Wireless & Overcrowding

I gave a talk to the Hertfordshire section Institute of Measurement & Control on the 18th April about Wireless Network and the configuration in the Urban Environment, it concentrated on some of the security risks, why these should be taken serious in the Urban environment and on how performance can be affected by the RF environment. The talk was low on the technical side as it was aimed at the interested general public. The talk was well received with some good questions, however an interesting point was that a number of people mentioned the article in the telegraph paper "How do I stop wireless hackers?" http://tgr.ph/HVieXS on the 15th April. In which a person had written in with the following question.

"I live in a block of flats and connect to the web using a wireless connection. My router is security enabled but can someone in another flat utilise my signal via their laptop? If so, is this legal? The reason for asking is that for some time now when I am on the web, I get a mystery pop-up message that states ‘I am now connected’."

The Telegraph writer did a good job in answering the question. The pop being mentioned was very likely the result of a poor connection or a possible DoS (accidental or deliberate) rather than hackers who have broken into his system. It is likely that the pop-up was caused by his device reconnecting to the wireless router after some interference on the channel he is using.

Possible sources of interference are

• Microwave Oven which operates at 2.45GHz but leaks a wider bandwidth of energy than the WiFi usage of the 2.4GHz band
• Phone on the 2.4GHz band
• AV sender using the 2.4GHz
• Wireless Baby alarm
• Wireless CCTV camera
• Access point closer to him than his on the same or neighbouring channel.

WiFi works on a number of channels and in the 2.4GHz band in the UK there are 13 allow channels, however most overlap and there are other sources of interference that can affect the channels as shown in the two diagrams below below.

The current urban environment is saturated with wireless networks the vast majority in the 2.4GHz band. Surveys I have done on some Urban areas show multiple Access Points (AP) in close proximity in the 2.4GHz with none in the 5GHz band. In a block of flats there is a 3D distribution of AP as opposed to the more 2D in terraced housing estate.

Most people when there set-up a new wireless access point will either use the default channel or select one of the three recommend in the manuals which are 1,6 & 11. Very few will change to the 5GHz band and most will not do a survey of the channel usage to select a channel with least interference ie the least number of strong other wireless networks.



Screen shot of the beta version of my tool

As part of my research I am working on a tool that would sit in the notification area of the windows taskbar and could indicate the number of access points per channel in the selected frequency band, a screenshot of beta tool is included above. The tool should be able to give a simple site survey ability that is easy to understand to all users. There are a number of other features I will be building into the tool over the next few months.

During the talk I showed examples of the interference from a bluetooth phone, microwave ovens, AV senders can have on the 2,4GHz environment using a spectrum analyser.

The high point for me was that one of the audience emailed me the next day to say there had looked at the number of AP's on the same channel and moved their channel selection and where getting better performance.