Since data ultimately consists of bits, the transmitter needs a way of sending both 0s and 1s to transmit data from one location to another. An AC or DC signal by itself does not perform this task. However, if a signal is fluctuated or altered, even slightly, the data can be properly sent and received.
This modulated signal is now capable of distinguishing between 0s and 1s and is referred to as a carrier signal . Three components of a wave that can be fluctuated or modified to create a carrier signal are amplitude, frequency, and phase.
All radio-based communications use some form of modulation to transmit data. To encode the data in a signal sent by AM/FM radios, cellular telephones, and satellite television, some type of modulation is performed on the radio signal that is being transmitted.
The average person typically is not concerned with how the signal is modulated, only that the device functions as expected. However, to become a better wireless networker, it is useful to have a better understanding of what is actually happening when two stations communicate.
Amplitude and Wavelength
RF communication starts when radio waves are generated from an RF transmitter and sent to a receiver at another location. RF waves are similar to the waves that you see in an ocean or lake. Waves are made up of two main components: wavelength and amplitude (see Figure below).
Amplitude is the height, force, or power of the wave. If you were standing in the ocean as the waves came to shore, you would feel the force of a larger wave much more than you would a smaller wave.
Antennas do the same thing, but with radio waves. Smaller waves are not as noticeable as bigger waves. A bigger wave generates a much larger electrical signal in an antenna, making the signal received much more easily recognizable.
Wavelength is the distance between similar points on two back-to-back waves. When measuring a wave, the wavelength is typically measured from the peak of a wave to the peak of the next wave. Amplitude and wavelength are both properties of waves.
Frequency describes a behavior of waves. Waves travel away from the source that generates them. How fast the waves travel, or more specifically, how many waves are generated over a 1-second period of time, is known as frequency.
If you were to sit on a pier and count how often a wave hits it, you could tell someone how frequently the waves were coming to shore. Think of radio waves in the same way; however, they travel much faster than the waves in the ocean.
If you were to try to count the radio waves that are used in wireless networking, in the time it would take for one wave of water to hit the pier, several billion radio waves would have also hit the pier.
Phase is a relative term. It is the relationship between two waves with the same frequency. To determine phase, a wavelength is divided into 360 pieces referred to as degrees (see Figure below).
If you think of these degrees as starting times, then if one wave begins at the 0 degree point and another wave begins at the 90 degree point, these waves are considered to be 90 degrees out of phase.
In an ideal world, waves are created and transmitted from one station and received perfectly intact at another station. Unfortunately, RF communications do not occur in an ideal world. There are many sources of interference and many obstacles that will affect the wave in its travels to the receiving station.