Timing Advance Estimation Restriction for NB-IoT NTN Synchronization
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Solution Overview
Problem
The conventional TAC-based timing synchronization solution in NB-IoT non-terrestrial networks (NTN) is disrupted due to the long Round Trip Time (RTT) and disabled HARQ ACK feedback, leading to multiple corrections of the same timing error in the gNB, causing operational disruptions.
Innovation Solution
Introducing a 'TA estimation restriction duration' where the gNB ignores new TA estimations for a specified duration after issuing a TAC, ensuring that any subsequent NPUSCH transmissions are based on the initial TAC, preventing multiple corrections of the same TA error, with the duration set to be equal to or greater than the sum of RTT plus 12 milliseconds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If TAC-based timing synchronization is used in NB-IoT NTN with long RTT, then timing alignment can be achieved, but multiple corrections of the same timing error occur causing operational disruptions
Solution Approach 1:
The gNB applies preliminary action by implementing a restriction mechanism that prevents new TA estimations during a specified duration after issuing a TAC. This preliminary constraint ensures that the timing correction process completes fully before allowing subsequent estimations, preventing multiple corrections of the same error while maintaining timing alignment precision.
2Productivity
If HARQ ACK feedback is disabled to reduce stalling impact, then productivity improves, but TAC-based synchronization is disrupted due to long RTT
Solution Approach 1:
The invention extracts the timing restriction mechanism from the HARQ feedback process. By separating the TA estimation restriction from the HARQ ACK feedback loop, the system can disable HARQ ACK feedback to improve productivity while the independent restriction mechanism continues to protect synchronization stability without being disrupted by long RTT conditions.
3Measurement precision
If gNB issues TAC based on first NPUSCH reception, then timing error is corrected, but subsequent NPUSCH transmissions with same error trigger additional TACs
Solution Approach 1:
The gNB applies preliminary action by establishing a restriction duration that spans from the first NPUSCH reception through the expected arrival of corrected transmissions. This preliminary time constraint prevents redundant TAC issuance for the same error, eliminating wasted processing time while ensuring accurate timing correction is applied.
Data Source
AI summary
A system and a method are provided for optimizing application of timing advance command (TAC) mechanism in a Narrow Band Internet of Things (NB-IoT) non-terrestrial network (NTN) system utilizes a timing advance (TA) estimation restriction duration. After one operation of a timing advance (TA) estimation resulting in issuing of an initial TAC, the gNB ignores the results of new TA estimations until specified X seconds after the initial TAC is sent. TA estimation restriction duration refers to the time duration between the initial TA estimation and X seconds after the initial TAC. The value of X is specified such that X represents the minimum duration starting from the transmission of the first TAC in which any received NPUSCH within this duration is not based on a new TAC. By applying the TA estimation restriction duration, multiple corrections of the same TA error are prevented.