Blind Fast CFO Estimation and Performance Analysis for OFDM

Estimation of carrier frequency offset (CFO) is a crucial task for orthogonal frequency-division multiplexing (OFDM) systems, and it should be performed with affordable computational complexity for practicality. This paper proposes two blind and fast CFO estimators for OFDM systems based on null subcarriers. Compared with the existing null subcarriers based estimators, the computational complexity is significantly reduced by avoiding an exhaustive grid searching or a high-order polynomial rooting procedure. The mean squared error (MSE) performance of the proposed CFO estimator is also studied in theory. In addition, the Cramér-Rao bound (CRB) of the CFO estimation for OFDM systems with null subcarriers is derived. Numerical results are provided by computer simulation to verify the validity of theoretical performance analysis and demonstrate the superiority of the proposed estimators.

I. Introduction

Orthogonal frequency-division multiplexing (OFDM) technology has been widely used in wireless communication systems, for instance, WiFi [1], WiMAX [2] and 3GPP Long Term Evolution (LTE) [3] systems. However, OFDM systems are sensitive to carrier frequency offset (CFO) that is caused by the frequency deviation of transceiver oscillators or Doppler shift. CFO destroys the orthogonality among subcarriers and results in inter-carrier interference (ICI), which seriously degrades the system performance [4]. Hence, the estimation and compensation of CFO is of crucial importance for OFDM systems.