Wireless access function of wireless router

The wireless access function of a Wireless Router is referred to as Wireless Local Area Network (WLAN). At present, WLAN only has Wi Fi as the mainstream technology, so it can be considered that the two are equivalent.

The Wi-Fi Alliance conducts technical certification and trademark authorization for Wi Fi. In practical applications, Wi Fi is often written as WiFi or WiFi, but these two writing methods have not been recognized by the alliance. 5G CPE

Wi-Fi Alliance (full name: International Wi-Fi Alliance, English: Wi Fi Alliance, WFA for short) is a Business alliance, which owns the trademark of Wi Fi.. It is responsible for Wi Fi authentication and trademark authorization, headquartered in Austin, Texas, USA.

The catchy name Wi Fi is widely believed to be an abbreviation for Wireless Fidelity, but it is actually a misreading. It is just a simple name with no actual meaning, and of course, it does not have a full name. 4G Cat4 Cpe

The technical standard behind Wi Fi is the 802.11 series protocol developed by the Institute of Electrical and Electronics Engineers (IEEE) in the United States. 4G CAT6 CPE

One. The Development of Wi Fi Protocol

Starting from the first version in 1997, the 802.11 series protocols have continuously evolved, going through multiple versions such as 802.11a/b/g/n/ac, and the supported internet speeds have also been continuously improved. The latest protocol version currently is 802.11ax, which is the rapidly developing Wi Fi 6 in recent years.

In the early years, although Wi Fi evolved from generation to generation, there was no such thing as a few generations of Wi Fi in the world. Simply adding a few letters after 802.11 as the protocol number was very unfriendly to ordinary users.

It was not until 2018 that the Wi-Fi Alliance decided to promote the next generation of technical standard 802.11ax with the simpler and easier to understand Wi Fi 6. The previous generation of 802.11ac and 802.11n naturally became Wi Fi 5 and Wi Fi 4. As for the earlier technology, no one is paying attention to it anyway, so there is no need to wear a vest again.

On September 16, 2019, the Wi-Fi Alliance announced the launch of the Wi Fi 6 certification program. Since then, the name of Wi Fi 6 has spread throughout the world, and currently, most newly released devices have already supported Wi Fi 6.

II. Wi Fi channel and frequency band used

Wi Fi mainly operates in the 2.4GHz and 5GHz frequency bands. These two frequency bands are called the ISM (Industrial Scientific Medical) frequency band, and as long as the transmission power meets the national standard requirements, they can be used directly without authorization.

As the earliest ISM frequency band enabled globally, 2.4GHz has a spectrum range of 2.40GHz to 2.4835GHz, with a total bandwidth of 83.5M.

Our commonly used Bluetooth, ZigBee, and wireless USB also operate in the 2.4GHz frequency band. In addition, the frequency band used by microwave ovens and cordless telephone is also 2.4GHz. Even when the internal chip of the wired USB interface is working, it will emit useless signals of 2.4GHz, causing interference.

It can be seen that there are many devices operating simultaneously at 2.4GHz, with overcrowded frequency bands and severe interference. When the lights are on and you and your neighbors upstairs and downstairs are happily surfing the internet using Wi Fi, the router silently selects channels behind you to coordinate interference.

Wi Fi divides the 83.5M bandwidth on 2.4G into 13 channels, one per 20M. Note that these channels are overlapping. Originally, only 3 could be put down, but now 13 have been forcefully squeezed in. The interference between them is difficult to avoid, and we can only try to reduce it as much as possible. If not, everyone can slow down and queue up to use it.

To what extent do channels overlap? From the figure below, it can be seen intuitively that among these channels, only groups 1, 6, 11 or 2, 7, 12, or 3, 8, and 13 are completely non overlapping, indicating the degree of congestion in the 2.4GHz frequency band. Just like a very narrow road, there are many cars passing on it, and frequent traffic jams inevitably lead to a decrease in traffic speed.

By 802.11n, users can use a 40M channel, but the 2.4GHz frequency band still only has a total bandwidth of 83.5M, which can only accommodate two channels. Therefore, only when the network is idle in the dead of night can a single user use a 40M channel, coupled with interference from the neighboring Lao Wang family, the high-speed rate of 802.11n is largely difficult to achieve.

