current position:Home>[Special Topic on wireless network technology (IV)] Why is your Wi Fi network so slow?

[Special Topic on wireless network technology (IV)] Why is your Wi Fi network so slow?

2021-08-26 03:06:49 Network engineer Dapeng


 

Wireless topics in total 12 piece , This is the fourth article ( 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 ): Your home Wi-Fi Why is the network speed so slow ?

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

 

Do you have such a question , The wireless router has a nominal address 300M、450M、867M、1167M And so on , How are these rates calculated , What does it mean ?

First, share a little joke :

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there 450M It doesn't mean the propagation distance 450 rice , It's bandwidth Mbps, It shows that the maximum download rate of this wireless router can reach 450Mbps, It has nothing to do with the distance covered and the ability to pass through the wall . Wireless bandwidth is calculated differently from wired bandwidth , Extremely complex . This article focuses on analyzing the calculation method of wireless network rate .

 

 

02

Understand how wireless rate is calculated

 

To understand Wi-Fi The rate calculation method must first understand 802.11, We have shared the previous articles 802.11 Development history of , The latest generation Wi-Fi6(802.11ax), Let's look at the past dynasties through the figure below 802.11 The nature of Technology .

 

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From the picture, you can find ,Wi-Fi The development of is a process of increasing speed , From the earliest 802.11 Of 2M Up to date 802.11ax Of 9.6G. The increase of speed is determined by many factors .

 

Let's look at the formula for wireless rate :

The speed of the whole machine = Number of spatial streams * 1/(Symbol+GI) * Encoding mode * Bit rate ( Modulation technology ) * The number of effective subcarriers ( Modulation technology )

Explain each key factor :

 

1、 Number of spatial streams

Spatial flow is actually AP Antenna of , The more antennas , The larger the overall throughput , Like a viaduct on a highway , When the pavement Lane cannot be expanded , Viaducts can be built , Thus, the lane can be doubled . Vehicle traffic will also increase exponentially .

 

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2、Symbol And GI

Symbol  It's the transmission signal in the time domain , Two adjacent Symbol There needs to be a Fixed gap ( GI), To avoid Symbol Interference between . Just like the high-speed railway in China , Each train is equivalent to one Symbol, There must be... Between two trains from the same station A time gap , Otherwise, the two trains may collide . Different Wi-Fi The clearance under the standard is also different , Generally speaking, when the transmission speed is fast GI It needs to be increased appropriately , It's like two columns in the same driveway 35 0KM/h The departure time gap of high-speed rail at an hour is higher than that at an hour 250 KM/h when High-speed railway hair The car clearance should be larger .

 

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3、 Encoding mode

The coding method is modulation technology , namely 1 individual Symbol It can carry bit Number . from Wi-Fi 1 To Wi-Fi 6 , Every improvement in modulation technology , Can at least bring... To each spatial velocity rate 20% The above promotion .

 

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4、 Bit rate

Theoretically, it should be transmitted losslessly according to the coding mode , But the reality is not so beautiful . Some information codes for error correction need to be added during transmission , Trade redundancy for high reliability . The code rate is the ratio of the actual data code transmitted to the theoretical value after excluding the error correction code .

 

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5、 The number of effective subcarriers

The carrier wave is similar to that in the frequency domain Symbol , A subcarrier carries a Symbol, The number of subcarriers is different under different modulation modes and different bandwidth .

 

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there HT20/40/80/160 It represents the bandwidth , We've talked about it in previous articles 2.4G and 5G Available non overlapping channels , The bandwidth of each channel is 20Mhz,HT40 That is to say 40Mhz, Is to bind two non overlapping channels together , Improve AP Rate , This technology is also an important means to improve the wireless rate , Similar to link aggregation technology in wired network . It can be understood as highway 2 The lane changes 4 Vehicle Lane , Capacity doubled .

