Orthogonal Frequency-Division Multiple Access (OFDMA) is a multi-user version of the Orthogonal Frequency-Division Multiplexing (OFDM). OFDMA is used in the mobility mode of IEEE 802.16 Wireless MAN Air Interface standard, commonly referred to as WiMAX. Multiple access is achieved in OFDMA by assigning subsets of subcarriers to individual users,. The performance of these systems depends on the orthogonality between the transmitted subcarriers allocated to different users. The important advantages of OFDMA are that it enables orthogonality in the uplink by synchronizing users in time and frequency and multipath mitigation without using equalizers and training sequences.