Wifi6 features, in-depth study together, OFDMA, QAM modulation, BSS

focusing ： Core products , Core market , Core technology

( Zhilian network , iotthings)

I believe we talked WiFi6 The benefits of , Even non industry ones can speak faster , More access ;

Industry practitioners can blurt out WiFi6 Characteristics of ：OFDMA,1024-QAM,BSS Coloring,TWT etc. ;

But these technical points are specific , It's a little difficult ;

This article follows the previous article WiFi6 Market articles , Review with you WiFi6 Characteristics of , Learn from time to time , Not to mention ~

This article altogether 1192 typeface , Reading time is expected to 15 minute ;

Main technical points ：

• Higher order QAM modulation

• Higher order OFDMA

• BSS To color

01

Faster prime mover  , 1024-QAM

WiFi6 Than WiFi5, Theoretically, it is close to 40%, A very important reason here is the higher-order modulation ;

You say? FSK,QFSK,BPSK these , Maybe it's easier to understand

For example, the following figure ,BPSK, Represented by waveforms of different phases 0 and 1, Such a waveform can be carried 1 individual bit Data information ;

QPSK Through  (0,90,180,270） Phase shift of four angles , A waveform can be carried 2bit data ;

and QAM, It is modulated by two dimensions of phase and amplitude , Carry more information , such as 16-QAM, Can represent 4 individual bit Information ,256-QAM, Can represent 8bit,1024-QAM Can represent 10bit 了

Let's have a little more theory  , Understand quadrature modulation （ The picture is cut from the micro signal  < Primary school students in the field of information >）

With the above foundation , We can understand it as QAM The modulation can be converted to a point under the coordinate system , This point is located based on amplitude and angle ; Combined with the following figure, it is easy to understand ;

Of course ,QAM The higher the modulation , The higher the requirement of signal-to-noise ratio , The higher the requirements for RF circuit design and computing power ;

Of course ,WiFi6 Faster and faster, there are other mechanisms , Including wider bandwidth - 160MHz,8x8 MU-MIMO;

02

More stable transmission  , OFDMA

stay Wi-Fi 4/5 in , Communication is single user , That is, every time you send data , No matter the amount of user data , A user needs to occupy all subcarriers .

We regard all subcarriers as a delivery car , If the user's packet is small , Like instant messaging , Browse web pages , Not all subcarriers are used , Then the car is not loaded , The remaining idle subcarriers are wasted .

In order to solve the transportation efficiency problem of subcarriers ,Wi-Fi 6 Introduced 5G Orthogonal frequency division multiple access in OFDMA(Orthogonal Frequency Division Multiple Access).OFDMA and OFDM Although it looks like a letter is missing , but OFDMA It is essentially a multiple access technology .

OFDMA Divide the channel into different resource units RU(Resource Unit), Of course these RU They are orthogonal to each other . Sending data , Different users will only use one resource unit instead of the whole channel , In this way, data can be sent to multiple users at one time .

Yes no OFDMA The transportation diagram of is as follows

03

Less space interference , BSS color

In order to avoid the interference of wireless communication ,802.11 stay MAC Layer designed a simplified detection mechanism  - CSMA-CA (Carrier Sense Multiple Access , Collision Avoidance)

Before sending data , Listen in the air first   message , If someone is talking , I'll wait , I'll send it again when it's quiet ;

This brings about a problem that the message has nothing to do with me , I must also wait ; Thus reducing the number of parallel communication connections in the same space ;

To solve this problem ,WiFi6 Introduced BSS Coloring;

BSS Coloring, Just for different AP Message sent , Envelopes with different colors , The receiver receives AP Message of , Don't open the envelope , Look at the color directly to know whether it is related to you ;

The same color means it has something to do with yourself , Different colors have nothing to do with yourself ; For messages that have nothing to do with themselves , It's as if it doesn't exist , The receiving end can avoid , Directly initiate communication , So as to achieve the effect of spatial reuse ;

Pictured above , Use BSS After coloring , Only the same color 36 channel , Will interfere ;

BSS Coloring Color marking , from AP Put 6bit Color marker bit of , This is PHY/MAC Layers complete , In this way, the receiving end does not need to parse the message ; This is also the envelope opening mentioned above , The reason why you don't have to read the contents of the letter ;

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