Wireless Waffle - A whole spectrum of radio related rubbish
Wire-More LAN (Part VI) - Maximise WiFi coverage and reliabilitysignal strength
Thursday 28 August, 2008, 17:12 - Radio Randomness
Posted by Administrator
Like all radio systems, wireless LANs can never be 100% reliable. Many factors affect radio transmission and even in situations where something might be expected to work well, problems can often occur. Wireless LANs suffer from a number of particular problems, not least the frequencies they use (around 2.4 GHz) are easily absorbed and reflected and can suffer from high levels of interference. But with a little care, their coverage and the reliability of the connection can be improved quite easily. Here are the Wireless Waffle top 5 tips for improving WiFi signals.

1. Choose the right channel

Interference from other wireless LANS is the most common cause of network quality degradation. The various surveys that Wireless Waffle has conducted have generally shown that channels 1 and 13 are the least likely to suffer from interference from other wireless LANs. Further, channels 10 upwards are the least likely to suffer interference from other users of the 2.4 GHz band. So generally speaking, in an area with a low likelihood of finding other WiFi users, channels 11, 12 or 13 are likely to be best. In congested areas (i.e. where interference from other WiFi systems is likely to be worse than from other users in the band), channel 1 is the best choice.

2. Position your WiFi hub centrally

Radio coverage from most transmitters radiates in all directions from the point of the transmitter, and this is certainly the case for wireless LAN equipment. It therefore makes total sense to position your central WiFi hub as close as possible to the middle of the area you wish to cover. Further, radio signals travel best if there is a clear path between both ends of the link. If you put the central unit in a cupboard or behind a bookshelf, where the path is already obstructed, coverage will reduce. Place the unit in an place with a clear view of the area you wish to cover, the higher the better (look at hubs installed in public places such as coffee shops and hotels - they are almost always mounted on the roof!)

bluetooth side effects3. Keep your wireless equipment away from other wireless equipment

There are many other sources of radio signals in the typical home or office environment and many of these are on frequencies similar to (or even the same as) WiFi. Placing these other radio sources near to wireless LAN equipment can result in reduced performance from the LAN as it struggles to cope with the interference caused by the other equipment. It's especially important to make sure that equipment such as digital cordless phones, satellite TV downleads, bluetooth and zigbee devices, mobile phones and digital baby alarms are not used in close proximity to a wireless LAN if service quality is not to suffer.

4. Use equipment with proper aerials

Devices such as USB WiFi adapters are generally quite small and this means that the aerial inside them is also small. Smaller antennas pick up less signal and thus range and the quality of the connection will be adversely affected. If you are installing a wireless network for your home computer, use a proper PCI wireless card with an external antenna, rather than a USB wireless 'dongle'. This step alone can easily double or more the range you achieve from your wireless network and such cards are often cheaper than their dongle sidekicks.

5. Upgrade your antenna

It's easy to extend the range of a WiFi network by using higher gain antennas on hubs and on PC cards. Changing the antenna on the hub will affect all of the network, whereas changing it on a remote device will affect that device only. Most standard antennas have 2dB gain but 5, 7 or even 9 dB gain antennas can be purchased relatively cheaply. Changing from 2 to 7dB gain antennas will virtually double the range of your network. And if you replace the antennas on both the hub and the remote units with 7dB gain antennas, range will nearly quadruple.
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Hang Fire a Minutesignal strength
Saturday 26 July, 2008, 16:01 - Radio Randomness
Posted by Administrator
Watching a number of hot air balloons float gracefully past recently, the question arose as to whether or not they used radio to communicate with the ground and, indeed, whether they used radios to communicate with air traffic controllers. A bit of digging around revealed that they do indeed carry aeronautical radios with them, and what's more they have a special 'balloon to ground' frequency. Not just that, but the same is also true of gliders, parachutists, microlights and hang- and para-gliders.

Below are all the commomn frequencies (in MHz) which are set aside, in the UK, exclusively for these special purposes, including a frequency set aside for fire services at airfields:

