Multi-carrier modulation (MCM) is a method of transmitting data by splitting it into several components, and sending each of these components over separate carrier signals. The individual carriers have narrow bandwidth , but the composite signal can have broad bandwidth.
orthogonal frequency-division multiplexing (OFDM)
Orthogonal frequency-division multiplexing (OFD...(SearchNetworking.com)
The advantages of MCM include relative immunity to fading caused by transmission over more than one path at a time (multipath fading), less susceptibility than single-carrier systems to interference caused by impulse noise, and enhanced immunity to inter-symbol interference. Limitations include difficulty in synchronizing the carriers under marginal conditions, and a relatively strict requirement that amplification be linear.
MCM was first used in analog military communications in the 1950s. Recently, MCM has attracted attention as a means of enhancing the bandwidth of digital communications over media with physical limitations. The scheme is used in some audio broadcast services. The technology lends itself to digital television , and is used as a method of obtaining high data speeds in asymmetric digital subscriber line ( ADSL ) systems. MCM is also used in wireless local area networks ( WLAN s).