Comprehensive Guide to WiFi Concepts

The Origin of the WiFi Name

The term Wi-Fi is often mistakenly thought to refer to Wireless Fidelity, similar to the long-established categories of audio equipment: long-term high fidelity (adopted since 1930) or Hi-Fi (adopted since 1950). Even the Wi-Fi Alliance itself frequently uses the term “Wireless Fidelity” in press releases and documents, but in fact, the term Wi-Fi has no specific meaning.

In 1999, several visionary companies came together to form a global non-profit association—the Wireless Ethernet Compatibility Alliance (WECA)—aiming to ensure the best user experience with a new wireless networking technology, regardless of brand. In 2000, this group adopted the term “Wi-Fi” as a proprietary name for its technical work and announced the official name: Wi-Fi Alliance.

Wireless Frequencies

Wireless is a method of transmitting digital signals through electromagnetic waves. When using a wired connection, there is a physical cable; when using a wireless connection, you can imagine a virtual cable between your mobile phone, computer, and wireless router.

Main Wireless Classifications, Frequencies, and Uses

2.4G operates in the UHF band, classified as decimeter waves. The 2.4G band is very crowded, with Bluetooth, microwaves, Zigbee (IoT devices), and amateur radio all operating in this frequency range, leading to significant interference with 2.4G WiFi in daily life. However, the coverage of 2.4G is greater than that of 5G, which is why you can often find wireless signals from neighboring houses at home. The signals that can be detected are mostly 2.4G signals.

5G operates in the SHF band, classified as centimeter waves. There is relatively less interference in daily life, with the main sources of interference being radar and others. The coverage area of 5G is much smaller compared to 2.4G.

During transmission, wireless signals can be absorbed by different materials, leading to signal attenuation, which is the primary form of wireless loss. Generally, the denser the material and the more metal it contains, the stronger the absorption of wireless signals. Other factors causing wireless signal loss include reflection, scattering, refraction, and diffraction.

In China, most houses are built with load-bearing walls and reinforced concrete structures, which significantly attenuates wireless signals. Therefore, the so-called wall-penetrating ability of home wireless routers is ineffective against load-bearing walls.

Electromagnetic Wave Penetration Loss by Material

Electromagnetic waves exhibit both wave and particle properties. During transmission, they can penetrate, reflect, diffract, refract, and scatter when encountering obstacles. The wireless signals we connect to are the result of these complex processes.

802.11 Standards

Wi-Fi and IEEE 802.11 are often confused; the difference can be summarized as IEEE 802.11 being a wireless LAN standard, while Wi-Fi is an implementation of the IEEE 802.11 standard.

The formulation period for the 802.11 standard is approximately 4-5 years; typically, when the latest generation standard is released, the previous standard remains the mainstream.

Technically, there is no need to pursue new standards immediately; one should base it on actual needs. Currently, most routers still primarily use Wi-Fi 5 and Wi-Fi 6. Wi-Fi standards are backward compatible.

Major Milestones in the Development of the 802.11 Standards

Devices supporting 802.11a and 802.11b are now very rare.

WiFi1: 802.11b 1999 2.4G 11Mbps

WiFi2: 802.11a 1999 5G 54Mbps

WiFi3: 802.11g 2003 2.4G 54Mbps

Comparison of WiFi4, WiFi5, and WiFi6

2.4G Frequency Channels

Countries’ support for the 2.4G frequency band varies; in China, the supported 2.4G frequency range is 1 to 13.

Each channel’s center frequency is an integer multiple of 5MHz apart.

Some devices may not support channels beyond 11, so care must be taken during setup.

There are few non-interfering channels in 2.4G, and many civilian devices also use the 2.4G band, which is why the 2.4G channels are crowded.

This leads to significant interference in the 2.4G channels, and many people’s phones often show full Wi-Fi signal but cannot connect to the internet, which is the reason.

The maximum power specified for the 2.4G band by the Ministry of Industry and Information Technology is EIRP ≤ 500mw or EIRP ≤ 27dBm.

