Maritime Communications – Internet at Sea
VSAT – Always On, Fixed Price
Technically, all parabolic dish satellite terminals less than 3.8 m could be called Very Small Aperture Terminals, or VSATs, but the term VSAT generally refers to transmit/receive (TX/RX) satellite terminals used for two way, data and voice traffic, like the comforts of having the Internet at Sea or also telephone services.
A VSAT service is typically billed on a monthly contract, rather than by the minute, or by the megabyte like Inmarsat satcoms. With VSAT terminals you get the communications you need and you can even specifically tailor them to the resources you require to operate more smoothly.
Ku-Band VSAT – Fixed Price Regional Internet at sea
For full-service Internet at Sea with unrestricted web browsing, email, and telephone, the most common system is the 1 meter, Ku-Band VSAT, combined with an iDirect modem, for which you pay a fixed price, billed by the month, for virtually unlimited usage.
Like DSL at home, the system is always on, and the access for your Internet at Sea connection is shared among several other vessels contending for the same bandwidth. If the overall bandwidth is sufficient, and the number of vessels (contention ratio) is kept reasonably low, this is the most cost-effective way of providing full-service Internet access to vessels at sea. Depending on your bandwidth requirements, the typical monthly costs run between $1000 to $4000 and up.
The system uses a 1 meter, stabilized, Ku-band antennae like the SeaTel 4006 or 4009, the Orbit 7103 or the KNS Z10 costing in the region of $50 000 to $60 000. The antennas weigh about 120-240Kg (250-500 lbs) and are housed in a radome of about 1.2m (50″) diameter.
Satellite services are provided by companies like Stratos, Marlink, MTN, Caprock and a rapidly growing number of smaller companies and resellers. OmniAccess provides tailored VSAT services to some of the most elite superyachts.
Unlike global beam C-Band, Ku-Band provides regional coverage of certain areas, such as continental North America, Caribbean, South America, Europe and Mediterranean, select regions of Asia and the Pacific, and most recently, a Transatlantic beam covering the North Atlantic shipping routes. When a vessel moves from one region to another it will be necessary to change satellites, change satellite beams on the same satellite, or in some cases even change providers.
The high cost of the antenna equipment is driven by the tracking precision required to keep the antenna pointed at a tiny satellite 22,300 miles above the earth while the vessel rocks, rolls and turns in the ocean below, and the relatively small maritime VSAT market, with only about 5000 stabilized VSAT terminals, to share the costs of development and production of this precision equipment.
With the cost to build, launch, and operate a geostationary satellite over a lifespan of 10 years, at about $300 million one can understand the high, $2000-$4000, cost that the end users must pay for a small portion of the bandwidth. But it is worth it for having the Internet at Sea to help with keeping everyone safe and in touch.
Prices could range from something like $1500 per month for a 128/128 kbps circuit to $4700 per month or more for a 2048/256 kbps circuit. If you are quoted prices much less than this, you can be assured that the operator is cutting costs somewhere, probably by over-subscribing and reselling the same bandwidth to multiple users.
Even though low priced, over-subscribed networks can sometimes meet one’s needs quite adequately and cost-effectively, one must remember that you get what you pay for.
A correctly proportioned satellite network with an appropriate number of contenders should provide perfectly satisfactory Internet access unless one of the users is hogging all the bandwidth by continually downloading huge movie or music files. Some providers put bandwidth limits on each user to prevent this from happening.
Some providers will offer the option of a committed information rate (CIR) where they guarantee that your bandwidth will never drop below a certain (usually quite small 16-32kbps) level.
This just means that your Internet will not grind to a halt, but simply slow way down at times of heaviest contention. Often a certain CIR is included in your monthly cost, but increasing the CIR can be quite costly.
If you need higher guaranteed bandwidth, you might be better off with a dedicated (uncontended) service if you can justify the cost.
While there is no fixed formula for calculating a satisfactory contention ratio, the best providers will monitor bandwidth usage, and adjust bandwidth accordingly to accommodate the needs of the subscribers.
This is usually only possible with larger providers that have open-ended bandwidth agreements with the satellite companies.
Ku-band VSAT Terminals
Ku-Band satellites operate in the 12-14 GHz band and provide spot beam or regional coverage to certain areas on the earth. They require smaller, 1-meter VSAT antennas and provide more economical coverage to vessels that operate in a particular region for some period of time.
When the vessel relocates, it will need to change to a different satellite and a different satellite beam. Only high traffic areas are covered with Ku-Band, with the first Transatlantic beam becoming available in 2009.
Vessels that require more seamless coverage in less trafficked areas would need C-Band service.
Fixed Price, Shared Bandwidth
Time Division Multiple Access (TDMA) is like a timeshare in the sky except that you are not buying a week or two per year, but rather a few milliseconds every second. While you are downloading your Internet or speaking on the phone, you don’t even realize that there are several other users doing the same thing on the same satellite link. When there are fewer people using the link, there is more bandwidth available for you, and when there are more people, you will have a bit less.
Due to the extreme cost of building and launching a satellite, higher bandwidth links are very expensive. Dedicated Single Carrier Per Channel (SCPC) circuits are not only expensive but are also very inefficient, due to the bursty nature with which we use them. There are gaps between files, gaps between bits and bytes, gaps between phone calls and even gaps between words on a phone call. The only way to make efficient use of a satellite circuit is to share the bandwidth and the cost among several users.
What Size Antenna
The area of the reflector dish is directly proportional to the receive and transmit gain. The area of the dish is calculated by the formula
π x R2 or 3.142 x 1/2 Diameter squared
Doubling the size of the dish increases the area and the gain by four times.
In other words, a 60cm antenna has 4 times the area and the gain of a 30cm and a 2.4 meter antenna has four times the gain of a 1.2 meter. Doubling the antenna size increases the gain by 6 dBs.
This can make a huge difference to the amount of data that can be received or transmitted in a particular satellite footprint, and it will also determine how far out to the edge of the footprint one can travel.
In the case of VSAT your satellite provider will determine the size of dish required for a given area. On TV systems the size of the antenna determines how far you can travel to the edge of coverage, and how much rain fade you can withstand.
As a rule, it costs more to deliver the same VSAT services to a smaller dish, and less for a larger dish. If you have a VSAT antenna that is larger than normal, you may be eligible for a discount from your satellite provider.
|Diameter||Area||% of 1m||Gain|
|30 cm (12″)||0.07m²||9.6%||31dBi|
USATs – Ultra Small Aperture Terminal
The amount of interference that a VSAT will cause, depends on the spectral density of the transmitted signal when it reaches the satellite. Some networks are now employing new technologies that spread the signal out over several frequencies, thus reducing the spectral density at any given frequency and allowing the use of much smaller antennas in the range of 60cm(24″) and 82cm(32″) which are commonly called USATs. This extends the VSAT market to a much larger market of smaller vessels that could not support a 1m dish. The KVH V7 is an example of a USAT.
C-Band satellites operate in the 4-6GHz range and provide global beams that cover about 1/3 of the globe that is in sight of the satellite at a time. This requires larger, 2.4m-3.0m VSAT terminals and is usually employed by vessels that need seamless coverage as they move from region to region.