| With good capacity of countering multi-path fading and high spectrum-efficiency,Orthogonal Frequency Division Multiplexing (OFDM) technique has been widely usedin communication area. In high-speed condition, quick and effective estimation oftime-varying channel is one key technique to assure the performance of OFDM system.Based on the project “Study of high speed communication systems overdoubly-selective channels”, this thesis mainly focuses on the design of the pilotstructure and the algorithms of OFDM channel estimation in fast time-varying channel.It includes three following aspects:(1). With regard to the project’s frame structure based on burst OFDM system, wediscuss the pilot structure in the frame for fast time-varying channels, study someconventional estimating algorithms, including comparative analysis, then propose onesuitable channel estimation algorithm for the project.(2). Take high Doppler frequency shift into account, this thesis studies the estimationalgorithm based on Basis Expansion Model, which can effectively estimate the fastfading channel. Its basic idea is the orthogonal decomposition of channel, transformingthe estimation of many channel parameters to the estimation of a few orthogonalcomponent weights (BEM coefficients). And then, the comparative simulation resultsare presented.(3). Conventional BEM estimation is mainly based comb-type pilot. Consideringengineering application and the characteristic of BEM estimation, this thesis proposesthe algorithm of BEM estimation based block-type pilot, the basic principle is: afterorthogonal decomposition, the orthogonal components (BEM functions) remainsunchanged during the signal processing, the variation between the OFDM symbols canbe regarded as the change of the orthogonal component weights, so the BEMcoefficients at the non-pilot symbols can be gained by interpolating the BEM coefficients at the pilot symbols. And the simulation results show the effectiveness ofthe algorithm. |
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