What is the need for OFDM

Synchronization Algorithms for OFDM Systems (IEEE802.11a, DVB-T): Analysis, Simulation, Optimization and Implementation Aspects

Synchronization algorithms for OFDM systems (IEEE802.11a, DVB-T): analysis, simulation, optimization and implementation aspects

Please always quote using this URN: urn: nbn: de: bvb: 29-opus-9125

Charbel El Hajjar

  • 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. We focus on the implementation 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. 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. Chapter 1 is a short introduction. The use of OFDM in high data-rate communication systems is presented. In addition, the necessity of synchronization in OFDM systems opens way for the research done in the following chapters. Chapter 2 is a general overview of OFDM systems. It deals with the basics of the OFDM technique in addition to the IEEE802.11a Wireless Local Area Network (WLAN) standard and the DVB-T standard which are explained briefly. Two important synchronization problems are presented: Timing and frequency errors and their consequences. Chapter 3 gives an overview on synchronization principles of IEEE802.11a and DVB-T which will be used later in Chapter 4 and 5. The above chapters give the needed background for the research done in this thesis. In addition, the following chapters deal with the newly performed results for the two OFDM applications: IEEE802.11a and DVB-T, which include algorithmic and implementational optimizations. In chapter 4, IEEE802.11a synchronization is treated in details. This includes a fixed point implementation of an IEEE802.11a in SystemC. In addition, possible algorithmic optimizations aiming at decreasing the complexity of an IEEE802.11a synchronizer and maintaining a very well performance are presented. In chapter 5 a similar treatment for the DVB-T system is presented. A fixed point implementation is studied, as well as algorithmic optimizations for increasing the performance and robustness of the DVB-T synchronizer with the lowest cost are discussed. Cost analysis methods are presented in chapter 6. Effort and manpower for the studied algorithms are estimated. The new optimization ideas presented in the previous chapters are used to develop a new model for choosing the optimal synchronization algorithm depending on the cost, time-to-market, and performance desired. The thesis concludes in chapter 7 which is a general overview summary of the work, opening new issues for further continuing research. ...
  • Orthogonal Frequency Division Multiplexing ”(OFDM), orβ€œ Multi-carrier Modulation ”(MCM) is a powerful digital transmission method. It allows high data rates with sufficient protection against interference, as typically occurs when transmitting via wireless channels, in particular with multipath reception due to reflections in the transmission channel. Thanks to this property, OFDM has increasingly developed as the modulation technique that is best suited for the latest generation of digital wireless transmission systems (IEEE802.11a and DVB-T). A disadvantage of using OFDM, however, is that this modulation technique is very sensitive to interference with Orthogonal Frequency Division Multiplexing (OFDM), or Multi-carrier Modulation (MCM), a powerful digital transmission method. It allows high data rates with sufficient protection against interference, as typically occurs when transmitting via wireless channels, in particular with multipath reception due to reflections in the transmission channel. Thanks to this property, OFDM has increasingly developed as the modulation technique that is best suited for the latest generation of digital wireless transmission systems (IEEE802.11a and DVB-T). A disadvantage of using OFDM, however, is that this modulation technique is very sensitive to interference in the synchronization. This justifies the need to optimize synchronization algorithms for OFDM applications such as IEEE802.11a and DVB-T. In the present work different algorithms for synchronization are presented. The work concentrates on implementation aspects of such algorithms for IEEE802.11a and DVB-T applications. Optimization strategies are proposed that lead to powerful and robust realizations in fixed-point arithmetic. In addition, a cost model is being developed which also includes the aspects of complexity and costs for implementation. Furthermore, the various algorithms are classified and included in the evaluation with regard to costs, time-to-market and performance. Chapter 1 provides a brief introduction to OFDM theory for high-speed data transmission. The need for synchronization is particularly emphasized. Chapter 2 gives a general overview of OFDM systems. Special features of OFDM for use in IEEE802.11a systems (WLAN) and DVB-T are discussed in more detail. Two special problems with synchronization are presented: Errors in time and frequency estimation and their consequences. Chapter 3 goes into detail on the principles and special features that occur during synchronization in IEEE802.11a and DVB-T receivers. It forms the basis for Chapters 4 and 5. The following chapters deal with the new results, which result in optimizations both in algorithms and in implementation for both applications (IEEE802.11a and DVB-T). Chapter 4 focuses on implementation details for IEEE802.11a systems. It includes the implementation of a fixed point implementation with SystemC. In addition, approaches are shown how algorithms can be optimized if the goal is to reduce complexity without reducing performance at the same time. Chapter 5 shows a similar approach for DVB-T systems. Here, too, fixed-point arithmetic is examined and the optimization of the algorithms is presented. On the one hand, these aim to improve interference behavior and, on the other hand, to implement them at minimal cost. Chapter 6 includes methods for cost analysis. Effort and work performance are estimated for the examined algorithms. ...