Technology Update
by Gary Allen
Three dispatchers were sitting around the break room, speculating on what one essential item to have while stranded on a deserted island. The first dispatcher wanted a month's supply of food and water. The second dispatcher wanted the companionship of a certain soap opera star. The third dispatcher said, "I want my Inmarsat."
No doubt about it. Satellites have become the way to communicate in the `90s. The TV and radio networks use them, the International Atomic Energy Commission used them in Iraq, and even Steven Seagal used them in Under Siege
It's time that public safety comm centers caught up.
The Technology
When the public switched telephone network (PSTN) stops working, your comm center may come to a grinding halt. If your city is devastatedd by a natural disaster, HAZMAT incident or explosion, you may be cut off from the rest of the world. How do you call for help?
The solution may be a satellite telephone earth station, which has a giant advantage over land-based systems--it doesn't have to leap over mountains or boomerang round buildings. The signal goes straight up, providing universal access to any point on earth
The satellites themselves can be geosynchronous or non-geosynchronous. The former rotate at the same rate as the earth and appear to stay in one point, while the latter appear to move across the sky.
The satellites can also be either high orbit--about 22,500 miles up--or low-earth orbit (LEO)--about 400 miles up. High orbit satellites are geosynchronous and low-earth orbit satellites are non-geosynchronous.
A satellite's altitude also determines the necessary power of the satellite's transponder and the earth station's transmitter. The lower the orbit, the less power required and, generally, the smaller and more compact the ground-based unit can be.
Inmarsat
The International Maritime Satellite Organization (Inmarsat) is based in London, England and consists of members from 73 countries. It was founded in 1979 by international treaty to operate a maritime communications system.
Inmarsat took the original point-to-point satellite concept and added a twist--the customer owns and operates their own satellite earth station, and pays a per-minute charge only when the service is used.
The idea proved successful, especially with shipping companies who needed up-to-the-minute information on their vessels and a reliable method of emergency communications.
Initially, the satellite link was used to send location, speed, fuel level and other operating data back to office headquarters. Now, ships also receive weather, news and other information from shore, and routinely use the phone connection for ship scheduling.
Inmarsat operates four primary satellites that provide world-wide coverage for over 40,000 maritime, land and aeronautical customers. The satellites beam voice, data, fax, telex and video using a combination of private networks and the public telephone system.
Inmarsat-approved equipment has evolved from huge, gyro-guided, shipboard antennas, to suitcase-sized luggable units, to terminals no larger than a personal computer. Transmission technology has also changed, from high-power analog units to low-power, narrow bandwidth digital stations.
While originally intended strictly for voice only, Inmarsat has grown to include almost every type of transmission. Communications services are designated by a letter (A, B, C, M and P) and each offers different types of connections--analog or digital--and connection costs.
Inmarsat A
Inmarsat-A offers high-quality voice, fax, data, telex using analog technology. Data rates are available at both 9600 bps and 64 kbps. Terminals cost about $30,000 and uplink time is $8 per minute.
Inmarsat-A was widely used during the 1991 Gulf War to send voice, fax and telex messages. This service is the most popular, with over 20,000 users on land and sea. However, despite the large installed customer base, most new equipment purchasers are looking at B and M-type terminals.
Inmarsat-B
Inmarsat-B was first offered in 1993 and offers the same services as Inmarsat-A, but its spectrum efficiency allows charges about one-third less than Inmarsat-A.
A B-type terminal offers a high-quality, 16 kbps voice channel, a choice of data channels (one at 9.6kbps, one at 16kbps), Group 3 fax and a standard 56/64 kbps high speed data channel. With the proper equipment, it will also transmit compressed--but not real-time--color video or up to 11 voice channels.
These terminals are popular with companies that have remote locations with multiple-line service. Equipment is available to link B-terminals to PBXs, allowing almost-copper service.
Inmarsat C
Inmarsat-C is the little baby of Inmarsat. It offers mobile and portable data-only service at the rather slow rate of 600 bps. The advantage--terminals cost only about $5,000. It can connect with private data networks using X.400 and X.25 protocols, and with the public telephone system for standard analog modem connections.
