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This SpringerBrief investigates the performance of semi-blind independent component analysis (ICA) based equalization and carrier frequency offset estimation approaches (CFO) for a number of orthogonal frequency division multiplexing (OFDM) based wireless communication systems. It provides a comprehensive overview of the challenges of channel equalization and frequency synchronization for different wireless systems.

The authors present the wireless communication channel and system models. Key existing CFO estimation methods are reviewed, along with a number of the training based and non-training based (blind) channel estimation methods. This is followed by a study of ICA and its applications to OFDM-based wireless communication systems. Later chapters provide a detailed description of recent research on semi-blind CFO estimation and ICA based equalization approaches for various wireless communication systems including multiple-input multiple-output (MIMO) OFDM and coordinated multipoint (CoMP) systems.

Semi-blind CFO estimation and equalization structures provide a spectrum-efficient and high-performance solution for high speed wireless communications. This book is suitable for postgraduate students, researchers or professionals in the area of wireless communications.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract
In this chapter, a number of wireless communications structures are introduced briefly. Then, the Orthogonal Frequency Division Multiplexing (OFDM) technology is presented. For OFDM systems, a number of challenging issues are addressed. To solve these problems, an efficient Higher Order Statistics (HOS) based Blind Source Separation (BSS) technique, Independent Component Analysis (ICA), is discussed.
Yufei Jiang, Xu Zhu, Eng Gee Lim, Yi Huang, Hai Lin

Chapter 2. OFDM Based Wireless Communications Systems

Abstract
In order to combat frequency-selective fading, the OFDM technology has been developed and widely used in wireless communications. The principle of OFDM is provided in this chapter. Carrier Frequency Offset (CFO), one of challenges in OFDM systems is discussed. The Orthogonal Frequency Division Multiple Access (OFDMA) technique, which is closely related to OFDM, is presented. Finally, a number of OFDM based wireless communication systems are discussed in detail, including Multiple-Input Multiple-Output (MIMO), Coordinated Multi-Point (CoMP) and Carrier Aggregation (CA).
Yufei Jiang, Xu Zhu, Eng Gee Lim, Yi Huang, Hai Lin

Chapter 3. CFO Estimation and Channel Equalization for OFDM Based Wireless Systems

Abstract
In this chapter, a number of state-of-the-art CFO estimation methods and channel equalization approaches are reviewed. The relevant existing work can be divided into two categories: training based methods and semi-blind/blind methods. A number of training based CFO estimation methods, including Moose’s CFO estimation, Maximum Likelihood (ML) CFO estimation and Constant Amplitude Zero Auto-Correlation (CAZAC) sequences based CFO estimation are reviewed. The blind/semi-blind CFO estimation methods presented include diagonality criterion based blind CFO estimation, CP based CFO estimation and semi-blind CFO estimation by precoding or pilots. We also review training equalization including ZF, MMSE, Vertical Bell Laboratories Layered Space-Time (V-BLAST) and Maximum Likelihood (ML) methods. SOS and HOS based blind/semi-blind equalization methods are also reviewed, with a focus on ICA, an HOS based method, and its applications in wireless communications.
Yufei Jiang, Xu Zhu, Eng Gee Lim, Yi Huang, Hai Lin

Chapter 4. Semi-Blind CFO Estimation and Equalization for Single-User MIMO OFDM Systems

Abstract
In this chapter, we present a semi-blind MIMO OFDM system including a precoding aided CFO estimation approach and an ICA based equalization structure. A number of reference data sequences are carefully designed offline and superimposed to source data via a non-redundant linear precoding process, which can serve two purposes without introducing any additional total transmit power and spectral overhead. First, the reference data sequences are selected from a pool of carefully designed orthogonal sequences, which help CFO estimation. Second, the same reference data enable elimination of the permutation and quadrant ambiguity in the ICA equalized signals. Simulation results show that the presented semi-blind system achieves a bit error rate (BER) performance close to the ideal case with perfect CSI and no CFO. Also, the precoding aided CFO estimation outperforms the CAZAC sequences based CFO estimation approach.
Yufei Jiang, Xu Zhu, Eng Gee Lim, Yi Huang, Hai Lin

Chapter 5. Semi-Blind Multi-CFO Estimation and Equalization for Multiuser CoMP OFDM Systems

Abstract
In the previous chapter, a single-CFO estimation method is presented. In this chapter, we present a low-complexity semi-blind structure with multi-CFO estimation and ICA based equalization structure for multiuser CoMP OFDM systems. A short pilot is carefully designed for each user and has a two-fold advantage. On the one hand, using the pilot structure, a complex multi-dimensional search for multiple CFOs is divided into a number of low-complexity mono-dimensional searches. On the other hand, the cross-correlations between the transmitted and the received pilots are explored to allow simultaneous elimination of permutation ambiguity and quadrant ambiguity in the ICA equalized signals. Simulation results show that, with a low training overhead of 1.6 %, the presented semi-blind system not only outperforms the existing multi-CFO estimation schemes in terms of BER and MSE of multi-CFO estimation, but also achieves a BER performance close to the ideal case with perfect CSI and no CFO at the receiver.
Yufei Jiang, Xu Zhu, Eng Gee Lim, Yi Huang, Hai Lin

Chapter 6. Semi-Blind Joint ICI Mitigation and Equalization for CA Based CoMP OFDMA Systems

Abstract
In this chapter, we present a joint ICA based equalization and CFO estimation scheme for OFDMA systems, which requires only a single pilot, resulting in a very low spectral overhead. On the one hand, a low-complexity ambiguity elimination method is proposed for the ICA equalized signals. By designing and exploring a fixed order of correlation in the transmitted signals, the permutation ambiguity problem is resolved, while the remaining quadrant ambiguity is eliminated by one pilot symbol. One the other hand, linear CFO estimation is performed with a closed-form solution based on the phase difference between adjacent rows in the CFO corrupted channel structure. Simulation results show that the presented semi-blind ICA based scheme not only outperforms existing CFO estimation approaches, but also achieves a BER performance comparable to the ideal case with perfect CSI and no CFO.
Yufei Jiang, Xu Zhu, Eng Gee Lim, Yi Huang, Hai Lin

Chapter 7. Conclusions

Abstract
In the previous chapters, a number of OFDM based wireless communications systems are presented and a number of state-of-the-art CFO estimation methods and channel equalization approaches are reviewed. Also, our work on the application of ICA to wireless communications systems with CFOs has is presented. In this chapter, we summarize the important conclusions and findings, and suggest on possible future research.
Yufei Jiang, Xu Zhu, Eng Gee Lim, Yi Huang, Hai Lin
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