The WiFi at home becomes slow at night, and you don’t even have a slow device at home? It's probably your neighbors who are occupying your line. I wrote down the investigation process.

This matter has troubled me for half a year. The broadband at home is Gigabit and the router is AX3000T. During the day, the speed is stable at around 940 Mbit/s. However, after 8pm, the speed of the mobile phone is only around 100 Mbit/s and it is shaking badly. Watch a short video and spin around, and the game delay jumps from 18 milliseconds to 120 milliseconds. The first stupid thing I did was restart the router, it didn't work ； The second stupid thing I did was to change the WiFi password to prevent network fraud, but it was useless - I flipped through the device list and still found the same 20 or so devices, all of which were my own.

Later I realized that I had asked the wrong question. I have been looking for the murderer inside my home, but the "doorway" of WiFi is not within the walls of your home at all.

Let’s clarify something counterintuitive first: Invisible neighbors are also queuing up in your home WiFi

We need to explain the underlying rules of WiFi first before we can investigate further. WiFi is not a phone line. No matter who is on the other line, there will be no delay. It's more like a group of people sharing a walkie-talkie channel: Before speaking, listen carefully to make sure there is no one on the street before speaking. If you hear it, just shut up and wait. After the other party has finished speaking, you have to wait for a random small back-off time to prevent both people from grabbing the microphone at the same time.

The key is the three words "heard". It doesn't recognize people. Regardless of whether the person talking on the channel is your camera or the neighbor's router upstairs, as long as your network card hears that there is energy on the channel, it will shut up. Therefore, all devices on the same channel - note that they are physically on the same channel, regardless of network, password, or your home or mine - are all in an invisible queuing list.

The first time I really understood this was when I counted the WiFi in my building. The phone has a WiFiAnalyzer installed (that is Check channel interference App that I have used), stand in the living room and scan around: There are 11 signals on optical channel 1, 8 on channel 6, and 9 on channel 11. The channel of my router is set to "auto". At that time, it happened to be on channel 1, and it took turns to use the same intercom channel with 10 other companies. During the day, everyone went to work and the channel was empty. I just said ； When people came back in the evening, 11 family members scrambled for the microphone, and my 940 MB was lost.

We have to draw a clear line here from another old pit.: Old equipment slows down the entire network. That's because the slow device "in your home" is taking up air time. My mother-in-law's old iPad becomes stuck when connected to the whole family. The airtime article Calculate the account. But this article is about another matter: You don't have a single slow device in your home, and all negotiated rates are good, but you are still being slowed down - because the person who is busy is on the other side of the wall. They are two different things, and the handling methods are completely different. One touches the equipment at home, and the other touches the channel.

How to confirm it’s the neighbor’s fault?: Three features plus one control experiment

There is no point in guessing. I have summarized three characteristics. The more you are satisfied, the greater your suspicion.

The first one is divided into periods. It's good during the day but bad at night, and gets worse as you get to peak times. Weekend afternoons are a bit worse than weekday afternoons. Because your neighbors are also human beings, and they come home at about the same time as you. Second, 2.4G is worse than 5G and worse than 5G. There are only three non-overlapping 2.4G lanes nationwide: 1, 6, and 11. There are dozens of signals in the building, and crashes are common. ； The 5G frequency band has many channels and a large area, so it will only become crowded later. The third one has nothing to do with broadband. Plug the network cable directly into the router's LAN port to measure the speed. It can still reach full speed during the evening rush hour - the exit is not blocked, but the air from your home to the router is blocked.

A controlled experiment is just one step: Open the speed measurement page on your mobile phone and stand next to the router to measure (excluding attenuation through walls, the signal strength is measured in dBm article After calculation, the environment is considered clean if it is within -60). The test is still slow when held against the face, and there is no slow device at home, so "there is someone in the air" is basically the only explanation.

A more rigorous verification is to temporarily change the router's 5G channel to an unpopular value, such as changing it from 36 to 149, and test it immediately after the change. The speed came back a bit on the spot, a real hammer. At nine o'clock that night when I actually measured it, channel 36 was on 100 Mbit/s. I changed it to 149 and immediately returned to 560 Mbit/s. The next night, it was fixed at 149 and measured again, and it was 610 Mbit/s. There is not much change in one line of settings, just this one action.

Take a look at your channel map to see clearly the enemy situation first

Scout before taking action. Install WiFiAnalyzer on mobile phone (Android ； The iPhone cannot install this kind of App. You can also use a family member’s Android phone or a laptop to type commands. The method is: netsh article (written in), the channel page will give you a histogram: The horizontal axis is the channel number, and each column is a signal, the higher it is, the stronger it is.

