GNSS-Assisted Cell Ranking for NTN Mobility
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Solution Overview
Problem
Conventional cell reselection in non-terrestrial networks (NTN) faces challenges due to limited signal level variations and slow signal drop-off in satellite networks, making reliable cell reselection based on RSRP measurements difficult.
Innovation Solution
The method involves using GNSS measurements to determine geographical location information and adjust RSRP rankings for cell reselection, incorporating distance, round-trip time, and angle of elevation to improve cell ranking accuracy in NTN environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional RSRP-based cell reselection is used in NTN, then the cell reselection process is simple to implement, but the cell reselection reliability is poor due to limited signal level variations and slow signal drop-off
Solution Approach 1:
The patent combines GNSS location-based cell ranking with RSRP measurements to create a hybrid cell reselection mechanism. The network provides both location information (distance, angle of elevation, round-trip time) and RSRP measurements to the UE, which then uses a weighted combination or priority-based selection between location-based ranking and RSRP-based ranking to determine cell reselection, thereby improving reliability while managing complexity
Solution Approach 2:
The network acts as an intermediary by providing location information and assistance data to the UE. The network calculates or provides distance, angle of elevation, and round-trip time information based on satellite ephemeris and UE location, serving as a mediator between the complex satellite geometry calculations and the UE's cell reselection decision process
2Measurement precision
If RSRP measurements are used for cell ranking in NTN, then the measurement process is straightforward, but the measurement precision is insufficient due to limited signal level variations
Solution Approach 1:
The patent segments the cell ranking measurement into multiple independent components: location-based distance measurement, angle of elevation measurement, round-trip time measurement, and RSRP measurement. Each component is calculated or measured separately using different methods, then combined to form the overall cell ranking, improving precision by diversifying measurement sources
Solution Approach 2:
The patent introduces spatial dimension information (location, angle of elevation, distance) to complement the traditional signal strength dimension (RSRP). By adding geographic and geometric dimensions to the cell ranking process, the system overcomes the limitation of limited signal level variations in NTN, as location-based metrics provide discriminatory power independent of signal strength
3Measurement precision
If GNSS location-based cell ranking is implemented, then cell ranking accuracy improves, but the device complexity and processing requirements increase
Solution Approach 1:
The network performs preliminary calculations of satellite ephemeris, UE location, distance, angle of elevation, and round-trip time before the UE needs to make cell reselection decisions. The network provides pre-computed location information and assistance data to the UE, reducing the real-time processing burden on the UE and enabling accurate cell ranking without excessive device complexity
Solution Approach 2:
The UE uses its own GNSS receiver to independently determine its location and calculate distance to serving and neighboring cells. The UE autonomously performs location-based cell ranking using its own processing capabilities, reducing reliance on network-provided calculations and distributing the processing burden to the device that has the necessary GNSS hardware
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 approach enhances RRC idle and connected mode mobility by providing more accurate cell ranking, improving cell reselection reliability and efficiency in NTN environments.
Implementation Method 1
The GNSS receiver determines the travel time of a signal from a satellite by comparing the pseudo random code the receiver generates with an identical code in the signal from the satellite. The receiver 'slides' its code later and later in time until it synchronizes with the satellite's code. The amount that the GNSS receiver must slide the code is equal to the signal's travel time.
Implementation Method 2
In addition to position and time, the velocity of the device can be obtained by measuring the Doppler shift of the GPS signal
Implementation Method 3
In the first case the base station is located on earth behind the gateway, and the satellite operates as a repeater forwarding the feeder link signal to the service link, and vice versa.
Data Source
AI summary
According to some embodiments, a method performed by a wireless device comprises: determining geographical location information of the wireless device with respect to each cell of a plurality of cells; adjusting a cell reselection ranking for the plurality of cells based on the geographical location information for the plurality of cells; selecting a cell from the plurality of cells based on the adjusted ranking; and camping on the selected cell.