Surf’s up with VSAT
by Nick MarshallVSAT stands for ‘Very Small Aperture Terminal’ and refers to the comparatively modest (3.8 meter diameter and below) antenna that can send and receive data to a communications satellite in space. Since the mid 1980s to early 1990s, oil companies and the military were using VSAT to transmit data from remote areas. Today, even fast food restaurants and chain stores sport the familiar domes, and use has progressed from sporadic communications ‘bursts’ to ‘always-on’ broadband internet.
With maritime broadband, the main concern is bandwidth speed and how to deliver fast access across the vessel’s local network, as well as to and from shore. While Email requires very little bandwidth, and Web surfing barely 8kbps, a dedicated connection of at least 128kbps is desirable to allow page downloads in less than 4 seconds. The more users on the local network, the slower the performance. Currently, if the boss or guests are on board, the internet is off-limits for crew.
The other factor is stability. VSAT uses geostationary satellites. Over North America, these are generally spaced at 2 degree intervals. In the States, FCC regulations state that antennas must point to within 0.2 degrees of their satellite to prevent interference with other satellites. On a ship, where pitch and roll are added to the equation, this requires a stabilization system and a narrow beam, which equal a big antenna and restrictions on available bandwidth.
Take a look at the skyline of any megayacht marina today, and the chances are you’re looking at SeaTel antennas. In 2002, SeaTel launched its smallest antenna (1.5/ 1M) for the megayacht market, with a fixed cost, 24/7 availability – countering the fluctuating (and hefty) cost of Inmarsat.
In August 2007, the company introduced the new 2406 Ku Band VSAT antenna, which measures just 60 cm. Using a patented 3-axis stabilization system which isolates the antenna from the ship’s motion, the SeaTel antenna can maintain a pointing accuracy of +/- 0.2 degrees in up to 15 degree pitch and 25 degree roll. With a -20° to +115° range of elevation, the antenna is able to track low and high elevation satellites, too.
The 4006 is a 1-meter Ku Band VSAT which also meets the FCC regulations and can handle image transfer, video conferencing, Virtual Private Networds (VPN) and data backup.
From 2008, the shift will gradually be towards enhanced tracking and smaller antennas, according to Dave Quarders, Sales Manager for the Americas.
KVH’s TracPhone V7 and mini-VSAT antenna are focusing on this ‘shrinking’ market. 85% smaller and 75% lighter than existing domes, manufactures claim a ship-to-shore speed of 512kb and shore-to-ship at 2mb.
Using Code Division Multiple Access (CDMA) transmission rather than Time Division Multiple Access (TDMA) theoretically allows the antenna to use a wider beam, because there is less risk of interference with other satellites. As a result, the antenna can be smaller and there is no need for a gyro input to maintain accuracy.
The mini-VSAT has yet to receive FCC approval and is on a temporary license, but uses ViaSat ArcLight technology which is used by the US Government. As for performance, according to Marketing Manager Chris Watson, “We’re in the process of gathering testimonials from the dealers and distributors working with and installing the product but it’s still a bit early for any consumer testimonials.”
Linkscape’s Typhoon Maritime Broadband service is targeted at the Caribbean market and the company recently added a new spot beam to its Typhoon Ku Band Service. As Senior Network Engineer Dave Cinege explained in a press release, "most satellite spot beams covering the Eastern Caribbean end right beyond the island chain with marginal signal strength and require a very low antenna angle which can be easily obstructed by buildings and other boats."
The new satellite gives 53db EIRP signal strength over the islands, from the center of the Gulf to 400 miles east of Barbados into the Atlantic. As Cinege has said, "It’s easy to show someone a coverage map and say you can provide service to them. However it’s another matter to actually deliver good usable service to a demanding superyacht."
(*source: www.comsys.co.uk).
Credit:
The VSAT Buyer’s Guide, IDRC