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     Mobile communication is the communication between the mobile body or between the mobile body and the fixed body. The moving body can be a person, or an object in the moving state, such as a car, a train, a ship, a radio, etc.

     One or both sides of the communication are in motion. Including land, sea and air mobile communications. The frequency bands used are LF, IF, HF, VHF and UHF. Mobile communication system consists of mobile station, base station and mobile exchange office. In order to communicate with a mobile station, the mobile switchboard sends out calls to the whole network through each base station, and the called station sends out a response signal after receiving the response. After receiving the response, the mobile switchboard allocates a channel to the mobile station and transmits a signal to the telephone channel to make it ring.

Mobile communication system consists of two parts:
     (1) Space systems;
     (2) Ground system: satellite mobile radio station and antenna; gateway station and base station.
Since the birth of mobile communication system in the 1980s, it will go through five generations of development in 2020, and will transit from the third generation to the fourth generation (4G) in 2010. To 4G, in addition to cellular telephone system, broadband wireless access system, millimeter-wave LAN, intelligent transmission system (ITS) and homotopy platform (HAPS) systems will be put into use. [2] The most obvious trend of future generations of mobile communication systems is to require high data rate, high mobility and seamless roaming. Achieving these requirements will face greater technical challenges. In addition, system performance (such as cell size and transmission rate) will largely depend on the frequency. Considering these technical issues, some systems will focus on providing high data rates, while others will focus on enhancing mobility or expanding coverage.

   From the user's point of view, access technologies available include cellular mobile wireless systems such as 3G; cordless systems such as DECT; short-range communication systems such as Bluetooth and DECT data systems; wireless local area network (WLAN) systems; fixed wireless access or wireless local loop systems; satellite systems; broadcasting systems such as DAB and DVB-T; ADSL and ableModem.

   1.5 band
   The use of frequency bands throughout the low frequency, intermediate frequency, high frequency, very high frequency, ultra high frequency and microwave. For example, 160, 450, 800 MHz and 900 MHz bands are often used in China's land mobile telephone communication system; 108-136 MHZ bands are often used in the Air-to-Ground mobile communication system; 150 MHz bands are often used in the maritime mobile communication system between shore stations and ship stations; 1.5 GHz/l.6 GHz L band is used in the international maritime satellite mobile communication system; and L band is used in the land satellite mobile communication system. It can also be used in 11/14 and 12/14 GHzKu bands.

   1.6 networking mode
   According to whether there is a center or not, it can be divided into two ways: non-central network and central network. Centerless network is the establishment of direct links between mobile stations to achieve communication between mobile users. For example, the same-frequency singlework network of the intercom telephone system, the same-frequency singlework network of the non-central location system, etc. There is a link between the mobile station and the control center in the central network, so the communication between the mobile users can only be realized through the control center. For example, the second generation cordless telephone network, cellular mobile telephone network and cluster dispatching system. According to the service object, there are public mobile communication network and private mobile communication network. The public mobile communication network is a part of the public telecommunication network. Mobile communication networks are either connected to the public telephone network by user lines or to the automatic telephone network by terminal office through relay lines.

   1.7 signaling
   It refers to the telecommunication information (non-language) related to the connection and control of communication and management in mobile communication network, which has dual meanings of signals and instructions. There are analog signaling and digital signaling in signal form, wireless signaling and wired signaling in transmission medium, along-way signaling and common-way signaling in transmission mode. In the 1980s, analog along-the-way signaling was widely used in wireless signaling of small capacity mobile communication networks, that is, to share a channel with voice in multi-audio (or pulse) mode, and to transmit signaling before and after the transmission of voice signals. In large and medium capacity mobile communication networks, digital common-channel signaling is often used in wireless signaling mobile communications, that is, special signaling channel (also known as control channel) is set up in multi-channel shared mobile communication systems.

   1.8 number
   Private mobile communication networks are numbered separately. The number of the public mobile communication network is related to the way to enter the public telecommunication network. If the user line is used to enter the telecommunication network, the numbering method of the mobile user number is the same as that of the local telephone user number. For example, E213 of CCITT recommends two Numbering schemes for land public mobile communication network: one is consistent with the numbering method of public telecommunication network, and the other is "network number", i.e., the way of individual numbering.