Hello,
everyone!
Today, I will continue to write about WiFi. In this article, I will explain basic working principles.
All IEEE 802.11 standards have common features. All standards use the same medium access protocol – CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance). They all use the same frame structure on the link layer. Most of these standards can reduce speed and thus provide greater range. Devices that support IEEE 802.11 standards are compatible with earlier versions of these standards.
As seen in Table 1, in the previous article, these standards differ greatly on the physical layer. The standards use one or two frequency bands to operate - 2.4 GHz and 5 GHz. In addition, the new standards, such as IEEE 802.11n and IEEE 802.11ac, use MIMO technology.
There are two main frequency bands: 2.4 GHz and 5 GHz.
Figure 1. 2.4 GHz and 5 GHz of WiFi standards in the world
The 2.4 GHz frequency band is from 2,402 GHz to 2,483 GHz. The default number of channels is 11, in China 13 channels are used, while in North America 11 channels are used. This frequency range is ubiquitous. Many devices use this frequency range: microwave ovens, Bluetooth/ZigBee devices, drones, some wireless phones, etc. Channel bandwidth is 22 MHz (Standard: 20 MHz), and it can be extended up to 40 MHz. In this frequency range, with 11 or 13 channels, there are only 3 channels that do not overlap with each other. These are 1, 6, and 11 channels. The maximum rate in the 2.4 GHz frequency band is up to 600 Mbps (802.11n, 4x4 MIMO, 40 MHz).
The 5 GHz frequency band is composed of two bands 5.1 GHz to 5.8 GHz. Frequency band 5.1 GHz is from 5.1550 GHz to 5.350 Hz, and 5.8 GHz is from 5.725 GHz to 5.850 GHz. China uses both frequency bands. Band 5.1 GHz includes eight sub-channels and 5.8 GHz includes five sub-channels. The standard channel bandwidth is 20 MHz. It can be extended to 40 MHz, 80 MHz, or higher. Currently, the theoretical maximum is 9.6 Gbps (WiFi 6).
Using the 5 GHz frequency band enables data transmission at higher speeds but over shorter distances. Channel bonding – e.g. two channels (20 MHz) to one (40 MHz), increases bandwidth.
In the next article, I will continue to explain WiFi >> WiFi (3): Problems with WiFi
Thank you!
