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Satellite

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Overview Edit

This article is written from a point of view of a single traveller or a small group. It doesn't speak about backhaul technologies like O3b which require steerable antenna of a size of a house.

There are 5 ways of connecting to the internet without terrestrial infrastructure:

  • VSAT
  • Irridium
  • Inmarsat
  • Globalstar
  • Thuraya

Of those 5 only first one is generally affordable and fast for general-purpose internet use. The drawback is that it needs at least 80cm dish (depending on location) which needs to be pointed at satellite. So this is a possibility to provide an internet access to a parked minivan in remote areas but isn't a possibility if you need access on the move or a portable device.

For other 4, unless you want to spend thousands of dollars, you need to evaluate what exactly do you need. Most of usecases are covered by a specialized devices or apps which allow for examine:

  • Tracking
  • Voice calls
  • Messages
  • Weather

Different devices have different feature sets as detailed in individual sections. If your usecase is not covered by listed devices it might be cheaper to have someone else research the info you need and give you relevant data by short messages. Paying him would still be cheaper than trying to browse the web yourself.

Orbits, latency and coverage Edit

There are 3 types of commonly used orbits for communication satellites:

  • Low Earth Orbit
  • Middle Earth orbit
  • Geostationary orbit, about 36000 km above ground.

A satellite in geostationary orbit will be always above the same point of Earth and will be seen at the same point in the sky. This provides several advantages like being able to cover a fixed geographic area with few satellites, absence of handoffs and easier antenna setups. There are how drawbacks:

  • Latency. It takes 120 ms for the signal to reach satellite and then another 120 ms to reach the gateway. So it means 480 ms theoretical low limit for ping times. Real life ping times are in 1000-1500 ms range. This makes any latency-sensitive activity impossible and audio and video calls sluggish. Web browsing is affected as well resulting in slower page loads but bulk transfers are fine.
  • Coverage. Satellite above the equator can't see latitudes near the poles and in Arctic and Antarctic even if it's above the horizon it's easily obstructed. Coverage of the whole world other than Arctic and Antarctic requires 3 satellites. With 1 or 2 satellites only partial coverage can be achieved.

VSAT, Inmarsat and Thuraya use geostationary orbits. Irridium and Globalstar use low earth orbits. Details on coverage and latency are detailed in relevant sections.

Connection typesEdit

There are 3 different types of connections commonly used in satellite networks:

  • Always-on. This is similar to mobile data or broadband connection. As long as equipment is setup and on, it will be connected to network ready to send your packets. Usually it means billing per days or per traffic.
  • Circuit. You need to "dialup" to establish internet connection. You will be usually billed per minute.
  • Burst. Equipment connects for a fraction of a second to few seconds to send and receive the data needed. Billing is usually per seconds spent connected which depends on traffic. This method is not used cut conventional internet connection but is useful for messages and special applications.

Different networks provide different access models.

VSAT Edit

VSAT for Very Small Aperture Terminal is a general term for internet using a dish smaller than 3 meters. Typically dish is 75-120cm, similar to TV dish. There are many VSAT providers using different satellites. Typical prices are USD 30/month for 15 Mbps/1 Mbps with few Gigabytes of FUP, often called fair access policy in satellite world. Different providers use different, often incompatible, equipment. Sometimes the same equipment can be used for several providers. As VSAT uses geostationary satellites, the latency is pretty high.

Mobility Edit

Primary target audience of VSAT is fixed internet in rural areas but installation on a vehicle is possible. While theoretically there is equipment able to keep satellite connection while driving, it's rate and expensive. So in most cases using VSAT means parking, planting stick into the ground, installing dish in the ground near your vehicle, spending 10-20 minutes directing your antenna and only then being able to access internet. Some installations can be installed on the vehicle and sometimes even motorized for an easy pointing at the cost of additional drag and height and/or width of the vehicle. Systems with tracking can even be used while driving but those are rare with satellite internet.

Components Edit

The main components are:

  • Dish
  • iLNB receiver (the head in the center of the dish, two-way)
  • Satellite modem
  • WiFi router (optional)

Pointing Edit

You will need a way to find out general direction where to point your dish. Best way is to install an app which will compute azimuth and elevation based on GPS coordinates and show where to point the antenna. Then you'll need to find exact direction by slowly moving antenna and using a signal indicator (satellite finder). Motorized systems may be able to direct automatically.

Coverage Edit

VSAT typically uses directed beams so coverage is limited to a continent typically. As there are many VSAT providers it's impossible to list them all here. You'll have to contact your local VSAT provider for installation.

Security Edit

Same information as you receive can be received across large area. If satellite provider doesn't encrypted connection your downlink will be visible to anybody within your large geographic area and right equipment. So it's heavily recommended to use encrypted protocols like https.

IridiumEdit

Iridium ist named after the precious metal Irridium, the element with atomic number 77 as original design included 77 active satellites.

CoverageEdit

If you have a good view of a sky, you can use Iridium, no matter where you are on the planet.

Irridium has a constellation of low Earth orbit satellites in polar orbits. So from every point on Earth including poles a satellite is always visible. Irridium supports bouncing signal through several satellites until it is able to get to terrestrial gateway hence if you see the satellite, you can connect to the network. This is in contrast to Globalstar which has additional restrictions.

SpeedEdit

Except their maritime product Iridium Pilot, every Iridium data access is 2400 bit/s=2.4kbit/s. It's 20 times slower than GPRS and 100 times slower than EDGE. In a minute you can download 15 kB under ideal conditions. This works out to over an hour to download a single megabyte. Obviously most of "normal" usecases completely break down at such speeds and only specifically designed apps and websites are still comfortable to use.

WIP.

InmarsatEdit

Inmarsat is an abbreviation of International Maritime Satellite. Despite its name it covers both land and sea. Inmarsat operates satellites from 4 geostationary orbits covering the whole world except Arctic and Antarctic regions. coverage map

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GlobalstarEdit

Like Irridium, Globalstar uses a constellation of low Earth satellites. Unlike Irridium those satellites are on 52° inclination and not polar orbit. This means that Arctic and Antarctic regions are not covered. Furthermore their satellites are unable to relay data between them. This means that satellite must be able to see both you and a gateway. Practical implication is lack of coverage on the oceans including islands, South-East Asia, Central America and most of Africa. For more details see coverage map

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ThurayaEdit

Thuraya is named after Arabic word for constellation of Pleiades. They operate geostationary satellites in 2 orbital positions covering EMEA and APAC. Americas, Arctic and Antarctic are not covered. Due to spot configuration southern Africa is not covered either. For more details consult their coverage map. Ignore their M2M map as it includes GSM roaming and make sure to choose "Satellite network" and not "GSM roaming".

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