A Low-Complexity Blind Carrier Frequency Offset Estimator for MIMO-OFDM Systems

Carrier frequency offset (CFO) is an important problem in multi-input multi-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems. This letter proposes a blind CFO estimator for MIMO-OFDM systems with constant modulus constellations in the frequency-selective fading channels. A closed-form CFO estimate is also provided, which greatly reduces the computational complexity of the proposed method. Analysis and simulation results demonstrate that the proposed estimator is very effective for MIMO-OFDM systems.

I. Introduction

Multi-Input multi-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems have received much attention for the high capacity and the robustness against fading. However, as the generalization of orthogonal frequency-division multiplexing (OFDM), MIMO-OFDM systems are also very sensitive to carrier frequency offset (CFO), which can cause significant performance degradation [1]. To solve this problem, many CFO estimators have been proposed, which can be classified as the data-aided ones [2]–[4] and the blind ones [5], [6]. Blind methods become more attractive due to the high bandwidth efficiency. Zeng and Ghrayeb have developed a blind CFO estimator in [5], called the ZG estimator in this letter, which is based on minimizing the difference between the signal power of two neighboring subcarriers. However, since the channel gains on adjacent subcarriers are approximately the same, the performance of the ZG estimator is degraded. Another blind method, called the Kurtosis method [6], utilizes the non-Gaussian property of the received signal to estimate CFO, but it suffers from performance degradation in frequency-selective fading channels.