Research On The Techniques For Synchronization And Channel Estimation In MIMO-OFDM Systems

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. In MIMO-OFDM systems the techniques for synchronization and channel estimation are very important. This thesis focuses on the training symbol aided synchronization and channel estimation techniques in MIMO-OFDM systems. In the thesis a new training sequence aided synchronization algorithm is proposed through the study of the available classic algorithms based on sequence orthogonal or time orthogonal training sequence. In the proposed algorithm, the training sequences with the combination of weighted constant amplitude zero correlation (CAZAC) sequences are designed, and the methods to estimate the timing and frequency offsets are also given. The whole synchronization process includes the coarse time synchronization, frequency offset estimation and fine time synchronization. Furthermore, the time-domain and frequency-domain channel estimation schemes based on least square (LS) criteria and method using space time block coding (STBC) training pattern are introduced. The analysis and comparison of these algorithms are made through computer simulation. According to the research of these algorithms, a new channel estimation method is proposed. In this method, the training sequences are formed with CAZAC sequences with different cyclic shift for different transmit antennas. As the CAZAC sequence has nice property of shift-orthogonal, the channel state information (CSI) is derived through the time-domain correlation between the received training sequences and local training sequences.