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The Wi-Fi killers

Is your Wi-Fi not working? Interference could be getting in your way

What’s the number one threat to the smooth running of your Wi-Fi network? Interference, and plenty of it.

It isn’t only interference from neighbouring networks that you have to worry about – indeed, some experts suggest conflicting Wi-Fi traffic is relatively harmless – but all manner of electrical devices inside and outside of your premises.

Overlapping networks

The sheer ubiquity of wireless networks is staggering. From the fifth floor of the Rustyice office in Glasgow, for example, there are no fewer than 36 different Wi-Fi networks (both business and domestic) fighting for attention in the 2.4GHz band.

That’s only the 802.11 networks; anything from wireless security cameras to Bluetooth headsets, to the microwave in the office kitchen may also be operating in that unlicensed spectrum or creating interference.

Not only do the majority of homes and businesses now operate Wi-Fi networks, but they’re also increasingly likely to be using 802.11n equipment, which offers a far greater range than previous generation 802.11abg networks.

With an indoor range of up to 70m and the ability to pass through multiple brick walls, there’s every chance that the router from next-door-but-one is sharing the same airspace as yours, whereas that simply wouldn’t have been the case even two years ago.

In flats or apartments, where the signal comes from all sides, the problem is multiplied. The congestion is exacerbated by standard router setups that often leave neighbours sharing the same Wi-Fi channel.

“A lot of [Wi-Fi router] manufacturers have a default Wi-Fi channel. Many choose channel 1,” said Roger Tao, European strategic technology product manager at D-Link. Indeed, 11 of the 36 Wi-Fi networks accessible from the Rustyice office were fighting for space on channel 1.

With Britain’s biggest ISPs handing out millions of the same router to their customers, you’ll often find clusters of routers sharing the same channel.

Three of the 11 routers using channel 1 that were visible from the Rustyice office were BT Home Hub devices, while our tests in a domestic environment revealed all three Sky routers within range were also clinging to channel 1.

BT has recognised this problem: the last generation of Home Hub routers automatically scanned for the least congested Wi-Fi channels, while the new Home Hub 3 also switches channels to avoid other RF interference from, say, wireless video senders.

Too many cooks

With Wi-Fi traffic reaching rush-hour M25 levels in urban areas, some people are tempted to cheat.

By downloading an American or Asian version of your router’s firmware – or even changing the location settings in the current firmware – it’s often possible to unlock the 14th Wi-Fi channel in the 2.4GHz spectrum.

This is technically illegal in the UK because it creeps outside of the unlicensed spectrum: 2.4000-2.4835GHz is the allocated spectrum, while channel 14 operates at 2.484GHz.

While some people might be tempted to bend the rules to avoid Wi-Fi channel congestion – just as many people were when in-car FM transmitters were still illegal – switching your router to channel 14 isn’t necessarily a panacea: some client devices simply refuse to operate on channel 14.

Another commonly used tactic to overcome interference is to increase the number of access points, especially in business premises. Yet, according to a Cisco white paper “20 Myths of Wi-Fi Interference”, this can often make matters worse.

“Some networks are being deployed with an AP in every room,” the paper states. “It seems intuitive that by having more APs spread around, it’s more likely that a client will be able to operate successfully even when interference is present.

“Unfortunately, when you deploy a dense network of access points, it’s necessary to reduce the transmit signal power of each of the access points. If you don’t reduce the power, the access points generate interference to each other, a phenomenon known as co-channel interference. The reduction in the transmit power of the access point exactly offsets the potential benefit of interference immunity. So, in the end, the interference immunity of a network with a dense deployment of access points isn’t significantly better than that of a less dense deployment.”

In fact, although overlapping networks and co-channel interference can undoubtedly harm the performance of your Wi-Fi devices, it’s more likely that other forms of RF interference are doing more damage to your speeds than the router next door.

“Lots of Wi-Fi doesn’t necessarily mean you’re going to have a problem,” explained Adrian Pote, general manager of broadband devices at BT. “Lots of networks tend to be able to coexist quite well.”

D-Link’s Roger Tao agrees, explaining that routers are designed to cope in regions with a far higher population density than the UK, such as Korea or Japan, where the average dwelling will be within range of between 15 and 20 different access points.

“The housing density is much lower in the UK. It’s between six and eight clients you can see from a household,” he said.

The hidden killers

Aside from interference, there are other “hidden” Wi-Fi speed killers – your choice of router security protocol, for instance.

“WEP has a greater overhead and can, in some cases, cause a performance loss of up to 30%,” a spokesman for router manufacturer Belkin told PC Pro, providing yet another reason to dump the outdated and now insecure mode of traffic encryption.

“WPA/WPA2 is more efficient and should, on any modern router, only reduce performance by a maximum of 5-10%. In most cases, however, it won’t be measurable.”

Running a completely unsecured router is the easiest way to maximise traffic throughput, but also the easiest way to hand access to your data to eavesdroppers and give your neighbours carte blanche to download anything they like on your account.

As Belkin points out, the small loss of performance using WPA/WPA2 “should be seen as an acceptable exchange” for security.

The positioning of your router can also have a tremendous impact on performance. “Problems start to occur when you get the router in the wrong position, such as on the floor or behind a cabinet,” said D-Link’s Roger Tao. “People are hiding it because they don’t want to see it.”


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