5 ms·

Aiming for 20 ms later this year. (Elon time) A bigger dish would not lower latency but may increase signal strength leading to better throughput. But it's not

Aiming for 20 ms later this year. (Elon time) A bigger dish would not lower latency but may increase signal strength leading to better throughput. But it's not a simple parabolic antenna. It is the first consumer oriented phased array antenna tracking the satellites as they move across the sky, so that would increase the antenna cost even more. https://en.wikipedia.org/wiki/Phased_array https://en.wikipedia.org/wiki/Phased_array

Reventlov 6y ago
« A bigger dish would not lower latency but may increase signal strength leading to better throughput. » A better signal strength would probably lead to better modulations being used, therefore, less transmission and reception time, and a better latency, or am I wrong ? (at least that's the case for Wi-Fi: the better the signal strength, the lower the transmission time so the better the latency).
- swiley 6y ago
  It could also mean less retransmission, depending on how the MAC works. That would lower the average latency.
- labcomputer 6y ago
  Latency in this case is dominated by time-of-flight to the satellite. At 100 Mbps with a 40 ms latency, there are about 2 megabits in the air between the ground station and CPE.
  - Denvercoder9 6y ago
    > Latency in this case is dominated by time-of-flight to the satellite. Is it though? Starlink orbits at 550 km, time-of-flight from ground to satellite to ground would be only 3.7ms, twice that makes ~20% of the roundtrip latency.
    - Robotbeat 6y ago
      550km is the closest approach. Usually it will be at least sqrt(2) times that (ie at least a slant angle of 45 degrees), maybe 2 times that. Plus the latency from the Gateway to the actual server. And the Gateways can have even greater slant angle to the satellite than the mobile terminals.
      - Denvercoder9 6y ago
        I don't think it'll usually be at a slant angle of at least 45°. The beta requires a field of view of 100° after tilting. I can't find the maximum tilt angle, but SpaceX has authorization to transmit only 25° degrees above the horizon, so the maximum slant angle is 65°.
        Robotbeat 6y ago
        But think what that means in terms of SOLID angle, not linear angle.
        Denvercoder9 6y ago
        Orbital planes are so close together that it doesn't make much difference. However, now that I've actually calculated it, your sqrt(2) factor seems to be about right for the average distance -- there's too few satellites per plane in the current phase. In this phase Starlink uses 72 orbital planes, with 22 satellites per plane, so 1440 satellites in total (they're almost there). It orbits at 550km above Earth's surface, so the orbit has radius 6921km, which gives an orbital length of 43486km. Separation between orbital planes varies depending on your latitude, but assume the worst case, where it is 43486km / 72 / 2 = 302km¹. Thus, the nearest orbital plane is at most 302km / 2 = 151km away from the orbital plane directly overhead. However, since the planes process, on average the nearest orbital plane is only half that, or 76km away from the plane overhead. Satellites within each plane have a separation of 43486km / 22 = 1976km. Thus, there's always a satellite at most 1976km / 2 = 988km away¹ from any point in each orbital plane, and on average there's a satellite half that away, or 494km. Adding all this together, the nearest satellite is on average √(550^2 + 76^2 + 494^2) = 743 km away (at the worst latitude). [EDIT: Actually, that's improper averaging, the correct average is obtained with ∫√(550^2 + x^2 + y^2) dx dy / ∫ dx dy on x=0..151, y=0..988, which yields 777km]. The original plan used 24 planes with 66 satellites, which reduces average distance to 617km. At more favorable latitudes the difference with the current design would be even larger. [EDIT: This should be 635km.] ¹ This is distance on the surface of the orbital sphere, straight-line distance is a bit less. It probably doesn't make much difference.
- deleted 6y ago
  [deleted]
BurningFrog 6y ago
I read that as "future versions of the antenna will be much improved", in price and performance. I know Moore's Law is being repealed, but that's still how new types of electronics work, right?
- kube-system 6y ago
  Moore’s law was specific to the way IC manufacturing worked. While it does (/did?) help reduce the price of electronic simply because they relied on ICs, the big price decreases you see in products after their early-adopter phase are likely just general economies of scale. Making small early batches of anything is more expensive per unit than making a ton of them —- regardless of whether it’s cutting edge tech or a plastic chair.
- geerlingguy 6y ago
  I think in the antenna's case, the primary goal would be to reduce costs for now (while still maintaining reliability), since the things currently cost $1500 per unit to make (SpaceX takes a loss on each new customer initially, for now).
walrus01 6y ago
I have seen as low at 15.85 ms from my starlink terminal to downtown Seattle. On average it's more like 22-23 ms.
- toast0 6y ago
  Centurylink DSL from across the sound to Seattle is generally 21ms, although there is little deviation. (Two line bonded vdsl)
  - walrus01 6y ago
    just the segment from your modem to the DSLAM is probably 14-16ms, which can be typical for VDSL2.
daniellarusso 6y ago
So, could multiple single units be coupled together? I assume that would be less expensive than creating larger circuit boards, shipping and packaging.

