Research On Channel Estimation Techniques For OFDM And Multiple Antennas Communication System

High data rate techniques in communication systems have gained a considerable attraction in recent years. Orthogonal frequency-division modulation ( OFDM) , a multicarriers modulation technique, due to its simple implementation and robustness against frequency selective channels by converting the channel into flat fading sub channels.In this paper, On the basis of knowledge about wireless communication system and characteristic of wireless channel, we discuss the principle of Orthogonal Frequency Division Multiplexing (OFDM) based on the introduction of fading channels. Furthermore, as the main work of this paper, the channel estimation technique in SISO-OFDM and MIMO-OFDM system is investigated. Finally, the analysis and comparison of these algorithms is made by computer simulation.First, the channel estimation technique in SISO-OFDM system is investigated, with the emphasis on decision-directed channel estimation methods and pilot-symbol-aided channel estimation methods. The decision-directed channel estimation makes use of time-domain correlation of channel statistics. It firstly gets an origin estimate result of initial training sequences, then for data sequences use FIR channel estimator. The pilot-symbol-aided channel estimation uses LS (Least square) , MMSE (Minimum mean squared error) and Low-pass at pilot frequencies, and for data sequences use interpolation techniques, such as, linear interpolation, spline cubic interpolation, and frequency domain MMSE interpolation.Second, the channel estimation technique in MIMO-OFDM system is investigated. Due to complexity of MIMO channel compared with SISO one,channel estimation is achieved by sending training sequence. Though, these training sequences are not random ones, but are specifically designed to obtain as accurate channel estimation as possible. Further, pilot-symbol-aided channel estimation in two dimensions are explored. We first derive a minimum mean-square error (MMSE) pilot-symbol-aided parameter estimator. Then, we discuss a robust implementation of the pilot-symbol-aided estimator that is insensive to channel statistics. The analysis of these algorithms is made by computer simulation.Finally, combinating with the application of channel estimation , we present two techniques: STBC (space-time block coding) and STTC (space-time trellis coding) to improve the performance of channel parameter estimation.In the author's opinion, research on channel estimation in wirelesscommunication system needs to be further penetrated by considering all kinds of practical communicating factors that may impair the given model in this paper. In this sense, this paper will destine to be harbinger that can lead to a thorough solution.