By 802.11n, users can use a 40M channel, but the 2.4GHz frequency band still only has a total bandwidth of 83.5M, which can only accommodate two channels. Therefore, only when the network is idle in the dead of night can a single user use a 40M channel, coupled with interference from the neighboring Lao Wang family, the high-speed rate of 802.11n is largely difficult to achieve. If the 2.4GHz frequency band is a narrow path, then the 5GHz frequency band is undoubtedly a promising path.

The available range of the 5GHz frequency band is 4.910GHz to 5.875GHz, with a bandwidth of over 900 megabytes, which is more than 10 times that of 2.4G! This spectrum is too wide, and different countries have defined the range of Wi Fi usage based on their own situation.

For example, there are 13 20M channels available for Wi Fi in China's 5GHz spectrum, and continuous 20M channels can also form 40M, 80M, or even 160M channels.
The bandwidth of 5GHz is large, and there are few devices running on it. It is naturally fast to use and has little interference. Therefore, if you want the home network to achieve a good speed experience, you can consider using 5GHz to cover the whole house.

However, feet have their own shortcomings and inches have their own strengths. Although the bandwidth of 5GHz is large and interference is small, the signal propagation attenuation is fast, and it is also easy to be blocked. The ability to pass through walls is weak.

Therefore, compared to 2.4GHz, the 5GHz signal is usually much weaker. As for how many meters each of them can cover, it is difficult to provide specific information due to the correlation between the antenna gain, reception sensitivity, distribution of walls and obstacles in the home, and the expected internet speed that individuals can achieve.

If only considering the networking of various smart homes at home, 2.4GHz coverage and capacity are usually sufficient. But if high-speed internet access is needed to maximize the value of home broadband, it must rely on 5GHz to achieve it.

Therefore, it is recommended not to consider 2.4GHz for Wi Fi coverage, but to directly consider 5GHz full house coverage as the design goal. In general, it is difficult for a single router to achieve dead corner coverage in a complex home environment. It is necessary to consider the networking and roaming issues between multiple routers, which will be discussed later.

III. Key Wi Fi Technologies

Why is Wi Fi getting faster and faster? In fact, the IEEE 802.11 series protocols have been borrowing from the 4G and 5G of 3GPP, and the underlying technologies used are universal.

OFDM/OFDMA

The full name of OFDM is orthogonal frequency division multiplexing. The system will divide the carrier bandwidth into multiple orthogonal subcarriers in the frequency domain, which is equivalent to dividing a road into parallel multiple lanes, naturally greatly improving traffic efficiency.

Before Wi Fi 5 (802.11a/b/g/n/ac), the subcarrier width was 312.5KHz. However, in Wi Fi 6 (802.11ax), the subcarrier width was reduced to 78.125KHz, which is equivalent to dividing roads of the same width into more lanes.
In OFDM, each user must simultaneously occupy all subcarriers in the full bandwidth. If there is not as much data to send and the frequency resources are not fully utilized, other users will not be able to flexibly use it and can only queue up dryly, resulting in low efficiency in the use of spectrum resources.

To solve this problem, Wi Fi 6 introduced OFDMA technology, followed by the letter A, which became the full name of orthogonal frequency division multiplexing multiple access. Multi address means multi user reuse.
OFDMA can support multiple users to share all subcarriers at the same time. It is equivalent to the transportation company unifying the data of multiple users, loading them together, and fully utilizing the capacity of the carriage. As a result, everyone's shipping speed is accelerated, and spectral efficiency is improved.

MIMO/beamforming

The number of antennas on the router is increasing, from invisible antennas to one, two, three, four, six, eight... Nowadays, regardless of the price of the router, it looks like a crab, showing off its teeth and claws.

Why use so many antennas? It is to better implement MIMO (Multiple Input Multiple Output) technology. Simply put, it means using multiple antennas to simultaneously transmit multiple different data channels during signal transmission, naturally doubling the speed; When receiving, multiple antennas simultaneously receive signals from mobile phones, just like wearing a hearing aid, the reception sensitivity is also enhanced.