3GPP NTN for D2D: NR-NTN UE requirements, timing, HARQ

Adapting 5G NR for Satellite Delays

The 3GPP NR-NTN standard, introduced in Release 17 and enhanced in Release 18, adapts the 5G New Radio air interface to accommodate the long propagation delays inherent in satellite communication. A LEO satellite at 600 km altitude introduces approximately 4 ms one-way delay, while the full round-trip through satellite to gateway and back exceeds 20 ms. Standard 5G NR procedures assume sub-millisecond propagation, so NTN requires fundamental changes to timing advance management, HARQ feedback, random access procedures, and scheduling to function correctly over satellite links.