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> In-flight wifi (and otherwise all other transmissions) have pretty much always been air to ground This has not been the case for several years. Most in fligh

> In-flight wifi (and otherwise all other transmissions) have pretty much always been air to ground This has not been the case for several years. Most in flight Wifi is now being provided by Viasat which, as the name suggests, is air to space. Even Gogo started rolling out satellite service in 2015. Very few services are now air-to-ground. Random pictures: https://i.stack.imgur.com/I7Yfd.jpg https://i.stack.imgur.com/I7Yfd.jpg https://cdn.arstechnica.net/wp-content/uploads/2018/01/DSC00095-Medium.jpg https://cdn.arstechnica.net/wp-content/uploads/2018/01/DSC00...

zuhayeer 4y ago
I stand corrected, edited above.
kensai 4y ago
If this has been working correctly for many years, how is it that we still lose planes? :( Isn't such connection bulletproof for the trajectory of the plane, even if simply passively tracking?
- postingawayonhn 4y ago
  Not all plans have these systems installed.
- cjrp 4y ago
  Several changes came in post-MH370 https://en.wikipedia.org/wiki/Malaysia_Airlines_Flight_370#Aircraft_tracking https://en.wikipedia.org/wiki/Malaysia_Airlines_Flight_370#A...
coffeeblack 4y ago
They are air to geo stationary, and that’s a long way. 50,000 km instead of Starlink’s 300 km, iirc.
- rtkwe 4y ago
  The operational height is around 550km they're just launched to ~300km then boost and spread themselves out.
rkangel 4y ago
There's a new air-to-ground provider though: https://smartskynetworks.com/connectivity/ https://smartskynetworks.com/connectivity/ (I worked on this technology)
- mytailorisrich 4y ago
  Interesting. Is it based on 4G/5G or something ad-hoc?
  - rkangel 4y ago
    <goes and checks press-releases to remember which bits I can talk about...> It's basically LTE in the 2.4 GHz band, with a load of extra bits for beam forming, coping with speed and distance etc. Using the 2.4 GHz band allows them to build a network covering the US without spending billions on spectrum. Yes, it's the same 2.4GHz ISM band that wifi uses, with the same power limits. And yes, it works well enough that you can do video calls hundreds of kilometres from the base station. That's how shit wifi is, and how well this stuff works.
    - deleted 4y ago
      [deleted]
    - JTon 4y ago
      > That's how shit wifi Seems like you know a bit about this. Could you indulge my curiosity and elaborate why wifi is shit? I assume some combo of DSP bottleneck (i.e. want to keep hw cheap) and maintaining backwards compatibility with older standards?
      - rkangel 4y ago
        Wifi is improving now. Newer standards like Wifi 6 are doing that basically by taking the good ideas from LTE (4G) and applying them to Wifi. The cellular radio community has been much better about evolving standards, coming up with new technology and rolling it out. Maybe they have it easier because everyone gets a new phone every two years, but they've still had fairly good backwards compatibility support. Multiple Access - this is the general term for 'multiple devices on the same spectrum'. Cellular divides up the spectrum into frequency bands (Frequency division multiplexing) and time slots in those bands (time division multiplexing). The base station then assigns each device a slot in a band (or potentially several), it also provides the time reference for this scheduling. This makes efficient use of your available spectrum and nothing interferes with or talks over anything else. Wifi gets none