Introduction

The wireless arena has been experiencing exponential growth in the past decade. We have seen great advances in network infrastructures, rapid growth of cellular network users, the growing availability of wireless applications, and the emergence of omnipresent wireless devices such as portable or handheld computers, personal digital assistants (PDAs), and cellular phones, all becoming more powerful in their applications. The mobile devices are becoming smaller, cheaper, more convenient, and more powerful. They can also run more applications on the network services. For example, mobile users can rely on their cellular phones to check e-mail and browse the Internet. They can do so from airports, railway stations, cafes, and other public locations. Tourists can use the global positioning system (GPS) terminals installed in cars to view driving maps and locate attractions. All these factors are fueling the explosive growth of the cellular communication market. As of 2006, the number of cellular network users approached two billion worldwide. Market reports from independent sources show that worldwide cellular users have been doubling every 1.5 years.

In addition to that of the traditional cellular networks, an exponential growth of the wireless access point (AP), which is a device that connects wireless communication devices together to create a wireless network, is also being experienced. The AP is usually connected to a wired network and can relay data between devices on each side. Many APs can be connected together to create a larger network, which is a so-called ad hoc network.