 

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thus , Based on the above parameters , We can calculate that 802.11ac and 802.11ax stay HT80 The maximum rate of a single spatial stream in bandwidth :

 

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802.11ax(Wi-Fi6) Maximum support will be 5.2G Of 8 A non overlapping channel bundle , That is, the bandwidth is 160Mhz, Maximum support at the same time 8 Space flow . therefore ,802.11ax The maximum speed can reach 600Mbps * 2 * 8=9.6Gbps, Of course, this is the theoretical maximum , No practical significance . The real wireless rate will receive the number of connected terminals , The size of the data frame sent by the terminal , And physical environment , Therefore, the wireless rate should be subject to the actual test .

 

03

Home level wireless router rate calculation

 

therefore , In response to the questions raised in the preface , The wireless router has a nominal address 300M、450M、867M、1167M And so on , How are these rates calculated ?


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Product 1 :450M rate , It can be judged directly that 802.11n Of 3 Flow regulating products , however 802.11n Outdated , So the price is relatively cheap , But it can still be used in a home environment .

 

Product 2 :1200M rate , It must be 802.11ac product , Calculated from the rate , It's a two-way, two stream product ,2.4G and 5G The rates add up to :150M*2+433M*2=1167M≈1200M

 

Product 3 :2100M rate , For two streams 802.11n+4 Flow regulation 802.11ac product ,150M*2+433M*4≈2100M

 

Product 4 :2200M rate , by 3 Streams 802.11n+4 Streams 802.11ac product ,150M*3+433M*4≈2200M

 

At present, the mainstream product of home router is 802.11ac product , The more antennas, the higher the rate , The more expensive it is .

 

04

Enterprise wireless router rate calculation

 

 

Before talking about enterprise equipment , Let's start with a few concepts : Dual frequency 、 dual 、 Double current

Dual frequency : refer to 2.4G and 5G Two bands , Early devices only supported 2.4G, because 2.4G Limited spectrum resources , Bandwidth is limited , And the interference is serious , So the introduction of 5G Frequency band , Now enterprise class AP All support 2.4G and 5G, It's called dual band AP.

 

dual : refer to AP There are two RF cards inside , All the way 2.4G service , Another way to provide 5G service , Therefore, the number of belt conveyors increases . Enterprise class AP In order to expand the number of belt conveyors , There are even 3 An RF card AP.

 

Double current : Double flow means 2 Space flow , It can be understood as 2*2MIMO, For example, as mentioned above 802.11n A stream 150M, Two article 300M, Three 450M wait .

 

Let's look at a AP Parameters of :

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Maximum speed of the whole machine 2.966G, How is this value calculated ?

First analysis , this AP It's three-way AP, That is, there are 3 An RF card .

 

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Total rate 2.966G Is the sum of the three RF card rates , What are the rates of the three RF cards ? How many space streams does each RF card have ?AP-740-I, In product naming 4 Represents that the product is 4 Space flow , This is Ruijie's naming rule . Then you can judge ,2.4G and 5G RF cards are 4 Space flow ,2.4G/5G The optional RF card has only one space stream . Rate is :

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Be careful :

1、 there 2.4G Why is a single stream 200M, I'm not saying 150M Do you ? Because in 802.11ac wave2 The coding efficiency has been improved , So I upgraded to 200M.

 

2、2.4G/5G Optional RF card , Why is the rate 433M? This RF card has only a single stream ,2.4G The maximum is 200M,5G The maximum is 433M, Calculate the limit rate , take 5G Maximum .

 

3、 The overall speed is 2.966G, A single user can only connect one RF card at the same time , Therefore, for a single user, the most ideal situation is to connect to a pure network 5G RF card , The theoretical maximum rate is 433M*4=1732M. If the user is connected to 2.4G/5G On the RF card , Then the theoretical maximum rate is 433M. Therefore, we should rationally look at the maximum rate claimed by manufacturers , A single user cannot achieve . Even multiple users will compete , Unable to reach maximum rate .

 

Okay , Let's talk about the rate calculation of wireless network .

 

05

reflection

 

Wi-Fi How to measure the signal strength ? Does a strong signal mean a high wireless rate ?

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

 

 

Wireless topics in total 12 piece , This is the fourth article ( 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 ): Your home Wi-Fi Why is the network speed so slow ?

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 !

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author[Network engineer Dapeng],Please bring the original link to reprint, thank you.
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