This article is the most detailed about WiFi 6 technology.

12 spatial stream and 256-QAM modulation.

Two spatial streams and 256-QAM modulation.

Three spatial streams and 64-QAM modulation.

Wi-Fi has become a ubiquitous technology in today's world, providing connections for billions of devices, and it is also the first choice for more and more users to access the Internet, and it has a tendency to gradually replace wired access. In order to adapt to new business applications and reduce the bandwidth gap with wired networks, the speed of each generation of 802.438+0 1 standard has been greatly improved.

1997 IEEE formulated the first wireless LAN standard 802. 1 1, and the data transmission rate was only 2Mbps, but the birth of this standard changed the access mode of users and freed people from the shackles of cables.

With the increasing demand for network transmission rate, IEEE issued the standard of 802.438+05438+0B in 1999. 802. 1 1b runs in the 2.4 GHz band, and the transmission rate is 1 1Mbit/s, which is five times that of the original standard. In the same year, IEEE released the 802. 1 1a standard, which adopted the same core protocol as the original standard, operating at 5GHz, and the maximum original data transmission rate was 54Mbit/s, which met the requirements of medium throughput (20Mbit/s) in real networks. Since the 2.4GHz band has been used in various places, the 5GHz band is used for 802.6438+068.

In 2003, as the standard of 802. 1 1a, OFDM was also adapted to work in the 2.4GHz band, resulting in 802. 1 1g with a carrier frequency of 2.4 GHz (compared with 802.1/kloc-)

The standard that has an important impact on Wi-Fi is 802. 1 1n released in 2009. This standard has greatly improved the transmission and access of Wi-Fi, introduced new concepts such as MIMO, secure encryption and some advanced functions based on MIMO (such as beamforming and spatial multiplexing ...), and the transmission speed has reached 600 Mbit/s. In addition, 802. 1 1n is also the first Wi-Fi technology working in both 2.4 GHz and 5 GHz bands.

However, the rapid development of mobile services and high-density access put forward higher requirements for the bandwidth of Wi-Fi networks. The 802.1AC standard released on 20 13 introduces wider RF bandwidth (upgraded to 160MHz) and higher-order modulation technology (256-QAM), and the transmission speed reaches 65438. In addition, the 802. 1 1ac wave2 standard was released in 20 15, which pushed the functions of beamforming and MU-MIMO into the mainstream and improved the system access capacity. Unfortunately, 802. 1 1ac only supports terminals in the 5GHz band, which weakens the user experience in the 2.4GHz band.

However, with more and more commercial applications such as video conferencing, wireless interactive VR, mobile teaching, and more and more Wi-Fi access terminals, the development of the Internet of Things has brought more mobile terminals to access wireless networks. Even home Wi-Fi networks with fewer access terminals will become crowded because of more and more smart home devices. Therefore, the speed of Wi-Fi network still needs to be continuously improved, and it is also necessary to consider whether more terminals can be accessed to adapt to the expanding number of client devices and the user experience requirements of different applications.

The next generation of Wi-Fi needs to solve the problem that the access of more terminals leads to the decrease of the efficiency of the whole Wi-Fi network. As early as 20 14, the IEEE 802. 1 1 working group has begun to meet this challenge. It is expected that the 802. 1 1ax (why it is called Wi-Fi 6 in the next chapter) standard officially launched in 20 19 will introduce technologies such as uplink MU-MIMO, OFDMA frequency division multiplexing, 1024-QAM high-order coding, etc., to solve the network capacity and multi-user access. The goal is to increase the average throughput of users by at least 4 times and the number of concurrent users by more than 3 times compared with the current Wi-Fi 5 in a dense user environment. So Wi-Fi 6(802. 1 1ax) is also called HEW.