Just look at the picture to get the idea: Look for the emptiest channel, not the strongest signal. 2.4G looks for the three integer digits 1, 6, and 11 - only these three do not overlap each other. If you choose 12 or 13, it will overlap with 11 for the most part, and you will be happy for nothing. Counting the number of pillars on each lane and the height ranking of your signal is more intuitive than any "automatic optimization" in the router's background. My home has 11 signals on channel 1, 8 on channel 6, and 9 on channel 11. However, my home signal is among the top two on channel 6 - then choose channel 6. The one with the strong signal can win over others.

By the way, let’s take a look at a common oolong: Some optical modem have built-in WiFi that is still on and collides with the channel of your own router. This is a "neighbor at home". Just turn it off or stagger it. Determine and deal with it. optical modem WiFi and router WiFi crash It was specifically written in that article. Let’s get rid of this first before we blame people upstairs.

2.4G and 5G are handled separately, with completely different ideas.

2.4G I advise you to give up and accept your fate. There are three lanes and dozens of signals. This is a physically insurmountable squeeze. All you can do is choose a lane with relatively few people and rush all important 5G-capable equipment to 5G. Those that only recognize 2.4G, such as sweepers and cameras, will be left behind, while mobile phones and computers will all use 5G. If the dual-band combination is turned on, some mobile phones will be "guessed" to be on 2.4G, and the name of 5G will be returned after manually connecting once.

5G is the real main battlefield. There are many channels, add 100 to 165 from 36 to 64, and you will get more than a dozen channels, and four 20MHz channels can be combined into an 80MHz wide channel. There are only two things to do: First, the bandwidth is an honest and practical 80MHz. I’ve seen tutorials that teach you to turn on 160MHz to gain speed, but don’t learn from it – 160MHz takes up eight lanes at once, and half of the neighbors in the building are overwhelmed by you. At night, everyone squeezes together and compares their feelings. I’m here to account for this. How to choose bandwidth It was calculated in that article. Second, move the channel back to 100. The segments 36, 40, 44, and 48 are the "low segments". Old routers tend to get together, and the automatic channel selection will most likely stop at 36. ； 149, 153, 157, and 161 have much fewer people living together. I checked the buildings of three friends, and this is the pattern. Just copy it if you want to save trouble.: 149 starting hand.

WiFi6 router also has a free bonus, BSS color: For neighbors on the same channel but far away, WiFi6 can continue to transmit as if they are inaudible. But this thing only saves "those who are far apart" and cannot save "strong neighbors who are separated by a wall". You still have to divide the territory among yourself. I have its temperament and temperament BSS color article Don't expect it to select the channel for you if you have already done so.

It’s still slow after moving, and there are only three finishing methods left.

After moving the channel, I still can't get up during the evening rush hour. Check these three things in order.

The second type is the most irritating and the most widely deceived. The purpose of selecting "Auto" for the router's channel is to avoid congestion, but you don't know the timing of its re-evaluation. It jumps to a channel it thinks is good at two o'clock in the middle of the night, and the next day you just think "this router is not good." Nail it manually and leave it alone for a year. When the sweepers at my cousin's house collectively lost contact, we found out that the root cause was that the channel automatically jumped to 12 in the middle of the night, and then stopped after being nailed to 1 - the judgment idea is the same. Six slow ways to troubleshoot The branches that are slow in time in that article are the same set.

The third kind of reminder is not to go astray: Bandwidth and latency are two different things. Just because the speed test goes up doesn't mean that the game won't freeze. What the game cares about is packet loss and jitter. Things like secretly changing gears when the speed is dropped by half and the signal is only dropped by one bar. I'm here The article about changing gears It has been specifically written here that you can just copy the troubleshooting methods and use them to locate packet loss. three pings .

How did your neighbor’s WiFi trick you?: A queue bill

Here is a mechanism account. Once you understand it, you can judge for yourself what type of slowness your family has. Opportunities to talk on the same channel come in turns, and whoever has a higher speed can move more in one round. If your neighbor upstairs has an old laptop crowded in your aisle, with a negotiated speed of 72Mbps, it will take you enough time to move one bag and twenty mobile phones - but it will take up a lot of turns. Every time you shut up and give way, you spend all your time acting as a porter for it.

Two tricks for WiFi6 versus two squeezing methods: OFDMA cuts a round into small grids, allowing multiple people to send them together in one round. Scenarios with many small packages solve the problem of "queuing up and waiting for rounds" - I'm here OFDMA and MU-MIMO article After dismantling it, what you save is the queuing time, not the bandwidth. ； BSS color treatment "It's so polite even if it's far away". If these two tricks are enabled by default, don’t move them. There is only one thing you have to do.: Let your own farewells overlap with those of your neighbours. The channels are staggered, so there will naturally be fewer people on the queue.

One sentence to end: When WiFi becomes slow, you should first ask three questions: "When is it slow, is it slow next to the router, and is the network cable fast?" If no one is occupying the road outside your home, there are no slow devices at home, and the exits are not blocked, then it is the router itself's turn to blame. My AX3000T was wrongly accused for half a year, but the case was overturned after the channel was moved.