In the traditional 802.11 standard, a small portion of bandwidth is reserved for every 20MHz, which can be bonded for a 40MHz bandwidth to enhance bandwidth. However, due to significant interference in the 2.4G band, using 40MHz is not highly recommended.

The non-interfering channels in the 2.4G band are 1, 6, and 11, but due to the wide propagation range of 2.4G, many nearby neighbors’ 2.4G signals can often be detected at home, and many channels are occupied, making it nearly impossible to find a clean channel to use. Moreover, most routers can optimize channels automatically, so manually setting a channel for 2.4G is not very meaningful and does not significantly improve network performance.

5G can use 20MHz, 40MHz, 80MHz, and 160MHz; the specific frequencies supported depend on the SOC used by the router.

5G Frequency Channels

The supported 5G frequency bands in China are: 36, 38, 40, 42, 44, 46, 48, 149, 153, 157, and 161.

If you purchase a Japanese version of an electronic device and want to connect to 5G wireless, you need to change the 5G frequency to those supported by both Japan and China (36, 40, 44, 48) for the device to search for 5G signals and connect normally. Some older devices may not support 5G channels above 149 and may require channel adjustments.

When at the same distance from the router, the 5G signal is relatively weaker than the 2.4G signal, which is determined by the physical properties of electromagnetic waves: the longer the wavelength, the less attenuation, and the easier it is to bypass obstacles and continue propagating. The 5G signal has a higher frequency and shorter wavelength, while the 2.4G signal has a lower frequency and longer wavelength, so the 5G signal attenuates more when passing through obstacles, making its wall-penetrating ability weaker than that of the 2.4G signal; this is a common situation with dual-band wireless routers.

Below is the loss formula for 2.4G and 5.8G in free space (where F is the frequency in MHz; D is the distance in km): the attenuation formula for radio electromagnetic waves in free space: L=32.5+20lgF+20lgD. The attenuation formula for the 2.4G band: L1=100+20lgD; the attenuation formula for the 5.8G band: L2=108+20lgD. From these formulas, it can be seen that the attenuation of 5.8G is higher compared to 2.4G, resulting in a shorter coverage distance.

Advantages and Disadvantages of 2.4G and 5G

If the terminal (e.g., TV) is close to the router and there are few obstacles, it is recommended to connect to 5G; if the terminal (e.g., mobile phone) is far away from the router with many obstacles, you can choose 2.4G based on the situation.

Wireless Propagation Diagram

This shows the barrier effect of walls on wireless signals.

Wireless Power and Antennas

When we look at routers, they often highlight “wall penetration” and multiple large external antennas as selling points. Many people believe that more, thicker, and longer antennas mean better signal. Conversely, they think that routers without external antennas have poor signals. So, how much does the number of antennas actually affect wireless coverage?

According to the principle of the barrel, the wireless speed of the terminal depends on the negotiation between the terminal and the router. Based on the type of terminal, wireless attenuation, etc., the wireless terminal will negotiate with the router to arrive at a suitable rate, which is usually less than the maximum rate supported by the router. The upper limit is the maximum rate supported by the router. Therefore, simply increasing the wireless power of the router does not necessarily yield good results, and each country has strict regulations on the wireless power of routers.

Wireless Power

Milliwatts (mW)

Power unit; the maximum power for 2.4G is 100mW. The maximum power for 5G is 500mW.

Wireless routers have low power and are strictly controlled by national regulations. As long as they meet national standards, they are safe to use without worry. Those who believe that wireless routers are dangerous are merely under a psychological misconception.

Decibel Milliwatts (dBm)

The absolute value unit of wireless power is dBm.

The calculation formula for dBm: 10lgP, where P = wireless power/1mW

0dBm=1mW

17dBm=50mW

20dBm=100mW

[Example 1] If the transmission power P is 1mW, it converts to 0dBm.

