Blind estimation of carrier frequency offset, I/Q imbalance and DC offset for OFDM systems
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RESEARCH
Open Access
Blind estimation of carrier frequency offset, I/Q imbalance and DC offset for OFDM systems Tao Liu1* and Hanzhang Li2
Abstract Sensitivity to carrier frequency offset (CFO) is one of the biggest drawbacks of orthogonal frequency division multiplexing (OFDM) system. A lot of CFO estimation algorithms had been studied for compensation of CFO in OFDM system. However, with the adoption of direct-conversion architecture (DCA), which introduces additional impairments such as dc offset (DCO) and in-phase/quadrature (I/Q) imbalance in OFDM system, the established CFO estimation algorithms suffer from performance degradation. In our previous study, we developed a blind CFO, I/Q imbalance and DCO estimation algorithm for OFDM systems with DCA. In this article, we propose an alternative algorithm with reduced computation complexity and better accuracy. Performance of the proposed algorithm is demonstrated by simulations. 1 Introduction As one of the most popular technologies for wireless communications, orthogonal frequency division multiplexing (OFDM) [1], on the one hand, has attractive advantages such as high spectrum efficiency, robustness to multi-path fading and efficient implementation based on fast Fourier transform, which make it suitable for wide-band wireless communications. However, on the other hand, OFDM suffers from performance degradation caused by carrier frequency offset (CFO) which damages the orthogonality among sub-carriers and introduces inter-carrier interference [2]. Since compensation of CFO is straightforward as long as estimate of CFO can be obtained, a lot of efforts have been taken on algorithms for CFO estimation in OFDM systems [3-10]. The established algorithms can be divided into two categories, data-aided and blind (or non-dataaided). The data-aided algorithms, e.g., [3], can achieve better performance than the blind ones [4-10] at costs of data rate reduction due to transmission of pilots or training sequences. What we are concerned with in this article are blind estimation algorithms that on the contrary do not depend on pilots or training sequences and therefore retain data rate of system. Among the blind algorithms, the MUSIC-like algorithm [5] was widely * Correspondence: [email protected] 1 School of Automation & Electrical Engineering, University of Science and Technology Beijing, Beijing, 100083, China Full list of author information is available at the end of the article
adopted in literatures [6,11-13] as baseline due to the facts that first it was proved to be the maximum likelihood (ML) algorithm for CFO estimation in OFDM system under fading channel [7]; second it can be applied for both constant modulus modulation, e.g., phase shift keying (PSK), and inconstant modulus modulation, e.g., quadrature amplitude modulation (QAM), on sub-carriers; third it is available for estimation of both integer CFO and fractional CFO; and finally it achieves reasonable compromise among performance and complexity within single OFDM symbol duration. With the evolution of wi
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