ML integer frequency offset estimation for OFDM systems with null subcarriers:Estimation range and pilot design

In this paper the estimation range(ERG) of any null subcarriers(NSC) placement is further investigated and sufficient and necessary conditions of an NSC allocation that achieves a full ERG are defined.Then,a perfect distributed NSC allocation with the NSC distance larger than coherent bandwidth is devised to fully exploit frequency diversity of wireless channels and achieve a full ERG.Simulations confirmed that the propsoed FFT-based ML method of using this NSC placement has a smaller bandwidth overhead,achieves a fuller ERG and provides a better performance than the existing methods of using the consecutive NSC allocation at middle and high signal-to-noise ratios(SNRs).