120.900, 130.100, 130.125 and 130.400 Gliders
129.975 Gliders (to mobile field units)
122.475 Hot Air Balloons
130.525 and 129.900 Parachutes
129.825 Microlights
118.675 Hang/Paragliders
121.600 Ground Fire Services

hang glider interferenceThe very observant amongst you may note that the frequency for Hang/Paragliders is just 25 kHz away from the Heathrow Airport (arrivals) tower frequency of 118.700 MHz. Typically, frequencies this close are not used in the same area so that any Hangglider flying near to Heathrow may cause disruption to the tower communications (and indeed the governing body for aero frequencies, ICAO, does not allow such clashes). The exceptionally observant amongst you will realise that if a hangglider got close enough to Heathrow airport to cause interference, it would have greater things to worry about than radio! So by simple spatial collision avoidance, interference is likewise stopped.
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Wire-More LAN (Part V)signal strength
Thursday 26 June, 2008, 06:51 - Radio Randomness
Posted by Administrator
Another long train journey, another opportunity to run Netstumbler to find out what is going on in the world of WiFi. On this journey 425 WiFi (802.11b and 802.11g) access points were identified. No 802.11a (5 GHz) access points were spotted. Of these, 24% were not encrypted or protected in any way (however, some of these are public access points such as 'BT OpenZone' and so would not be expected to be encrypted). This means that the proportion of home WiFi nodes that are now protected has gone up significantly since the last time this was tested.

The graph below shows, in orange, the number of times that each channel was found to be in use. As expected, channels 1, 6 and 11 were the most commonly used, with channel 1 winning out over channel 11 in terms of usage for a change.

wifi channel usage

What the graph also shows is the combined interference effect of all the nodes across the whole WiFi frequency band. This has been done by adding the use of a channel with (5-n)/5 times the use of the frequency n channels away. So a channel 3 frequencies away from the channel in question would add 2/5ths of its interference to the total combined effect. This takes account of the OFDM nature of WiFi and thus the fact that the less two channels overlap, the lower the interference problem.

What's interesting about this result is that interfernece remains fairly constant across the whole band, with the exception of channels 12 and 13. This is perhaps not surprising as, channel 9, for example, will suffer 3/5ths of the interference in busy channel 11, and 2/5 of the interference in busy channel 6. Only when we get above channel 11 does interference fall as only one busy channel (11) is now adding to the combined interference 'mush'.

The frequencies above channel 13 (i.e. above 2483.5 MHz) are not used for WiFi and although no account has been taken of usage above (or below) the band, if usage is not widespread (at present it is reserved for an as yet non operational satellite system), then the overall level of interference in channels 12 and 13 will, indeed, be lower.
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Frequency Sharpenersignal strength
Tuesday 1 April, 2008, 10:24 - Radio Randomness
Posted by Administrator
frequency sharpenerYou've no doubt heard of pencil sharpeners and knife sharpeners, both designed to ensure the maximum of performance from the devices on which they operate. Well, on April 1 this year, researchers at the University of Al Tayr, in Tripoli, Libya released details of the results of a 5 year study that they have been conducting in which they believe they have discovered the world's first 'frequency sharpener'. Details are somewhat scant but if the device can deliver the kind of results that have been quoted in the research, the frequency sharpener could be being included in many new digital radios of the future as soon April of next year.

In the University's press release, Prof. Ali Lo says of the frequency sharpener:
With weak signals, it is like a thousand camels standing through your receiver to blunt the sound. The frequency sharpener acts between these blunt and dull edges using a special digital encoded Saif Al Nisan algorithm that swipes away and cuts off the noise to leave only clear oasis of surrounding signal.

The release is rather thin on technical details of how the sharpener functions but goes on to claim:
Tests in laboratory of testing have shown, masha'allah, that 12 times improvement in frequency sharpness can be made to receive signal with almost no hump blockage in background or foreground. Works of programme suggest that remaining disturbance no worse than size of golden sand rabbits of similar proportion. By development, frequency sharpener will deliver 20 to 25 times decrease in annoyance of radio camel noise for new design of radio receiver in Arabian region. Better results with Saif Al Nisan algorithm than traditional threshold extension or synchronous detection methods employed before this discovery.

desert radioWe've sent an e-mail to the professor to see whether he could provide more information on how the frequency sharpener works, however from reading between the lines of the press release, we have been able to piece together how we think the device works:
  • The sharpener first stores ambient noise received when the wanted signal is gone, or from areas around the wanted signal.
  • When required, this noise can be metabolised to act as a source of 'anti-noise' (similar to noise cancelling headphones) which cancels out the incoming 'live' received noise.
  • This yields both a reduction in noise and, as a bi-product, generates spare energy that can be used to boost the wanted signal.
  • The process of noise metabolisation generates a net reduction in both the stored and received noise, as well as amplifying the wanted signal.
  • The system though, if it works as we suspect, requires the noise store to be 'topped up' from time-to-time. Once the noise store is empty (for example, if there is no longer noise on the received signal), the device returns to the normal state with no noise reduction taking place.
This fascinating development is something we, at Wireless Waffle are keen to keep an eye on and will bring you updates as we get them.
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