Research And Optimization Of Channel Estimation Algorithms Based On OFDM System

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 network (WLAN) systems and so on. The system with OFDM technology can combat frenquency-selective fading efficiently and have high spectral efficiency. It is especially one of the technical difficulties to estimate and equalize the dispersive channels. In this thesis, we are working on the topic based on some of the precedents' results.At first, the principle and features of OFDM system are introduced, including the modulation way based on Discrete Fourier Transform (DFT) and the system structure of OFDM. Then mathematic model of multi-path Rayleigh fading channels are presented based on the discussion of mobile fading channel characteristics. At last, the simulation results and analysis are given.Three kinds of channel estimator based on pilot signals are discussed. The first is channel estimator based on block pilots, including Least Square (LS) estimator, Maximum Minimum Square Error (MMSE) estimator and Linear MMSE estimator. The second is channel estimator based on comb pilots. The third is channel estimator based on star pilots. The channel estimators based on block pilots are suitable for static fading channel, and estimators based on comb pilots and star pilots are suitable for time-varying fading channel.Since the effects of LS channel estimator decline in the environment of serious frequency-selective fading channel, an improved method is proposed in this paper. Aim at decreasing the high computing complexity of LMMSE estimator, two simplified way are proposed. Computing complexity of LMMSE estimator can be reduced by lesson the dimension of linear transform matrix and by ignoring the correlation of channel transform function.At last, simulation is performed based on IEEE802.11a standard. The results indicate that these improved channel estimator are effective.