Analysis and Suppression of MAI in WiMAX Uplink Communication System with Multiple CFOs

Nowadays, OFDMA (Orthogonal Frequency Division Multiple Access) technique has been used in WiMAX communication system to achieve very high data rate as well as multi-user service. However, similar with other OFDM-based systems, OFDMA system is very sensitive to frequency synchronization errors, especially in the uplink communications where different users always have different CFOs (Carrier Frequency Offset). When multiple CFOs exist, the orthogonality which separates different subcarriers will be lost, and ICI (Inter Carrier Interference) as well as MAI (Multi-Access Interference) will be generated to disturb the received signals. Then, the system performance will be highly degraded. To overcome this problem, it is of great importance to do research on the suppression to the interferences caused by multiple CFOs. In this paper, we first analyze the interferences, including ICI and MAI, caused by multiple CFOs in the uplink communications of OFDMA system. Next, the suppression method based on block type pilots is proposed to overcome the interferences simultaneously. Compared with other interference suppression methods, the proposed method could directly get the interference components from inverse matrix, thus it doesn’t need to do the CFO estimation. From the simulation results, it can be seen that the multiple CFOs will make serious degradation to the system performance. But through the proposed suppression algorithm, the system performance can be significantly improved.