An Efficient Maximum Likelihood CFO Estimation Technique for OFDMA Uplink Transmissions

We propose a null subcarrier based carrier frequency offset (CFO) estimation technique for the uplink orthogonal frequency division multiple access (OFDMA) communication system. Here each user may experience a different CFO relative to the base station. This results in a multiple parameter estimation problem. The estimation is done by minimizing a cost function that computes the energy in null subcarrier locations due to the impact of frequency offset. The computational complexity and training overhead of the proposed technique are much lower as compared to some of the existing schemes in the literature. The mean square error of the CFO estimator and bit error rate performance of the OFDMA receiver that employs the proposed estimation scheme are studied through computer simulations. Our algorithm is shown to achieve a comparable performance as that of a recently reported method but with a much lower computational complexity and bandwidth overhead.