Synchronization Techniques For Ofdm

FDMA, TDMA and CDMA are the well known multiplexing techniques used in wireless communication systems. While working with the wireless systems using these techniques various problems encountered are (1) multi-path fading (2) time dispersion which lead to intersymbol interference (ISI) (3) lower bit rate capacity (4) requirement of larger transmit power for high bit rate and (5) less spectral efficiency. In a typical terrestrial broadcasting, the transmitted signal arrives at the receiver using various paths of different lengths. Since multiple versions of the signal interfere with each other, it becomes difficult to extract the original information. The use of orthogonal frequency division multiplexing (OFDM) technique provides better solution for the above mentioned problems. OFDM technique distributes the data over a large number of carriers that are spaced apart at precise frequencies. This spacing provides the "orthogonality", which prevents the demodulator from seeing frequencies other than their own. The benefits of OFDM are high spectral efficiency, resiliency of RF interference, and lower multi-path distortion. OFDM is a powerful modulation technique that is capable of high data rate and is able to eliminate ISI. The use of FFT technique to implement modulation and demodulation functions makes it computationally more efficient. The OFDM based wireless communication system design includes the design of OFDM transmitter, and OFDM receiver. Using MATLAB, simulation of OFDM was done with different modulation techniques using different transform techniques. The digital modulation schemes such as BPSK and QPSK were From the simulation results, it is observed that the BPSK allows the BER to be improved in a noisy channel at the cost of maximum data transmission capacity. Use of QPSK allows higher transmission capacity, but at the cost of slight increase in the probability of error. From the results, use of OFDM with QPSK is beneficial for short distance transmissio.

Wireless networking technologies are witnessed to become the integral part of industry, business, entertainment and daily life. Encyclopedia of Wireless Networks is expected to provide comprehensive references to key concepts of wireless networks, including research results of historical significance, areas of current interests, and growing directions in the future wireless networks. It can serve as a valuable and authoritative literature for students, researchers, engineers, and practitioners who need a quick reference to the subjects of wireless network technology and its relevant applications. Areas covered: 5G Network | Editors: Rahim Tafazolli, Rose Hu Ad hoc Network | Editor: Cheng Li Big Data for Networking | Editor: Song Guo Cellular Network, 2G/3G Network, 4G/LTE Network | Editor: Hsiao-hwa Chen Cognitive Radio Network | Editor: Ning Zhang Cooperative Communications | Editor: Kaoru Ota Cyber Physical Systems | Editor: Shiyan Hu Data Center Network | Editor: Lei Lei Delay Tolerant and Opportunistic Network | Editor: Yuanguo Bi Equalization, Synchronization and Channel Estimation | Editor: Yingying Chen Future Network Architecture | Editor: Wei Quan Game Theory in Wireless Network | Editor: Dusit Niyato Interference Characterization and Mitigation | Editor: Lin Cai Internet of Things | Editors: Xiuzhen Cheng, Wei Cheng Internet of Things and its Applications | Editor: Phone Lin Interworking Heterogeneous Wireless Network | Editor: Ping Wang Medium Access Control | Editors: Hassan Omar, Qiang Ye Millimeter-wave Communications | Editor: Ming Xiao MIMO-based Network | Editor: Prof. Wei Zhang Mobility Management and Models | Editors: Sandra Cespedes, Sangheon Pack Molecular, Biological and Multi-scale Communications | Editor: Adam Noel Network Economics and pricing | Editors: Jianwei Huang, Yuan Luo Network Forensics and surveillance, Fault Tolerance and Reliability | Editor: Hongwei Li Network Measurement and Virtualization | Editor: Yusheng Ji Quality of Service, Quality of Experience and Quality of Protection | Editors: Rui Luis Aguiar, Yu Cheng Resource Allocation and Management | Editors: Junshan Zhang, Nan Cheng Routing and Multi-cast, Router and Switch Design | Editor: Richard Yu Scaling Laws and Fundamental Limits | Editor: Ning Lu Security, Privacy and Trust | Editor: Kui Ren Short Range Communications, RFID and NFC | Editor: Zhiguo Shi Smart Grid Communications | Editor: Vincent W. S. Wong Vehicular Network | Editors: Lian Zhao, Qing Yang Video Streaming | Editor: Zhi Liu Wireless Body Area Network and e-healthcare | Editor: Honggang Wang Wireless Security | Editors: Haojin Zhu, Jian Shen Wireless Sensor Network | Editors: Jiming Chen, Ruilong Deng WLAN and OFDM | Editor: Xianbin Wang

Orthogonal Frequency Division Multiplexing (OFDM) or Multi-carrier Modulation (MCM) is a digital modulation technique that supports high-rate data with sufficient robustness to radio channel impairments (especially multi-path propagation). Due to that, it is emerging as the modulation technique used for the new generation of wireless communication systems (IEEE802.11a and DVB-T). However, one of the arguments against OFDM is that it is highly sensitive to synchronization errors. This raises up the need for optimum synchronization algorithms for OFDM applications such as IEEE802.11a and DVB-T. In this thesis, several synchronization algorithms are presented. Those algorithms deal mainly with two important synchronization problems: Timing and frequency errors and their consequences. We focus on the implementation aspects of synchronization algorithms and propose optimizations which lead to well performing and robust fixed point implementations. In addition, complexity and cost needed for such a project are analyzed leading to a model for classifying different algorithms depending on cost, time-to-market, and performance.

Broadband Wireless Access (BWA) systems have gained a lot of attention in the industry for providing flexible and easy deployment solutions to high-speed wireless communications technology such as WiMAX. Orthogonal Frequency Division Multiplexing (OFDM) system is one of the technologies that can offer BWA efficiently. However, there are certain problems with the OFDM system that need to be solved. In this thesis, a system based on OFDM scheme and principles has been designed to deliver high-speed mobile broadband services with great efficiency and reliability, with emphasis on resolving the problems that current OFDM systems face. A comprehensive investigation of OFDM systems are performed. We highlight and analyze in detail the current problems with channel estimation, synchronization and resource allocation of OFDM systems. We propose a new efficient channel estimation technique for the OFDM technology. Furthermore, we present an enhanced synchronization technique to mitigate frequency errors from which OFDM systems normally suffer in certain multipath environment.

This practical guide helps readers to learn how to develop and implement synchronization functions in digital communication systems.

Synchronization is a critical function in digital communications; its failures may have catastrophic effects on the transmission system performance. Furthermore, synchronization circuits comprehend such a large part of the receiver hardware that their implementation has a substantial impact on the overall costs. For these reasons design engineers are particularly concerned with the development of new and more efficient synchronization structures. Unfortunately, the advent of digital VLSI technology has radically affected modem design rules, to a point that most analog techniques employed so far have become totally obsolete. Although digital synchronization methods are well established by now in the literature, they only appear in the form of technical papers, often concentrating on specific performance or implementation issues. As a consequence they are hardly useful to give a unified view of an otherwise seemingly heterogeneous field. It is widely recognized that a fundamental understanding of digital synchronization can only be reached by providing the designer with a solid theoretical framework, or else he will not know where to adjust his methods when he attempts to apply them to new situations. The task of the present book is just to develop such a framework.