tem as long as all these multi-paths are within the cyclic prefix window. OFDMA systems therefore more robust towards multipath effects than other multiple access schemes. In CDMA systems, RAKE receivers only have a fixed number of receive fingers and one finger corresponds to one multipath component. After detecting the multipath components the Rake receiver coherently combines them. RAKE receivers operate based on the assumption that the average interference in a large window is small. The assumption can lead to incorrect conclusions due to the presence of other impairments such as frequency offset, Doppler effect4 and lack of time synchronization. The CDMA interference can be mitigated by equalizer, however complexity increases rapidly with system bandwidth. Therefore, in broadband wireless systems where multipath effect is very common, OFDMA systems are considered to be more robust and less complex than CDMA systems. 2.7.1.3 Downlink Multiplexing OFDMA, due to its orthogonal nature, does not require very robust power control and can utilize maximum available power in downlink transmission. When channel is frequency selective, OFDMA allows users to be scheduled to their best subchannels respectively within the same OFDMA symbol while the TDMA system does not have such flexibility. 2.7.1.4 Uplink Multiple Access OFDMA uplink access is performed through orthogonal sub-channels. By eliminating intra-cell inter- ference, an OFDMA system can achieve higher reverse-link capacity than a traditional CDMA system. OFDMA uplink can also take advantage of frequency selectivity the same way as downlink does by allocating best sub-channels to the respective access users to further improve the overall system perfor- mance. 2.7.1.5 Smart Antenna Benefits Smart Antenna techniques MIMO (Multiple Input Multiple Output), Receive Diversity and Transmit Diversity can be applied to both CDMA and OFDMA systems. These techniques provide higher capacities as well as better coverage. For CDMA systems, the function of RAKE receiver makes