Orthogonal frequency-division multiplexing (OFDM) effectively mitigates intersymbol interference (ISI) caused by the delay spread of wireless channels. Therefore, it has been used in many wireless systems and adopted by various standards. In this paper, we present a comprehensive survey on OFDM for wireless communications. We address basic OFDM and related modulations, as well as techniques to improve the performance of OFDM for wireless communications, including channel estimation and signal detection, time- and frequency-offset estimation and correction, peak-to-average power ratio reduction, and multiple-input-multiple-output (MIMO) techniques. We also describe the applications of OFDM in current systems and standards.

OFDM and Its Wireless Applications: A Survey

This chapter contains sections titled: Introduction Overview of Multicarrier CDMA Systems Channel Model Performance of MC-CDMA System Performance of Overlapping Multicarrier DS-CDMA Systems Performance of Multicarrier DS-CDMA-I Systems Performance of AMC DS-CDMA Systems Performance of SFH/MC DS-CDMA Systems Chapter Summary and Conclusion 
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Overview of Multicarrier CDMA

Orthogonal frequency-division multiplexing (OFDM) access schemes are becoming more prevalent among cellular and wireless broadband systems, accelerating the need for smaller, more energy efficient receiver solutions. Up to now the majority of OFDM texts have dealt with signal processing aspects. To address the current gap in OFDM integrated circuit (IC) instruction, Chiueh and Tsai have produced this timely text on baseband design. OFDM Baseband Receiver Design for Wireless Communications covers the gamut of OFDM technology, from theories and algorithms to architectures and circuits. Chiueh and Tsai give a concise yet comprehensive look at digital communications fundamentals before explaining modulation and signal processing algorithms in OFDM receivers. Moreover, the authors give detailed treatment of hardware issues -- from design methodology to physical IC implementation. Closes the gap between OFDM theory and implementation Enables the reader to transfer communication receiver concepts into hardware design wireless receivers with acceptable implementation loss achieve low-power designs Contains numerous figures to illustrate techniques Features concrete design examples of MC-CDMA systems and cognitive radio applications Presents theoretical discussions that focus on concepts rather than mathematical derivation Provides a much-needed single source of material from numerous papers Based on course materials for a class in digital communication IC design, this book is ideal for advanced undergraduate or post-graduate students from either VLSI design or signal processing backgrounds. New and experienced engineers in industry working on algorithms or hardware for wireless communications devices will also find this book to be a key reference.

OFDM Baseband Receiver Design for Wireless Communications

A novel multiple-input multiple-output (MIMO) transmission scheme, called space-time block coded spatial modulation (STBC-SM), is proposed. It combines spatial modulation (SM) and space-time block coding (STBC) to take advantage of the benefits of both while avoiding their drawbacks. In the STBCSM scheme, the transmitted information symbols are expanded not only to the space and time domains but also to the spatial (antenna) domain which corresponds to the on/off status of the transmit antennas available at the space domain, and therefore both core STBC and antenna indices carry information. A general technique is presented for the design of the STBC-SM scheme for any number of transmits antennas. Besides the high spectral efficiency advantage provided by the antenna domain, the proposed scheme is also optimized by deriving its diversity and coding gains to exploit the diversity advantage of STBC. A low-complexity maximum likelihood (ML) decoder is given for the new scheme which profits from the orthogonality of the core STBC. The performance advantages of the STBC-SM over simple SM and over V-BLAST are shown by simulation results for various spectral efficiencies and are supported by the derivation of a closed form expression for the union bound on the bit error probability.

Space-Time Block Coded Spatial Modulation

Providing reliable broadband wireless communications in high mobility environments, such as high-speed railway systems, remains one of the main challenges faced by the development of the next generation wireless systems. This paper provides a systematic review of high mobility communications. We first summarize a list of key challenges and opportunities in high mobility communication systems, then provide comprehensive reviews of techniques that can address these challenges and utilize the unique opportunities. The review covers a wide spectrum of communication operations, including the accurate modeling of high mobility channels, the transceiver structures that can exploit the properties of high mobility environments, the signal processing techniques that can harvest the benefits (e.g., Doppler diversity) and mitigate the impairments (e.g., carrier frequency offset, intercarrier interference, channel estimation errors) in high mobility systems, and the mobility management and network architectures that are designed specifically for high mobility systems. The survey focuses primarily on physical layer operations, which are affected the most by the mobile environment, with some additional discussions on higher layer operations, such as handover management and control-plane/user-plane decoupling, which are essential to high mobility operations. Future research directions on high mobility communications are summarized at the end of this paper.