Wi-Fi 6 is the abbreviation of the next generation 802. 1 1ax standard. With the evolution of Wi- Fi standard, WFA chose to rename Wi- Fi with digital serial number, so that Wi-Fi users and device manufacturers can easily know the Wi-Fi models connected or supported by their devices. On the other hand, the new generation naming method is chosen to better highlight the great progress of Wi-Fi technology, which provides many new functions, including increased throughput and faster speed, as well as support for more concurrent connections. According to the announcement of WFA, the current Wi-Fi naming respectively corresponds to the following 802. 1 1 technical standards:

Similar to the previously released new 802. 1 1 standard, the 802.111ac/n/g/a/b standard will also be compatible with the previous 802. 165436.

4G is synonymous with high-speed mobile network, and similarly, Wi-Fi 6 is synonymous with high-speed wireless LAN, but how this high-speed came about is determined by the following factors.

1. The number of spatial streams is actually the number of antennas of the AP. The more antennas, the greater the throughput of the whole machine. Just like the lanes of an expressway, the traffic volume of eight lanes will definitely be greater than that of four lanes.

Table 2 corresponds to the number of spatial streams of different 802. 1 1 standards. Symbol and GI symbol are transmission signals in time domain, and there should be a certain gap (GI) between two adjacent symbols to avoid interference between symbols. Just like the high-speed train in China, each train is equivalent to a symbol, so there must be a time difference between two trains leaving the same station, or they may collide. The gap under different Wi-Fi standards is also different. Generally speaking, when the transmission speed is fast, it is necessary to increase GI appropriately, just like the departure time difference between two high-speed trains with a speed of 350KM/h in the same lane is greater than that of a high-speed train with a speed of 250 km/h.

Table 3 corresponds to the symbols and GI data of 802. 1 1 standard.

3. Coding mode The coding mode is the modulation technology, that is, 1 number of bits that can be carried by a symbol. From Wi-Fi 1 to Wi-Fi 6, the rate of each spatial stream can be increased by at least 20% every time the modulation technology is improved.

Table 4 QAM 4. 802. The code rate corresponding to11standard should be lossless transmission in theory according to the coding method, but the reality is not so beautiful. It is necessary to add some information codes to correct errors during transmission and exchange redundancy for high reliability. The code rate is the ratio of the actual transmitted data code to the theoretical value after excluding error correction code.

Table 5 corresponds to the code rate of 802. 1 1 standard 5. Effective number of subcarriers Carrier is similar to the symbol in frequency domain, one subcarrier carries a symbol, and the number of subcarriers is different under different modulation methods and different bandwidths.

Table 6.802. 1 1 corresponds to the number of standard subcarriers.

At this point, we can calculate the maximum rate of 802. 1 1ac and 802. 1 1ax in the HT80 bandwidth:

Wi-Fi 6 (802.1/ax) inherits all the advanced MIMO features of Wi-Fi 5 (802.1/ac) and adds many new features for high-density deployment scenarios. The following are the core new features of Wi-Fi 6:

These core new functions will be described in detail below.

Figure 2- 1 OFDM working mode 802. 1 1ax introduces a more efficient data transmission mode, which is called OFDMA (because 802.1/ax supports uplink and downlink multi-user mode, it can also be called MU-OFDMA), and it is by allocating sub-users to different users. So far, it has been adopted by many wireless technologies, such as 3GPP LTE. In addition, the 802. 1 1ax standard also imitates LTE, and the smallest subchannel is called "resource unit (RU)". Each RU contains at least 26 subcarriers, and users are distinguished according to the time-frequency resource block RU. Firstly, we divide the resources of the whole channel into small fixed-size time-frequency resource blocks RU. In this mode, the user's data is carried on each RU, so from the perspective of total time-frequency resources, it is possible for multiple users to transmit simultaneously on each time slice (as shown below).

Figure 2-2 OFDMA working mode OFDMA generally has three advantages over OFDM:

Figure 2-3 Frequency Domain Channel Quality of Different Subcarriers

Because 802. 1 1ac and the previous standards all occupy the whole channel to transmit data, if a QOS packet needs to be sent, you must wait for the previous sender to release the whole channel, so there will be a long delay. In OFDMA mode, because a sender only occupies part of the resources of the whole channel, it can send data of multiple users at one time, so the access delay of QOS nodes can be reduced.

