Sending Data over the Airwaves

To successfully manage your wireless network, you don't need to understand all the details of signal processing. When sending data over radio frequencies (RF), however, remember these details:

  • A lot of other traffic is out there, as well as natural phenomena such as atmospheric disturbances and electrical storms (you have to love a good lightning storm) that can cause interference with these signals. Either data sent on the same frequencies or blocked signals can interfere with your wireless communications.

  • You need to modify a standard signal to transmit data. There are many standard methods to perform this task.

  • RF bands are only so wide and can therefore only handle so many discrete sessions or channels at a time. The entire FM radio spectrum has been broken up into 100kHz channels used to assign frequencies to radio stations. This means that there are only so many possible FM channels available for use.

Managing a wireless network does require a basic understanding of signals and their characteristics.

Understanding signals in wireless communication

When referring to a signal in relation to wireless communications, it is an electromagnetic field with specific characteristics, being its oscillation frequency.

When working with computer data, copper wires are used to send electrical signals; fiber-optic cables can send optical signals. If you want to send wireless signals, you use light waves for line-of-sight technologies (such as IrDA) or RF for non-line-of-sight technologies (such as Bluetooth).

When you listen to a radio station in your local area, this radio station broadcasts its content over a radio-wave signal that operates at a base waveform or wave of a specific set of dimensions consisting of an amplitude, period, and phase. This wave can be modified through one of the modulation techniques to change its form, and thereby transmit information.

All signal waves have the same common characteristics. These are as follows:

  • Amplitude: The height of the wave

  • Period: The length of the wave to repeat one cycle

  • Phase: The offset of the wave from zero or how far a wave is through its cycle

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You can measure the amplitude of the wave in many ways: From either peak (peak-to-peak) or from the center of the wave to the peak (peak or semi-amplitude). The frequency of the wave is the number of times it repeats over a given timeframe.

There is a good chance you know more about frequencies than you give yourself credit for, because you likely tune your car stereo (or your stereo auto-tunes them for you) to your favorite frequencies on a daily basis to change channels. Those channels are just different spots on that frequency.

Modulating signals in wireless communication

You can now identify a waveform at a frequency. Modulation allows you to add data to that waveform by changing its basic form. The changes that you can make include the amplitude, the frequency, and the phase.

In all cases, what you do to the wave prior to transmitting it (modulating) can then be undone by the receiver (demodulating) if the receiver knows what type of modification you are performing. When dealing with computers, which are composed of circuits that are either open or closed, you deal with only two states.

As long as you can create two distinct states in the waveform, you can identify them as open or closed, on or off, or 0 or 1. Creating two distinct states then allows you to transmit binary data over RF. The following illustration shows two basic types of modification of the initial carrier wave, which could be used to show binary number patterns.

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The two signal modulation techniques that you have likely heard the most about are amplitude modulation (AM) and frequency modulation (FM). The base waveform to which data will be added is referred to as the carrier signal. In the case of broadcasting a radio show, the added information is voices or music, whereas in the case of computer data, it is a series of 1s and 0s that represent binary data.

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