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Introduction 3

The following factors were major contributors to the success of GSM:

•    The liberalization of the monopoly of telecommunications in Europę during the 1990s and the resulting competition, which conseąuently lead to lower prices and morę “market”;

•    The knowledge-base and professional approach within the Groupe Speciale Mobile, together with the active cooperation of the industry;

•    The lack of competition: For example, in the United States and Japan, competitive standards for mobile services started being defined only after GSM was already well established.

The futurę will show which system will prevail as the next generation of mobile Communications. ETSI and the Special Mobile Group (SMG), renamed GSM, are currently standardizing the Universal Mobile Telecommunication System (UMTS). Japan is currently improving PHS.

The various satellite Communications systems that now push into the market are another, possibly decisive, factor in providing mobile Communications on a global basis.

1.2.1 The System Architecture of GSM: A NetWork of Cells

Like all modern mobile networks, GSM utilizes a cellular structure as illus-trated in Figurę 1.1.

The basie idea of a cellular network is to partition the available freąuency rangę, to assign only parts of that freąuency spectrum to any base transceiver station, and to reduce the rangę of a base station in order to reuse the scarce fre-ąuencies as often as possible. One of the major goals of network planning is to reduce interference between different base stations.

Anyone who starts thinking about possible alternatives should be reminded that current mobile networks operate in freąuency ranges where attenuation is substantial. In particular, for mobile stations with Iow power emission, only smali distances (less than 5 km) to a base station are feasible.

Besides the advantage of reusing freąuencies, a cellular network also comes with the following disadvantages:

•    An inereasing number of base stations inereases the cost of infrastruc-ture and access lines.

•    All cellular networks reąuire that, as the mobile station moves, an active cali is handed over from one celi to another, a process known as handover.