Communication technology is divided into wired communication and wireless communication.

　　Information and data are either spread in the air or in kind. If it is spread on physical materials, it is wired communication. For example, copper wires and optical fibers are collectively referred to as wired media. Transmission of data on wired media can reach very high speeds. The current mainstream mobile communication standard is 4G LTE, with a theoretical rate of only 150Mbps (not including carrier aggregation).

Wireless communication is the use of electromagnetic waves for communication. Electric waves and light waves are both electromagnetic waves. The functional characteristics of electromagnetic waves are determined by its frequency. Electromagnetic waves of different frequencies have different attributes and characteristics, and thus have different uses.

　　We currently mainly use electric waves for communication. Lightwave communications are also on the rise. Electric waves are a kind of electromagnetic waves, and their frequency resources are limited. In order to avoid interference and conflict, we further divide the lanes on the radio wave and allocate them to different objects and uses. We mainly use IF~UHF for mobile phone communication. For example, the frequently mentioned "GSM900" and "CDMA800" actually mean GSM with a working frequency band of 900MHz and CDMA with a working frequency band of 800MHz.

　　The current global mainstream 4G LTE technology standard belongs to UHF and UHF. Our country mainly uses ultra-high frequency. With the development of 1G, 2G, 3G, and 4G, the frequency of radio waves used is getting higher and higher. The higher the frequency, the more abundant frequency resources can be used. The richer the frequency resources, the higher the achievable transmission rate. Frequency resources are like cars. The higher the frequency and the more cars, the more information can be loaded in the same time.

　　The frequency range of 5G is divided into two types: one is below 6GHz, and the other is above 24GHz.

　　The salient characteristics of electromagnetic waves: the higher the frequency, the shorter the wavelength, and the closer it is to a straight line (the worse the diffraction ability). The higher the frequency, the greater the attenuation in the propagation medium; the lower the frequency, the cheaper the network construction, and the more advantageous the competition.

　　 As time changes, the communication frequency of our mobile phones is getting higher and higher, and the wavelength is getting shorter and shorter, and the antenna is also getting shorter.

　　 This is the killer of 5G—Massive MIMO (multiple antenna technology), MIMO is "Multiple-Input Multiple-Output", multiple antennas for transmission, multiple antennas for reception. In the LTE era, we already have MIMO, but the number of antennas is not too large, and it can only be said that it is the primary version of MIMO. In the 5G era, MIMO technology continued to be carried forward, and now it has become an enhanced version of Massive　MIMO (Massive: massive, massive).

　　 In the 5G era, if two users under the same base station communicate with each other, their data will no longer be forwarded through the base station, but directly from the mobile phone to the mobile phone. This saves a lot of air resources and reduces the pressure on the base station. That is Device to Device.

　　 Communication technology is not a mystery. As the most dazzling gem in the crown of communication technology, 5G is not an unreachable innovative and revolutionary technology. It is more an evolution of existing communication technology. The limits of communication technology are not technical limitations, but inferences based on rigorous mathematics. How to further explore the potential of communication within the scope of scientific principles is the tireless goal of many pursuers in the communication industry.