Blind And Semi-blind Channel Estimation Algorithm Based On OFDM Systems

The goal of future mobile communications is personal communications, which means the users could access to the capabilities of the global network at anytime without regarding to the location and mobility and be provided with speech or high-rate data service. With the increase of the demand for the multimedia and the rapid development of internet, the broadband wireless communication systems need higher spectral efficiency and higher data-rate in the future. Currently multi-carriers modulation represented by OFDM is one of the most promising ways in all the wireless schemes.This paper mainly deals with the problems of channel estimation in OFDM systems. Above all, the basic principle and key technologies of OFDM are analyzed. Then blind and semi-blind channel estimation methods for OFDM are discussed in detail. Firstly, we propose a subspace method for estimating the channel in the OFDM system, where the zero-padding OFDM (ZP-OFDM) other than the traditional cyclic prefix OFDM (CP-OFDM) is used. The property of zero-padding simplifies the channel estimation, and the proposed subspace method can eliminate the inter-block interference (IBI) completely and no longer need precise order information.Secondly, a space time coding OFDM (STC-OFDM) channel estimation algorithm based on subspace is proposed in this paper. It not only contains the diversity gain of STC, but also involves the advantage of the anti multi-path of OFDM system. Meanwhile, the advantage of this algorithm lies in that the condition of coprime, constant modulus transmitted signal and precoding are unnecessary.In the end, combining the characteristic of the vehicular test channel of IMT2000, performances of the proposed methods are demonstrated by computer simulation. The results and analysis of simulation are proposed in the end.