Fast query and application of wireless network technology

The development of wireless networks is very mature, so we may not be clear about some of the commonly used network technologies on the network. Here we will provide some help in detail.

Wireless networks are a product of the combination of computer networks and wireless communication technologies. They provide an effective method to support communications between computers using wireless multi-access channels, it also provides potential means for mobile, personalized, and multimedia applications of communication. Generally, any computer network that uses wireless transmission is called a wireless network. From WLAN to Bluetooth, from infrared to mobile communication, all of these are examples of wireless network applications. It does not use traditional cables to provide all functions of traditional wired LAN. The infrastructure required by the network does not need to be buried in the ground or hidden in the wall. The network can be moved or changed as needed. To put it bluntly, it is the Wireless connection form of the LAN, that is, the Wireless Local-area Network (WLAN ).

1. Wireless Network Transmission Principle

Similar to a common wired network, a wireless LAN uses an ISO/RM layer-7 network model, which is only in the two lowest layers of the model: Physical Layer and data link layer, wireless transmission is used. Although the standards and specifications of various types of wireless networks are not uniform at present, the transmission methods must be one of the following two types: radio wave mode and infrared mode. The infrared transmission method is currently the most widely used wireless network technology. Currently, almost all Home Appliance Remote controls that are frequently used in household appliances use the infrared transmission technology. As a wireless LAN transmission method, the biggest advantage of infrared transmission is that it is not affected by radio waves, and the use of infrared rays is not restricted by the National Radio Management Board. However, the transmission quality of infrared transmission is greatly affected by the distance, and the penetration of infrared rays to non-transparent objects is also very poor, this directly causes the infrared transmission technology to become the main character in the computer wireless network. In contrast, radio wave transmission is widely used. Radio waves are used for transmission, which not only covers a large scope and has a high transmit power, but also features concealment and confidentiality. It does not interfere with systems of the same frequency and has high availability. The following describes several main radio wave modulation methods.

(1) spectrum Expansion Method

The basic feature of spread spectrum communication is to use pseudo-random codes that are many times higher than the transmission rate of information data to expand the spectrum of the baseband signal carrying information data, form a broadband low-power spectrum density signal to launch. The increased bandwidth can transmit information reliably with the same information transmission rate at a low signal-to-noise ratio. When the signal is overwhelmed by noise, as long as the signal bandwidth is increased accordingly, reliable communication can still be maintained, that is, the signal-to-noise ratio (SNR) benefit can be exchanged through the Spread Spectrum Method for broadband transmission information. This is the basic idea and theoretical basis of spread spectrum communication. Although this method sacrifices the bandwidth, it improves the anti-interference capability and security of the communication system.

Currently, the Extended Spectrum Wireless LAN generally uses the ISM band. Here, ISM is obtained from the first letter of Industrial, Scientific, and Medical. The frequency of transmitting many industrial, scientific research, and medical devices is concentrated in this band. For example, the us ism frequency ranges from 902MHz ~ 928 MHz, GHz ~ 2.48 GHz, 5.725GHz ~ 5.850GHz is composed of three frequencies. If the transmit power and bandwidth radiation meet the requirements of the US Federal Communications Commission (FCC), you do not need to submit a special application to the FCC to use the ISM band.

There are four basic methods to implement Spread Spectrum Communication: Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping) work mode (FH mode for short), hop-to-change Time (Time Hopping) work mode (TH mode for short), and linear frequency Modulation (Chirp mode for short) work mode (Chirp mode for short ). Currently, the most widely used and most typical method of spread spectrum is direct expansion (DSSS), which is used in wireless network communication.

(2) narrowband Modulation

As the name suggests, in this modulation mode, data signals are directly transmitted without any expansion. Compared with the extended spectrum method, the narrowband debugging method occupies less band and has a high utilization rate. However, a wireless LAN Using narrowband modulation occupies a special frequency band and can be used only when it is approved by the national radio administration.

2. Advantages of Wireless Networks

Compared with wired networks, wireless LAN has the following advantages:

Easy installation: network wiring has the greatest impact on the surrounding environment during network establishment. The establishment of a wireless LAN hardly needs to consider its impact on the environment. Generally, you only need to place one or more Wireless Access Point devices in the area to establish network coverage.