L
Admin
[Technical article, rfforum Editorial Team]
LEO UT link budgets often freeze EIRP and G/T, then discover on the air that ACLR / spectral mask and Doppler-driven PA operating point eat the margin that looked fine on a static spreadsheet.
1. What moves in LEO that GEO budgets ignore
- Large, fast Doppler and Doppler rate force the modem / PLL and sometimes the PA bias or DPD training window to track; a PA optimised at one average power can fail mask while ramping
- ACLR and SEM are regulatory and gateway-sharing constraints; backing off for mask can cost more EIRP than rain fade in some bands
- Phased-array UT: element failures, scan loss, and beam-hop timing interact with the PA pool — a single "PA P1dB" line item under-states the story
2. Freeze list for an uplink claim
- Mask / ACLR at the EIRP and constellation you actually ship, including during Doppler ramp or beam switch if that is in the profile
- PA back-off vs DPD capability vs DC power at that back-off (thermal is part of the link budget for a handset-class UT)
- Whether gateway ACLR or local SEM was the tighter gate in your last campaign
- Modem AGC / PA cooperation: who owns crest factor and how fast
3. Habit
Put ACLR/SEM and Doppler-track notes on the same sheet as EIRP. A link budget that only has path loss and antenna gain is incomplete for LEO UT uplink reviews.
Discussion: on your last LEO UT uplink bring-up, what ate margin first — mask/ACLR back-off, Doppler/PLL, or array scan loss — and do you require a ramped-Doppler ACLR plot before CDR?
— rfforum 编辑部 / Editorial Team
LEO UT link budgets often freeze EIRP and G/T, then discover on the air that ACLR / spectral mask and Doppler-driven PA operating point eat the margin that looked fine on a static spreadsheet.
1. What moves in LEO that GEO budgets ignore
- Large, fast Doppler and Doppler rate force the modem / PLL and sometimes the PA bias or DPD training window to track; a PA optimised at one average power can fail mask while ramping
- ACLR and SEM are regulatory and gateway-sharing constraints; backing off for mask can cost more EIRP than rain fade in some bands
- Phased-array UT: element failures, scan loss, and beam-hop timing interact with the PA pool — a single "PA P1dB" line item under-states the story
2. Freeze list for an uplink claim
- Mask / ACLR at the EIRP and constellation you actually ship, including during Doppler ramp or beam switch if that is in the profile
- PA back-off vs DPD capability vs DC power at that back-off (thermal is part of the link budget for a handset-class UT)
- Whether gateway ACLR or local SEM was the tighter gate in your last campaign
- Modem AGC / PA cooperation: who owns crest factor and how fast
3. Habit
Put ACLR/SEM and Doppler-track notes on the same sheet as EIRP. A link budget that only has path loss and antenna gain is incomplete for LEO UT uplink reviews.
Discussion: on your last LEO UT uplink bring-up, what ate margin first — mask/ACLR back-off, Doppler/PLL, or array scan loss — and do you require a ramped-Doppler ACLR plot before CDR?
— rfforum 编辑部 / Editorial Team
