SDT Failure Timer Adjustment for NTN Coverage Gaps
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Solution Overview
Problem
Current wireless communications networks face challenges in efficiently supporting communications with a wide range of devices, including reduced complexity devices, machine type communication devices, and high-resolution video displays, especially in non-terrestrial networks where coverage gaps frequently occur.
Innovation Solution
A method for operating communications devices in an inactive state by adjusting the small data transmission (SDT) failure timer based on an estimate of the coverage gap, preventing the timer from expiring during coverage gaps and thus reducing the need for re-establishing SDT sessions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the SDT failure timer is set for a fixed time period, then the network can efficiently manage SDT sessions, but the timer may expire during coverage gaps in non-terrestrial networks causing session re-establishment
Solution Approach 1:
The SDT failure timer is changed from a static fixed duration to a dynamic adjustable duration. The network equipment determines the appropriate timer value based on the UE's mobility state, coverage gap characteristics, and channel conditions. This dynamic adjustment allows the timer to adapt to varying network conditions, preventing premature expiration during coverage gaps while maintaining efficient session management when conditions are stable
Solution Approach 2:
The timer parameter is modified based on multiple factors including UE mobility indicators, coverage gap duration predictions, and signal quality metrics. By changing the timer parameter dynamically rather than using a fixed value, the system optimizes the balance between session continuity and resource efficiency, directly addressing the contradiction between reliability and time loss
2Reliability
If the SDT failure timer is extended to prevent expiration during coverage gaps, then session continuity is improved, but signaling overhead and power consumption increase due to timer management
Solution Approach 1:
Different timer extension strategies are applied to different UEs based on their specific characteristics. Mobile UEs experiencing frequent coverage gaps receive longer timer values, while stationary or low-mobility UEs use standard timer values. This localized quality approach ensures that power consumption and signaling overhead are optimized for each UE's actual needs rather than applying a blanket extension to all users
Solution Approach 2:
The network equipment predicts coverage gap duration in advance using orbital information and UE mobility data, then proactively sets the timer duration before the gap occurs. This preliminary action prevents timer expiration without requiring reactive timer extensions mid-session, reducing both signaling overhead and power consumption associated with dynamic timer adjustments during active sessions
3Productivity
If the SDT failure timer is adjusted based on coverage gap estimates, then communication efficiency is improved, but the complexity of timer management increases
Solution Approach 1:
The network equipment acts as an intermediary that centralizes the complex timer management logic. Rather than requiring each UE to independently calculate and adjust timers based on coverage gap predictions, the network equipment receives mobility information from UEs, determines appropriate timer values, and configures them centrally. This intermediary approach maintains communication efficiency while managing complexity at the network side where resources are more abundant
Data Source
AI summary
A method of operating a communications device for transmitting signals to and/or receiving signals from a non-terrestrial network, NTN, while the communications device is in an inactive state is provided. The method comprises commencing a small data transmission, SDT, failure timer setting a time period during which the communications device can communicate one or more SDTs with the NTN when the communications device is located inside a coverage area provided by the NTN. The method comprises determining that the communications device is expected to enter a coverage gap before the SDT failure timer expires. The coverage gap is a time period during which the communications device is located outside the coverage area provided by the NTN. The method comprises adjusting the commenced SDT failure timer based on an estimate of the coverage gap.