Low complexity LS and MMSE based CFO compensation techniques for the uplink of OFDMA systems

Orthogonal frequency division multiple access (OFDMA), where different subcarriers are allocated to different users, has been adopted for the uplink of several standards and has attracted a great deal of attention as a result. However, OFDMA is highly sensitive to carrier frequency offset (CFO) between the transmitter and receiver. In the uplink, different carrier frequency offsets due to different users can adversely affect subcarrier orthogonality. We propose a low complexity CFO compensation approach that addresses this problem while maintaining optimal performance. This approach is based on the least squares and minimum mean square error criteria applicable to interleaved and block interleaved carrier assignment schemes. The proposed algorithms use the special block circulant property of the interference matrix. In contrast to existing CFO compensation techniques, our algorithms do not rely on iterations or approximations. We present our approach in this paper and describe how a considerable reduction in computational complexity can be achieved by adopting it.