Fuzzy Based Adaptive Weighted Multiuser Interference Cancellation in Ofdma Systems

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 WirelessMAN Air Interface standard, commonly referred to as WiMAX. Multiple access is achieved in OFDMA by assigning subsets of subcarriers to individual users [1], [2]. The performance of these systems depend on the orthogonality between the transmitted subcarriers alloted 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. However, the orthogonality between codes is often disturbed by the carrier frequency offset due to the Doppler effect in fading channels, time delay due to multipath components and poor synchronization at the receiver.