Inmarsat stores data from C-type earth stations and then forwards it to the proper destination as an entire block of messages, making much more efficient use of the communications channel. This allows Inmarsat to base charges on the amount of data transmitted, rather than the amount of time on-line.
Besides two-way data communications, Inmarsat-C can also perform Enhanced Group Calling, which allows broadcasting data to specific user groups or geographic areas. This capability is used by several companies to frequently update their mobile employees on staffing, inventory or prices.
Inmarsat M
Inmarsat-M is the latest offering and is based on narrowband, digital technology. It carries medium-quality digital voice(4.8kbps), fax and data (2.4kbps) on portable terminals. Briefcase-sized, 13-pound terminals are available for about $19,000. The service is about $5 per minute.
Inmarsat-M electronics is specifically optimized for voice communications. A voice encoder breaks down the voice signal using a mathematical model of human voice sounds. The digital data is uplinked to the satellite and back to the earth station, where it's reassembled and sent on to its destination. The technique minimizes the transmitted data yet maintains the highest possible voice-quality.
Inmarsat-P
Just over the horizon is Inmarsat-P, a $1,500 hand-held unit that will transmit and receive digitally direct to satellites, with all the advantages of current portable cellular phones--small size, good voice quality, and the ability to call or be called anywhere on earth. Just this September Inmarsat kicked off fundraising for the $2.6 billion P-satellite system.
The system is targeted at voice telephone users, but Inmarsat plans to eventually include fax machines and data connections on P-service telephones. To support this service, Inmarsat is considering changes to its system, including more satellites, LEO satellites, or even intermediate circular orbit (ICO) satellites.
An Inmarsat global pager service is also under development that will allow worldwide receipt of messages up to 64 characters long. Besides the familiar belt-clip device, the service will be integrated into other communications devices, automobiles or other locations. It ultimately could carry news, weather, sports and financial information.
Competitors
Inmarsat is not alone is seeking revenue from global communicators. In the next few years there may be several companies operating satellite telephone systems that public safety comm centers can rely on for emergency communications.
The biggest challenger is Iridium Inc., a 66-satellite venture led by Motorola Inc. The project has already raised more than $1 billion for a constellation of six satellites in each of 11 orbital planes. It's scheduled to begin service in 1998.
Microsoft and McCaw Communications have announced an even more ambitious blanket of 840 satellites providing 24-hour coverage for voice, data or anything else. Under the corporate name Teledesic, they will launch 40 LEO satellites in each of 21 paths, 435 miles up. At $9 billion, it tops anything ever attempted in wireless communications. They must still obtain FCC approvals and find financing, but they say it will be finished by 2001.
There are at least five other schemes still on the drawing board, with such visionary names as Globalstar, Ellipso, Celstar, Orbcomm.
Analysts are doubtful that all these satellite ventures will survive. Their skepticism focuses on the amount of money required to build the systems, the projected number of users, and the cost per minute charges. Are there enough users willing to pay $1 a minute to repay the $2 billion cost of a system? No one knows for sure.
Equipment Sources
For more information on Inmarsat earth stations, contact:
Mobile TeleSystems, Inc., 300 Professional Drive, Gaithersburg, MD 20879; 301 590-8500; fax 301 590-8558.
Olivia Communications Group, 1 Park Place, 621 NW 53rd Street, Boca Raton, FL 33487-8211; 407 995-1422; fax 407 995-1499.
Mackay Communications, 300 Columbus Circle, Edison, NJ 08837; 908 225-0909; fax 908 225-2848.
Calian Communications Systems, Ltd., 300 Leggett Drive, Kanata, Ontario K2K 1Y5 Canada; 613 592-3020; fax 613 592-3378.
Comsat Mobile Communications, 22300 Comsat Drive, Clarksburg, MD 20871; 301 428-2222; fax 301 601-5951.
GTE Government Systems, 1700 Old Meadow Road, McLean, VA 22102; 703 848-1000; fax 703 848-0004.
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