What are the modes of electrical communication?
It has been pointed out that the communication system can be divided into analog communication system and digital communication system according to the analog signal or digital signal transmitted in the channel.
When messages are transmitted from one place to another, the communication medium can be divided into two broad categories: one is called wired communication, and the other is called wireless communication. The so-called wired communication, refers to the transmission medium for communication overhead, cable, cable, waveguide and other forms, which is characterized by medium can be seen, touched. The so-called wireless communication, is the transmission of information medium, invisible and can not touch the medium (such as electromagnetic wave) of a form of communication. Usually, the wired communication can be further classified, such as communication, cable communication, cable communication etc.. The common forms of wireless communication are microwave communication, short wave communication, mobile communication, satellite communication, scatter communication and laser communication, and so on.
According to the working frequency of communication equipment, communication system can be divided into long wave communication, medium wave communication, short wave communication, microwave communication and so on.
According to the communication business, the communication system can be divided into traffic communication and non telephone communication. Telephone service has always been dominant in the field of telecommunications, and it belongs to the communication between people. In recent years, the rapid development of non traffic communication, which mainly includes data transmission, computer communication, electronic mail, telegraph, fax, videotex and video conferencing, image communication also from a broad perspective, radio and television, radar, navigation, remote control, telemetry communication should also be included in the category, because they all meet definition of communication. With the continuous development of broadcasting, television, radar and navigation, they have been derived from communication and formed an independent discipline.
It has been pointed out that the communication system can be divided into baseband transmission and frequency band (modulation) transmission according to whether modulation is adopted. Baseband transmission is the direct transmission of signals that have not been modulated, such as audio local calls. The frequency band transmission is a general term for transmitting various signals and then transmitting them to the channel.
