New satellite technology makes it possible to use your PC to receive and transmit data to and from any place on earth. You can even talk back!.

Imagine a small electronic device, not much bigger than a car radio that, moving or stationary can send or receive E-mail, faxes or binary files with total reliability from anywhere in the globe. Or imagine phoning to and from anywhere on this globe from your briefcase, or have a live video conference anywhere on the planet. Well, imagine no more: Inmarsat, the largest and most sophisticated satellite network ever created is at this moment hovering above your head, providing users with unparalleled flexibility with their computing and telephony needs.

Inmarsat gained worldwide exposure during the Gulf War in early 1991, when war correspondents like CNN's Peter Arnett were able to give live reports from Baghdad or isolated areas in the Gulf, of missiles flying overhead or bombs going off around then. While at that stage they needed to worry about their safety, they certainly didn't need to worry about their satellite link. Inmarsat (International Maritime Satellite) is a UK based organisation that comprises a consortium of 60 member countries who have placed a constellation of 11 satellites in geostationary orbit, providing reliable coverage to every corner of this planet. Some of these satellites carry commercial communications traffic while others are in orbit as "back up" spares to ensure continuity of the service.

Inmarsat's prime task is to establish, maintain and operate the satellite system required to provide global mobile communications for maritime, aeronautical and land mobile users. Inmarsat signatories usually own and operate the land earth stations (LES) that provide interconnection between the Inmarsat satellites and the national and the international fixed telecommunications networks. The Inmarsat system uses different satellite to provide four different services, called Inmarsat A, B, C and M. Each service is targeted towards a particular niche market.

The way in which you access the Inmarsat A, B and M services is quite simple. Once you've signed up with Inmarsat, they give you your own telephone number. You then need a dedicated terminal geared for the system you've signed up for. Inmarsat have certified a number of manufactures who provide this equipment. Each unit, called a "satphone" uses either a parabolic or flat satellite antenna, between 90 cm and 1.3 m in diameter. You set the inclination of the antenna to a position specified by coordinates supplied by Inmarsat, using either a compass or a voice activated system to guide you.

You also choose the Land Earth Station (LES) that you want the satellite to use. These LES's provide varying services, including support for high speed data lines - for which you of will course pay extra. Your call charges will thus depend on the LES that you choose, since the LES might have to route your call through other terrestrial (land) telephone networks or satellites. Africa's only Inmarsat LES is based in Egypt. The signal strength and the LES you've chosen is displayed on an LCD panel. Once the LCD gives you the "ready" signal you can now dial out. You precede the call with two zeros to establish the satellite connection, then the country code of your destination country, followed by the phone number. One of four network control stations then allocates a channel to your call from a choice of 340 per satellite. From there the call goes through the chosen LES and then to a telephone network. You are charged for both the Inmarsat toll and the cost of the call from the LES to the call destination.

Inmarsat A has developed considerably since it was launched in 1982. The system is now more than the world's only global portable satellite phone (satphone) and telex machine. With a 64 Kbps transmission speed, users can also send data and faxes, transmit compressed live video and, since 1988, use one terminal to handle a number of calls simultaneously, using a technology called multiplexing. Many Inmarsat terminals offer second ID's which enable users to receive place and even charge calls on two separate telephone numbers using the same terminal. For simultaneous transmissions of more than one call over the Inmarsat A system, users need to specify a multi user channel. An Inmarsat A terminal has an antenna approximately 90 cm in diameter, while the box of electronics is the size of a desktop PC. A notebook PC, fax machine, or cordless phone can all be connected to the unit.

Inmarsat B, launched in July 1993, is an advanced version of the analogue Inmarsat A, featuring smaller terminals and digital transmission. It is based on a 16 Kbps data channel that coverts the human voice into a data stream using a special CODEC (coder/decoder) built into the satphone. It then transmits the data over the satellite system before translating it back into speech via another CODEC at the LES. The digital system means that voice and data transmissions are protected from noise and distortions, so often characteristic of analogue satellite systems. If part of the voice is lost, the voice wave pattern can be reassembled based on data that has been received.

In an analogue conversation any "missing" elements are simply lost, producing gaps in what is heard by the receiver. The digital approach also provides greater security as every transmission is converted into a scrambled data stream that is hard to uncode. Inmarsat B call charges are lower than the older Inmarsat A, simply because its digital design allows it to access more frequencies using lower satellite power. Call charges for using the Inmarsat B system are US $5.50 per minute, some 30% less than for Inmarsat A. Although Inmarsat B's voice channel supports 2,400 bps data transmission, dedicated data and fax lines support the new high speed 64 Kbps system which permits expansion of up to 11 voice channels or 20 data channels over a single line and terminal. Video teleconferencing, store and forward full motion video at 30 frames per second, and the new Group 4 high speed fax transmission standard are all supported. One unit that supports all these features is the new ViaSat Lynxx satphone. It weighs just over 18 kg and features a series of communications ports to provide a high quality 16 kbps voice channel, a Group 4 fax port, and a 64 Kbps high speed data port. The HSD data facilities will also support transmission of compressed colour video, 15 KHz broadcast audio and up to eleven voice, or 4 data channels or Group 4 fax. The Lynxx is supplied as a single case complete with a self contained flat panel antenna. All operations are menu driven and are controlled by a cellular type handset with a small LCD display. Although it is not designed specifically for the task, Inmarsat A is also capable of integration into ISDN (Integrated Switched Data Networks). A 256 Kbps and 384 Kbps service is also planned.

