Multi-RTT Positioning in Non-Terrestrial Networks
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Solution Overview
Problem
In Non-Terrestrial Networks (NTNs), the movement of network transmission points, such as satellites, leads to timing drifts and Doppler shifts, making it challenging for User Equipment (UE) to perform accurate multi-Round Trip Time (RTT)-based positioning due to lack of measurement gaps and understanding of neighboring satellites.
Innovation Solution
The UE receives assistance information from a Location Management Function (LMF) via a serving network node, which includes ephemeris data and measurement gap configurations to determine and perform multi-RTT measurements, accounting for satellite movement and Doppler shifts, ensuring accurate positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multi-RTT-based positioning is performed in NTN, then positioning accuracy is improved, but the complexity of timing synchronization and measurement coordination increases due to satellite movement and Doppler shifts
Solution Approach 1:
The network node pre-calculates and provides measurement gap configurations to the UE before the actual positioning measurement takes place. This preliminary action accounts for satellite movement and Doppler effects in advance, allowing the UE to perform measurements during predetermined gaps without real-time complexity
Solution Approach 2:
The network node acts as an intermediary that centralizes the complexity of timing synchronization and measurement gap calculation. Instead of the UE handling complex synchronization independently, the network node computes optimal measurement gaps based on satellite ephemeris and Doppler parameters, then provides these configurations to the UE
2Reliability
If measurement gaps are configured for neighboring satellite measurements, then positioning reliability is improved, but the available time for data transmission and reception decreases
Solution Approach 1:
The system configures measurement gaps selectively and partially - only during specific time intervals when satellite geometry and Doppler conditions are favorable. Rather than continuous measurement gaps, the solution uses targeted partial measurements that maintain positioning reliability while preserving data transmission time during other intervals
Solution Approach 2:
The measurement gap configuration is made dynamic rather than static. The network node continuously monitors satellite positions, Doppler shifts, and UE data traffic requirements, then dynamically adjusts measurement gap timing and duration to balance positioning reliability with data transmission needs in real-time
3Measurement precision
If ephemeris information is provided for multiple satellites, then the UE can determine accurate measurement gaps, but the amount of assistance information and processing load increase
Solution Approach 1:
The solution extracts only the essential ephemeris parameters needed for measurement gap calculation from complete satellite orbit data. Instead of providing full ephemeris information, the network node extracts and provides only the critical timing and position parameters relevant to Doppler compensation and gap scheduling, reducing information overhead while maintaining measurement accuracy
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables efficient, flexible, and reliable multi-RTT-based positioning in NTNs by providing the UE with necessary timing and frequency information, overcoming the challenges of satellite movement and Doppler shifts, thereby enhancing location estimation accuracy.
Implementation Method 1
this (satellite) movement might also lead to potentially large Doppler shift (and Doppler drift when observing over longer time durations)
Data Source
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AI summary
Described herein is a user equipment, UE, served by a serving network node and configured for supporting multi-round trip time, RTT, -based positioning over non-terrestrial network, NTN, which involves the serving network node, at least one further network node relevant for the multi-RTT-based positioning and a location management function, LMF, the UE comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the UE at least to: receive, from the LMF via the serving network node, assistance information for supporting the multi-RTT-based positioning, wherein the assistance information comprises ephemeris information related to the serving network node and to the further network node relevant for the multi-RTT-based positioning; determine, based on the received assistance information, measurement gap for performing the multi-RTT related measurement; and perform the multi-RTT related measurement for the serving network node and the further network node in accordance with the determined measurement gap and preferably report a result thereof to the LMF.