[Example 2] For a power of 40W, the value converted to dBm should be:

10lg(40W/1mW)=10lg(40000)=46dBm

dBi

dBi is the unit for measuring the gain of a wireless antenna. A higher dBi does not mean that the WiFi signal is enhanced; rather, it means that the signal is emitted and received more directionally. The higher the dBi value, the greater the gain, and the smaller the vertical angle, which allows for longer transmission distances.

Equivalent Isotropic Radiated Power (EIRP)

A common concept in the field of radio communication, it refers to the radiation power of a satellite or ground station in a specified direction, ideally equal to the amplifier’s transmission power multiplied by the antenna’s gain. EIRP is typically understood as the configuration of transmission power and reflects the power at the strongest point. The unit is dBW.

EIRP = Effective Power + Antenna Gain – Antenna Feedline Loss

Antennas and Gain

The role of the router’s antenna is to transmit and receive radio waves.

On wireless routers, the external antennas are commonly whip omnidirectional antennas, while internal antennas are also omnidirectional. Outdoor base stations, etc., may use both omnidirectional and directional antennas.

When radiating, the antenna’s electromagnetic field strength direction typically has two types: vertical polarization and horizontal polarization.

Horizontal polarization is subject to significant loss due to the Earth’s magnetic field and is less commonly used; monopole antennas usually adopt vertical polarization.

At the same power level, the more gain, the stronger the antenna’s directionality, and the smaller the directional angle.

The gain value is expressed in dBi. The gain of an antenna, in the direction of maximum radiation, is the multiple by which the input power is amplified compared to an ideal isotropic point source.

The signal strength diagram of an omnidirectional antenna resembles a donut shape.

After gain, the donut shape becomes flatter, increasing the coverage range. The energy becomes more concentrated, with stronger signals in the horizontal direction and better resistance to interference, while the signal weakens in certain directions.

The number of antennas should match the MIMO technology supported by the router, whether external or internal antennas.

If it is 2*2 MIMO, only 2 antennas are needed. Since many routers are dual-band routers for 2.4G and 5G, they can use separate antennas to transmit 2.4G and 5G signals, thus having more antennas.

For example, the Redmi AX6 has 6 antennas, 2 for 2.4G and 4 for 5G.

Router Placement

Based on the previous discussion about antennas and wireless specifics, when placing the router, it should be positioned as high as possible, ideally in the center of the room, with minimal obstructions, and the router’s antennas should be oriented 90 degrees vertically to the ground. This way, the wireless signal is strongest in the horizontal direction and has the widest coverage. If the router has more than 2 antennas, other antennas can also be adjusted at different angles for more uniform coverage.

MIMO Technology

MIMO (Multiple Input Multiple Output) is a key technology that enhances wireless performance, first proposed in the 802.11n standard.

Using multiple antennas at both the sending and receiving ends can greatly increase channel capacity, improving transmission reliability, range, and throughput.

Before MIMO, there was SISO (Single-Input Single-Output).

When using a wired connection, the cable acts as a physical channel. When using a wireless connection, to achieve faster speeds, it is necessary to combine the virtual cables (channels) for data transmission.

MIMO is expressed as AxB MIMO, where A indicates the number of antennas at the sending end and B indicates the number of antennas at the receiving end.

MIMO is further divided into SU-MIMO and MU-MIMO.

SU-MIMO (Single-User Multiple-Input Multiple-Output)

MU-MIMO (Multi-User Multiple-Input Multiple-Output) can further enhance speed. MU-MIMO was first proposed in Wi-Fi 5.

WIFI6

The 802.11ax standard adopted by the Wi-Fi Alliance on January 3, 2020, introduced the new naming Wi-Fi 6 for easier memorization and promotion.

Wi-Fi 6 is backward compatible with 802.11a/b/g/n/ac.

