Time Division Duplexing in 3GPP based Non-Terrestrial Networks
Authors
Fasken, Lukas William Ninn ; Dybkjær, Rasmus Haupt
Term
4. semester
Education
Publication year
2026
Submitted on
2026-06-04
Pages
77
Abstract
As 6G evolves, there is renewed interest in using Time Division Duplex (TDD) for Low Earth Orbit (LEO) Non-Terrestrial Networks (NTN). In these space-based links, signals travel long distances, so networks insert long guard periods (GPs)—short silent gaps—to avoid self-interference between uplink (UL) and downlink (DL). Longer GPs increase end-to-end latency. This thesis designs and evaluates two ways to make TDD more efficient in LEO NTN: (1) A cluster-based method that permits concurrent UL and DL transmissions when user equipments (UEs) are separated by at least a minimum UE-to-UE distance, making cross-link interference (CLI) negligible. (2) An SRP-based method that exploits the long propagation delay to schedule synchronous UL and DL transmissions so they fit entirely within the simultaneous propagation duration, enabling overlap without interference. Using system-level simulations, we compare both methods with a naive baseline under two traffic scenarios. Across all latency metrics, both methods improve performance: the cluster-based method reduces 95th-percentile UL latency by 21%, and the SRP-based method reduces 95th-percentile DL latency by 65%.
Efterhånden som 6G udvikles, er der fornyet interesse for at bruge tidsdelt dupleks (Time Division Duplex, TDD) i Low Earth Orbit (LEO) ikke-jordbaserede net (Non-Terrestrial Networks, NTN). I disse rumbaserede forbindelser har signaler lange udbredelsestider, så nettet indsætter lange beskyttelsesperioder (guard periods, GP) – korte stille pauser – for at undgå selvinterferens mellem uplink (UL) og downlink (DL). Længere GP’er øger latenstiden. Denne afhandling designer og vurderer to måder at gøre TDD mere effektivt i LEO-NTN: (1) En klyngebaseret løsning, der tillader samtidige UL- og DL-transmissioner, når brugerudstyr (user equipment, UE) er adskilt af mindst en vis UE-til-UE-afstand, så krydslink-interferens (cross-link interference, CLI) er ubetydelig. (2) En SRP-baseret løsning, der udnytter den lange udbredelsesforsinkelse til at planlægge synkrone UL- og DL-transmissioner, som er fuldt indeholdt i den samtidige udbredelsesvarighed, så overlap kan ske uden interferens. Ved hjælp af systemniveau-simuleringer sammenlignes løsningerne med en naiv basisløsning i to trafiksituationer. Begge løsninger sænker latenstid på tværs af alle mål: den klyngebaserede løsning reducerer 95.-percentil UL-latenstid med 21 %, og SRP-løsningen reducerer 95.-percentil DL-latenstid med 65 %.
[This apstract has been rewritten with the help of AI based on the project's original abstract]