Orthogonal Frequency-Division Multiplexing (OFDM) is a multi-carrier modulation scheme, which uses a large number of closely-spaced orthogonal sub-carriers.  Each sub-carrier is modulated with a conventional modulation scheme (such as phase-shift keying (PSK) and quadrature amplitude modulation (QAM)) at a low symbol rate, maintaining data rates similar to conventional single-carrier modulation schemes in the same bandwidth.  OFDM has become popular for its ability to efficiently detect symbols under frequency selective channels at a low cost through a simple one tap equalization per sub-carrier in frequency domain.  Under severe frequency selective channel, however, bit error rate performance may deteriorate. 
Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.