Bookmark and Share Email this page Email Print this page Print

Sea is for cellular

Jan 1, 2003
From Ocean Navigator #60 March/April 1994

From Ocean Navigator #60 March/April 1994

There is an explosion going on telecommunications. Keeping up with the competing systems can be a challenge for the voyaging yachtsman.

Choices are increasing for mariners in the field of satellite communications: Inmarsat A, B, C, M, and still to come, Inmarsat P. There is Motorola's upcoming Iridium system, and a similar low Earth orbit (LEO) system called Orbcom (while Iridium is a voice system, Orbcom will be data and text only, like Inmarsat C).

Another satellite communications service angling for marine users is called Oceancell, and is being offered by Seven Seas Communications, Inc., located in Fort Lauderdale. Users within roughly 200 miles of the North American coast will be able to direct dial phone numbers using a handset much like a cellular phone. The Oceancell service will hitch a ride on a new geosynchronous satellite scheduled to be launched in August of this year and operated by the American Mobile Satellite Corporation (AMSC). A joint venture of Hughes Communications (owned by GM), McCaw cellular (owned by AT&T), Mtel, and others - AMSC has been granted a license by the FCC to provide mobile satellite service in the U.S. Even though this mobile communications satellite is primarily intended for land-based users, its coverage area includes coastal waters of the U.S. Thus, Seven Seas Communications is offering the Oceancell mobile communications service to marine users.

"This satellite will be one of the most powerful mobile communications satellites ever launched," says Paul Adkins, general manager for Seven Seas Communications. "With a powerful satellite, users' antennas can be smaller and less expensive." Power is an important consideration for geosynchronous communications systems for one reason: distance.

Geosynchronous satellites "hang" over a single point on Earth. In order to do this, they must be in a 19,000-nautical-mile-high orbit. For radio energy to reach a user on the surface, the signals must be sufficiently powerful to be picked out of atmospheric background noise. One way to do this is to use a large, high-gain, dish antenna. Obviously, this approach has its drawbacks for smaller vessels. Another way to approach the problem is to boost transmitter power on the satellite. Then, a smaller antenna can be used on the surface because there is more signal available and the antenna doesn't have to be as efficient in gathering it. A powerful satellite, then, would seem to do the trick - we can use a geosynchronous system with only a small receiving antenna. (Hughes Communications is scheduled to launch another satellite in 1994 that will provide direct broadcast television. Since this will also be a high-power satellite, one will be able to receive hundreds of TV channels with a two foot diameter dish antenna and the appropriate receiver. This type of direct broadcast TV is already in use in Europe.)

If we are only interested in receiving satellite signals, we are all set. Two-way communications, however, require that we also send a signal to the satellite. This can be done with a large, high gain antenna on the satellite or by boosting one's transmission power. Either way, it is the distance the signal has to travel from the surface to a satellite 19,000 miles up that makes it impossible to get by with a small antenna like that on a handheld VHF radio.

Seven Seas Communications is offering three sizes of antenna for use with Oceancell: a 10-inch diameter, one-axis stabilized antenna package, termed "medium gain," with an equipment price of $3,500 to $5,000; a 16-inch "high gain" actively stabilized antenna package for $4,500 to $6,000; and a 21-inch "super high gain" actively stabilized antenna package for $7,000 to $9,000. The equipment price includes the antenna, a belowdecks transceiver, and a cellular phone-type handset.

Estimated service prices will depend on the type of equipment used. The price, in continental U.S. waters, for the medium gain antenna package will be $2.00/minute. This decreases to $1.50/minute for the high gain or super high gain packages. Since higher gain antennas can gather more signal and thus overcome background noise, they require less satellite transmitter output and so have lower associated costs.

"Oceancell can be used for fax and data transmission, but at a data rate of 2400 to 4800 bps, it isn't the fastest way to send that kind of information," says Adkins. "It will be primarily used for voice messages. This type of mobile voice satellite system is being put in place in Australia and is working well in its early stages."

Essentially, Oceancell will be analogous to Inmarsat M service, with digitized voice, fax, and data capabilities. Unlike Inmarsat M, which can be used worldwide, Oceancell is limited to 200 miles, but user equipment and connection time is cheaper.

The primary projected users for Oceancell are commercial fishing vessels and larger yachts. According to Seven Seas Communications, there are 100,000 commercial fishing vessels in the U.S., only 200 of which are currently Inmarsat users.

According to Adkins, users will purchase their antenna/transceiver/handset package from marine electronics dealers. Seven Seas Communications will only sell air time.

In addition to transmitting via satellite, Oceancell equipment will reportedly be able to access local cellular telephone networks. When the unit is turned on, it will first search for a cellular network signal. If that signal is found, the unit will route the call over the less expensive cellular network. A user can continue to use the land-based cellular system until the vessel passes out of range. At that point the call will be automatically switched over to the satellite. The process will supposedly be invisible to a user and the phone call won't be interrupted. The system will not be able to work in the other direction (i.e., handing off a satellite call to the land-based cellular network as one approaches the coast).

All of the three antenna types will reportedly have some amount of stabilization. The low-end medium gain antenna was primarily designed for the land mobile market and has a dish that can rotate around a central axis. The 16- and 21-inch models both use active stabilization and can respond on all axes of movement.

For small vessel use, the medium gain antenna seems to make the most sense in terms of antenna size, but since the unit is not fully stabilized as a boat pitches and rolls, there is a chance that the unit will lose lock with the satellite and break off the link. So, for use at sea, the 16-inch antenna would seem the best solution.

Oceancell is set to become yet another element in a increasingly complex mix of telecommunications choices. The best solution for a mariner will depend on the type of voyaging one does, the size of one's vessel, and how urgently one feels the need to communicate.

Edit Module