Mimo-ofdm System Key Technology

The combination of multiple-input multiple-output (MIMO) and orthogonal frequency division multiplexing (OFDM) can not only enhance the capacity of wireless communication system, but also offer the potential of high spectral efficiency and mitigate the effects of frequency-selective fading. Therefore, MIMO and OFDM will be the key technologies for the next generation wireless communication system.In MIMO-OFDM system, the Orthogonal Space frequency block code is more and more widely used to fight against frequency selective fading caused by multi-paths. Bit interleaved coded modulation-iterative decoding is already integrated with MIMO-OFDM, and adopted in many communication standards. Signal-to-Noise Ratio is the basis for many techniques, such as MIMO diversity receiving technique and adative coded modulation technique. The SNR estimation is badly needed. Thus, three techniques above are all important in MIMO-OFDM system. So, this dissertation focuses on the three key points.Chapter 1 reviews the basic conception of wireless communication, and introduce the basic knowledge of MIMO-OFDM system.Chapter 2 introduces the knowledge of decoding techniques for OSFBC system, a traditional one is for qasi-static fading channel and the modified one is for frequency-selective fading channel. Then it introduces the MAP detection algorithm under the two decoding techniques. Simulation proves the modified algorithm has a better performance than the traditional one under the strongly frequency-selective fading channel.Chapter 3 introduces the BICM-ID structure in both single antenna and multiple antennas system, and research on the system's performance factor is investigated. The key point is how the modulation labling maps affect the performance of BICM-ID system. Through theoretic analysis and simulations under fading channels, a conclusion is draw that the harmonic mean of the minimum Euclidean distance before feedback and after feedback and the mean harmonic distance is determined factor in BICM-ID system. GRAY labling is best for BICM-ID system using Turbo decoding. Chapter 4 introduces SNR estimation principles in MIMO-OFDM system, and dicusses two exsiting estimation algorithms, one is subspace decomposing based and the other is channel correlation fuction based. After that, we proposed a channel estimation based technique. Simulations are shown that the channel correlation fuction based technique and channel estimation based technique both have good performance.Chapter 5 uses three key techniques reserch results above to design a MIMO-OFDM communication system, and proves its good performance through simulations.Finally, chapter 6 provides the conclusion and some suggestions for the further research.