" Although many router manufacturers claim that their routers can achieve extremely high speeds, in fact, it is difficult for users to buy and use them to achieve very fast speeds. Because the WiFi transmission rate is in line with the barrel effect, the speed is often limited The WiFi terminal performance of the access router. Only the speed that can be achieved by the whole link is the speed that users feel. "
01
Barrel Effect in the Communication Field
No matter how high a bucket is, its water-holding height depends on the lowest board among them. To increase the water-holding capacity of the bucket, the only way is to replace the short board or lengthen it. This is the barrel effect. In the field of communication, data transmission generally involves multiple terminals. The processing capacity of each terminal and the transmission lines between terminals are all planks of buckets. If there is a short link in one link, the communication of the entire link will be blocked. . As for the optimization of communication, the most commonly used method is to analyze the location of the short board, and then find a way to solve it. Or monitor and compare each link, and consider improving the speed of each link as a whole, and finally achieve an increase in the overall speed.
The most frequently used WiFi terminal is the mobile phone, which connects users of different mobile phones closely through the data transmission of the WiFi network. At home, the mobile phone is connected to WiFi to surf the Internet. At present, the more common network connection framework is as shown in the figure below.
The first is the operator's fiber-to-the-home. The home will purchase an operator's network service (such as China Telecom, China Mobile, China Unicom, etc.), and there will be a description of the bandwidth when purchasing. For example, if the price is higher, the bandwidth will be higher. Then when the operator installs the network, it will send an optical modem and provide a network account and password. This optical modem generally has two functions, one interface is used to connect to the live TV box (the operator will also give a live TV box), live broadcast The box is connected to the TV via HDMI so that you can watch live TV. The other interface of the optical modem is used to connect to the WAN port of the router, so that the router at home can access the Internet. The LAN port of the router can be expanded to the next-level router or wireless AP in each room (this may not be installed, WiFi terminals such as mobile phones can be easily accessed, and the signal covers the whole house well), and the router itself will also be turned on Wireless hotspot, the signal can cover most of the home space.
Therefore, as in the above situation, the network bandwidth of operators, the performance of wireless routers, wireless transmission interference, and the performance of mobile phone WiFi may all become the bottleneck of network transmission speed.
02
Basic situation of mainstream WiFi devices
At present, mainstream WiFi terminal devices (tablets, notebooks, mobile phones) on the market generally support 2x2 MIMO (multi-antenna), high-quality routers now generally support WI-FI 5 or Wi-Fi 6, 4x4 MIMO multi-antenna, and beamforming and other characteristics.
Compared with the Ethernet rate provided by operators (hundreds of Mbps, or Gigabit bps), WiFi is used on limited wireless spectrum resources, and usually many different devices will use the limited spectrum resources at the same time, so It will cause congestion of the WIFI channel, and the transmission speed cannot keep up with the speed of Ethernet. In view of this, more and more WIFI devices support 5G frequency band, WiFi 6 and even future WiFi 7 to achieve higher WIFI speed.
Currently, mobile phones basically only support 2x2 MIMO. The possible reasons are as follows:
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There is no urgent need for the time being. The 4x4, 300Mbps WIFI rate has met the application requirements of all Apps. (Metaverse is still in the concept exploration stage)
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More antennas will increase power consumption and affect the battery life of mobile phones
The following figure is a reference to the support of mobile phone MIMO statistics on a website:
03
The gap between the advertised rate of the router and the actual rate
Here is a reference to the actual measurement data of a router rate on a website to illustrate the gap between the declared rate of the router and the actual rate. This actual measurement takes the AC5300 router as an example, which supports 80.211ac (Wi-Fi 5):
The test method and the measured rate data are shown in the figure below, which are the router and a mobile phone terminal with a 2x2 antenna, and the router and a 4x4 development board terminal.
The following is a detailed description based on the measured data of routers and mobile phones:
5300 -> 2166: Maximum band rate
5300 is the rate declared by the router. In fact, it is calculated by aggressively accumulating the rates of all frequency bands, but in fact its maximum rate can only reach the peak value of the 5 GHz frequency band (using all MIMO antennas).
5300 = 2166 + 2166 + 1000
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1000: 2.4GHz band rate
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2166: 5GHz band rate
2166 -> 2166: actual channel bandwidth
The speed of the 2.4GHz frequency band of the router manufacturer is declared to the outside world with a bandwidth of 40MHz, but in fact, users basically use a bandwidth of 20MHz (the transmission distance is longer). The 5GHz frequency band is declared with a bandwidth of 80MHz. If it is declared with a bandwidth of 160MHz, the actual use rate will have to be cut in half.
2166 -> 1083: WiFi terminal MIMO multi-antenna
Generally, mobile terminals only support 2x2 MIMO, so although the router is 4x4, only 2x2 MIMO is available when the mobile phone is actually connected to the router, and the rate has to be cut in half.
1083 -> 866: Router QAM
Router manufacturers generally use 1024-QAM to declare the rate (Router DOES support), but basically WiFi terminals do not support 1024-QAM at present. Even if they support it, the communication distance needs to be very close. Generally, the actual use is 256 -QAM.
866 -> 650: modulation and code rate
Router manufacturers like to declare the maximum PHY (physical layer) rate, but the maximum PHY rate can only be achieved when the WiFi terminal device is very close to the router. When the distance is farther, the rate will decrease. The modulation method/bit rate is an index that determines how much information can be transmitted at one time, and is directly related to the transmission distance. The farther the distance is, the less information can be transmitted at one time.
650 -> 357: MAC efficiency
What was discussed above is the rate on the PHY (physical layer), and the actual rate to the application layer. Because of the consumption of the packet headers of the underlying protocols, the actual data of the general user is 50% to 70% of the PHY rate. Experience Select 55% for evaluation, 650x55%=357.
357 -> Further reduction: Interference
If there is interference on the WIFI channel, the rate will continue to drop.
04
How to get the actual WiFi speed
You can use the speed measurement tool, which can be found through search engines. It is more convenient to have a web version of the tool.
In addition, you can check the PHY rate of your wireless device and multiply it by 55% to roughly estimate the rate of the actual application data. Determinants of PHY rate:
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bandwidth
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Modulation method and transmission distance
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MIMO Multiple Antennas
