Inactive UE Timing Advance Handling for NTN Resume Scheduling
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Solution Overview
Problem
In non-terrestrial networks (NTNs), user equipment (UE) experiences propagation delays during UL transmissions due to unknown satellite-to-UE delays, leading to inefficient TA reporting in RRC connection resume and small data transmission (SDT) procedures, causing increased latency and resource wastage.
Innovation Solution
Network entities (NEs) manage TA information by selectively transmitting TA reports based on predetermined rules, considering UE's inactive state conditions and SDT size, avoiding unnecessary signaling and resource waste.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the RAN schedules every UL transmission assuming the UE is at the edge of the cell (longest possible round-trip-delay), then the scheduling is conservative and ensures coverage, but the UL transmission is significantly delayed, increasing latency
Solution Approach 1:
The UE performs preliminary timing advance evaluation by measuring the satellite-to-UE delay and reporting it to the RAN before actual UL transmissions. This preliminary action enables the RAN to obtain accurate timing information in advance, eliminating the need to assume worst-case delays for all transmissions and thereby reducing scheduling latency while maintaining reliability.
2Measurement precision
If the UE transmits TA report during RRC connection resume or SDT procedure, then the RAN obtains accurate timing information for scheduling, but the signaling overhead and procedure duration increase
Solution Approach 1:
The UE autonomously evaluates the satellite-to-UE delay using its own measurements and directly reports the timing advance information to the RAN without requiring additional network-side measurement procedures. This self-service approach enables the UE to provide accurate timing information independently, reducing the overall procedure duration while maintaining measurement precision.
3Productivity
If the UE reports TA information frequently, then the RAN maintains up-to-date timing information for optimal scheduling, but communication resources are wasted due to unnecessary signaling
Solution Approach 1:
The UE reports timing advance information selectively rather than continuously - specifically during RRC connection resume procedures and small data transmission procedures. This partial action approach provides the RAN with sufficient timing information at critical moments to maintain scheduling efficiency, while avoiding unnecessary signaling overhead and energy consumption that would result from frequent continuous reporting.
Data Source
AI summary
Methods and wireless communication devices operating as network entities (such as base stations or distributed units of a distributed base station) in radio access networks using satellites manage efficiently timing advance information of user equipment (UE) transitioning from an inactive state to a connected state or performing small data transmission. A method performed by a network entity includes preserving pre-inactive-state time advance information pertinent to communications of the UE via a non-terrestrial network before the UE switches to an inactive state. The method further includes receiving, from the UE, a request for resuming an active state, and transmitting, to the UE, a resume-TA correction calculated using the pre-inactive-state TA information, when the UE does not provide a current full TA value with the request.