Principles of Wireless Network_Shang pin China focuses on high quality website construction - 上海1314龙凤鲜花坊_上海419贵族宝贝

The biggest difference between wireless transmission and wired transmission is that it does not use electric energy or light energy to transmit signals on wired communication carriers, but uses the atmosphere and outer layers Website production Space is used as a channel to transmit electromagnetic waves and realize the transmission of data signals. Due to its unique nature, wireless transmission is very suitable for network applications in remote areas or coastal islands where it is difficult to lay cables.

At present, the most common wireless network transmission modes include microwave communication, satellite communication, etc.

1. Microwave communication

Microwave communication uses a wavelength of 0 The electromagnetic wave between 1mm and 1m, that is, the communication conducted by microwave. The frequency of microwave is extremely high and the wavelength is very short. Because of its strong penetrability, it cannot be reflected by the ionosphere and is easy to be absorbed by the ground, so microwave communication can only be transmitted in a straight line. The main mode of microwave communication is line of sight communication, and relay transmission is required after exceeding the line of sight. In order to gather microwaves into beams and send them to the distant place, parabolic antennas are generally used, whose focusing effect can greatly improve the transmission distance, as shown in Figure 1-13.

The characteristic of microwave communication is that it can only communicate within the visible range; It has good disaster resistance performance. Microwave communication is generally not affected by floods, wind disasters, ground craft and other natural disasters. However, microwave is easily interfered by air transmission, and the absorption and scattering of microwave signals by ground and buildings are also greatly affected. Therefore, microwave communication is suitable for a range of several kilometers with low speed requirements, usually hundreds of kbps, It can only be used for point-to-point communication.

2. Satellite communication

Satellite communication refers to the communication between radio communication stations on the ground, which uses satellites as relays. The satellite communication system consists of satellites and ground stations, as shown in Figure 1-14.

The satellite acts as a relay station in the air, that is, it amplifies the electromagnetic waves sent by the ground station and returns them to another ground station. The time of a geostationary satellite circling the earth at 36000 kilometers above the equator is exactly the same as the time of the earth's rotation (23 hours, 56 minutes and 4 seconds). From the ground, it looks as if it is still. Therefore, three satellites 1200 apart can cover the whole equatorial circle. Therefore, satellite communication is easy to achieve trans ocean and intercontinental communication.

Satellite communication is characterized by a large communication range. As long as it is within the radio wave coverage range launched by satellites, any two points can communicate with each other; It is not easy to be affected by land disasters. As long as the ground station circuit is set quickly, satellite communication can be opened immediately. However, satellite communication has large transmission delay and high cost.

Satellite communication can be used in emergency situations, remote villages, mountains and seas and other areas that need communication.

Principle of wireless network

Date：2015-06-19 Source: Shangpin China Type: website encyclopedia
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