Dynamic TAC Lists for LEO-NTN Tracking Area Updates
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Solution Overview
Problem
In Low Earth Orbit (LEO) Non-Terrestrial Networks (NTN), the high speed of satellites leads to frequent cell reselection, causing excessive tracking area update (TAU) signaling due to earth-fixed tracking areas, which increases network load.
Innovation Solution
A mechanism where each cell broadcasts a dynamic list of multiple Tracking Area Codes (TACs) corresponding to the areas it covers, allowing UEs to initiate a TAU only when their registered TA does not match any TAC in the list of the reselected cell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If earth-fixed tracking areas are used in LEO-NTN, then network coverage is maintained, but frequent cell reselection triggers excessive TAU signaling
Solution Approach 1:
The patent applies dynamics by transitioning from static earth-fixed tracking areas to satellite-moving tracking areas. The tracking area is dynamically associated with the satellite's current position and orbit, allowing the same physical area to belong to different tracking areas as the satellite moves. This dynamic approach eliminates frequent TAU signaling while maintaining continuous coverage.
Solution Approach 2:
The patent changes the parameter of tracking area assignment from fixed to variable. Instead of assigning tracking areas based on fixed geographical boundaries, the system assigns tracking areas based on the satellite's real-time position and orbit parameters. This parameter change allows the network to maintain coverage while avoiding unnecessary TAU updates during satellite movement.
2Area of stationary object
If high speed LEO satellites are used, then coverage area is increased, but cell reselection frequency increases
Solution Approach 1:
The patent makes the tracking area assignment dynamic by linking it to the satellite's orbit and position rather than fixed geographical boundaries. As the satellite moves at high speed across the coverage area, the tracking area changes accordingly, allowing the UE to remain registered without frequent TAU signaling even though the physical location changes rapidly.
Solution Approach 2:
The patent applies preliminary action by pre-calculating and broadcasting the Tracking Area Code (TAC) list in system information before cell reselection occurs. The UE receives the TAC list in advance and can determine whether a TAU is needed before actually performing the reselection, preventing unnecessary signaling updates.
3Device complexity
If single TAC is broadcast by each cell, then system information is simple, but TAU signaling increases during cell reselection
Solution Approach 1:
The patent segments the tracking area information by broadcasting a list of multiple TACs in the system information of each cell, rather than a single TAC. This segmentation allows the cell to associate with multiple tracking areas simultaneously, enabling the UE to check whether its current TAC is still valid after cell reselection without triggering unnecessary TAU signaling.
Solution Approach 2:
The patent applies preliminary action by including the complete TAC list in the system information broadcast before cell reselection. The UE receives this information in advance and can perform local comparison to determine if a TAU is necessary, eliminating the need for real-time TAU signaling during cell reselection events.
Data Source
AI summary
A method (and associate apparatus) operates by receiving a first tracking area code (TAC) list corresponding to Non Geostationary (NGSO) Non-Terrestrial Network (NTN); performing cell selection in a mobile network based NGSO NTN, wherein the UE selects a first cell associated with the first TAC list; performing a registration procedure with a first TAC from the first TAC list; performing cell reselection and selecting a second cell, wherein the second cell is associated with a second TAC list; and determining whether the first TAC is included in the second TAC list, wherein the UE initiates a TA update (TAU) procedure when the first TAC is not included in the second TAC list, wherein the TAU procedure involves the UE sending a TAU Request message, and wherein the UE receives a TAU Accept message and the UE is registered to a second TAC from the second TAC list.