The difference between mobile and traditional communications

The difference between mobile communication and wired communication has two points in short: different channels and different interfaces.

The signal of fixed telephone is transmitted through telephone line, which belongs to wired channel transmission; the signal of mobile communication is transmitted through electromagnetic wave in space, which belongs to wireless channel transmission.

Fixed telephone interface, telephone lines can be accessed through this interface to the PSTN network; and cell phones and base station communication interface is invisible, touch and feel, called the air interface.

The earliest mobile communication system uses a large area system to realize the electromagnetic wave coverage within the service area, that is, the highest point in the service area to build a high-power transmitter to cover an area. There is only one base station in the large area responsible for communication contact and control. The antenna erection height is usually more than 30m, and the radius of the service area reaches 30~50km. in the large area system, the cell phone needs to transmit with the base station in line-of-sight, which is limited in the horizontal distance, and the number of supported users is limited.

Unlike the macro-area system, cellular cells use low-power transmitters to serve small areas in order to achieve electromagnetic wave coverage instead of broadcasting. A city is divided.

Divided into small areas called cells. Each cell, rather than a city, has a transmitter. With cell division, the same frequencies can be reused in different cells. In practice, the coverage of the cell is not a regular shape, in order to achieve full coverage and no dead space, the shape of the cell is mostly positive polygonal, such as a positive hexagonal shape, hence the name cellular cell.