Main Features of Wi-Fi 6

Comparison of Wi-Fi 6 and Wi-Fi 5

Main Enhanced Features of Wi-Fi 6

Wi-Fi 6 supports MU-MIMO for both uplink and downlink, while Wi-Fi 5 only supports downlink.
Wi-Fi 6 supports OFDMA (Orthogonal Frequency Division Multiple Access), while Wi-Fi 5 supports OFDM (Orthogonal Frequency Division Multiplexing).

Difference Between OFDM and OFDMA

Because Wi-Fi 6 has a theoretical speed of up to 9.6Gbps, it is suitable for scenarios with large internal data transfers. Currently, the mainstream home broadband is still below 1G. Wi-Fi 6 will only become a bottleneck when the external bandwidth reaches 10G. However, the new features brought by Wi-Fi 6, when paired with Wi-Fi 6-supported terminals, will provide a better wireless experience.

CPU and Wireless Chips

For wireless routers, the number of functions and performance mainly depend on the CPU and the wireless power amplifier chip. The router’s system is more of a bonus. If you have specific OS-level needs, you can consider router models that allow for system flashing.

CPU

The CPU determines the functions that the router can provide. The CPU also performs a lot of calculations, so high-end routers tend to generate more heat.

Currently, routers mainly use CPUs from Qualcomm, Broadcom, and MTK. Previously, there were also Huawei’s HiSilicon CPUs.

For example, Qualcomm’s Wi-Fi 6 chip solution, the most advanced platform is the Qualcomm Networking Pro 1200 Platform, which can support up to 12 spatial streams; followed by Pro 800, Pro 600, and Pro 400, supporting up to 8, 6, and 4 spatial streams, respectively. The specific specifications are as follows:

The teardown image of NETGEAR’s RAX120 AX6000M, sourced from Koolshare, highlights this CPU chip as the most important component.

Wireless Chips

Working in conjunction with the CPU, these are divided into 2.4G chips and 5G chips. High-end routers can use multiple wireless chips to increase wireless bandwidth.

The following image shows the teardown of NETGEAR’s RAX120 AX6000M, sourced from Koolshare.

The wireless chip shown is Qualcomm’s QCN5024, a 2.4G chip that supports 4×4 MIMO and 802.11ax, with a maximum rate of 1200Mbps.

The wireless chip shown in the image is Qualcomm’s QCN5054, a 5G chip that supports 802.11ax and 4×4 MU-MIMO, with 80MHz support.

Router Chip Topology Diagram

MESH Technology

MESH distributed technology creates a mesh network between routers, allowing different access points to form a complete mesh network in star, tree, series, and bus configurations. In this large network, not only is the SSID unified, but wireless devices can also freely seek the best signal node for data transmission, enabling seamless connection as users move between different nodes.

For large wireless coverage areas, MESH is easy to deploy and flexible while ensuring a good roaming experience. However, most MESH networking products require occupying wireless bandwidth; for optimal user experience, it is best to use wired connections for MESH networking or choose tri-band routers that have dedicated frequency bands for wireless MESH, ensuring that terminal speeds are not affected and providing a better experience.

MESH Networking is Suitable for Users Who Meet the Following Requirements

1. Need wireless coverage of over 100 square meters or have many load-bearing walls within the coverage area.

2. Did not reserve network cables during renovation.

3. Require a good wireless roaming experience.

MESH Networking Diagram

AC+AP

Introduction to AC+AP

For large houses, duplex buildings, villas, hotels, shopping malls, and enterprises, multiple routers are needed for coverage and a good roaming experience. In this case, the best experience is to use the AP method of networking, paired with an AC for unified management. The AC can be independent hardware or implemented via software. Some brands require all data to be processed by the AC, with the AC’s performance determining the overall network performance. In some brands, the AC only performs management functions without data forwarding. APs need to be paired with POE-supported switches for power supply, so when deploying an AC+AP network, not only must network cables be pre-deployed, but the number of involved devices is also considerable, requiring higher network technology knowledge from the user.

