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How Wi-Fi works

Posted on 27 May 2011 at 15:10

If you want to know how to fix your Wi-Fi, first you need to understand how it works

Before you set about fixing your Wi-Fi, it helps to know how the technology works.

That way, you can make an informed decision about the equipment you need to solve your issues, or whether a change of settings might help.

It’s a complicated subject, and we won’t attempt to cover everything (such as packet data, TCP/IP, or the ins and outs of wireless security), but by the end of this section, you should have a firm grasp of Wi-Fi’s fundamentals.

Signals and spectrum

Wi-Fi’s core premise is pretty simple – routers and adapters send and receive data using radio waves. It’s the same basic technology that’s used by radio and TV to receive terrestrial signals, mobile phones to make and receive calls, as well as video senders, baby monitors, and all sorts of other wireless devices.

In effect, all a wireless router or adapter does is translate the data it receives into a radio signal, which is decoded back into data at the other end.

All a wireless router or adapter does is translate the data it receives into a radio signal

Specifically, wireless routers use frequencies of 2.4GHz (or the range 2.412GHz-2.484GHz to be more precise) and, in the case of more expensive dual-band routers, 5GHz (4.195GHz-5.825GHz) to send and receive information.

But there’s far more to it than simply slinging streams of data to and fro. Each of these bands is further divided into channels, of which your router can use one or two simultaneously (when two are used simultaneously, it’s called channel bonding – see below for more details). In the 2.4GHz band there are up to 14 channels available, and up to 42 in the 5GHz band.

The idea is that by using different channels, neighbouring networks avoid stepping on each other’s toes. In an ideal world, for maximum performance and stable operation, your router should be running on a channel that no other network in range is using.

Channel crossings

In reality, the true number of available channels is lower than these theoretical maximums, depending on where you live and which router you’re using.

In the UK and Europe, you’re legally allowed to use only channels 1 to 13 in the 2.4GHz space, and you’re restricted to 18 of the 42 in the 5GHz space. A Netgear router we use in the office, meanwhile, makes only four channels in the 5GHz space available for use.

This is compounded by the fact that when your router transmits on each channel, the effective width of its signal is about 20MHz, which, in the 2.4GHz space, means it can overlap up to eight neighbouring channels.

It doesn’t take a genius to work out that when more than three wireless networks are in close proximity to one another, co-channel and adjacent channel interference can become a problem.

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Channel bonding (the ability some routers have to group two channels together, doubling the potential throughput) makes the congestion even worse – with several 40MHz wide channels hogging such a narrow spectrum, it’s like trying to squeeze several 21-stone men into a small lift.

Why 5GHz?

There is a solution to hand, however – 5GHz wireless. The advantages it holds over 2.4GHz are threefold. First, it’s far less congested. Fewer people own dual-band 5GHz routers and devices, so the chances are you’ll be able to set up your network on a completely congestion-free channel, which you perhaps wouldn’t over 2.4GHz.