Table 7 number of ru in different bandwidths

Figure 2-4 Location Map of RU at 20MHz The more RUs, the higher the multi-user processing efficiency and throughput when sending small packets. The following figure shows the advantages of simulation:

Figure 2-5 Multi-user throughput simulation in OFDMA and OFDM modes

Figure 2-6 throughput difference between su-MIMO and MU-MIMO

Figure 2-7 Scheduling Sequence 2-7 8x8 MU-MIMO AP Downlink Multiuser Mode

Figure 2-8 Uplink Scheduling Order of Multiuser Mode Although the 802. 1 1ax standard allows OFDMA and MU- MIMO to be used at the same time, do not confuse OFDMA and MU-MIMO. OFDMA supports multi-users to improve concurrency efficiency by subdividing channels (subchannels), while MU-MIMO supports multi-users to improve throughput by using different spatial streams. The following table is a comparison between OFDMA and MU-MIMO:

Comparison between OFDMA and MU-MIMO

Figure 2-9: Comparing constellation figure 2-9 256-QAM and 1024-QAM, it should be noted that the successful use of 1024-QAM modulation in 802. 1 1ax depends on the channel conditions, and the denser constellation point distance requires stronger EVM (.

Figure 2-10 802.11Default CCA Threshold

For example, as shown in figure 12, STA 1 on AP 1 is transmitting data. At this time, AP2 also wants to send data to STA2. According to the principle of Wi-Fi RF transmission, it is necessary to monitor whether the channel is idle first. The default CCA threshold is -82dBm. It is found that the channel has been occupied by STA 1, and AP2 will delay transmission because it cannot transmit in parallel. In fact, all co-channel clients associated with AP2 will delay sending. A dynamic CCA threshold adjustment mechanism is introduced. When AP2 detects that the same-frequency channel is occupied, it can adjust the CCA threshold monitoring range (for example, -82dBm to -72dBm) according to the interference intensity, so as to avoid the influence caused by interference, and thus realize the same-frequency concurrent transmission.

Figure 2- 1 1 Dynamic CCA Threshold Adjustment Due to the mobility of the Wi-Fi client device, the co-channel interference detected in the Wi-Fi network is not static, but will change with the movement of the client device, so it is very effective to introduce the dynamic CCA mechanism. 802. 1 1ax introduces a new identification mechanism of co-frequency transmission, which is called BSS coloring mechanism. A BSS color field is added to the PHY header to "color" data from different BSS, and a color is assigned to each channel, which identifies a set of basic service sets (BSS) that should not be disturbed. The receiver can identify the interference signal transmitted in the same frequency as early as possible and stop receiving it, so as to avoid wasting the transmitting and receiving time. If the colors are the same, they are considered as interference signals in the same BSS, and the transmission will be delayed; If the colors are different, it is considered that there is no interference between them, and two Wi-Fi devices can transmit in parallel on the same channel and frequency. In this designed network, those channels with the same color are far away from each other. At this time, we use dynamic CCA mechanism to make this signal insensitive, and in fact they are unlikely to interfere with each other.

Figure 2- 12 Comparison between BSS-free color mechanism and BSS color mechanism

Figure 2- 13 Long OFDM symbols and narrowband transmission increase coverage distance

Previous core technologies have proved that 802. 1 1ax brings high-efficiency transmission and high capacity, but 802. 1 1ax is not the final standard of Wi-Fi, it is only the beginning of an efficient wireless network. 802. The new standard11ax still needs equipment compatible with the old standard. The following are other new features of the standard:

These new functions will be described in detail below.

We all know that the bandwidth of 2.4GHz is very narrow, and there are only three interference-free channels (1, 6 and 1 1) of 20MHz, which have been abandoned in the 802. 1 1ac standard, but it is undeniable that 2.4GHz is still an available Wi. Therefore, the 802. 1 1ax standard continues to support 2.4GHz to make full use of the unique advantages of this frequency band.

