WiMAX-3

OFDM exploits the frequency diversity of the multipath channel by coding and

interleaving the information across the sub-carriers prior to transmissions. OFDM

modulation can be realized with efficient Inverse Fast Fourier Transform (IFFT), which

enables a large number of sub-carriers (up to 2048) with low complexity. In an OFDM

system, resources are available in the time domain by means of OFDM symbols and in

the frequency domain by means of sub-carriers. The time and frequency resources can be

organized into sub-channels for allocation to individual users. Orthogonal Frequency

Division Multiple Access (OFDMA) is a multiple-access/multiplexing scheme that

provides multiplexing operation of data streams from multiple users onto the downlink

sub-channels and uplink multiple access by means of uplink sub-channels.