In order for a wireless network to function, signals must have a path from sender to receiver, arriving with the signal strength is still sufficient to be translated. Signal strength can be measured by two units:
• dBm (decibels above 1 mW) in units of Watts or Volt
• S / N Ratio (Singnal-to-Noise) shows the ratio between the power signal and noise power. For digital signal, S / N Ratio is less than at S / N for analog signals.
Another thing to note for the propagation of radio signals is attenuation (attenuation) signals. The weakening can be affected by distance. The picture signal attenuation can be shown with light from two different sources.
Ommidirectional
Directional
The formula for converting Watts to dBm or vice versa:
The cause of signal attenuation is rain. A signal that has higher frequencies will have a density (wavelength) more shorter. Electromagnetic waves can pass through some objects, but also could be reflected by an object. This reflection is often called baunching or scattering. Baunching can decrease the performance of a system and can also enhance other performance. As an example of a radio broadcast signal PM could be reflected by a layer of Earth's atmosphere.
Some applications that use low frequencies to using the atmosphere as a reflector to increase the distance scope. But for high frequencies can not be reflected in layers of the atmosphere, because of the high frequency will be absorbed by the atmosphere. So for high frequencies required an artificial reflector, which called satellites. Not all obtained from bounching good result, one of them called multipath scattering in mobile communications.
Multipath Scattering is a signal that reaches the recipient of several path is the result of bounching. If the signal is received outside of the phase, then the signal is canceled. If the signal received in phase but not synchronized, will be received echo signal. Examples of applying this is CDMA (Code Division Multiple Accessing)
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