In the wireless communication system, the signal with higher frequency is easier to penetrate obstacles than the signal with lower frequency, and the lower the frequency, the longer the wavelength, the stronger the diffraction ability, the worse the penetration ability, the smaller the signal loss attenuation and the farther the transmission distance. Although the 5GHz frequency band can bring higher propagation speed, the signal attenuation is also greater, so the transmission distance is shorter than that of 2.4GHz. Therefore, when we deploy high-density wireless networks, the 2.4GHz frequency band is not only used for compatibility with old equipment, but also plays a great role in covering the edge areas to make up for blind spots.

At this stage, there are still hundreds of millions of 2.4GHz devices online. Even the Internet of Things network devices that have become the trend now use the 2.4GHz frequency band. For some business scenarios with low traffic (such as electronic fence and asset management), there are many terminal devices, and the terminal that only supports 2.4GHz with low use cost is a very cost-effective choice.

Figure 2- 14 Broadcast Target Wake-up Time Operation

Why Wi-Fi 6 (802 438+05438+0AX)?

802. 1 1ax was originally designed to be suitable for high-density wireless access and high-capacity wireless services, such as outdoor large public places, high-density venues, indoor high-density wireless offices, electronic classrooms and other scenes.

Figure 3- 1 High-density and high-bandwidth application scenarios In these scenarios, the client devices accessing the Wi-Fi network will show a huge growth. In addition, the increasing voice and video traffic will also bring adjustments to the Wi-Fi network. According to the forecast, by 2020, global mobile video traffic will account for more than 50% of mobile data traffic, and more than 80% of mobile traffic will be carried by Wi-Fi. We all know that 4K video stream (bandwidth required 30Mbps/ person), voice stream (delay less than 30ms) and VR stream (bandwidth required 50Mbps/ person, delay 10~20ms) are very sensitive to bandwidth and delay. If network congestion or retransmission leads to transmission delay, it will have a great impact on user experience. The existing Wi-Fi 5(802. 1 1ac) network can also provide large bandwidth capability, but with the increase of access density, the throughput performance encounters bottlenecks. Wi-Fi 6 (802. 1 1ax) network makes these services more reliable than before through OFDMA, UL MU-MIMO, 1024-QAM and other technologies, which not only supports access to more clients, but also balances the bandwidth of each user. For example, if the electronic classroom used to be a large class with more than 100 students, it would be a great challenge to transmit video or interact up and down. The 802.438+05438+0AX network can easily cope with this scene.

Relationship between * * * and Wi-Fi 6(802. 1 1ax)

This is not a novel topic. 1999 ~2000, it was suggested that 2G would replace Wi-Fi. From 2008 to 2009, it was also speculated that 4G would replace Wi-Fi. Now some people are discussing the topic of 5G replacing Wi- Fi. But the application scenario mode of 5G and Wi-Fi is different. Wi-Fi is mainly used in indoor environment, while 5G is a wide area network technology with more outdoor application scenarios. So we believe that Wi-Fi and 5G will survive for a long time. We further analyze it from the following angles:

Assuming that 5 G technology replaces Wi-Fi, it is necessary to launch an unlimited-traffic package, otherwise the cost will be far greater than the cost of using broadband. Moreover, the current broadband price is getting lower every year, and no one will choose the more expensive 5 G. In the current 4G era, the unlimited-traffic package is a gimmick. The three major operators have successively launched unlimited traffic packages. At that time, when the traffic exceeds the package traffic, the network will automatically be in 2G mode, and the highest speed is only 128Kbps. Watching videos at this speed is not as good as watching comics, so the so-called unlimited traffic is nonsense.

