Slashdot Mirror

Covering the globe with internet via low earth orbit would take a LOT of satellites, or you could use just three. Like these folks are planning. https://www.viasat.com/product...

If they are geostationary, they won't have low latency because too far away. If they are leo then they will be moving and three won't be enough to cover everything, so how can 3 sats work?

Covering the globe with internet via low earth orbit would take a LOT of satellites, or you could use just three. Like these folks are planning. https://www.viasat.com/product...

http://www.viasat.com/news/high-speed-internet-now-flying-jetblue-launches-service-using-viasat-high-capacity-ka-band-broadband

I remember reading this a year ago or so when the home service launched, but I guess /. missed it. This kind of portable/mobile use is being heavily marketed for homeland security, SNG (Satellite News Gathering), and other high-end markets, while they continue to give the middle finger to RVers, truckers, etc--I guess the home system is locked to the spotbeam its activated on so you can't roam outside it, unlike HughesNet. Personally, I'd love their little portable flyaway system, but at a price of $20k or so, oh well.

Simple answer is you won't.

Ever heard of Exede? Viasat has its own satellite in orbit and offers consumer internet. Pricing starts at $50 for 12 down, 3 up. Yes, latency may ruin your Skype session, but you know that will happen with any satellite link.

Caps can be an issue....

ViaSat just formally announced the service. $50 gets you 7.5GB/month. There are higher level plans with more transfer available for a significant price increase.

What's the total bandwidth of the satellite?
If you can get 12Mbps when nobody else is using it, that sounds great until they have about 5 customers.

140 Gbps/1 satellite - approx 12000 users downloading at full capacity in the same time.

Unless the downloaded data originates on the satellite.. it has to be transmitted up from the ground first so actual user capacity would be about half that. Not great when you consider the area one satellite covers. It would be interesting to know if they are using some sort of advanced caching or multiplexing routines when it comes to things like netflix.

What's the total bandwidth of the satellite? If you can get 12Mbps when nobody else is using it, that sounds great until they have about 5 customers.

140 Gbps/1 satellite - approx 12000 users downloading at full capacity in the same time.

• near end echo cancellation; a wide dynamic range receiver that can subtract the station's own forward transmission from the mix of forward and reverse transmissions on the line, many modern 2-wire digital line systems (eg. DSL, V.90) work this way
• A variation of the above for satellite transmission that tracks the phase and frequency offsets in the satellite transponder to achieve a similar forward channel cancellation eg. PCMA
• an iterative variation whereby you can receive all signals in a given frequency space and as you learn what each signal is, you can subtract a recreation of it from the jumble and reveal even more signals underneath it

This one is cool because it seems it can be retro-fitted to an existing transmitter, it works by creating local interference tending to cancel the forward transmission so that the station's receiver is unaffected by it.
I'd be interested to know what it does to the radiation pattern of the transmitting antenna and how sensitive it is to the way in which the antenna is mounted. I'm sure it works great on a flat plate.

That's not exactly true. There's a huge demand for inline network encryption and cross domain filtering devices that DO allow Secret/Top Secret data to go out on insecure public networks. For example, products like this

Or contact the experts.

http://viasat.com/broadband-satellite-networks

I'm a little biased, but I truly believe that for a broadband satellite solution specializing in IP over satellite this is your best bet.

Double hop routing is already solved... Here's an example. Notice the text about "...can support star, mesh or hybrid network topologies..."? Any site can "talk" directly to any other.

While I'm not the original poster, I'm still at a loss as for what advantage this development gives.

You have two options: Direcway or VIASAT.

VIASAT I have no idea on the expense, but that's what's powering your morale computers. It's the best solution you're going to find out there bar none. The ISP they're using is called Segovia, but there are other ISPs who will sell you access to VIASAT. The dishes are huge (6ft+), you need a SAT phone to engineer your link (three way call between your ISP and a VIASAT tech), and I think the cost will be prohibitive. But I don't know how crazy you want to get ;)

While we were stationed in Iraq, we bought a Direcway system from one of the locals. It was about $3k for the equipment and another $300-400/mo for the service. But you're an officer so you can afford it ;) We got the Army to pay for it. If you're in Bagram or Kabul, you should be able to find a "local contractor" who will be willing to deal with you. Unfortunatly, most of them only deal in cash. You may be able to pay Segovia with a credit card...

