Research Of Channel Estimation And Hidden Pilots Analysis In OFDM Systems

With the development of the digital techniques, the demand for mobile communication system increases greatly. As a new modulation, orthogonal frequency division multiplex (OFDM) has high frequency efficiency and strong ability to resist the interference. After abundance of research and study about OFDM technology by scholars all over the world, it is being considered as a key technology of the 4G systems.In order to support high-speed transmission, multi amplitude and multi phase modulation schemes are adopted. Therefore, channel estimation has to be done to eliminate the interference of the fading channel.In this thesis, the history of mobile communication system is introduced. After that, it describes the background of OFDM as well as the principle of OFDM. And the channel characterizes and channel estimation techniques are introduced.Then we discuss the channel estimation algorithms in OFDM systems, especially under multi-path time changing environment. We mainly focus the time-domain, frequency-domain and time-frequency domain channel estimation methods. Time-domain method tends to estimate the channel impulse response (CIR), and it is according to MMSE, LS. Frequency-domain method mainly uses the PSAM to do channel estimation. Different interpolation methods are proposed to implement the channel estimation, after which their performance is studied. And according to the DFT based channel estimation method, propose improved method to overcome the shortcoming of the edge effect.Because of the previous schemes' limitation, hidden pilots scheme is taken into consideration. However, this scheme is not so suitable for OFDM system in that it uses periodic pilots which bring high PAR(Peak to Average Ratio) and thus deprave the system performance.