5G • 5G-Advanced (Rel-18)
NTN Selective HARQ Disabling
Long-Latency Hybrid ARQ Bypass Protocol for Satellite Links
Allows the network to disable Layer-1 HARQ retransmissions on long-delay satellite paths, relying on robust RLC ARQ to prevent buffer stall.
Technical Explanation
In Geostationary (GEO) satellite links, round-trip delay exceeds 540 milliseconds. Traditional Layer-1 HARQ requires holding packets in memory buffers until ACK/NACK arrives, which exhausts base station buffer queues and causes throughput collapse. Rel-18 allows selective disabling of HARQ on a per-bearer basis, relying on RLC layer ARQ.
Key Functions
- Disables Layer-1 HARQ feedback on satellite links with extreme propagation delays
- Prevents catastrophic memory buffer exhaustion and bufferbloat in base station modems
- Delegates reliable retransmission duties to the higher Radio Link Control (RLC) layer
- Maximizes TCP window sizes and sustained throughput across GEO and MEO orbits
Specifications
3GPP TS 38.321, TS 38.300 (Rel-18)
Interfaces
Uu (MAC/RLC)
Related 5G Concepts
Want to memorize 5G concepts like this one?
Study it with SuperMemo SM-2 spaced repetition flashcards.