Research On Phase Noise Suppression In OFDM Systems

The goal of wireless mobile communication system will be to achieve high-quality and high-speed mobile multimedia and data transmission business, at any moment. Since Orthogonal Frequency Division Multiplexing (OFDM) has a higher utilization rate, can provide a higher transmission rate for information and can effectively resist the multi-path fading of wireless channels, OFDM is well suitable to the future high data rate wireless multimedia communications. However, OFDM system requires the orthogonality between sub carriers, and due to long symbol duration, it is very sensitive to phase noise. Phase noise can bring the common phase error (CPE) and inter-carrier interference (ICI) to OFDM signal, if we do not suppress it, the performance of OFDM system will significantly decline. This paper mainly focuses on the analysis of algorithms to suppress the phase noise in OFDM systems, and the main contents are as follows:At first, this thesis elaborates the development status of mobile communications, the development and application of OFDM, its advantages and disadvantages, and research contents of this paper's studies status at home and abroad. Then, the thesis introduces the principle of the OFDM systems and the phase noise, focuses on the impact of phase noise in OFDM system, a general analysis and a first order approximation analysis are, respectively, given and all of these lay the foundation for below studies.After that, the suppression algorithms for CPE are discussed in detail, including ZF algorithm, MMSE algorithm and decision feedback based algorithm, and MATLAB simulations are performed to analyze the performance of these algorithms. On this basis, an improved method for CPE suppression is proposed, whose performance is simulated in AWGN channel. Comparing with other methods, the simulation results show that the improved method has a better performance in phase noise suppression.Then the basic principle of the phase noise suppression for ICI algorithms is discussed in detail, including the traditional ICI self-cancellation algorithms, such as adjacent data-conversion method, adjacent data-conjugate method and symmetric data-conjugate method. The realization of these three algorithms is introduced in detail. Next, the characteristics of the ICI coefficients are observed. And base on this, a novel method for ICI suppression is proposed, that is, symmetric-conjugate at two ends and adjacent conjugate at middle. The best parameters for this new method are determined through simulations, and then its performance is simulated by using MATLAB. Comparing with traditional self-cancellation methods, the better performance of the proposed method is verified.