Characteristics of Wireless Channels
- The wireless channel is different and much more unpredictable than the wireline channel because of factors such as multipath and shadow fading, Doppler shift, and time dispersion or delay spread.
- These factors are all related to variability introduced by mobility of the user and the wide range of environmental conditions that are encountered as a result.
- Multipath delays occur as a transmitted signal is reflected by objects in the environment between a transmitter and a receiver.
- These objects can be buildings, trees, hills, or even trucks and cars.
- The reflected signals arrive at the receiver with a random phase offset, since each reflected signal generally follows a different path to reach the user’s receiver, resulting in a random signal that fades as the reflections destructively or constructively superimpose on one another.
- This effectively cancels or adds part of signal energy for brief periods of time. The degree of fading will depend on the delay spread of the reflected signals as embodied by their relative phases, and their relative power.
#Ref book: Wireless Communication and Networking – V.K. Garg