| Summary: | 碩士 === 國立清華大學 === 電機工程學系 === 97 === In this thesis, a MIMO-OFDM system which is designed for high mobility environment is proposed. In order to fight with the time varying channel, the system uses space frequency block coding (SFBC) algorithm to obtain additional diversity gain without any extra communication resource. Furthermore, a flexible and low complexity intercarrier interference (ICI) mitigation module is also proposed in the thesis.
Doppler Effect causes ICI in high mobility environment. The ICI destroys orthogonality between subcarriers and degrades the system performance. In other words, the channel matrix is not a diagonal matrix anymore, non diagonal elements are the equivalent ICI factors and need to be eliminated. The channel matrix estimation uses a linear approximation algorithm. In order to adapt the module to MIMO systems, the proposed method substitutes for ZF ICI compensation algorithm to mitigate the ICI. So as to avoid calculating the inverse matrix, we take subtraction instead of inversion computation. The computational complexity can be reduced from O(N3) to O(N). The module can be applied not only in SISO systems but also in MIMO systems flexibly.
The proposed SFBC-OFDM baseband transceiver is constructed by SystemC language. The receiver includes a timing synchronization module, a carrier frequency offset estimation and compensation module, a channel estimation module, a SFBC decoder with soft output, and a flexible and low complexity ICI mitigation module. In order to model a high mobility environment, ITU-VA channel model, which is constituted by 3GPP, is employed for the simulation. Also, Jakes’ model is added to simulate the high mobility environment. According to the simulation result, the proposed SFBC-OFDM system with ICI mitigation obtains about 3dB gain after ICI compensation in the high mobility environment.
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