As explained in Chapters 3 and 4, in the DFT-SC-FDMA and DCTSC-FDMA systems, each user employs a different set of orthogonal subcarriers as in the OFDMA system. For perfect time and frequency synchronization, the different orthogonal subcarrier sets for the different users make it possible to avoid the MAI [9,14]. However, similar to the OFDMA system, the DFT-SC-FDMA and the DCT-SCFDMA systems also suffer from frequency mismatches between the transmitter and the receiver. As a result, in these systems, the CFOs disrupt the orthogonality between subcarriers and give rise to ICI and MAI among users because of the loss of subcarriers orthogonality [18,67]. Moreover, carrier frequency synchronization for the uplink systems is more difficult, since the frequency recovery for a certain user may result in the misalignment of the other synchronized users [67]. Thus, research on the suppression of the interference caused by several different CFOs is of great importance.