[Special Topic on wireless network technology (III)] does wireless network transmit data through air?

Wireless topics in total 12 piece , This paper is the third one （ Click the title to jump to the historical article ）：

Special topic of wireless network technology （ One ）： The past and present of wireless network

Special topic of wireless network technology （ Two ）：Wi-Fi6 And 5G The battle of

Special topic of wireless network technology （ 3、 ... and ）： Does the wireless network transmit data through the air ？

Special topic of wireless network technology （ Four ）：Wi-Fi How is the bandwidth calculated ？

Special topic of wireless network technology （ 5、 ... and ）：Wi-Fi If the signal is full, the network speed must be fast ？

Special topic of wireless network technology （ 6、 ... and ）： Introduction to enterprise wireless network equipment

Special topic of wireless network technology （ 7、 ... and ）： You've never heard of these basic wireless concepts ！

Special topic of wireless network technology （ 8、 ... and ）： Analysis of typical networking architecture of wireless network

Special topic of wireless network technology （ Nine ）： Typical indoor scenario wireless network deployment scheme

Special topic of wireless network technology （ Ten ）： Wireless network engineering survey and design case analysis

Special topic of wireless network technology （ 11、 ... and ）： Common software and tools for wireless networks

Special topic of wireless network technology （ Twelve ）： Common optimization methods for wireless networks

……

 

01

Preface

 

How does the wireless network transmit data ？ I believe this problem must perplex many students . Compared with wireless , Wired networks are obvious , Data transmission through network cable and optical fiber , And the wireless network can't see or touch . Dapeng has handled countless network failures , The most annoying thing is the wireless network problem , The reason is that the wireless network is invisible and untouchable , It is also very vulnerable to environmental factors . Next, let's talk about the media through which wireless networks transmit data .

 

02

Media for wireless network transmission - electromagnetic wave

 

In fact, no matter Wi-Fi, still 4G/5G, Or infrared 、 bluetooth , Even radar 、 Satellites and so on , All invisible communication modes are basically transmitted through the same medium —— electromagnetic wave , It's just that electromagnetic waves differ in wavelength and frequency , With incomparably rich frequency band .

 

 

Wi-Fi The frequency band used is ISM Frequency band ,ISM Full name IndustrialScientific Medical, The Chinese meaning is industrial (Industrial)、 The scientific (Scientific) And medical (Medical), So as the name suggests ISM Frequency band means that countries move a certain frequency band, which is mainly open to industry , Scientific and medical institutions use . No license or fee is required to apply these bands , Just follow a certain transmit power （ Generally lower than 1W）, And don't interfere with other frequency bands .

ISM The frequency band is not uniform in different countries . For example, there are three frequency bands in the United States 902-928 MHz、2400-2484.5 MHz And 5725-5850 MHz, And in Europe 900MHz And part of the spectrum is used for GSM signal communication . and 2.4GHz For all countries ISM Frequency band . So WLAN （IEEE 802.11b/IEEE 802.11g）, bluetooth ,ZigBee Wait for the wireless network , Can work in 2.4GHz On the frequency band .

 

 

Wi-Fi The frequency bands used are mainly 2.4G and 5G Frequency band . Please note that , What I'm talking about here 5G And the operators mentioned above 5G Different , The operator, 5G Refer to generation, It means the fifth generation mobile communication technology . Let's popularize it , The first generation is analog communication , It means big brother ; The second generation is GSM, That's what we're talking about 2G, A month 50M The kind of traffic that can't be used up ;3G、4G、5G I don't need to say more , Everyone is very familiar now .

 

 

Wi-Fi Medium 5G Refers to the use of 5G This band transmits data , In the early Wi-Fi Only open 2.4G Frequency band , Early wireless terminals only supported 2.4G, Only support 2.4G Your terminal cannot receive 5G The signal . Remember early Lenovo claims 2.4G The frequency band is enough to meet the needs of network use , Notebooks only need to support 2.4G that will do , The result is slapping , It's not a good time to support 5G.

