Research On Channel Estimation Slgorithms For OFDM System

In the wireless mobile channel, to realize high speed and high quality service is the goal and demand of date communications. To be a high-speed date transmission technique, orthogonal frequency division multiplexing (OFDM) has been widely used in wireless communication systems due to its high spectrum efficiency and capability to combat mufti-path fading. Only when the channel information from received data is estimated accurately, date from sending terminal can be correctly demodulated because the channel is time-varying and frequency selective fading. Therefore channel estimation becomes one of significant techniques in OFDM system.This paper analyzes and compares several kinds of conventional channel estimation algorithms at first and concludes that all of the previously mentioned pilot-based methods have been designed for regular pilot lattices which satisfy 2-D Nyquist-criterion,and these pilot-based channel estimation algorithms are no longer applicative if the Nyquist-criterion is violated or the pilot arrangement is irregular.Therefore, for this situation using nonuniform sampling techniques we propose a pilot-assisted channel estimation algorithm based on irregular pilot arrangements in this paper. In this method, first we estimate the channel frequency response at the pilot positions by using the LS algorithm.Then all channel informations are obtained by utilizing adaptive weights, block Toeplitz matrices and the iterative conjugate gradient (CG) algorithm.Secondly, we introduce a heuristic stopping criterion for early termination of the conjugate gradient iterations. Additionally, channel estimator implementatio-ns and applications of our method to multiple-antenna and multiuser OFDM systems are discussed.Finally,Simulation results of 2-D channel estimation for a WLAN-Like system and 1-D channel estimation for MIMO-OFDMA demonstrate the usefulness and availability of the approach.