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In this paper, we deal with the multiple carrier frequency offsets (CFOs) estimation issues for orthogonal frequency-division multiple access (OFDMA) based uplink system. In such system, the interleaved carrier assignment scheme (CAS) has gained much attention for it brings maximum frequency diversity though it undergoes severe CFO problem than other schemes. The multiple-CFO estimation problem in this scheme uses a similar signal structure as that of Direction of Arrival (DOA) estimation problem in array signal processing, so subspace based multiple signal classification (MUSIC) algorithm can be exploited to estimate multiple CFOs. Compared with the conventional MUSIC algorithm utilizing eigenvalue decomposition of complex-value covariance matrix, the proposed unitary MUSIC and unitary root-MUSIC CFO estimation algorithms have comparable performance but lower computational complexity because of real-value covariance matrix used, which is verified by computer simulation.