What is mobile communication technology

The so-called mobile communication is the communication between the moving body, or the communication between the moving body and the fixed body. A moving body can be a person or a vehicle, a train, a ship, a radio, etc. in a moving state.

The communication between the mobile communication and the fixed object has a series of characteristics, mainly: (1) mobility. is to keep the object in the moving state of communication, so it must be wireless communication, or wireless communication and wired communication. (2) The propagation conditions of radio waves are complex. Because the moving body may move in various environment, the electromagnetic wave will produce the reflection, the refraction, the diffraction, the Doppler effect and so on in the propagation, produces the multipath interference, the signal propagation delay and the broadening and so on effect. (3) Noise and interference is serious. In urban environment, automotive spark noise, various industrial noise, intermodulation interference between mobile users, adjacent channel interference, the same frequency interference and so on. (4) System and network structure is complex. It is a multi-user communication system and network, must make the user not interfere with each other, can work in harmony. In addition, the mobile communication system should also be connected with the local telephone network, satellite communication network, data network and so on, the whole network structure is very complex. (5) Require high frequency band utilization, good equipment performance.

There are a wide variety of mobile communications. According to the use of requirements and the different working situations can be divided into (1) trunking mobile communications, but also called-zone system mobile communications. It is characterized by only a base station, antenna height of dozens of meters to hundreds of meters, covering the radius of 30~km, transmitter power can be as high as 200W. The number of users is about dozens of to hundreds of, it can be a car, but also a handheld platform. They can communicate with the base station, but also through the base station and other mobile stations and local users to communicate, base station and the city station wired network connection. (2) Cellular mobile communication, also known as the cell system mobile communication. It is characterized by the whole wide range of service areas divided into many communities, each community set up a base station, responsible for the mobile units of the community contact and control, each base station through the Mobile Exchange center and contact each other, and with the local Bureau connection. Using ultrashort wave propagation distance of the limited characteristics, leaving a certain distance of the community can be reused frequency, so that the frequency of resources can be fully utilized. Each community's users in more than 1000, the total coverage area of the final capacity of up to 1 million users. (3) satellite mobile communication. Using satellite forwarding signal can also realize mobile communication for vehicle mobile communication can be used equator fixed satellite, but for handheld terminals, the use of medium and low orbit constellation satellite is more advantageous. (4) Cordless telephone. For indoor and outdoor slow mobile handheld terminals of communication, the use of small power, communication distance near the portable cordless telephone. They can communicate in one-way or in two directions through communication points with local users.

The existing large number of mobile communications are held using analog identification signals, known as analog mobile communications. However, in order to solve the increase of capacity, improve the quality of communication and increase service function, digital recognition signal, namely digital mobile communication, has been applied. On the standard, it is sometimes divided into multiple access (TDMA) and Code Division multiple Access (CDMA) two kinds. The former has Europe's GSM system (Global Mobile Communication system) and North American dual-mode standard IS-54 and Japan's JDC standard. For Code Division Multiple access, there is a IS-95 standard system developed by American Qualcomnn Corporation. The general trend is that digital mobile communications will replace analog mobile communications. The CDMA system will be more dominant. and mobile communication will develop to personal communication. In the near 21st century, it became an important part of the global information superhighway. Mobile communications will have a more glorious future.