Code Division Not Frequency Division
We are all familiar with one signal channel per frequency.
How the heck do you put multiple signal channels into one wide frequency?
Orthogonal signals such as Walsh (Hadamard) codes support doing this.
(Sines and Cosines are orthogonal analog signals.)
See the Wiki entry on IS-95, cdmaOne, or first generation cdma, especially the forward (cell tower to mobile) direction. The reverse direction (mobile to cell tower) still depends on orthogonal coding, but it uses very long codes and not Walsh codes.
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