As far as your reqt #2: The dish is about 1.5 meters and the TX/RX assembly is about 2.5ft long. Hopefully you'll get a decent free standing base, but the better they are, the bigger they are unfortunately. The modem we had was three parts (TX/RX/net) each about the size of a normal cable/dsl modem. It was all 110/220 exept for the mini-hub they gave us which had a 220 only wall wart.

3: You can use any of the numerous aiming programs out there. To see the signal strengths on the modem itself you need a F-F null modem serial cable, so either buy two of them and splice or get the appropriate adaptors. The menu system, once you connect is pretty self expanitory. Get your TX and RX to at least 90 and tighten your bolts carefully.

4: You'll have to handle throttling yourself. Our system came with about 10 IPs, but we used a single IP as firewwall/NAT just to be safe.

Service was OK. Your connection will likely hit the ground in Germany, so most slowdowns happen according to their timezone. You will have to be death on infections. A single computer (sans throttling) will completely dominate the connection. Good luck!

The product that Boeing has announced was acutally developed by
Viasat in Carlsbad CA. I strongly suspect that Boeing is only the launch customer for this service.

See their April press release about it here.

See Boeing's FAQ about it here. The only technical info I saw was that Boeing has "a proprietary solid-state phased array receive and transmit antenna" that they will use, which solves the antenna gain problem.

Based on ViaSat's other [publicly announced] activities, I would expect that the link from the hub (ground) to the remote (aircraft) will be a standard fat DVB carrier, and the return transmitted from the aircraft will be a CDMA / spread spectrum modulation of some sort. ViaSat has some patents on technology that allow them to acheive dramatic savings in bandwidth, which is outrageously expensive on satellites. This returnlink is the real sexy part of the system, the kind of thing that makes engineers want to toil long hours to make it work ...

Further, it's interesting to note that Boeing's FAQ says that the space segment will be "leased satellite transponders". This is the same old "bent pipe" design that has worked well for the past 30 years -- for example, Ku-band is 14 GHz up, 12 GHz down, and all the satellite does is mirror the signals it receives on the up frequency back down to the ground at the down frequency. This is interesting because there has long been talk of "smart" satellites that do more than just this analog bent-pipe work -- say, demodulating the data and switching in the sky. Some LEOs do this (Teledesic), but none of the GEOs do it yet.

Finally, I saw no mention of band. Is this Ku-band (12-14 GHz) or Ka-band (20-30 GHz)? ViaSat is charging forward in the Ka-band market, but there is very very little satellite coverage in that band, so perhaps this is designed to roll out at Ku-band at first with future upgrades to Ka-band possible.

It appears to me that Green Bank is just a standard offset feed design. This is the same design used in your dinky DBS TV dish and virtually every small satellite antenna in the world. That said, there certainly are other things that distinguish Green Bank, including the colossal size (and [oink] price) and the dynamically adjustable surface.

One of my work colleagues once provided me with the following explanation to help understand how these offsets works.

Visualize a standard "prime focus" antenna. This is the kind that has the struts from the edge of the big reflector to a point in the air above the exact center of the dish. Energy from space hits the metal reflector and is bounced towards the focus point, where the struts meet and your receivers are. Here's a PDF of a prime focus antenna.

Now imagine that the antenna is pointed straight up, so it's like a bowl catching rain. If you sliced vertically through it, you'd see a perfect parabola, which would go further out and up if you extended the curves of the reflector. The receiver is sitting at the focus point of that parabola.

Imagine that perfect, mathematical parabola sitting there, with the sides extending out and up. The reflector just happen to be a metal realization of the very bottom of that parabola. We could make antennas where the reflector extends furhter up the sides of that mathematical parabola, but eventually it's just lots of expensive metal structure for not much gain (pun intended :)).

Here's the cool part: Now imagine that instead of the metal reflector occupying the bottom of the parabola, you slide the metal "skin" UP THE SIDE of the mathematical parabola that you're envisioning. The parabola doesn't move, and thus neither does the focus point. Just slide the metal "realization" of that paraboloid curve up one side.

