Telephony Radiotelephone Essay Research Paper RADIOTELEPHONEIn addition — страница 3

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of government-owned public telephone bodies within the European Community announced the digital global system for mobile (GSM) communications, the first such system that would permit a cellular user in one European country to operate in another European country with the same equipment. Airborne systems. In addition to the terrestrial cellular radiotelephone systems, there also exist several systems that permit the placement of telephone calls to the PSTN by passengers on commercial aircraft. These in-flight radiotelephones, known by the generic name aeronautical public correspondence (APC) systems, are of two types: terrestrial-based, in which telephone calls are placed directly from an aircraft to an en route ground station; and satellite-based, in which telephone calls are

relayed via a geostationary satellite to a ground station. In the United States the North American terrestrial system (NATS) was introduced by GTE Corporation in 1984. Within a decade the system was installed in more than 1,700 aircraft, with ground stations in the United States providing coverage over most of the United States and southern Canada. A second-generation system, GTE GenStar, employs digital modulation. In Europe the European Telecommunications Standards Institute (ETSI) adopted a terrestrial APC system known as the terrestrial flight telephone system (TFTS) in 1992. This system employs digital modulation methods and operates in the 1,670-1,675 and 1,800-1,805-megahertz bands. In order to cover most of Europe, the ground stations must be spaced every 50 to 700

kilometres. The second type of APC system, based on satellite transmission, is available through the use of Inmarsat geostationary-orbit satellites. Because they do not depend on ground stations, satellite-based systems may be employed anywhere in the world. Personal communication systems. Although cellular radio systems provide a high degree of mobility within a given service area, they do so at the expense of providing voice-only service usually at a significant monthly fee. In recognition of this shortcoming, in a number of countries throughout the world a new radiotelephone service has been introduced that has been almost universally called the personal communication system (PCS). In the broadest sense, PCS includes all forms of radiotelephone communication that are

interconnected to the PSTN, including cellular radio and aeronautical public correspondence, but the basic concept includes the following attributes: ubiquitous service to roving users, low subscriber terminal costs and service fees, and compact, lightweight, and unobtrusive personal portable units. The first PCS to be implemented was the second-generation cordless telephony (CT-2) system, which entered service in the United Kingdom in 1991. The CT-2 system was designed at the outset to serve as a telepoint system. In telepoint systems, a user of a portable unit may originate telephone calls (but not receive them) by dialing a base station located within several hundred metres. The base unit is connected to the PSTN and operates as a public (pay) telephone, charging calls to the

subscriber. The CT-2 system transmits a digital signal at low power (10 megawatts) in the 864-868-megahertz band. Modifications that permit two-way call placement have been incorporated into the system. In 1988 the European Conference on Posts and Telecommunications (CEPT) began work on another personal communication system, which became known as the digital European cordless telephone (DECT) system. The DECT system was designed initially to provide cordless telephone service for office environments, but its scope soon broadened to include campuswide communications and telepoint services. DECT has been deployed in the United Kingdom and France as well as other countries. In Japan a PCS based loosely on the DECT concepts, the personal handy phone (PHP) system, was introduced to

the public in 1994. The PHP system operates in the 1,895-1,907-megahertz band and is intended for home, office, and telepoint applications. In the United States in 1994-95 the Federal Communications Commission (FCC) sold a number of licenses in the 1.85-1.99-gigahertz region for use in PCS applications. PCS operators in the United States will likely use many of the same technologies and systems that are employed in digital cellular systems at 800 megahertz. (See BTW: The FCC and personal communication systems.) Satellite-based radiotelephone communication. In order to augment the terrestrial and aircraft-based mobile radiotelephone systems discussed in Cellular radio and Personal communication systems , several satellite-based systems are planned for operation. The goal of these