SPC07-5: On the SNR-Optimal Null Subcarrier Placement for Blind Carrier Offset Estimation in OFDM Systems

A blind carrier frequency offset (CFO) estimation algorithm using the null subcarriers for orthogonal frequency diversity multiplexing (OFDM) systems was proposed in [1]. The optimal null subcarrier placement that minimizes the Cramer Rao bound (CRB) was studied in [3]. In this paper, we study the optimal null subcarrier placement from an SNR maximization point of view. We first derive the relationship between the SNR of the CFO estimation and the placement of null subcarriers. Based on that, we formulate the optimization problem and find the optimal solution using convex optimization for small CFO values. We also discuss the optimality of the null subcarrier placement in practical OFDM systems where guard bands are required at both ends of the spectrum.