UE Network Access During GNSS Coverage Loss in NTN
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Solution Overview
Problem
User equipment (UE) in Non-Terrestrial Networks (NTNs) may lose network access due to temporary or permanent lack of Global Navigation Satellite System (GNSS) coverage, which is essential for timing and frequency synchronization, leading to inability to perform autonomous timing advance and Doppler shift frequency pre-compensation.
Innovation Solution
A method where the UE detects loss of GNSS coverage and transmits a loss notification to the network node, allowing the network node to either keep the UE in a state to regain coverage or initiate a handover procedure to a cell with less stringent timing and frequency pre-compensation requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If UE relies on GNSS coverage for timing and frequency synchronization in NTN, then timing accuracy and frequency synchronization are improved, but network access is lost when GNSS coverage is unavailable
Solution Approach 1:
The network node acts as an intermediary to provide alternative timing and frequency reference signals when GNSS coverage is unavailable. The network node transmits reference signals that enable the UE to perform timing advance and frequency pre-compensation without relying solely on GNSS, thus maintaining network access during GNSS outages.
Solution Approach 2:
The system dynamically changes the timing and frequency parameters based on GNSS availability status. When GNSS coverage is lost, the UE transitions to using network-provided reference signals with adjusted timing advance values and frequency compensation parameters, allowing continuous operation under different parameter sets depending on the coverage condition.
2Manufacturing precision
If UE performs autonomous timing advance and Doppler shift frequency pre-compensation based on GNSS, then uplink synchronization is improved, but service continuity is interrupted when GNSS coverage is lost
Solution Approach 1:
The network node preliminarily provides reference signals and compensation parameters to the UE before GNSS coverage is completely lost. By maintaining a connection state and providing advance timing and frequency references, the system prepares the UE for potential GNSS outage, enabling seamless transition and preventing service interruption.
Solution Approach 2:
The system ensures continuous uplink synchronization by switching the source of timing and frequency references from GNSS to network-provided signals when GNSS coverage is unavailable. This continuous provision of synchronization references maintains the useful action of uplink transmission without interruption despite the change in reference source.
3Loss of energy
If network node releases UE to idle or inactive state when GNSS coverage is lost, then network resources are saved, but UE cannot regain access without GNSS coverage
Solution Approach 1:
The network node dynamically adjusts the UE's connection state based on GNSS coverage conditions. Instead of always maintaining connected state (wasting resources) or always releasing to idle (losing access capability), the system transitions between states adaptively: maintaining connected state when GNSS is available, and selectively maintaining it during temporary outages when quick recovery is expected, thereby optimizing both resource usage and access capability.
Data Source
AI summary
A method performed by a user equipment, UE, is provided. The method comprises detecting that the UE has lost navigation system coverage partially or wholly. The method further comprises, after the detection, transmitting towards a network node a loss notification indicating that the UE has the lost navigation system coverage.