The Communications Channel

 
The Communications Channel
All information systems employ a communications channel along which information flows
from source to destination. Ethernet networks may use twisted-pair or coaxial cable. Wireless
networks use air as the medium. At the earth’s surface, where most wireless networks operate,  pure air contains gases such as nitrogen and oxygen. This atmosphere provides an effective
medium for the propagation of radio waves and infrared light.
Rain, fog, and snow increase the amount of water in the air and can cause significant attenuation
to the propagation of modulated wireless signals. Smog clutters the air, adding attenuation
to the communications channel as well. In addition, leaves on trees will block transmissions in
the spring and summer. Attenuation is a decrease in the amplitude of the signal, and it limits
the operating range of the system. The ways to combat attenuation is to either increase the
transmission power of the wireless devices, which in most cases is limited by the FCC, or
incorporate special amplifiers called repeaters that receive attenuated signals, revamp them,
and transmit downline to the end station or next repeater