Research On Channel Estimation Of Wireless OFDM System

To be an high-speed data transmission technique, orthogonal frequency division multiplexing(OFDM) has been widely used in wireless communication systems due to its capability to combat multi-path fading. In mobile communication systems, a dynamical estimation is necessary since the channel is frequency-selective and time-varying. Channel estimation is one of the key techniques in wireless communication systems and it directly affects the performance of the system. It is challenging task to estimate time-varying channel quickly and accurately. This thesis mainly focuses on the time-varying channel estimation methods based on pilot tones in wireless OFDM systems. At present, the channel estimation of wireless OFDM systems has been still in the progress of research and exploring.In this paper, we first briefly introduce the development of OFDM and its application in communication fields. Secondly, the characters and statistic properties of wireless channel and the methods to model the wireless channel are discussed. After good study of them, the wireless OFDM systems channel model is constructed. Then we introduce the principle of OFDM system and some key techniques about it. At last, we mainly address the channel estimation methods based on pilot tones and briefly introduce the blind channel estimation in wireless OFDM systems.The pilot sub-channel frequency response can be estimated by using the LS or MMSE algorithm and the data sub-channel frequency response can be obtained by interpolating. We analyze the mechanism of LS, MMSE , modified MMSE algorithm and several popular interpolation methods and compare the bit error rate (BER) of LS and MMSE algorithm on AWGN and fading channels. At the same number of pilot tones, the pilot pattern makes great effects on the quality of channel estimation. We discuss the pilot patterns and investigate a modified pilot pattern. The simulation result shows that there is improvement of the system performance for this modified pilot pattern compared with other traditional pilot patterns.