Multi-carrier communications

In a multi-path channel, data transmission suffers from frequency-selective fading. At high symbol rates, this results in severe inter-symbol interference. An approach to overcome this problem is to divide the available bandwidth into many independent narrow sub-bands and to assign each sub-band to a so-called subchannel [9]. As a result the symbols are not transmitted serially over a single channel, but in parallel over the subchannels. This lowers the symbol rate per subchannel, effectively reducing the inter-symbol interference while maintaining the overall symbol rate. Additional measures, such as the use of a cyclic prefix, effectively annul the remaining inter-symbol interference.