Broadband at sea

31464 12a1

In the Internet age, the holy grail of computer users on land, and increasingly at sea, is more bandwidth. KVH Industries has just announced a new system called the TracPhone V7 and mini-VSAT Broadband that can provide maritime users with impressive broadband capability. While this system is fairly expensive and isn’t likely to be adopted by the average voyager, it does point the way to more capable and more affordable future systems for voyagers.

In the past, the standard method for improving bandwidth involved big, expensive and heavy antennas on board ships and increasingly more powerful satellites in space. In a broadcast system, such as Direct TV or XM radio, where the data is only flowing one way, increasing the power of the satellite works well, actually allowing the earth-based receiving dish to shrink.

In a two-way communications system, such as the very small aperture terminal (VSAT) systems you see on ships (and on the roofs of fast food restaurants and chain stores on land), there’s the need, however, to send data both down to the user and for the user to send data up to the geostationary satellite. So, while increasing the satellite’s radiated power can help, to a point, in increasing the downlink data rate, increasing the power at the user’s antenna makes the antenna more expensive and increases the likelihood of a user’s signal causing interference by splashing over to other satellites parked in nearby orbital slots. Over North America, for example, geostationary communications satellites are spaced approximately 2° apart. Due to the dangers of interference, there are strict requirements for user antennas to accurately point at a specific satellite and transmit a narrow beam that won’t interfere with other satellites. Regulatory agencies like the FCC mandate that antennas must point to within 0.2° of the satellite. These stringent pointing requirements mean a more complex and expensive antenna stabilization system. And the required narrow transmit beam means a bigger antenna, as the physics of antennas require a big antenna to make a narrow beam. These factors have limited the bandwidth capability of standard VSAT systems.

KVH’s latest system, the TracPhone V7 and mini-VSAT Broadband, gets around these issues by using a signal modulation technique already well proven by both GPS and cell phone networks. Called code division multiple access (CDMA), it allows many users to transmit on the same frequency without interference. For example, the entire constellation of GPS satellites broadcasts to your GPS receiver using the same frequency. Your GPS unit is able to differentiate the various satellites because each spacecraft broadcasts in a specific sequence or code, and the receiver knows the code each satellite transmits. It’s as if a group of people were each singing a different song. You can focus in on one singer by listening for the words of their particular song. Unlike the time division multiple access (TDMA) technique where each “talker” is allocated a time slot, the code division approach allows for “bursty” activity, typical of a data-based system.

One of KVH’s partners on the new V7 is ViaSat, a company that makes CDMA modems. ViaSat has developed its own version of CDMA, dubbed ArcLight, that ViaSat calls code-reuse multiple access (CRMA). The essence of CRMA is that the technique manages to combine uplink and downlink signals onto a single satellite transponder, freeing up transponder space for other users and resulting in more efficient transponder use.

GPS and the new V7 also share a transmission technique called spread spectrum that spreads the signal power over a wider frequency spectrum and lowers the signal’s power spectral density. This means that there is less signal power at any one specific frequency compared to a non-spread spectrum signal.

The end result of using the CDMA/CRMA and spread spectrum techniques is that V7 signals are far less likely to interfere with nearby satellites. And that produces attractive benefits for the mariner: user antennas can operate with wider-angle beams and thus be smaller; and the antenna pointing circuitry can be simpler, as less pointing accuracy is needed.

Another advantage to reduced size is a matching decrease in weight. A standard VSAT installation uses a radome roughly 48 inches wide and 59 inches high with the antenna assembly weighing in at 250 lbs. The TracPhone V7 dome, by comparison, weighs 60 lbs. and is 26 inches wide.

Though 85-percent smaller than the VSAT, the V7 can still handle impressive levels of data throughput. KVH is claiming up to 512 Kbps for upload and up to 2 Mbps for download. This type of data rate makes the use of the Worldwide Web at sea a viable prospect. The system’s capabilities include e-mail, Internet browsing, multiple voice over Internet protocol (VoIP) phone lines, secure network access and instant messaging — pretty much everything you do on your home computer now.
What about coverage? The V7 system makes use of geostationary satellites in the SES Americom constellation. These satellites provide good coverage in U.S., Canadian and European waters and also provide a lobe of coverage across the North Atlantic. But most of the North Atlantic and Pacific has no coverage. The South Atlantic and other ocean areas are also lacking service.

Subscription plans for the service vary, with a number of packages available. It’s in the cost per megabyte comparison where the V7 system shows its value. For example, Inmarsat’s Fleet77 service, which operates at a maximum upload/download data rate of 128 Kbps/128 Kbps, the cost per megabyte is $32, while KVH is quoting a price of $4.99 per megabyte at the V7’s max data rate of 512 Kbps/2 Mbps. Subscribing to a “bundle plan” lowers that to $2.99/MB.

Of course, for the average voyager the impressive capability of this system is counterbalanced a bit by the nearly $33,000 price tag for the hardware. Still, for the owner of a 50-foot or longer vessel who needs the best satellite communications available, the impressive new TracPhone V7 with mini-VSAT Broadband just might be an option. The next step for KVH, after producing a VSAT of impressively reduced size, is a downsized name!

By Ocean Navigator