中英论文翻译对照：全球移动通信系统

ABSTRACT

GSM is Global System for Mobile Communications acronym, which means Glob al System for Mobile Communications is the world's leading cellular systems in the w orld. GSM is based on narrowband TDMA standard that allows radio frequency in a gr oup call at the same time. GSM rised in Europe, put into use in 1991. In the end of 19 97, it has operationed in more than 100 countries, 162 countries have already built m ore than 400 GSM communications network until 2001. But the capacity of GSM s ystem is limited, users of the network are overload, it had to construct additional net work facilities. What is gratifying is that GSM performance in other areas, which in ad dition to providing a standardized list and signaling systems, but also opened up som e of the more intelligent business such as international roaming and so on. The conven ience of GSM mobile phone is that it provides a smart card, known as SIM cards, an d card could be separated, so that the replacement of mobile phone users and custom p ersonal information in this area are facilitated. GSM network have improved after year s of development, is now very mature, less blind spots, signal stability, automatic roam ing, and the communication distance from the impact of the surrounding environment.

GSM（Global System for Mobile Communication）

The success of mobile systems across the world is a sign that communication is moving towards a more personalized, convenient system. People who have to use a mobile phone on business soon begin to realize that the ability to phone any time, any place in one's personal life rapidly becomes a necessity, not a convenience.

The speed and rapidity with which the personal communications revolution takes place is, unlike fixed transmission systems, highly dependent on technology and communication standards.

For mobile the three key elements to achieving service take-up are the cost, the size and the weight of the phone, and the cost and quality of the link. If any of these are wrong, especially the first two, then market growth is liable to be severely restricted. The fixed telephone service is global and the interconnection varies from coaxial cable to optical fiber and satellite.

The national standards are different, but with common interfaces and interface conversion, interconnection can take place. For mobile the problem is far more complex, with the need to roam creating a need for complex networks and systems. Thus in mobile the question of standards is far more crucial to success than fixed systems. In addition, there is also the vexed question of spectrum allocation in the mobile area.

Mobile systems originally operated in analog mode in the 450 MHz band, moving later to 900 MHz with digital GSM and then to 1800 MHz with personal

communication systems. The history of mobility can split into generations. The first generation systems were the advanced mobile phone systems (AMPS) in the US, total access communication system (TACS) in most of Europe and Nordic mobile telephone system (NMT); which were all analogue systems. The second generation is vary much dominated by the standard first set out in Europe by the group special mobile (GSM) committee, which was designed as a global mobile communication system.

The GSM system is based on a cellular communications principle which was first proposed as a concept in the 1940s by Bell System engineers in the US. The idea came out of the need to increase network capacity and got round the fact that broadcast mobile networks, operating in densely populated areas, could be jammed by a very small number of simultaneous calls. The power of the cellular system was that it allowed frequency reuse.

The cellular concept is defined by two features, frequency reuse and cell splitting. Frequency reuse comes into play by using radio channels on the same frequency in coverage areas that are far enough apart not to cause co-channel interference. This allows handling of simultaneous calls that exceed the theoretical spectral capacity. Cell splitting is necessary when the traffic demand on a cell has reached the maximum and the cell is then divided into a micro-cellular system. The shape of cell in a cellular system is always depicted as a hexagon and the cluster size can be seven, nine or twelve.

The GSM system requires a number of functions to be created for a fully operational mobile system.

The cell coverage area is controlled by a base station which is itself made up of two elements. The first element is the transmission system which communicates out to the mobile and also receives information from it to set up and maintain calls when actually in operation. The base station transceiver (BST) is controlled by the base station controller (BSC), which communicates with the mobile switching center (MSC) ---- the essential link to the local public switched telephone network (PSTN), and to the subscriber data which is stored in registers within the system. The subscriber registers allow the GSM system to check a subscriber who requests the use of the network, allow access and then set up the charging function, etc.

The GSM system was allocated part of the 900 MHz band at the 1978 World Administration Conference (W AC), the actual bands being 890 to 915 MHz for the uplink transmission and 935 to 960 MHz for the downlink. The access method is time division multiple access (TDMA).

The GSM system operates in a burst transmission mode with 124 radio channels in the 900 MHz band, and these bursts can carry different types of information. The first type of information is speech, which is coded at 6.5 kbit/s or 13 kbit/s. The second type is data, which can be sent at 3.6 kbit/s, 6 kbit/s or 12.6kbit/s. These two forms of transmission are the useful parts of the transmission, but have to be supported by overhead information which is sent in control channels (CCH).

The use of digital radio transmission and the advanced handover algorithms between radio cells in GSM network allows for significantly better frequency usage than in analogue cellular systems, thus increasing the number of subscribers that can

be served. Since GSM provides common standard, cellular subscribers will also be able to use their telephones over the entire GSM service area. Roaming is fully automatic between and within all countries covered by GSM system. In addition to international roaming, GSM provides new services, such as high-speed data communication, Facsimile and short message service. The GSM technical specifications are designed to work in concert with other standards, e. g. ISDN. Interworking between the standards is in this way assured. In the long term perspective cellular systems, using a digital technology, will become the universal method of telecommunication.

The third generation mobile communication system being developed in Europe is intended to integrate all the different services of second generation systems and cover a much wider range of broadband services (voice, data, video and multimedia) consistent and compatible with technology developments taking place within the fixed telecommunication networks.