The Inmarsat M system provides a cheaper alternative to those who require voice transmission and some data transmission, but who cannot afford the terminal unit or call charges of the Inmarsat A and B satellites. The Inmarsat B satphones are a lot more transportable than the Inmarsat A and B terminals and look like your ordinary briefcase, with the detachable weather resistant flat plate lid of the briefcase acting as the satphones satellite antenna. Weighing in at just 8 kg, these battery operated units are so simple to use that they can be operational within a minute of opening up the case. They have been very popular with globe trotting journalists and news organizations, including CNN, who have acquired a number for use in war torn Bosnia. One of the newest units on the market, the Global Phone from Glocom guides the user in pointing the system's built in antenna towards the "nearest" satellite using a signal strength indicator, special software, and multi-lingual graphic and voiced synthesized instructions. Other units use built in compasses, maps of the Inmarsat system and LCD and audio signal strength meters which rise as the signal strength improves. These units even work through glass windows, and if for some reason the line of sight is obscured, the connection to the satellite will be sustained for over a minute. If the unit is not in line of sight of a satellite, the lid can be detached with a 2 or 3 m long cable, although longer extensions of up to 100 m can be added without degrading the transmission quality. As with the other Inmarsat systems, there is a large overlap between the "footprint" of each satellite (the area of the earth it covers) so in many parts of the world you can point the unit to two satellites. Some units use a RS 232 serial interface to support fax and data transmissions at 2,400 bps. Faster data transmission speeds are planned for next year. The average cost of an Inmarsat M terminal is around R85,000 and rates for each call are $3.95 (around R13) per minute.

Unlike the Inmarsat A, B and M which all have data and voice components, the Inmarsat C system is totally dedicated to data transmission. One of the main features of the Inmarsat C system is the size of the mobile terminals it requires. A typical Inmarsat C mobile terminal comprises a small system module, and a simple lightweight antenna, which together weigh just 4 kg. These units cost between R23,000 and R40,000 depending on the complexity of the unit - like the use of High Gain antennas. While the mainstay of the system is electronic messaging, navigation systems - like the indispensable Global Positioning System (GPS) - and other remote sensors can also be plugged in or integrated for automatic transmission of monitored data. Inmarsat C communications in both directions are handled on a store and forward basis. For mobile users this means that messages are transmitted via a number of packets of digital data, usually in 32 bytes segments contained in three packets. These packets of data travel by satellite to the user selected LES. When the next packet has been received, they are all reassembled, and the complete message is delivered within minutes to its destination via the existing terrestrial networks, such as telex, fax, LANs, E-mail or X.400 systems. The same thing happens in reverse for messages from a fixed network user to mobiles. A newer service called C-Link from Comsat now allows interactive, transparent access sessions to more than 60 E-mail systems in 30 countries, including AT&T Mail, GeoMail, MCI Mail, Sprint Mail, CompuServe, Dialcomm as well as private LAN E-mail systems. Binary files can also be transmitted over the Inmarsat C/E-Mail links so that users in remote sites can send and receive any fully formatted word-processing, database or spreadsheet files, albeit at a slow 1,200 bps. They can also send messages to fax terminals and carbon copy a single message to a number of E mail addresses, an approach which should cut communications costs. A Destination Selection (Call Forwarding) service allows mobile users to redirect messages to a home E-mail system or fax address. Many of these messages can be sent by using a PC loaded with a special program called TT CapMail which operates with Microsoft Mail to send E-mail over the Inmarsat C system as if the mobile user were logged on to the host LAN. A number of integrated Inmarsat C systems are also appearing on the market: the R35,000 Magnavox MX 1010 Magnaphone C system comprises an Inmarsat transceiver linked to a notebook PC, an AC/DC power supply, a portable Diconix printer, lead acid batteries, a remote alarm and a directional high gain Inmarsat C antenna. The equipment can also be installed in a vehicle complete with a 5 channel GPS receiver. Inmarsat's other services include a special polling and data reporting system which interrogates automatic data gathering platforms at fixed or variable intervals, mainly from vehicles or vessels. Such information can include location (via GPS), speed and heading, fuel stocks and consumption, and weather data. The system's polling facility allows the users' base to interrogate mobiles at any time, triggering the automatic transmission of the required information. Commands can also be issued from the host base via the system to activate certain mechanisms, such as valves and sluice gates.

Aircraft have also been incorporated into the Inmarsat network with the launch of the Inmarsat Aero system in 1990. It uses the existing Inmarsat satellites to provide two way voice, fax and data services for aircraft operating anywhere in the world. A number of US, Asian and European carriers now provide credit-card linked telephone handsets attached to the passenger's seat. Ground Earth Stations (GES) provide the interconnection between the satellites and the international telecommunications networks. CODECs operating at 9,600 bps are employed at the GES to convert terrestrial voice calls to digital code for efficient error free transmission to the aircraft. The digital signal from the aircraft is also converted to an analogue voice signal by the GES. Packet switched data communications for messaging and E-mail retrieval are supported by interfaces with public and private data networks using the X.25, X.400, and X.75 standards. Further developments over the next few years will add new capabilities, including passenger interaction with ground databases - like airline reservation systems - and audio and video broadcasts. The launch of the new Inmarsat 3 satellites in mid 1995 will mean that the extra power of the spot beams trained on high traffic areas will allow users of current equipment to get even more performance. Comsat plans to add 9,600 bps fax, 2,400 bps modem connections and secure voice transmission in the next few months on a number of carriers, based on a new system called the Circuit Mode Data Interface Unit (CDIU). It also includes a broadcast teletext news service called FlightNews that will provide up to the minute news flashes and travelers advisories.