of this. There's no base station planning so two access points can interfere with each other. There's no FDMA (access point runs on one channel of one band), and no TDMA. There's no uplink channel and downlink channel separation. Instead it's "Carrier sense with collision detection". Basically "try not to transmit at the same time as someone else, and if you do come back and try again later". This results in nodes competing, talking over each other, interfering (see "hidden node problem") etc. and makes inefficient use of the spectrum. The problem gets worse as the traffic gets busier. Wifi 6 is bringing in some actual scheduling. Modulation schemes (the fundamental way that you transmit bits on a radio) - cellular modulation schemes are now incredibly efficient and robust. They use a variety of techniques that allow scaling based on channel conditions so that you can get as close as possible to whatever Shannon currently says you're allows. A lot of wifi uses old-school spread spectrum, and newer standards use OFDM which is a bit better. Wifi 6 is finally moving to the Quadrature Amplitude Modulation stuff that LTE uses.
lxgr 4y ago
There‘s a new hybrid system in Europe called EAN, based on a specialized LTE network and an S-band satellite to fill in gaps in coverage (mostly over the oceans). I recently got to use it, and as expected latency is significantly better than on a pure GEO system.
- mytailorisrich 4y ago
  Gogo is also working on an air-to-ground 4G/5G network covering the continental US. The thing is that once Starlink has the service working, and they have, it does not require a lot of extra investment to support ships and aircrafts. On the other hand, an air-to-ground system requires a full cellular network on the ground (at the very least with dedicated RF and antennas), although with fewer sites because cells can be massive, and that still only covers land.
  - throwaway894345 4y ago
    > it does not require a lot of extra investment to support ships and aircrafts. Are you sure about that? I have a friend who worked in airspace comms his whole career (including at Gogo) and he described some of the challenges of the engineering problem (these systems have to be airgapped from the critical systems on the plane, the certification processes, the antennas have to be super highly directional to talk with satelites high overhead while both the plane and the satellite are moving at tremendous speed, etc). Maybe your "not a lot of extra investment" is relative, but it seems like there's still a bunch of work to make these things work on planes.
    - mytailorisrich 4y ago
      Yes, of course it is relative. Developing new terminals is orders or magnitude cheaper than developing and deploying a cellular network.
      - lxgr 4y ago
        True, but complex terminals increase the unit price and ongoing cost (higher weight and surface area both increase fuel consumption). EAN supposedly works with only 300 base stations – in terms of terrestrial networks, that‘s nothing.
rockemsockem 4y ago
I flew across the Pacific on Alaska Airlines last month and they specifically said they'd only have Internet until we left the continental US. Most of the trip had no Internet, just the in-flight movies that you can stream over their wifi.
- bombcar 4y ago
  Depending on the satellite provider, they may still be using satellite and still only work over the continental US. Even starlink basically bounces the signal off a satellite and down to a ground station; this doesn't work over the ocean. They just started doing satellite to satellite links to get "back to land".

