Understanding Satellite Downlink Transmissions and the Limitations of Earth’s Coverage

Not too bad, the limited ‘coverage’ on earth is mainly due to two factors: downtilt of sectors (to artificially limit the radius of a cell and thus keep cells smaller and increase the capacity per user) but also the curvature of the earth (sorry, flat-earthers): in practice, for a line of sight of more than 70 km, you need bizarrely high towers that they become too expensive. If I’m not mistaken, Starlink is at an altitude of 500 km. And although that is a lot more than the 70 km of normal cell towers, it is quite doable. The FCC filing says interesting things about it:

https://licensing.fcc.gov….file_numberC/File+Number

Satellite downlink transmissions will operate over a range of parameters more fully captured in the Schedule S, with no more than a peak antenna gain of 38 dBi, peak Effective Isotropic Radiated Power (“EIRP”) of 58 dBW, and peak EIRP density of -2.33 dBW/Hz (per 1.4 MHz channel).

A Reddit user explains further:

https://www.reddit.com/r/…phone_direct_to_starlink/

“Put 38 dBi antenna gain, 3 W cell phone transmit power (high power mode), 153 dB free space path loss (a receiving Starlink satellite is above you ) into a link budget calculator and you get -80 dBm received power. For comparison wi-fi receivers work down to -100 dBm, 100 times weaker than -80 dBm.
If the phone is in regular 0.6 W power mode received power drops to -87 dBm. If the receiving satellite is not above but closer to horizon free space path loss further reduces received power to -92 dBm. Still usable signal above -100 dBm. Your body attenuates 2 GHz signal by about 3 dB (I could misremember, feel free to check). Now -95 dBm. Still usable (of course you lose bandwidth with the loss of received power). Phone in high power mode adds 3 dBm. The devil is in the details. There are typically other miscellaneous losses.”

2023-12-15 13:36:27
#SpaceX #green #light #test #Direct #Cell #service