10.1. How We Got Here
Before we talk about where wireless is and where it is going, let's look at where it came from. Radio waves happen when electrons run down a wire, and the movement of current produces magnetic fields and electrostatic fields that ebb and flow with the current. Using that phenomenon to convey information is a matter of controlling the current changes and characteristics of this ebb and flow, a process called modulation. The names of two types of modulation can be seen on any radio dial: amplitude modulation (AM) increases and decreases the strength of the current to convey information. Frequency modulation (FM) changes the current's frequency of oscillation. Additional ways to change or modulate the currents abound. Pulse modulation (PM) emits sharp bursts of current, carrying information in the timing of bursts. PM was the basis of early digital transmission systems, but today's modulation methods are much more sophisticated. Without getting too lost in details, the modulation systems used in wireless today use combinations of these three to efficiently transmit digital information. Because these systems spread their information over wide sections of the radio spectrum, they are called spread spectrum systems. Because they vary their operating frequency rapidly, they are also called frequency hop systems. To understand too much more about them would require some serious arm waving discussion at a white board, or better yet, some military experience with the systems where these techniques were first used. For the purposes of this book, it is enough to know that the modulation systems used in wireless today can pack an amazing amount of information into a low-power signal. The result has been a proliferation of IEEE 802.11-type radio systems. Nearly any laptop purchased today has wireless connectivity built in. This is great, because it allows a computer to join the local area network without first having to string a wire to it. It has a number of security issues, however, which will be discussed in this chapter.