There are already many quality articles on Habré with a detailed explanation of how Wi-Fi works and how to configure it. However, all these articles have at least a few shortcomings that prevent them from being given as a guide to action for a conditional neighbor in a high-rise building or hanging a printout on the wall in the entrance:
1. without even the slightest engineering education, it is difficult to understand and put into practice most of the material
2. the articles contain “too many letters” so that it would be interesting for a person who is not motivated to do anything to master such a volume of text
2.1. people have no motivation because the already existing situation is: “why do something at all, if everything is already working”
2.2. most are sure that “it must work by itself” in the format “I bought it and plugged it into a socket”
2.3. people don’t even think that Wi-Fi can work better, they just take it for granted because often even the equipment they have from the provider
3. some points in existing articles are not specified at all or are not specified enough, for example, explicit recommendations on the physical location of equipment are not given
3.1. “in the wild” for people, equipment can stand on the floor with antennas in a “bouquet” or even lie in the corner
4. for the choice of channels in the 2.4 GHz band, recommendations are given that are relevant only for North America and are not optimal for the rest of the world
5. The authors of the articles, in view of the professional distortion of perception, like any experts, have the illusion that home users will use optimal solutions, for example, only 20 MHz channels
5.1. of course they won’t, because even those who tried to change something in the settings see that at 40 MHz shows a much higher speed
5.2. in the vast majority of equipment, especially in the budget segment, everything is very bad with the settings, you can select the channel, sometimes the 20/40 mode and, often, these are all available settings
The memo provides guidance on optimizing the physical layout of the equipment and properly configuring the position of the antennas. In practice, this is very important since a minimum space is needed around the antenna to enable it to work. Recommendations are also given on the need for proper grounding of interference sources.
As a recommendation for choosing channels, the memo used for regions other than North America, i.e. 1/5/9/13 channels.
Details
Channels in OFDM (802.11 a, g, n, ac) not only occupy 20 MHz, not 22 MHz like DSSS (802.11 b), but also contain guard (zero) subcarriers at the edges, so this use is most optimal because it allows use four 20 MHz channels instead of three in the 2.4 GHz band, or two 40 MHz channels instead of one. In the 20 MHz OFDM channel, out of 64 subcarriers, 8 extreme ones (4 on each side) are not used for data transmission, their energy tends to zero. For 40 MHz channels, 128 out of 8 are not used already. Here in the picture, white (not pink places) are protective subcarriers in the signal. The width of one subcarrier for 802.11 g/n/ac is 312.5 kHz.
Note: channels with a width of 40 MHz: "Channel 3" and "Channel 11" on the diagram on the air are two channels of 20 MHz each, in which service information is transmitted only in the main channel. For correct operation and no conflict between networks, it is necessary that all 40 MHz networks work with the same main and additional channels. Since the vast majority of equipment allows you to explicitly configure only the main channel, when using 40 MHz channels for all routers, you must select only channels 1 and 13 in the settings, choosing other channels for both 40 MHz and 20 MHz will lead to conflicts and poor network performance. everyone!
As an addition, in the context of turning off unused equipment, an example is given with a MGTS router, most of which are not used for the Internet (only a wired telephone is used), and they were often installed by force. So Wi-Fi in these routers is almost always useless and just crap beacons on the air 10 times per second.
Existing articles on Habré
Perhaps I have not indicated all the interesting links here, please add in the comments.
In general, I look forward to comments and additions. I don’t want to greatly inflate the volume of the memo, and there’s nowhere to go, all the same, I hope to get by with approximately the already existing one A4 sheet on both sides and the same sheet for additions, however, if something important should be added or something unnecessary should be deleted, be sure to write.
20.07.10 add-on: The memo has been updated (the text has been slightly cleaned up). The note has been around for a long time. I didn’t post it on Habr just for the reasons that the target audience of the memo is clearly not here. I posted exactly the memo, and not the article for the sake of constructive criticism. Actually constructive criticism , Gratitude , now slowly rewriting the document with a fresh look. After all the modifications, the document will be posted on Pikabu and JoyReactor, because it is there that its target audience, i.e., ordinary network users.
Source: habr.com