Carrier frequency offset estimation for OFDMA uplink using null sub-carriers

Carrier synchronization in OFDMA uplink systems comprises estimation and compensation of carrier frequency offsets (CFOs) corresponding to different users. We propose a null sub-carrier-based CFO estimation algorithm for OFDMA uplink systems, employing generalized or sub-band sub-carrier allocation scheme. We analyze the effect of location and number of null sub-carriers on the performance of the algorithm, in the presence of multi-user interference (MUI) and channel frequency selectivity. We calculate the acquisition range of the proposed estimation algorithm and prove that the identifiability of CFO estimation is guaranteed in the presence of MUI and channel nulls. We also evaluate the computational complexity and the performance of the proposed estimation algorithm and, compare it with some of the existing approaches in the literature.