Wireless = Radio!
Wireless LANs transmit signals across the air rather than across copper wires or fiber optic cable. For those of you who can remember back far enough before cable television, you may recall seeing antennas sticking up from the back of the set (remember rabbit ears?). Television stations transmitted one-way signals that reached the television set, were decoded, and turned back into light and sound to entertain the masses. In the “good old days” you turned a knob on the front of the set to change the channel (frequency) that was being displayed on the screen, and only a couple were usually available, NBC, ABC, and CBS, and maybe PBS. Understanding the basics of wireless LAN technologies actually start at this point, in getting a better grasp of how radio signals actually act and operate.
Radio signals travel through the air and require both a transmitter and receiver, which are actually separate operations, although at one time the term transceiver identified something that did both. Just as with human speech (using sound waves), wireless technologies are analog rather than digital. Digital signals have one of two values, namely Zero (0) or One (1), indicating on or off status of a computer circuit. Electromagnetic radiation, including radio frequency (RF), transmit information by changing some aspect of these waves, usually termed frequency (the measure of how many waves are repeated per interval), amplitude (strength of the signal), or phase (difference between the wave and some reference point). All wireless technologies use some form of encoding/modulation to change the signal to communicate the zeroes or ones in order to carry the digital information. For the sake of simplicity, let’s think of frequencies the way you typically use them: channels on your television or radio. When you want to receive a different stream of data (for example, ESPN instead of the Opera Channel), you use the remote control to change the frequency from one channel to another. In the United States, the Federal Communications Commission (FCC) sets the rules for who can use certain frequencies, as well as power levels so that they can coexist. Some organizations pay the “big bucks” for use of certain frequencies of operation, such as television and radio stations, and cellular telephone companies. These are referred to as licensed frequencies because they require a valid agreement in place with the FCC in order to use them. For our purposes, we need not worry about these RF signal families, but rather those that are part of the unlicensed frequencies group. Since this is a much deeper topic, we will discuss this next time.
– Joe
Joe Rinehart's Blog 