-Carry multiple signals on a single medium due to exceeding capacity of medium.
-There are different kinds of multiplexing: FDM,TDM,CDM.
Frequency Division Multiplexing: There are more bandwidth than required bandwidth.
-Carrier Frequency: Each signal requires a certain bandwidth centered on its carrier frequency.
-Guard Bands: Frequency separation to prevent interference.
Time Division Multiplexing: There are more available bit rate in the medium.
-Interleaving portion of each signal in time.
Code Division Multiplexing:It uses spread-spectrum technology and pseudo random code for multiple accessing.
-Pseudo Random Code: It is a spreading code that is unique for each user. It is XOR ed with the transmission signal and receiver of this user can only understand this XOR ed signal.
-Spread Spectrum: Using wider range of bandwidth
Wireless Communication & Networks by William Stallings