Basic Principles Of FDM, TDM, WDM, CDMA

The basic principle of frequency division multiplexing is to set up multiple channels on a communication line, the signals of each channel are modulated with different carrier frequencies, and the carrier frequencies of each channel do not overlap with each other, so that a communication line can simultaneously transmit multiplexed signals.

Time division multiplexing takes the channel transmission time as the division object, and is realized by the method of assigning non-overlapping time slices to multiple channels. Therefore, time division multiplexing is more suitable for the transmission of digital signals. It is further divided into synchronous time division multiplexing and statistical time division multiplexing.

Wavelength division multiplexing is the frequency division multiplexing of light, which uses diffraction gratings in the optical system to realize the synthesis and decomposition of multiple light wave signals of different frequencies.

Code division multiplexing is also a method of sharing channels. Each user can use the same frequency band for communication at the same time, but the method of dividing the channel based on the code pattern is used, that is, each user is assigned an address code. Each code type does not overlap and overlap with each other, and the communication parties will not interfere with each other, and the anti-interference ability is strong. Code division multiplexing technology is mainly used in wireless communication systems, especially mobile communication systems. It can not only improve communication Voice quality and data transmission reliability, reduce the impact of interference on communication, and increase the capacity of the communication system. Notebook computers or personal digital assistants (Personal Data Assistant, PDA) and handheld computers (Handed Personal COmputer, HPC), etc. The networking communication of mobile computers uses this technology.