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Research on Sidelobe Suppression for NC-OFDM Systems

Author: WuYongXi
Tutor: DaiXuChu
School: University of Science and Technology of China
Course: Communication and Information System
Keywords: NC-OFDM Cognitive radio Sidelobe suppression Power Distribution Weighted subcarriers PSK
CLC: TN919.3
Type: Master's thesis
Year: 2011
Downloads: 33
Quote: 0
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Abstract


In recent years, with high-speed data communications business continues to grow, the existing wireless spectrum resources is very tense. However, the authority of the organization of the current available spectrum for observation found that the current authorized users (primary users) on the spectrum utilization efficiency is relatively low, there is a long vacant spectrum and using only part of the allocated spectrum resources and so on. Thus, the spectrum resources with the current temporary shortage of resource allocation and use of spectrum policy-relevant, it is necessary to introduce new wireless transmission mechanisms and communication technology to improve the efficiency of spectrum use. Based on dynamic spectrum access (DSA) that belong to this category of cognitive radio technology, which uses advanced digital communications and signal processing technology that allows unauthorized users to temporarily \Orthogonal Frequency Division Multiplexing (OFDM) technology due to its faster data transfer rate, can be effective against multipath fading and other features, is recognized as the most competitive candidate for cognitive radio technologies. Non-contiguous OFDM (NC-OFDM) system inherits advantages of OFDM system characteristics, and can use the spectrum sensing provides information related to selectively control the band subcarriers on and off, highly flexible, just well suited for cognitive radio environment. But whether the OFDM or NC-OFDM systems are based on fast Fourier transform (FFT) signal processing technology, the transmission signal so there is a big leak sidelobes, be close to the user's transmission salesman cause interference. Based on the analysis and summary of previous work has been based on the NC-OFDM system structure, principle and some of the challenges faced by a brief introduction, focus on the OFDM and NC-OFDM systems sidelobe suppression problem by theoretical analysis and simulation experiment, gives the following few viable ideas and methods: 1. OFDM system based SER constraints sidelobe suppression algorithm subcarrier weighted by sidelobe suppression algorithm and adaptive power allocation policy combination proposed sidelobe suppression and SER performance of multi-objective optimization model joint optimization. By optimizing the SER objectives into constraints, the problem is reduced to a single objective nonlinear constrained optimization problem, the use of nonlinear optimization algorithm can obtain a unique optimal solution. On this basis, according to the sidelobe power mainly affected by the impact of this on both sides of the tape carrier principle, this paper presents a method for reducing the computational complexity suboptimal implementation. 2. NC-OFDM systems joint inter-IF block sidelobe suppression research in NC-OFDM systems, the proposed joint inter-frequency block sidelobe suppression and independent of the frequency blocks sidelobe suppression both methods. Through theoretical analysis and simulation comparison of the two side-lobe suppression mode power distribution, sidelobe suppression performance and computational complexity differences. On this basis, according to the NC-OFDM system wide frequency range, modulation of the frequency blocks and noise power may not be so on application conditions, of the type of block noise power and modulation frequency is different between the blocks in the frequency sidelobe suppression algorithm combined power distribution and sidelobe suppression performance, and gives simulation results.

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