Smart Phone and Next Generation Mobile Computing

114 Smart Phone and Next-Generation Mobile Computing

3.2.3.3 Code-Division Multiplexing

Code-division multiplexing (CDM) makes better use of a frequency

band than FDM and TDM. Signals from different transmitters are

transmitted on the same frequency band at the same time but each

has a code to uniquely identify itself. The orthogonal codes mathe-

matically ensure that signals cannot interfere with each other at the

receiver. CDM effectively converts the problem of limited frequency

space into ample code space but adds the overhead of implementa-

tion complexity. The transmitter and receiver must be synchronized

such that individual signals can be correctly received and decoded.

Compared to FDM, CDM provides greater security against signal tap-

ping