We propose an estimation algorithm tojointly estimate frequency/timing synchronization parametersand channels for the uplink transmission of Orthogonalfrequency division multiple access (OFDMA) companiedwith a generalized carrier assignment scheme (generalized-OFDMA). First, the proposed algorithm employs a Zadoff-Chu (ZC) sequence which exhibits an ideal circular autocorrelationproperty. The different circular-shifting formsof this ZC sequence are allocated to different users as theirtraining sequences, respectively. Furthermore, the proposedalgorithm implements correlation operations on themixed training signal received by the base station so as tojointly estimate Carrier frequency offsets (CFOs), Timingerrors (TEs) and Channel impulse responses (CIRs) of allusers. Simulation results show that the proposed algorithmnot only achieves joint CFO/TE/CIR estimation, but alsoprovides better CFO, TE and CIR estimation performancethan some existing estimation algorithms for OFDMA uplink.