Introduction

"Wireless Networks do not perform to their theoretical capability"

Wireless computer networks (WiFi) were originally a useful add-on to wired connections, but they are now becoming increasingly important in their own right. For instance, many homes have broadband connections solely through a wireless router with no cables to computers at all. What is less well known is that many wireless networks perform significantly less well than their theoretical capability. As we depend more on WiFi it becomes important to understand a little about how it works and how the buildings around us affect wireless performance.

In commercial buildings wireless network coverage must be carefully planned and the surrounding building or buildings must be included in this process. This is because structures such as walls and doors significantly affect how far WiFi channels reach from the wireless access points (that is the WiFi transmitters connected to a phone or network socket).

WiFi is known technically as IEEE 802.11 and comes in the 3 main standards shown in the table below:

WiFi Standard arrow-down Frequencies arrow-down Number of non-interfering channels arrow-down

An access point is capable of using any WiFi channel in its standard but in practice, they use only one at any time and this can be fixed. Although there are more than 3 channels available for the 802.11b and g systems, most of them overlap in frequency meaning they interfere and cannot be used by neighbouring access points at the same time. Therefore, when setting up a WiFi system with several transmitters in a building it is essential to choose channels that don’t overlap; these will be channels 1, 6 and 11 for the ‘b’ and ‘g’ standards.

The channel overlap interference problem is also present in streets or shared houses where different WiFi networks are visible in each home. These systems often don’t have fixed channel numbers but allocate channels as and when they are required making it very difficult to avoid problems when the wireless networks are busy. As a user, interference means your bandwidth goes down or in an extreme case there’s no connection at all.

Confused? The Wi-Fi Planning scenarios provide more information and an interactive application to make things more clear.