The antenna is still "looking" straight up into space, but now the reflector is off to the side a bit. The reflector on your DBS dish is actually a mathematically very complex section of a 3D paraboloid surface. But it's usually hard to tell because the reflector is relatively flat, and thus it's hard ot detect the complex curves involved. Here's a bunch of pictures of offset-feed dishes.

Green Bank has the feed overhead, unlike your DBS dish. It's still the same idea; they just spun the whole thing around on the line-of-sight axis.

What's the big advantage? As the article hinted, you don't have those struts in the way of the incoming energy, and thus the antenna is more efficient. Also, on a big system like GB, it's possible for them to lower the feed/receiver assembly closer to the ground where it's easier to service.

In my job, we usually have the antennas oriented like your DBS dish, with the feed close to the ground. But when you get to real high latitudes (like in Alaska or Siberia), the satellite you're trying to hit is real close to the horizon, and when we try to aim that low, the feed hits the ground. In those rare cases, we have to spin it around to put the feed high up in the air, like GB, only WAY smaller.

By the way, there's a kind of antenna (called a Cassegrain) that looks sort of like a prime focus, but has a second refector at the feed which bounces the energy back down to the receiver at the center of the main reflector. Here's a PDF of a Cassegrain antenna.

PDFs courtesy of my employer :)

It appears to me that Green Bank is just a standard offset feed design. This is the same design used in your dinky DBS TV dish and virtually every small satellite antenna in the world. That said, there certainly are other things that distinguish Green Bank, including the colossal size (and [oink] price) and the dynamically adjustable surface.

One of my work colleagues once provided me with the following explanation to help understand how these offsets works.

Visualize a standard "prime focus" antenna. This is the kind that has the struts from the edge of the big reflector to a point in the air above the exact center of the dish. Energy from space hits the metal reflector and is bounced towards the focus point, where the struts meet and your receivers are. Here's a PDF of a prime focus antenna.

Now imagine that the antenna is pointed straight up, so it's like a bowl catching rain. If you sliced vertically through it, you'd see a perfect parabola, which would go further out and up if you extended the curves of the reflector. The receiver is sitting at the focus point of that parabola.

Imagine that perfect, mathematical parabola sitting there, with the sides extending out and up. The reflector just happen to be a metal realization of the very bottom of that parabola. We could make antennas where the reflector extends furhter up the sides of that mathematical parabola, but eventually it's just lots of expensive metal structure for not much gain (pun intended :)).

Here's the cool part: Now imagine that instead of the metal reflector occupying the bottom of the parabola, you slide the metal "skin" UP THE SIDE of the mathematical parabola that you're envisioning. The parabola doesn't move, and thus neither does the focus point. Just slide the metal "realization" of that paraboloid curve up one side.

The antenna is still "looking" straight up into space, but now the reflector is off to the side a bit. The reflector on your DBS dish is actually a mathematically very complex section of a 3D paraboloid surface. But it's usually hard to tell because the reflector is relatively flat, and thus it's hard ot detect the complex curves involved. Here's a bunch of pictures of offset-feed dishes.

Green Bank has the feed overhead, unlike your DBS dish. It's still the same idea; they just spun the whole thing around on the line-of-sight axis.

What's the big advantage? As the article hinted, you don't have those struts in the way of the incoming energy, and thus the antenna is more efficient. Also, on a big system like GB, it's possible for them to lower the feed/receiver assembly closer to the ground where it's easier to service.

In my job, we usually have the antennas oriented like your DBS dish, with the feed close to the ground. But when you get to real high latitudes (like in Alaska or Siberia), the satellite you're trying to hit is real close to the horizon, and when we try to aim that low, the feed hits the ground. In those rare cases, we have to spin it around to put the feed high up in the air, like GB, only WAY smaller.

By the way, there's a kind of antenna (called a Cassegrain) that looks sort of like a prime focus, but has a second refector at the feed which bounces the energy back down to the receiver at the center of the main reflector. Here's a PDF of a Cassegrain antenna.

PDFs courtesy of my employer :)