ccess that's independent from terrestrial or radio-link networks would be ideal. But it will not be inexpensive.
Dual-Mode Phones
Before the turn of the century, several communications systems will combine today's cellular-radio transmission systems with mobile satellite services. The main players in this global market will be Globalstar, ICO, Iridium, and Odyssey. All four have announced their rollout plans and are close to launching their first satellites. Globalstar and Iridium expect to have services available in 1998. ICO and Odyssey will follow a year later and should be fully up to speed in the year 2000.
Established satellite hardware vendors have intensified their R&D efforts to produce new devices for the coming mobile satellite services. The technical hurdles they have to overcome are the design of digital signa
l processors (DSPs) for the GHz band, implementation of high-frequency antennas in PC Cards, and the design of dual-mode--cellular and satellite--mobile phones. It will be approximately two years before we begin to see prototypes of products. Shipping products will not be available until they can be tested with operational satellites.
The new
satellite phones
will weigh only a fraction of today's portable satellite phones; the present-day Inmarsat M satellite system, for example, weighs about 9 kilograms. Though some devices such as Nera's (Billingstad, Norway) have the antenna in the lid of the phone's briefcase, most need a massive dish as an external antenna. By contrast, the hand-held phones of Globalstar, ICO, and Iridium will eventually weigh not much more than today's GSM phones, about 400 grams.
Commercial communications satellites with specifications for portable equipment have been around for more than 15 years. The Inmarsat satellite system, for example, was laun
ched in 1979. The first service, called Inmarsat A, was offered in 1982. It was designed for maritime use only. We then saw the following services: Inmarsat C, for data and telex transmission; Inmarsat B, a digital system for voice, fax and data; and Inmarsat M, for voice and low-speed data.
However, portable is not mobile. To operate one of today's Inmarsat M systems, you have to locate the nearest satellite with map and compass and adjust the antenna toward the corresponding direction. While cellular communications systems were first aimed at voice communications, even the oldest Inmarsat services provided voice, data, and fax transmission.
A new--though unannounced--version of Inmarsat M promises to reduce equipment weight. Industry observers expect to see the service, code-named Inmarsat Mini-M, by the end of the year. It will enable usage of portable phones weighing about 2.5 kg, which is widely seen as a compromise between the heavy Inmarsat M terminals and the handy ICO terminals coming b
y the end of the century. Products for this service were shown at this year's CeBIT, with a suggested price of DM 7000 to 10,000.
Globalstar, ICO (initially called Inmarsat P), Iridium, and Odyssey are full digital services, which will provide mobile personal communications at a bandwidth of 9.6 Kbps. However, Globalstar and ICO will also introduce a combination of cellular and satellite services: dual-mode handsets. The first dual-mode phones for ICO will likely enter the market in 1999. They will look like today's GSM phones and should cost about $1000. In urban areas, these phones will work with GSM. In areas where GSM is not available, you will be able to switch to the satellite service with just a keystroke.
Joint Ventures
The design of dual-mode phones requires a good understanding of satellite and cellular technologies. Nera, one of the market leaders in Inmarsat devices and base stations, therefore signed a contract with Ericsson and NEC for the codevelopment of
the new systems. While Nera has a great deal of experience in satellite technology, Ericsson will add the GSM expertise and NEC will deliver the antennas.
Iridium will be the first mobile system on the market. However, initially, it will be bigger and heavier than, for example, today's GSM phones, and it will not be combined with cellular technology.
Globalstar and Odyssey will cover mainly the U.S. market with dual-mode services. Orbitel Mobile Communications (Basingstoke, U.K.), for example, announced early this year that it will develop Globalstar handsets using the code division multiple access (CDMA) cellular technology. The retail price for these devices will be about $800 in 1998.
Advanced Satellite Networks
These advanced satellite networks communicate over two different frequency bands, one for communication between the satellites, and one for the link between users and the satellite. Iridium, for example, will deploy the L-Band (1500 GHz) spectrum for
the subscriber link and the Ka-Band (1600 GHz) for communication between the satellites. ICO is set to operate at 1285 GHz for the satellite-to-earth link and at 2015 GHz for communication between the satellites.
Beams of Coverage
Satellite "beams" are the communications links to the earth. They are stationary relative to the satellite, but because the satellites circle the earth several times a day and subscribers may move out of one beam during a call, the satellite systems need to route the call from one beam to another. In a similar way, cellular systems automatically route the call from one cell to the next during the movement of a subscriber. Satellite systems automatically hand over calls to the next available beam when subscribers leave the reach of the initial beam. But the satellite systems will also change beams once a minute for security reasons.
The L-Band, for instance, will have up to 48 independent beams, covering an area of up to 600 square kilometers,
each with a capacity of 200 simultaneous calls. Though beams are independent, they can also overlap in coverage.
Huge Investments
To transfer satellite voice and data traffic into the fixed public network, satellite systems need numerous earth stations that act as gateways. Iridium, for example, plans to have 20 of these earth stations during the first phase of implementation. They will operate satellite dishes of more than 3 meters in diameter.
The investments in mobile satellite systems are enormous sums of money. ICO expects to invest about $2.6 billion for 12 satellites, Globalstar reckons it will spend $1.9 billion to launch 56 satellites, and Iridium expects to spend $3.4 billion for 66 satellites. Despite these massive investments, however, some experts believe that the announced rollout plans and time scales are very aggressive and perhaps unrealistic.
A Question of Security
More than money is involved, of course, in setting up l
arge international projects. In war zones, where satellite communications are critical and often the only link to the outside world, governments will not look favorably on telecommunications equipment carried around by foreigners. This fact alone may inhibit the spread of mobile satellite systems. Additionally, satellite equipment has to be in harmony with national telecommunications laws. An unfettered global communications service has more than just technical problems to overcome.
Where to Find
Comsat World Systems
Bethesda, MD
Phone: (301) 214 3448
Hughes Olivetti Telecom
Milton Keynes, U.K.
Phone: +44 1908 319101
Fax: +44 1908 221127
ICO Global Communications
London , U.K.
Phone: +44 181 600 1000
Fax: +44 181 600 1199
Iridium Services Germany
Dusseldorf, Germany
Phone: +49 211 4579 851
Fax: +49 211 4579 970
Nera
Billingstad, Norway
Phone: +47 66 84 47 00
Fax: +47 66 84 43 10
Orbitel Mobile Communications Ltd.
Basingstoke, U.K.
Phone: +44 1256 843468
Fax: +44 1256 818262
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illustration_link (11 Kbytes)
By the year 2000, mobile satellite services will provide global communications. Earth stations will act as gateways to the regional and national PSTN and cellular networks.
1.
Setting up a
call with a mobile satellite phone will be as easy as using today's cellular phones. Huge dish antennas will not be required.
2.
Satellites can handle up to 48 beams each, with a capacity of 200 simultaneous calls. If a subscriber moves out of a beam of one satellite, an adjacent satellite has to take over the call.
3.
Earth stations act as gateways to cellular and fixed-circuit networks.
a).
The mobile switching center routes calls from the earth station to the cellular infrastructure (and vice versa).
b).
Most calls will be directed to the Public Switched Telephone Network (PSTN). Intercontinental calls will be routed through the ground network of earth stations.
4.
Users of dual-mode mobile satellite phones will be able to choose between satellite or cellular connections. In areas without a cellular infrastructure, satellite links will still be available.
Elke Gronert is a telecommunications journalist in Munich, Germany. You can reach her by sending e-mail to
editors@bix
.com.
Global Mobile Communications
