The Practical Scheme And Blind Channel Estimation In MIMO-OFDM System

From the end of the 20th century to the beginning of the 21st century, the wireless communication technology develops forward within the whole world range with hitherto unknown speed. People also appears gradually urgent to the need for gaining information and realizing more medium business on mobile telephone at any time and any place. It establishes solid market base for the generation of the new generation wireless communication system, at the same time it has attracted a lot of scientific research personnel.MIMO and OFDM are two important techniques in future wireless communication system. MIMO-OFDM system, which combines MIMO with OFDM, can improve spectrum efficiency, the channel capacity and simplify the receiver structure under the multipath environment. So MIMO-OFDM is a key scheme for the future wireless communication system. Based on the importance of MIMO-OFDM, the encoding/decoding scheme, system scheme, channel analysis, channel estimation and system implementation are studied by more research personnel.In this thesis, the author deeply studied the MIMO-OFDM scheme. The TR-STBC-OFDM with lower compute complexity and better BER performance is brought forward. The channel correlation coefficient in microcellular has been derived by making use of geometry method. And the blind channel estimation algorithms which is based on second order statistics are studied under the TR-STBC-OFDM system.The main contributions of the thesis include:1. A novel decoding scheme for MIMO-OFDM system is brought forward. In this scheme, channel matrix is combined with encoding matrix to form new decoding matrix. Through this decoding matrix the complex signal is converted conveniently into real signal, at the same time the space-time decoding is completed.2. Combining TR-STBC technology with OFDM technology to form two novel TR-STBC-OFDM system schemes. In these two novel schemes, TR-STBC is adopted to convert multiple transmitting antennas into single transmitting antenna; OFDM is adopted to convert frequency-selective channel into a group of frequency-flat channels.1) TR-STBC-OFDM system scheme 1 changes the position of OFDM modulator and space-time encoder, so it only need one IFFT at transmitter and one FFT at receiver. Through this way, TR-STBC-OFDM system scheme 1 cuts down the compute complexity. Simulation results indicate that TR-STBC-OFDM system scheme 1 has better BER performace than tranditional MIMO-OFDM system.2) TR-STBC-OFDM system scheme 2 also changes the position of OFDM modulator and space-time encoder. At transmitter, the times of IFFT is the same with the tranditional MIMO-OFDM system but it decreace the points of the IFFT; at receiver the times of FFT is equal with the transmitting antennas and the points of the FFT are also decreased. Through this way, TR-STBC-OFDM system scheme 2 cuts down the compute complexity. Simulation results indicate that TR-STBC-OFDM system scheme 2 also has better BER performace than tranditional MIMO-OFDM system.3. Making use of geometry method to analyze the correlation of the wireless channel and the close expression of the correlation coefficient is derived. Here, the ellipse model is adopted, because it can better describe the microcellular which has rich scatters. These results can effectively help the design of the MIMO-OFDM system and the analysis of the correlation in MIMO-OFDM system.4. The blind channel estimation which is based on the second order statistics has been studied. The method for the situation that the receiving antennas are less or equal the transmitting antennas in downlink is brought forward. Under the TR-STBC-OFDM system, through the new characteristic of TR-STBC, 2 transmiting antennas 2 receiving antennas system can be converted into 2 transmiting antennas 4 receiving antennas system, and 3 transmiting antennas 1 receiving antenna system can be converted into 3 transmiting antennas 4 receiving antennas system. Through this way, the condition that the receiving antennas must be more than transmitting antennas in blind channel estimation algorithm which is based on the second order statistics is satisfied One hand this result can help the application of the blind channel estimation algorithm in downlink, at another hand, it indicates the TR-STBC-OFDM system brought forward by this thesis can powerfully support the application of the blind channel estimation which is based on second order statistics.