[Getting to Know Wi-Fi 02] 2.4 GHz Wi-Fi and 5 GHz Wi-Fi

萌妹子
萌妹子  Junior  (1)
8 months 7 days ago  View: 4530  Reply: 0

According to Wi-Fi standards, Wi-Fi works at the 2.4 GHz and 5 GHz frequency bands. Nowadays, devices that support dual-band Wi-Fi are more and more popular. What is the difference between the two frequency bands? How to choose between the bands?

Literally, the biggest difference is the working frequency bands. The differences are as follows:


Wi-Fi Frequency Band

Wi-Fi, like wireless broadcast and Bluetooth, uses radio frequency as the transmission carrier. A radio frequency is an electromagnetic wave whose frequency is between 3 Hz and about 300 GHz.

The radio frequency range of 2.4G Wi-Fi is 2.4 GHz to 2.4835 GHz, and that of 5G Wi-Fi is 5.150 GHz to 5.350 GHz, 5.725 GHz to 5.825 GHz, and 5.470GHz to 5.725 GHz. The following figure shows the positions of the two frequency bands in the radio spectrum.

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Note: The frequency ranges that can be used in each country are different. For example, the 5G Wi-Fi frequency bands that can be used in China are 5.150 GHz to 5.350 GHz and 5.725 GHz to 5.825 GHz.


Wi-Fi Channel

A Wi-Fi channel is a radio frequency with a fixed bandwidth, juts as a road has a fixed width for traffic to pass through. The 2.4 GHz frequency bandwidth is 2.4835 GHz – 2.4 GHz = 83.5 MHz, while the 5 GHz frequency bandwidth is 555 MHz.

In the IEEE 802.11 series standards, the 2.4 GHz/5 GHz frequency band is divided into multiple channels. This is because electromagnetic waves overlap or attenuate according to their phase difference if interference occurs on the waves of the same frequency. If there are different Wi-Fi access points in an area and the same channel is used to access the Internet, severe signal interference may occur. As a result, users cannot access the Internet smoothly. Just as different radio stations need to use different channels, if all the programs use the same channel, all we hear may be noises. Then how are channels divided?

l  2.4 GHz Channel Division

As shown in the following figure, the 2.4 GHz frequency band is divided into 13 overlapping channels. The bandwidth of each channel is 22 MHz (the bandwidth of each channel in IEEE 802.11g and IEEE 802.11n is 20 MHz, and that in IEEE 802.11b is 22 MHz), we can find three independent channels, such as channels 1, 6, and 11.


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Note: Channel 14 is used in Japan. The channels used in different countries are different. We

usually discuss 13 overlapping channels.

In actual network deployment, cellular channel distribution is usually used, and adjacent Wi-Fi access points use completely independent channels (such as channels 1, 6, and 11 shown in the following figure) to avoid signal interference caused by channel overlapping.

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l  5 GHz Channel Division

As shown in the following figure, the 5 GHz frequency band is divided into twenty-four 20 MHz channels, and each channel is an independent channel. This provides abundant channel resources for 5G Wi-Fi. If two or more adjacent channels are bound as one channel, more information can be carried over the channel, improving the data transmission rate by multiple folds. The red circles in the following figure indicate that two channels are bound.


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Binding two channels (40 MHz) or four channels (80 MHz) on the 5 GHz frequency band is a reasonable choice.

In the 2.4 GHz frequency band, two adjacent 20 MHz channels can be bound to form a 40 MHz channel. However, because the 2.4 GHz frequency band has fewer channel resources and more interference, it is recommended channel binding not be used for 2.4 GHz frequency bands.


Wall Penetration

Wi-Fi transmits data through electromagnetic waves. It has physical characteristics of waves. When waves meet obstacles, reflection, refraction, and diffraction may occur, causing attenuation. The relationship between signal attenuation and wavelengths is as follows:

l  The longer the wavelength, the stronger the diffraction, the stronger the penetration capability, the smaller the signal loss/attenuation, and the longer the transmission distance. For example, the wavelength used for wireless broadcast is long and its capability to bypass buildings is strong, therefore we can listen to broadcasts from far away.

Wave velocity = Wavelength x Frequency (frequency and wavelength are inversely proportional to each other). 2.4 GHz: lower frequency, longer wavelength; 5 GHz: higher frequency, shorter wavelength. Therefore, when 5G signals pass through obstacles, the attenuation is greater, and the wall penetration capability is weaker than that of 2.4 GHz signals.


How to Choose a Wi-Fi Frequency Band

The 2.4 GHz Wi-Fi and 5G Wi-Fi have their own advantages and disadvantages. You can select the optimal frequency band based on the actual environment. If the access point is in the living room:

l  In the living room or near the living room, select the 5 GHz frequency band.

l  In a room far away from the living room, select the 2.4 GHz frequency band with stronger wall-penetration capability.

Huawei ONTs and APs support Band Steering, which can select a proper frequency band based on the actual situation. No manual selecting is required.