A Survey on High Mobility Wireless Communications: Challenges, Opportunities and Solutions

This paper presents a VLSI architecture of QR decomposition for 4×4 MIMO-OFDM systems. A real-value decomposed MIMO system model is handled and thus the channel matrix to be processed is extended to the size of 8×8. Instead of direct factorization, a QR decomposition scheme by cascading one complex-value and one real-value Givens rotation stages is proposed, which can save 44% hardware complexity. Besides, the requirement of skewed inputs in the conventional QR-decomposition systolic array is eliminated and 36% of delay elements are removed. The real-value Givens rotation stage is also constructed in a form of a stacked triangular systolic array to match with the throughput of the complex-value one. Hardware sharing is considered to enhance the utilization. The proposed design is implemented in 0.18-μm CMOS technology with 152K gates. From measurement, the maximum operating frequency is 100 MHz. It generates QR decomposition results every four clock cycles and accomplishes continuous projection every clock cycle to support MIMO detection up to 2.4 Gb/s. The measured power consumption is 318.6 mW and 219.6 mW for QR decomposition and projection, respectively, at the highest operating frequency. From the comparison, our proposed design achieves the highest throughput with high efficiency.

Efficient Implementation of QR Decomposition for Gigabit MIMO-OFDM Systems

Fast Fourier transform (FFT) processing is one of the key procedures in the popular orthogonal frequency division multiplexing (OFDM) communication systems. Structured pipeline architectures and low power consumption are the main concerns for its VLSI implementation. In the paper, the authors report a variable-length FFT processor design that is based on a radix-2/4/8 algorithm and a single-path delay feedback architecture. The processor can be used in various OFDM-based communication systems, such as digital audio broadcasting (DAB), digital video broadcasting-terrestrial (DVB-T), asymmetric digital subscriber loop (ADSL) and very-high-speed digital subscriber loop (VDSL). To reduce power consumption and chip area, special current-mode SRAMs are adopted to replace shift registers in the delay lines. In addition, techniques including complex multipliers containing three real multiplications, and reduced sine/cosine tables are adopted. The chip is fabricated using a 0.35 /spl mu/m CMOS process and it measures 3900 /spl mu/m /spl times/ 5500 /spl mu/m. According to the measured results, the 2048-point FFT operation can function correctly up to 45 MHz with a 3.3 V supply voltage and power consumption of 640 mW. In low-power operation, when the supply voltage is scaled down to 2.3 V, the processor consumes 176 mW when it runs at 17.8 MHz.

Low-power variable-length fast Fourier transform processor

The Second Edition of OFDM Baseband Receiver Design for Wirless Communications, this book expands on the earlier edition with enhanced coverage of MIMO techniques, additional baseband algorithms, and more IC design examples. The authors cover the full range of OFDM technology, from theories and algorithms to architectures and circuits.The book gives a concise yet comprehensive look at digital communication fundamentals before explaining signal processing algorithms in receivers. The authors give detailed treatment of hardware issues - from architecture to IC implementation.Links OFDM and MIMO theory with hardware implementationEnables the reader to transfer communication received concepts into hardware; design wireless receivers with acceptable implemntation loss; achieve low-power designsCovers the latest standards, such as DVB-T2, WiMax, LTE and LTE-AIncludes more baseband algorithms, like soft-decoding algorithms such as BCJR and SOVAExpanded treatment of channel models, detection algorithms and MIMO techniquesFeatures concrete design examples of WiMAX systems and cognitive radio apllications Companion website with lecture slides for instructorsBased on materials developed for a course in digital communication IC design, this book is ideal for graduate students and researchers in VLSI design, wireless communications, and communications signal processing. Practicing engineers working on algorithms or hardware for wireless communications devices will also find this to be a key reference.

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Baseband Receiver Design for Wireless MIMO-OFDM Communications

This work presents an algorithm for joint estimation of carrier-frequency offset and timing offset for orthogonal frequency-division multiplexing (OFDM) systems in the tracking mode. The proposed weighted least-squares algorithm derives its estimates based on phase differences in the received pilot subcarrier signals between two symbols. Moreover, the optimal weights in two different channel conditions are derived. Both analysis and simulation show that the weighted least-squares algorithm can effectively and accurately estimate the carrier-frequency offset as well as the timing offset of OFDM signals in multipath fading channels.

Pei-Yun Tsai

Papers

OFDM Baseband Receiver Design for Wireless Communications

Efficient Implementation of QR Decomposition for Gigabit MIMO-OFDM Systems

Low-power variable-length fast Fourier transform processor

Baseband Receiver Design for Wireless MIMO-OFDM Communications

Joint weighted least-squares estimation of carrier-frequency offset and timing offset for OFDM systems over multipath fading channels