Wi-Fi channel congestion, read properly

Wireless problems at home are usually blamed on the router and are usually about the air around it. The two and a half gigahertz band is shared with every neighbour in range, plus microwave ovens, older cordless phones, wireless doorbells and a good deal of cheap electronics. Unlike a cellular network, nothing coordinates the participants: every device simply listens, waits for a gap and transmits. That works remarkably well until the gaps run out. Reading which channels are occupied, and by how strong a neighbour, is what separates a fix that helps from a fix that moves the problem sideways.

Three channels, not thirteen

The lower band is numbered from one to thirteen in most of the world, which suggests thirteen choices. It is not. Each standard channel is twenty megahertz wide while the numbering steps only five megahertz, so adjacent numbers overlap heavily. Only channels one, six and eleven are far enough apart to avoid overlapping at all, which is why every serious deployment uses those three and nothing else. A router sitting on channel three is not finding a quiet gap between one and six; it is interfering with both, and being interfered with by both, in a way that neither can politely work around.

Overlap costs more than sharing

There is an important asymmetry here. Two networks on the same channel can hear each other, so they take turns: throughput is halved, but the mechanism works. Two networks on partially overlapping channels cannot decode each other's transmissions, so neither knows to wait, and the result is collisions and retries rather than turn-taking. Counter-intuitively, moving onto the same channel as a strong neighbour is often better than choosing a channel three or four numbers away from it. That single fact is the most useful thing to know about the lower band.

Wide channels are a trap down low

Bonding two channels into a forty megahertz block doubles the theoretical rate, which is tempting. In the lower band there is not enough room for it: a forty megahertz channel occupies most of the space available, guaranteeing overlap with any neighbour, and the standard's own coexistence rules will often force the router back down to twenty megahertz anyway. Keep the lower band narrow and reserve wide channels for the five gigahertz band, where there is room for several of them side by side.

The upper bands change the arithmetic

Five gigahertz offers many more non-overlapping channels, and a good part of that range is subject to radar detection rules, which is why some channels appear and disappear or take a minute to come up. Those radar-protected channels are frequently the emptiest ones, because cheap equipment avoids them. The trade is range: the higher frequency loses more energy through walls, so a five gigahertz network that is uncontested may still be slower than a crowded lower band two rooms away. Six gigahertz, where it is licensed, is emptier still and shorter in reach again.

Distinguish a crowded band from a weak link

Two different problems produce the same complaint. A weak link shows a poor received strength from your own access point — the further you are, the lower the number, and the fix is placement or a second access point. A crowded band shows a healthy strength from your own network and several strong neighbours sharing the channel; throughput collapses at peak times while the strength reading barely moves. Look at both figures before touching anything: your own link strength, and the list of neighbours with their channels and strengths. Changing channel helps only the second case.

How the scan itself behaves

Android throttles Wi-Fi scanning deliberately, to protect battery life. A foreground app is allowed only a handful of full scans in any two minute window, so a nearby network list refreshes on a slow cadence rather than continuously, and a network that vanishes for one refresh has often simply not been heard in that scan. This is why a serious analyser shows when the list was last updated instead of pretending to be live, and why walking around while scanning gives a more honest picture than standing still and waiting. The app that hosts this guide requests a fresh scan on a fixed interval and shows the connected link separately from the surrounding networks, because the connected link is the one you can measure continuously.

Airtime is the resource, not bandwidth

The number a router advertises is a link rate, not a share. Every device on a channel takes turns, and a slow device occupies the air far longer to move the same data than a fast one does, which is why one distant laptop on an old standard can hold back a whole network of modern devices. That is also why signal strength and throughput are linked indirectly: a weak client falls back to a slower rate, spends longer transmitting, and steals airtime from everyone else. Moving that one device closer, or onto the upper band, often does more for the household than changing channel ever will.