AP stands for Wireless Access Point, which is responsible for releasing wireless signals and forwarding wireless data. The wireless coverage area relies on multiple APs to achieve this. Because of installation methods, APs typically have internal antennas. AP installation types are divided into ceiling-mounted APs and panel APs. Ceiling-mounted APs can be larger and more powerful, while panel APs, due to size and installation location limitations, generally have poorer performance, heat dissipation, and signal coverage. Whenever possible, ceiling-mounted APs should be chosen.

Ceiling-mounted AP Diagram

Panel AP Diagram

AC Wireless Controller

Responsible for controlling all settings of the AP. In some brands, the AC will centrally forward data; in others, the AC only manages without participating in data forwarding. For ACs that centrally forward data, the AC’s performance can become a bottleneck in the network, so it is essential to choose a high-performance AC. The AC and AP brands should be consistent.

Common ACs resemble the shape of switches

POE Switch

POE (Power Over Ethernet) is a system that can supply power to IP-based terminals (cameras, IP phones, APs, etc.) over a network cable while transmitting data, reducing the need for additional wiring and saving costs. It is essential to note the POE power standards and power ratings; the power standards must be consistent with the standards supported by the AP, and the power rating must exceed that of the AP.

POE Switch Diagram

POE System Architecture Diagram

There are three standards for POE power supply: 802.3af (PoE), 802.3at (PoE+), and 802.3bt (PoE++). Different standards have different voltage and power ratings. For POE power supply, it is best to start with Category 6 cables.

Device List for AC+AP Networking

AC: Required. Some brands have hardware ACs, while others have software ACs that need to be installed on a host or other system.

AP: Required. The wireless performance and coverage depend on this; the higher the performance, the better. Note that the AP and AC must be from the same brand.

POE Switch: Required. It needs to be a gigabit POE switch, ensuring that the POE protocol matches the one supported by the AP. Some brands may integrate the AC and POE together, which can save costs; high-end products are usually separate models. It can be from other brands.

Gateway Device: Required. Used for broadband access, it does not need to release wireless signals but should focus on network forwarding performance. It can be from other brands.

Network Cables: Required. Pre-deployment is necessary, and at least Category 6 cables should be used. Ensure the quality of the cables used in construction, ensuring all 8 cores are connected.

Cabinet: Optional. If many devices are used, a small cabinet should be configured to install devices, manage cabling, and dissipate heat. For fewer devices, based on their size and quantity, they can be installed in a weak current box, but to ensure system stability, heat dissipation must be considered.

Wireless Roaming

When using AP or MESH networking, multiple routers provide the same wireless signal, allowing terminals to achieve seamless roaming as they move, automatically connecting to the appropriate router without data loss or minimal data loss during roaming.

Wireless Roaming Diagram

Roaming requires that there are no blind spots in the wireless signal coverage. If blind spots exist, terminals will lose connection when moving into these areas. Even if they are on the edge of the coverage, they may connect but with poor performance.

As terminals roam, the more complex the authentication method (e.g., Radius authentication), the more steps are required for re-authentication, and the longer it takes to reconnect. To speed up the authentication process, three standards related to fast roaming have been introduced.

The three standards related to fast roaming are: 802.11k, 802.11v, and 802.11r.

STA: Terminal

802.11k helps the STA understand the distribution of nearby APs.
802.11v guides the STA to switch APs under the control of the AC rather than by the STA itself, facilitating better switching.
802.11r allows the STA to switch APs without re-authentication, speeding up the connection.

Apple’s official website clearly states which products support the 802.11kvr protocol, but with many Android phone brands, only some models from Samsung have explicit labels, and generally, Android phones may not support this. If the AP has kvr protocol support enabled but the terminal does not, it may cause roaming issues for the terminal. In complex network environments, it is recommended not to enable this function. Compatibility and stability of the network are paramount.

Conclusion

This concludes the introduction to WiFi-related knowledge. This is a relatively comprehensive description, and each small knowledge point could be the subject of its own article. I hope this helps everyone understand WiFi technology and provides more technical references when choosing routers.

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