Research Of Channel Estimation Algorithms Based On OFDM System

Multi-path fading and bandwidth efficiency are two most difficult challenges in the future broadband wireless communications system. OFDM reduces the effect of the multi-path fading by converting a frequency-selective channel into a parallel collection of frequency flat sub-channels. Because of enabling to provide high-rate and high-quality wireless and mobile communication service, Orthogonal Frequency Division Multiplexing (OFDM) system is becoming a very hot research topic recently. OFDM technology has been used in many fields, such as Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), Wireless Local-Area Network (WLAN) systems and so on. The system with OFDM technology can combat frequency selective fading efficiently and have high spectral efficiency.At first, the principle and features of OFDM system are introduced, including the modulation way based on Discrete Fourier Transform (DFT), the system structure of OFDM and its particular mechanism used to counteract frequency-selective fading. In this dissertation, we analyze the channel attributes in wireless communication system, and various channel models.In this essay, we investigate channel estimation technology in OFDM system. Introduce the basic principles of OFDM We mainly investigate the channel estimation technology in OFDM system. We analyze the LS, MMSE, their simplified algorithm-SVD algorithm, and various interpolation algorithms based on pilots, and introduce the Wiener filter algorithm base on MMSE. Performances of the channel estimation algorithm mentioned before is compared, and the advantages and disadvantages of these algorithms are analyzed. At last, a hybrid algorithm that can adapt to fast time-varying channel is proposed, including the simulation and analysis of it. As a result show than the new algorithm has good performances of anti time delay spread and anti Doppler frequency shift.This paper is organized as follows:In chapter one, the paper' s background and the research situation of the channel estimating technology of wireless OFDM system is introduced. And in the same time, the content' s structure is illustrated.In chapter two, the main principle and model of OFDM is introduced, including the application of FFT using in OFDM system, orthogonality principle, synchronization technology, guard interval, cyclic prefix, channel estimation and peak-to-average power ratio.In chapter three, the ideal channel is described first, and then the characteristic of wireless channels is noted, it is the theoretical basis of channel estimation, several models of wireless channels is introduced at last.In chapter four, in the beginning, the significance of channel estimation algorithm based on the OFDM system and the recent classification of it is summarized, furthermore, principle and characteristics of channel estimation algorithm based on LS, MMSE, SVD and pilot frequency.In chapter five, performances of the channel estimation algorithm mentioned before is compared, and the advantages and disadvantages of these algorithms are analyzed. At last, a hybrid algorithm that can adapt to fast time-varying channel is proposed, including the simulation and analysis of it.In chapter six, a summarization of this chapter is addressed, in the meanwhile, give a prospecting for the works in the future.