Reventlov 6y ago

« A bigger dish would not lower latency but may increase signal strength leading to better throughput. » A better signal strength would probably lead to better modulations being used, therefore, less transmission and reception time, and a better latency, or am I wrong ? (at least that's the case for Wi-Fi: the better the signal strength, the lower the transmission time so the better the latency).

swiley 6y ago
It could also mean less retransmission, depending on how the MAC works. That would lower the average latency.
labcomputer 6y ago
Latency in this case is dominated by time-of-flight to the satellite. At 100 Mbps with a 40 ms latency, there are about 2 megabits in the air between the ground station and CPE.
- Denvercoder9 6y ago
  > Latency in this case is dominated by time-of-flight to the satellite. Is it though? Starlink orbits at 550 km, time-of-flight from ground to satellite to ground would be only 3.7ms, twice that makes ~20% of the roundtrip latency.
  - Robotbeat 6y ago
    550km is the closest approach. Usually it will be at least sqrt(2) times that (ie at least a slant angle of 45 degrees), maybe 2 times that. Plus the latency from the Gateway to the actual server. And the Gateways can have even greater slant angle to the satellite than the mobile terminals.
    - Denvercoder9 6y ago
      I don't think it'll usually be at a slant angle of at least 45°. The beta requires a field of view of 100° after tilting. I can't find the maximum tilt angle, but SpaceX has authorization to transmit only 25° degrees above the horizon, so the maximum slant angle is 65°.
      - Robotbeat 6y ago
        But think what that means in terms of SOLID angle, not linear angle.
        Denvercoder9 6y ago
        Orbital planes are so close together that it doesn't make much difference. However, now that I've actually calculated it, your sqrt(2) factor seems to be about right for the average distance -- there's too few satellites per plane in the current phase. In this phase Starlink uses 72 orbital planes, with 22 satellites per plane, so 1440 satellites in total (they're almost there). It orbits at 550km above Earth's surface, so the orbit has radius 6921km, which gives an orbital length of 43486km. Separation between orbital planes varies depending on your latitude, but assume the worst case, where it is 43486km / 72 / 2 = 302km¹. Thus, the nearest orbital plane is at most 302km / 2 = 151km away from the orbital plane directly overhead. However, since the planes process, on average the nearest orbital plane is only half that, or 76km away from the plane overhead. Satellites within each plane have a separation of 43486km / 22 = 1976km. Thus, there's always a satellite at most 1976km / 2 = 988km away¹ from any point in each orbital plane, and on average there's a satellite half that away, or 494km. Adding all this together, the nearest satellite is on average √(550^2 + 76^2 + 494^2) = 743 km away (at the worst latitude). [EDIT: Actually, that's improper averaging, the correct average is obtained with ∫√(550^2 + x^2 + y^2) dx dy / ∫ dx dy on x=0..151, y=0..988, which yields 777km]. The original plan used 24 planes with 66 satellites, which reduces average distance to 617km. At more favorable latitudes the difference with the current design would be even larger. [EDIT: This should be 635km.] ¹ This is distance on the surface of the orbital sphere, straight-line distance is a bit less. It probably doesn't make much difference.
deleted 6y ago
[deleted]

BurningFrog 6y ago

I read that as "future versions of the antenna will be much improved", in price and performance. I know Moore's Law is being repealed, but that's still how new types of electronics work, right?

kube-system 6y ago
Moore’s law was specific to the way IC manufacturing worked. While it does (/did?) help reduce the price of electronic simply because they relied on ICs, the big price decreases you see in products after their early-adopter phase are likely just general economies of scale. Making small early batches of anything is more expensive per unit than making a ton of them —- regardless of whether it’s cutting edge tech or a plastic chair.
geerlingguy 6y ago
I think in the antenna's case, the primary goal would be to reduce costs for now (while still maintaining reliability), since the things currently cost $1500 per unit to make (SpaceX takes a loss on each new customer initially, for now).

walrus01 6y ago

I have seen as low at 15.85 ms from my starlink terminal to downtown Seattle. On average it's more like 22-23 ms.

toast0 6y ago
Centurylink DSL from across the sound to Seattle is generally 21ms, although there is little deviation. (Two line bonded vdsl)
- walrus01 6y ago
  just the segment from your modem to the DSLAM is probably 14-16ms, which can be typical for VDSL2.

daniellarusso 6y ago

So, could multiple single units be coupled together? I assume that would be less expensive than creating larger circuit boards, shipping and packaging.