 

that Wi-Fi How to transmit data ？ We said Wi-Fi The essence of is electromagnetic wave , So understand... In a simple way . First of all, we say that the network cable transmits data through electrical signals , Communication in the physical layer is based on bit stream （ Binary 0、1） transmission , So it can be expressed by the high and low frequency of current 0 and 1. Electromagnetic waves also have peaks and troughs , Therefore, it can be understood that a medium with two polarization states can represent binary . Of course, there will be complex coding technology at the bottom . Just in this way, we can understand more simply , Not exactly . as for Wi-Fi The underlying coding technology and the modulation technology that will be involved in subsequent articles, I don't suggest you go deep into , Unless you specialize in wireless networks .

 

 

As mentioned earlier, electromagnetic waves have different frequency bands according to different wavelengths and frequencies ,Wi-Fi Use 2.4G and 5G Frequency band for data transmission , The frequency band has another name — channel , stay 2.4G There are... In the frequency band 13 The spacing is 5MHz Channel of , Because of the modulation technology , therefore Wi-Fi When transmitting, you need to use 22MHz Bandwidth channel , therefore 2.4G Frequency band only 3 Non overlapping channels （ The most common is 1、6、11）. and 5G The frequency band is currently given to Wi-Fi There are... In the open channel 13 Non overlapping channels , Namely 802.11ac Before that 5.8G（149、153、157、161、165）, And from 802.11ac Start using 5.2G（36、40、44、48、52、56、60、64）.

 

 

 

 

therefore , From the propagation characteristics of electromagnetic waves, it is not difficult to find , At the same frequency , The longer the wavelength, the farther the propagation distance , This is what we mentioned in our first article , The coverage of high frequency band is small , Use... In the same range 5G The number of base stations to be deployed is higher than 4G Many reasons . Change the angle , At the same time , The higher the frequency, the higher the rate , That's why 5G Network speed ratio 2.4G Reason for speed , You can do it at home Wi-Fi test （ At present, home wireless routers support dual band ）. Electromagnetic waves have another very important characteristic , The longer the wavelength , The smaller the attenuation through obstacles , This can also be done at home Wi-Fi To test .

 

 

The attenuation intensity of wireless signal is also different for obstacles of different materials , Refer to the below , When you deploy wireless networks AP Try to avoid metal 、 Load bearing wall, etc .

 

 

Okay , Let's talk about this .

 

03

reflection

 

Wi-Fi How to calculate the bandwidth ？ Is bandwidth equal to bandwidth ？

For more information, please follow the follow-up articles .

 

Wireless topics in total 12 piece , This paper is the third one （ Click the title to jump to the historical article ）：

Special topic of wireless network technology （ One ）： The past and present of wireless network

Special topic of wireless network technology （ Two ）：Wi-Fi6 And 5G The battle of

Special topic of wireless network technology （ 3、 ... and ）： Does the wireless network transmit data through the air ？

Special topic of wireless network technology （ Four ）：Wi-Fi How is the bandwidth calculated ？

Special topic of wireless network technology （ 5、 ... and ）：Wi-Fi If the signal is full, the network speed must be fast ？

Special topic of wireless network technology （ 6、 ... and ）： Introduction to enterprise wireless network equipment

Special topic of wireless network technology （ 7、 ... and ）： You've never heard of these basic wireless concepts ！

Special topic of wireless network technology （ 8、 ... and ）： Analysis of typical networking architecture of wireless network

Special topic of wireless network technology （ Nine ）： Typical indoor scenario wireless network deployment scheme

Special topic of wireless network technology （ Ten ）： Wireless network engineering survey and design case analysis

Special topic of wireless network technology （ 11、 ... and ）： Common software and tools for wireless networks

Special topic of wireless network technology （ Twelve ）： Common optimization methods for wireless networks

……

 

Pay attention to me , Learn to improve network technology together ！