Wall Street journal has an article "Helpless, Hopeless, Wireless" on Wireless Networks detailing how that wireless networks are causing companies difficulties.

Wireless networks were meant to save wiring, time and money. Instead most tech departments are spending hours upon hours troubleshooting wireless networks.

The article states:

Wi-Fi was supposed to reduce complications, not create new ones. The wireless technology was designed to eliminate the cords and cables used to connect computers to the Internet, enabling users to be more mobile and to stay connected to the office even while on the go . . . But in many offices, Wi-Fi has been a headache. Like all radio signals, Wi-Fi is subject to interference. Its relatively low power -- less than even a typical cellphone -- means walls and cabinets can significantly reduce signal strength. Wi-Fi also creates a more open network than wired networks, raising security issues.

While all of these difficulties has an answer, perhaps the most important information about running a wireless network is that a lot more planning needs to go into establishing a network.

You need to consider where wi-fi antennae are located, where troublesome walls may be located and other blockages. There is no substitute to installing wi-fi antennae and roving the office with a computer connected to the wireless network. I have installed a number of networks for different people and what I have found there is no substitute for physically testing the network.