Browsing by Subject "Orthogonal Frequency Division Multiplexing (OFDM)"
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Item High speed 128-point Fast Fourier Transform circuit design for OFDM(2006-12) Wu, Tung-Yeh; Abraham, Jacob A.The Fast Fourier Transform (FFT) Algorithm is an efficient way to calculate the Discrete Fourier Transform, which is widely used in digital signal processing. Due to the increasing demand for Orthogonal Frequency Division Multiplexing (OFDM) wireless communication systems, it becomes even more important today. For the current Ultra Wide Band standard, the data sampling rate is 528 MHz. This thesis proposes a high-speed hardware FFT which targets next generation wireless communication systems with a 3.6 GHz sampling rate. This thesis is organized as follows. Chapter 1 introduces the motivation and the flow of the proposed design. Chapter 2 presents background knowledge of the Discrete Fourier Transform and the Fast Fourier Transform based on the Cooley- Tukey decomposition. It includes the basic theory and as well as the method to simplify the algorithm. Chapters 3 and 4 describe the design of the high speed arithmetic components for the FFT module. In Chapter 3, several high performance adders are implemented and compared. Chapter 4 discusses high speed multipliers. Implementation of a Dadda multiplier is also introduced. The conversion of the FFT from algorithm to hardware is explained in Chapter 5, which addresses several issues of concern as well as the tradeoffs between different approaches. Chapter 5 also presents the structure of the FFT and simulation results. Chapter 6 gives a summary of the work and points out the direction of future work.Item Study of efficient link adaptation schemes in wireless orthogonal frequency division multiplexing (OFDM) systems(2009-08) Choi, Eun Ho; Womack, Baxter F., 1930-; Andrews, Jeffrey G.Wireless communication systems require high spectral efficiency and throughput in order to be cost-effective. Link adaptation schemes are known to be a good solution to achieve this goal. However, the necessity of additional information or increased complexity prevents these schemes from being implemented. In this context, research on resource allocation based on different constraints, such as complexity or feedback, is important. The major contribution of this dissertation is the development of three novel techniques to enhance performance in practical implementations of the adaptive OFDM systems. This dissertation first introduces a new multiuser OFDM system to enhance performance in the low SNR regime. In this scheme, multiuser diversity can be efficiently amplified from random power allocation and opportunistic scheduling. Higher spectral efficiency can be achieved without an increase of complexity or feedback amount compared to conventional multiuser OFDM systems using equal power allocation. This dissertation also presents a modified multi-mode power loading scheme. A modified multi-mode power loading scheme can circumvent the limit of current multi-mode power loading schemes by significantly reducing search amount from 2N - 1 to N, where N is the number of subcarriers. Finally, this dissertation has introduced adaptive OFDM systems using channel gain order information in limited feedback environments. Adaptive OFDM systems using the order mapping technique achieve comparable performance to conventional adaptive OFDM systems in terms of bit error rate and average spectral efficiency, while the amount of feedback is significantly reduced. Furthermore, by simply exploiting order mapping and interpolation, the analyzing technique circumvents the practical shortcomings of previous limited feedback techniques for OFDM systems.