표 1. | Table 1.
TR 38.821, NTN 솔루션[3] | TR 38.821, NTN Solutions.

Issue Solution
Physical/MAC DL synchronization Doppler shift, long delay Pre-/Post-compensation of Doppler shift, common offset
UL synchronization (TA, RACH) TA variation, long delay, long procedure (4-step RA) Common timing/frequency offset, use of UE/Satellite position information, 2-step random access, Enhanced PRACH formats/preamble sequences
UL scheduling Long delay SR/BSR/Grant procedure optimization
Retransmission issue HARQ Long delay, need more HARQ processes UL HARQ ACK disabling, UL retransmission disabling
RLC/PDCP Timer Long delay Longer timers: t-Reassembly, discardTimer, t-Reordering
SN Large window size Longer RLC/PDCP SN
Mobility Tracking area Frequent TA change Handover, TAU, Paging