Research On Channel Estimation Techniques Of OFDM Communication Systems

Channel Estimation technique is one of the key techniques in OFDM communication systems. Communication systems can enhance their BER performance using coherence detection only when they could make precise and Real-time estimation of fading coefficients of multipath channel where the information symbol passes through. Recently, more and more researches are focused on channel estimation techniques of OFDM communication systems. According to the characteristics of various algorithms, we can classify them into three types: pilot-based, blind and semi-blind estimation. In this dissertation, the basic theories of semi-blind channel estimation, which are suitable for static, or slow fading multipath channel, and their applications in OFDM system are deeply and fully studied. The main contributions of this dissertation are as follows:1 According to different characteristics of multipath, the theories of two kinds of multipath are studied and their corresponding mathematical models are built. Three-path model without noise, which is fit for following algorithms, is made up. The characteristics of amplitude -frequency and phase-frequency of this channel impulse response are given by computer simulation.2 Two semi-blind block channel estimation methods respectively based on maximum likelihood and hidden Markov model are studied. Computer simulation result shows that two algorithms can estimate channel fading coefficients more effectively by setting bigger data block length N.3 Joint ML block semi-blind channel estimation is applied to OFDM system. The computer simulation results show that this algorithm is suitable forOFDM systems with static or slew fading channel. At the same time, the performance of Joint ML block semi-blind channel estimation and Pilot Symbol Assisted channel estimation is compared and evaluated.