI summary
Systems, methods, and instrumentalities are described herein for adapting mobility under discontinuous coverage (e.g., associated with gap(s) in coverage). In examples, a WTRU may determine the start and duration of discontinuous coverage. Discontinuous coverage may be explicitly indicated in SI (e.g., start UTC 10:00+90 s). The determination of the start and duration of discontinuous coverage may be implicitly determined via assistance information broadcasted in a SI cell stop time and a neighboring cell start time. The start and duration of discontinuous coverage may be calculated via location information (e.g., the distance between the WTRU and serving/neighboring cell center and the diameter of cell coverage). The WTRU may report it is about to enter a coverage gap at some configured offset from time (e.g., via a timer) of the coverage gap.