Subcarrier Multiplexing (SCM) is a method for
multiplexingmany different fiber optics based communication link into a single uplink fiber. The SCM (also known as SCMA, SubCarrier Multiple Access) is used in passive optical network (PON) access infrastructures as a variant for the Wavelength Division Multiplexing (WDM)
SCM follows a different approach compared to WDM. In WDM a terahertz optical carrier is modulated with a baseband signal of typically hundred of Mbit/s. In an SCMA infrastructure, the baseband data is first modulated on a GHz wide subcarrier, that is subsequently modulated in the THz optical carrier. This way each signal occupies a different portion of the optical spectrum surrounding the centre frequency of the optical carrier. At the receiving side, as normally happens in a commercial radio service, the receiver is tuned to the correct subcarrier frequency, filtering out the other subcarriers.
The operation of multiplexing and demultiplexing the single subcarriers is carried out electronically. The conversion into the optical carrier is done at the multiplexer side. This gives an advantage over a pure WDM access, due to the lower cost of the electrical components if compared with an optical multiplexer.
SCM has the disadvantage of being limited in maximum subcarrier frequencies and data rates by the available bandwidth of the electrical and optical components. Therefore, SCM must be used in conjunction with WDM in order to take advantage of most of the available fiber bandwidth, but it can be used effectively for lower-speed, lower-cost multiuser systems.
* [http://www2.rad.com/networks/1999/wdm/wdm.htm WDM - Wavelength Division Multiplexing]
* [http://www.ittc.ku.edu/publications/documents/Hui2002_Hui2002JoLTpp417.pdf Subcarrier Multiplexing for High-Speed Optical Transmission]
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