GLOBAL TELECOMMUNICATIONS

G L O B A L

   T E L E C O M M U N I C A T I O N S

CONSTELLATIONS OF LAW-ORBITING  satellite hold the key to today's flexible global telephone networks . These systems integrate satellite communication with existing land-line and cellular networks to provide truly global coverage from a mobile phone. This enables people in remote areas, even those on tiny pacific islands or high in the Himalayas, to keep in touch with the rest of the world. Satellite systems are the next logical step in the mobile-phone revolution that swept the world in the late 1990s. Iridium was the first system to offer a commercial service. It was conceived and developed by the US electronics company Motorola, and began operation on 1 November 1998. The system was named after the 77th chemical element in the periodic table, as there were originally to be 77 satellites in the network. Other networks offering a similar service include Globalstar, which operates with a constellation of 48 satellites. 

 The iridium network consist of 66 satellites, each providing a coverage of 16 million square km (6 million square miles). Its offers a constant service, as there will always be one or more satellites over the horizon. The network operates as a constellation, which means that a failed or malfunctioning satellite will not impede the system's ability to provide global coverage . When a call is made it is routed to the nearest satellite , and then relayed around the world to its destination is a land-based telephone , the last satellite in the chain feeds the signal to a "gateway" ground station. This gateway then connects with the existing land-line telephone system.

ENVIRONMENTAL CONCERNS

Mobile phones operate using radio signals. They have a transmitter that sends a signal to an aerial, which is part of a nationwide communication  network. These radios work at low power, so mobile users need to be within a few kilometres of an aerial for their signal to be received. The mobile-phone revolution of the late 1990s has resulted in hundreds of millions of users worldwide, and thousands of aerials have been built, both in town and country, to receive the ever-increasing number of signals. In environmentally sensitive areas, unsightly aerial masts are sometimes disguised as tress or flagpoles. They have been sited on buildings and church towers, and then camouflaged.

 MICROWAVE RELAY TOWER

The Iridium communications system can route calls through an ordinary mobile telephone network, if available, and also interconnected with conventional telephone networks. Land links, such as this microwave relay tower , are often needed to route  calls to their final destination.


                             

                    IRIDIUM HAND SET

Early satellite phones required briefcase-sized units to receive and process signals from communication satellites. The Iridium hand set has a similar features to a conventional mobile phone but is slightly large in size. It is also more expensive to purchase and operate but, unlike an ordinary mobile phone, can be used in any location on Earth.