5G network technology uses UHF spectrum (5G network band: 24 GHz ~ 52 GHz, 4G network band: 1.8GHz~2.6GHz, excluding 2.4GHz). As mentioned earlier, the higher the frequency, the weaker the diffraction phenomenon and the weaker the obstacle-crossing ability, so the 5G signal is easily weakened. If we want to maintain the coverage of 5G signals, we need to build more base stations than 4G. Moreover, due to signal attenuation, if there are several walls inside the building, the signal attenuation will be more serious. Another extreme example is the basement. Wi-Fi network can put the router into the basement to generate signals through wired connection, but it is impossible for 5G network to cover all the basements of buildings. With this shortcoming alone, 5G cannot replace Wi- Fi. In addition, almost all smart devices now have Wi-Fi modules, and most IoT devices are also equipped with Wi-Fi modules. Only one public IP address is used for the exit, and it doesn't matter if a large number of addresses are occupied inside the local area network. It is convenient for users to manage these devices under their own Wi-Fi networks. Using 5G will inevitably occupy more public IP addresses.

Bandwidth x spectrum efficiency x number of terminals = total capacity.

The advantage of 5G lies in its carrier aggregation technology, which improves the spectrum utilization rate and greatly increases the network capacity. In the 3G/4G era, when users use their mobile phones to surf the Internet in crowded places such as subways and stations, they can obviously feel that the Internet access delay becomes longer and the network speed becomes slower. In the 5G era, with the substantial increase of network capacity, the impact of the above phenomenon has been significantly reduced. It is this feature that makes people feel that there is unlimited access under the 5G network, but many people ignore it. With the advent of the Internet of Things era, the number of network access devices is also greatly increasing. If all the internet devices are directly connected to the base stations in the area, this 5G expressway will be blocked no matter how wide it is! In order to reduce the burden of the base station tower, we must rely on Wi-Fi for shunting.

The three most important features of 5G promoted by mobile device manufacturers are high speed, large capacity and low latency. In fact, the latest generation of Wi-Fi is even faster than 5G. The peak rate of the latest 802. 1 1ax(Wi-Fi 6) single stream is1.2 Gbps (the peak rate of 5G network is 1Gbps). On average, the time required to upgrade each generation of Wi-Fi is about half that of mobile networks, so the rate will continue to be ahead of mobile networks from the latest Wi-Fi 6.

Office, logistics, commerce, smart home and other industries are moving towards wireless. The first thing to do is to use all the devices, people and terminals on the Internet. Assuming that the existence of Wi-Fi is replaced by 5G, all networked terminals in the future need to be equipped with something similar to a mobile phone SIM card to access the Internet. This reason also doomed that it is impossible for 5G to replace Wi-Fi in indoor scenes at present. Similar devices include VR, game consoles, e-readers, set-top boxes and so on. ...

Everyone knows that mobile terminals such as mobile phones and PADs all use batteries. It is generally believed that the durability of the battery is related to the installed service and frequency of use, but people often ignore that the access quality of various mobile signals of the terminal is also related to the power consumption of the battery. When the signal becomes worse, the mobile terminal will automatically increase the transmission power to improve the signal quality in order to ensure a good user experience, which will lead to an increase in battery power consumption. Because the signal source of Wi-Fi is basically indoors, and the 5G signal is in the base station dozens of kilometers away, the transmission distance of Wi-Fi is far less than that of 5G signal when the mobile terminal uploads data. Under normal circumstances, the communication distance of 5G is thousands of times that of Wi-Fi, which requires the signal emission intensity of mobile phones to be greatly increased, which increases power consumption. Someone has done experiments. Take 4G as an example. Using network data for half an hour, Wi-Fi will save 5% power than mobile network. In addition, the latest generation of Wi-Fi 6 (802. 1 1ax) supports TWT function, which can automatically wake up when the service is needed and automatically sleep when the service is not applicable, further saving electricity.

Therefore, these problems make it impossible for 5G to completely replace Wi-Fi, and its integration with Wi-Fi is deeper, so enterprises and users who use Wi-Fi need not be too flustered. Today's Wi-Fi is no longer a device to provide wireless networks, but should be regarded as a necessary facility or central hub for the digital transformation of enterprises. For example, at present, the central hub of most smart retail, smart logistics, smart office and other solutions is Wi-Fi network.

Reference:

This article is the most detailed about WiFi 6 technology.

Different Wi-Fi protocols and data rates

Hertz (physical unit