A brief history of the development of communication transmission

Since the existence of human beings, they have always communicated ideas and transmitted messages

Humans in ancient times used expressions and movements to communicate information. This is the most primitive way of communication

Later, human beings created language and writing in their long life

Human beings also created many ways of transmitting information, such as ancient beacon towers, golden drums, silk flags, and navigation signals. Etc., these are all ways to solve the problem of long-distance information transmission

After entering the 19th century, people began to try to use electrical signals to communicate

Table 1-1 lists some communication-related Historical events:

Table 1-1 Historical events related to communication

Development and Prospects of Communication Technology

Cable communication is the earliest developed communication technology , it has been used for long-distance communications for more than 60 years and occupies a prominent position in communications

Before the development of optical fiber communications and mobile communications, the connection between user terminals such as telephones, faxes, and telegraphs and switches relied entirely on Local telephone cables

Cables were once the main means of long-distance communication and international communication. There are large-capacity transoceanic cables in the Atlantic and Pacific Oceans

According to statistics in 1982, my country's public network long-distance The total length of the lines is more than 180,000 kilometers, 90% of which are open wires

Currently, the proportion of coaxial cables has increased to about one-third. Analog single sideband modulation and frequency division multiplexing (SSB/FDM) are mainly used in cable communications

Internationally, the maximum capacity of each core of coaxial cable can reach 13,200 channels (or 6 channels of radio and television ), my country's Shanghai-Hangzhou, Beijing-Han-Guangzhou coaxial cable trunk lines can carry 1,800 carrier telephone lines. Since the advent of digital telephones, countries have vigorously developed baseband transmission technology of pulse code modulation time division multiplex signals in coaxial cables. The capacity of digital telephones can reach 4032 channels.

The second generation of mobile communications is currently widely used. The system adopts narrowband Time Division Multiple Access (TDMA) and narrowband Code Division Multiple Access (CDMA) digital access technologies. National and regional standards that have been formed include the European GSM system, the American IS-95 system, and the Japanese PDC system. Our country mainly uses the European GSM system

The second-generation mobile communication system has achieved regional unification of standards, covering large, medium and small cities, and has provided great convenience for people's information exchange. With the popularization of mobile communication terminals, the number of mobile users has doubled, and the defects of the second-generation mobile communication system have gradually emerged, such as global roaming problems, system capacity problems, spectrum resource problems, and problems in supporting broadband services, etc.

The third generation mobile communication system is an important stage in the development of personal communications in the future. It has milestone and epoch-making significance. Let us pay attention to its development trend and welcome its arrival

Currently, my country’s telephone network There have been qualitative changes in scale and technical level. It has been initially built with optical cables as the mainstay, microwave and satellite comprehensive utilization, fixed phone, mobile communication, and multimedia communication coexisting with multiple networks. It covers urban and rural areas across the country and reaches all parts of the world. It has large capacity and high speed. Fast, safe and reliable telecommunications network.