公共陆地移动网(PLMN)

A public land mobile network (PLMN) is a telecommunications network for mobile units, referred to as mobile stations or mobile phones.
Mobility is the hallmark of a PLMN. What is more, a PLMN can enhance the capability of other networks to provide mobility; for example, when it serves as a bearer for Internet access.
Mobile telephony is one of the fastest growing and most popular teleservices that has ever existed. It is likely that the majority of subscribers will eventually have some form of radio access to the telecommunications network. The radio-based service that at one time was used by the national defence, the police, taxi and other service organisations to maintain communication between their mobile and stationary units has now developed into a tool that many business professionals find natural to use and, lately, a tool for the average person.
One important reason for the fast growth of mobile telephony is the fact that the service is an extension of the world's most widespread teleservice - fixed telephony. Apart from being able to communicate with one another, subscribers of mobile telephony services are also able to communicate - via PSTN/ISDN gateways - with those who have fixed teleservice subscriptions.
The advantages of increased accessibility experienced by mobile users are attracting an increasing number of new subscribers. This, in turn, places great demands on the capacity of network radio elements - demands that operators have to meet through more efficient use of existing frequencies and by making new frequencies available.
Technically, the development of mobile telephony has progressed from analog to digital mobile systems. Terrestrial systems have also been complemented with satellite systems. The cordless technique - originally a mobile radio access technique for office environments - continues to develop, and the boundary between cordless and cellular is becoming less distinct.
Mobile telephony is advancing worldwide at a time when liberalisation is in full swing. For the majority of countries, deregulation and privatisation increase competition as the number of operators increases. Different systems, aimed at promoting mobility, operate in parallel in the same geographical area or in the same market. Analog and digital mobile systems, cordless systems and satellite systems are all able to satisfy user demand for mobile telecommunication in various ways.