zuhayeer 4y ago

I stand corrected, edited above.

kensai 4y ago

If this has been working correctly for many years, how is it that we still lose planes? :( Isn't such connection bulletproof for the trajectory of the plane, even if simply passively tracking?

postingawayonhn 4y ago
Not all plans have these systems installed.
cjrp 4y ago
Several changes came in post-MH370 https://en.wikipedia.org/wiki/Malaysia_Airlines_Flight_370#Aircraft_tracking https://en.wikipedia.org/wiki/Malaysia_Airlines_Flight_370#A...

coffeeblack 4y ago

They are air to geo stationary, and that’s a long way. 50,000 km instead of Starlink’s 300 km, iirc.

rtkwe 4y ago
The operational height is around 550km they're just launched to ~300km then boost and spread themselves out.

rkangel 4y ago

There's a new air-to-ground provider though: https://smartskynetworks.com/connectivity/ https://smartskynetworks.com/connectivity/ (I worked on this technology)

mytailorisrich 4y ago
Interesting. Is it based on 4G/5G or something ad-hoc?
- rkangel 4y ago
  <goes and checks press-releases to remember which bits I can talk about...> It's basically LTE in the 2.4 GHz band, with a load of extra bits for beam forming, coping with speed and distance etc. Using the 2.4 GHz band allows them to build a network covering the US without spending billions on spectrum. Yes, it's the same 2.4GHz ISM band that wifi uses, with the same power limits. And yes, it works well enough that you can do video calls hundreds of kilometres from the base station. That's how shit wifi is, and how well this stuff works.
  - deleted 4y ago
    [deleted]
  - JTon 4y ago
    > That's how shit wifi Seems like you know a bit about this. Could you indulge my curiosity and elaborate why wifi is shit? I assume some combo of DSP bottleneck (i.e. want to keep hw cheap) and maintaining backwards compatibility with older standards?
    - rkangel 4y ago
      Wifi is improving now. Newer standards like Wifi 6 are doing that basically by taking the good ideas from LTE (4G) and applying them to Wifi. The cellular radio community has been much better about evolving standards, coming up with new technology and rolling it out. Maybe they have it easier because everyone gets a new phone every two years, but they've still had fairly good backwards compatibility support. Multiple Access - this is the general term for 'multiple devices on the same spectrum'. Cellular divides up the spectrum into frequency bands (Frequency division multiplexing) and time slots in those bands (time division multiplexing). The base station then assigns each device a slot in a band (or potentially several), it also provides the time reference for this scheduling. This makes efficient use of your available spectrum and nothing interferes with or talks over anything else. Wifi gets none of this. There's no base station planning so two access points can interfere with each other. There's no FDMA (access point runs on one channel of one band), and no TDMA. There's no uplink channel and downlink channel separation. Instead it's "Carrier sense with collision detection". Basically "try not to transmit at the same time as someone else, and if you do come back and try again later". This results in nodes competing, talking over each other, interfering (see "hidden node problem") etc. and makes inefficient use of the spectrum. The problem gets worse as the traffic gets busier. Wifi 6 is bringing in some actual scheduling. Modulation schemes (the fundamental way that you transmit bits on a radio) - cellular modulation schemes are now incredibly efficient and robust. They use a variety of techniques that allow scaling based on channel conditions so that you can get as close as possible to whatever Shannon currently says you're allows. A lot of wifi uses old-school spread spectrum, and newer standards use OFDM which is a bit better. Wifi 6 is finally moving to the Quadrature Amplitude Modulation stuff that LTE uses.

lxgr 4y ago

There‘s a new hybrid system in Europe called EAN, based on a specialized LTE network and an S-band satellite to fill in gaps in coverage (mostly over the oceans). I recently got to use it, and as expected latency is significantly better than on a pure GEO system.

mytailorisrich 4y ago
Gogo is also working on an air-to-ground 4G/5G network covering the continental US. The thing is that once Starlink has the service working, and they have, it does not require a lot of extra investment to support ships and aircrafts. On the other hand, an air-to-ground system requires a full cellular network on the ground (at the very least with dedicated RF and antennas), although with fewer sites because cells can be massive, and that still only covers land.
- throwaway894345 4y ago
  > it does not require a lot of extra investment to support ships and aircrafts. Are you sure about that? I have a friend who worked in airspace comms his whole career (including at Gogo) and he described some of the challenges of the engineering problem (these systems have to be airgapped from the critical systems on the plane, the certification processes, the antennas have to be super highly directional to talk with satelites high overhead while both the plane and the satellite are moving at tremendous speed, etc). Maybe your "not a lot of extra investment" is relative, but it seems like there's still a bunch of work to make these things work on planes.
  - mytailorisrich 4y ago
    Yes, of course it is relative. Developing new terminals is orders or magnitude cheaper than developing and deploying a cellular network.
    - lxgr 4y ago
      True, but complex terminals increase the unit price and ongoing cost (higher weight and surface area both increase fuel consumption). EAN supposedly works with only 300 base stations – in terms of terrestrial networks, that‘s nothing.

rockemsockem 4y ago

I flew across the Pacific on Alaska Airlines last month and they specifically said they'd only have Internet until we left the continental US. Most of the trip had no Internet, just the in-flight movies that you can stream over their wifi.

bombcar 4y ago
Depending on the satellite provider, they may still be using satellite and still only work over the continental US. Even starlink basically bounces the signal off a satellite and down to a ground station; this doesn't work over the ocean. They just started doing satellite to satellite links to get "back to land".