Sparse Repeated Preamble-Based Direct Current Offset and Frequency Offset Estimator in OFDM Direct Conversion Receivers

Direct conversion receiver (DCR) architecture has drawn considerable attention in orthogonal frequency-division multiplexing (OFDM) systems. However, OFDM DCRs are sensitive to non-ideal front-end effects and suffer from direct current offset (DCO) and carrier frequency offset (CFO). In this paper, a novel method to estimate DCO and CFO is presented in OFDM DCRs by exploring the sparse symbols embedded in the preamble. In the proposed method, CFO and DCO estimations can be easily decoupled. Next, a robust low-complexity DCO estimation method is proposed by using the sparse properties of the preamble in the frequency domain. Moreover, a novel CFO estimation scheme independent of the DCO is presented based on the repeated preamble structure in which the DCO component focuses on the DC subcarrier when the received preamble signal was not CFO compensated in the frequency domain. The simulation results show that the proposed CFO and DCO estimators can achieve better performance than any available methods.