Research On Channel Estimation And Simulation For OFDM And MIMO-OFDM

Communication service in wireless channels with high speed and quality is required for future wireless communication systems. OFDM (orthogonal frequency division modulation) has gained more and more attraction in recent years due to its high bandwidth efficiency and robustness against frequency selective fading channels. Channel estimation is one of the most important part in OFDM system. This thesis focuses on channel estimation in both single-in single-out OFDM system and multiple-in multiple-out OFDM system, the analysis and comparison of these are made through computer simulation.Firstly, wireless channel characteristic, basic principle and key technology for OFDM System are introduced in this paper. There are brief description of basic principle and system model in MIMO and MIMO-OFDM system. The channel estimation algorithms based on pilot and the method of interpolation estimation in OFDM system are investigated in detail. Block structure and comb structure are two basic structure of training sequence, as the fast changing characteristic of wireless channel, this paper use comb structure.Secondly, on the channel estimation of OFDM system, the thesis mainly research on the LS and the MMSE algorithms, and gave both the simulation of the LS, the MMSE algorithms and their improved algorithms and analysis their performance. The correlation of channel is considered in the modified LS algorithms, the more accurate estimation is got without increasing the calculation complexity. In the modified MMSE algorithms, in order to simplify the MMSE algorithms high power signal components are reserved, and low ones are neglected. A modified channel estimation method based on decision feedback for OFDM system is proposed. Meanwhile, the frequency domain diversity method is exploited to decrease the initial channel estimation errors. Simulation shows that the proposed algorithm improves the performance of channel estimation effectively with lower computing complexity in Rayleigh fading channelLastly, this essay focuses on the channel estimation of MIMO-OFDM system. As a combination of orthogonal frequency division multiplexing (OFDM) with multiple input multiple output (MIMO) technique, MIMO-OFDM can not only effectively enhance the transmission rate and capacity of the wireless communication system but also combat multi-path fading and interference. Channel estimation is an important part for MIMO-OFDM. When the transmitter and the receiver use more than one antenna, MIMO channel is constructed. As information theory indicates, MIMO channel has larger capacity. A simplified MIMO-OFDM channel estimation method is proposed, with inserting pilot between the same interval, power normalizing and conjugate matrix are used to simplified the algorithms.