What are the main multiplexing techniques in communication systems?

Multiplexing combines multiple signals for transmission over a single channel. FDM (Frequency Division Multiplexing) assigns different frequency bands to each signal, used in radio/TV broadcasting. TDM (Time Division Multiplexing) assigns different time slots to each signal, used in digital telephony. WDM (Wavelength Division Multiplexing) uses different light wavelengths in fiber optics. CDM (Code Division Multiplexing) assigns different codes to signals, enabling simultaneous transmission at same time and frequency (CDMA).