Wireless channel has special characteristics that are challenging in communications enumerate as follows:
The capacity of wireless channel varies dynamically.
Many users are competing to get access to the wireless channel.
The uplink and the downlink are non-similar in capacity requirements.
Base station and
mobile impose restrictions on transmission power.
Shortage in channel state information in mobile user.
Due to the potential nature of wireless environment, communication in this medium faces difficulties. Wireless environments have various characteristics and different geographical.
Therefore this guides to different propagation mechanisms:
Reflection occurs when an electromagnetic wave hits an object that its dimension is very large compared to the wavelength of the electromagnetic wave. Some waves partially reflected and some partially transmitted. Such objects as the buildings, walls, and the table top. Also it is widespread appearance in offices because they have sophisticated construction. In
this action some of energy is absorbed