Wi-Fi feels like a cable without the cable. It is not. It is a radio in a room, shared with everybody nearby, and almost every complaint about it makes sense once you think of it that way.
It is a conversation, not a pipe
On a cable, two devices each have their own pair of wires and can talk at the same time. On Wi-Fi, everybody shares the air. Only one device can transmit at a time on a channel, so they take turns: listen, wait, talk, hope nobody else started.
Two things follow. The speed on the box is what one device reaches alone in an empty room, and you will not see it. And one slow device is expensive for everyone: while it talks slowly, nobody else can talk at all.
The bands, and the trade-off
Radio has one unavoidable trade-off: a lower frequency travels further and through more, a higher frequency carries more data.
- 2.4 GHz goes furthest and through walls best. It is also crowded, and not only by Wi-Fi: cordless phones, baby monitors, Bluetooth and microwave ovens live there. Use it for range and for old or cheap devices, not for speed.
- 5 GHz has far more room and is where your real throughput comes from. It loses more signal per wall.
- 6 GHz is newest, emptiest and fastest, and has the shortest reach. Only recent devices can use it.
So a phone in the garden is better off on 2.4 GHz, and a laptop near the access point on 5 GHz. Devices choose for themselves, and not always well.
Channels and overlap
A band is divided into channels. Two networks on the same channel take turns with each other. Two networks on channels that partly overlap are worse: they cannot hear each other properly, so they talk over each other and both slow down.
At 2.4 GHz this is the famous problem. The channels are numbered 1 to 13, but each one is wider than the spacing between them, so only 1, 6 and 11 avoid each other completely. A neighbour on channel 3 is interfering with both 1 and 6 without being on either. Set a channel at 2.4 GHz by hand and it should be 1, 6 or 11.
A wider channel is faster when it is free and worse when it is not: it is more likely to bump into somebody, and it spreads the same power over more spectrum, so it reaches less far. This is why a 40 MHz channel at 2.4 GHz is a bad idea almost everywhere, and why an office with several access points is usually better off at 40 or 80 MHz than at 160 MHz. The details are in channels, width and power.
Why walls matter
Every wall takes a bite out of the signal, and how big depends on what it is made of. Plasterboard costs little. Brick costs noticeably more. Reinforced concrete, a tiled bathroom, a mirror, a lift shaft, a fridge and an old plaster wall with metal mesh in it can cost almost everything.
Two consequences. An access point in a meter cupboard behind a concrete wall has lost half of what you paid for before it reaches anyone. And floors are usually the hardest direction, which is why one access point on the middle floor of a house disappoints above and below at once. You can map this out before you drill; see the Wi-Fi plan.
Why more power is not more coverage
A conversation needs both directions. The access point has a large antenna and mains power. A phone has a small antenna, a battery, and a fraction of the transmit power. Turning the access point up makes it audible further away, but the phone is as quiet as it was. So you get a spot where the phone shows four bars, connects, and nothing works, because the access point cannot hear the answer.
Worse, a loud access point holds on to devices that walked past a nearer one long ago. The phone decides when to move, and it is reluctant: it stays on the strong distant signal and crawls, in a room with an access point on the ceiling.
There is also a legal ceiling on transmit power, so there is no setting that makes this work anyway.
SSIDs
An SSID is the name of a wireless network, the thing you pick from a list. It is not the radio, and not the network. One radio can carry several SSIDs, and each of them can be tied to a different VLAN, which is how a guest network and an office network come out of the same box while staying apart.
A name that appears on several access points, with the same security and password, is one network as far as a device is concerned, and it can move between them. That is the recipe for roaming: the same name everywhere, not a name per room. Calling them "Wifi-downstairs" and "Wifi-upstairs" makes a device stick to whichever one it joined first. See Wi-Fi that keeps working as you walk.
Why two access points beat one loud one
If distance is the problem, the answer is to shorten the distance. Two modest access points, each covering its own part of the building, put every device close to one of them. Close means a strong signal both ways, a high speed, short airtime per device, and more room for everyone else.
The price is a cable to the second one, and that cable is the point. An access point that receives its traffic over Wi-Fi from another access point spends the air twice and halves what is left. Where you cannot pull a cable, a mesh link is a workable compromise, not an improvement.
Where the tool picks this up
You set names, security and bands in setting up Wi-Fi, and for several access points that should share one set of settings there is CAPsMAN.