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在快速时变信道环境下,传统MIMO-OFDM系统中载波间干扰严重,系统性能下降。文中以分数阶Fourier变换替代Fourier变换对OFDM符号进行调制与解调,构建了基于分数阶Fourier变换的MIMO-OFDM系统。该系统能通过选择合适的分数阶Fourier变换阶次,使调制后的信号更加匹配信道的时频特性,减轻载波之间的干扰,从而使系统达到更优的性能。文中在构建了系统模型的基础上,给出了最优阶次选择的方法,并且分析了各种系统参数对最优阶次的影响。理论分析及仿真结果表明,在快速时变的频率选择性深衰落信道环境下,基于分数阶Fourier变换的MIMO-OFDM系统能够比传统系统更好地聚集有用信号的能量,因而具有更好的性能。
In a fast time-varying channel environment, the interference between the carriers in a conventional MIMO-OFDM system is severe, and the system performance is degraded. In this paper, the fractional Fourier transform is used to replace the Fourier transform to modulate and demodulate the OFDM symbol, and a MIMO-OFDM system based on fractional Fourier transform is constructed. The system can achieve better performance by selecting the appropriate fractional order Fourier transform order to make the modulated signal more match the channel’s time-frequency characteristics and reduce the interference between the carriers. Based on the system model, the method of optimal order selection is given, and the influence of various system parameters on the optimal order is analyzed. The theoretical analysis and simulation results show that the MIMO-OFDM system based on fractional Fourier transform can gather the energy of the useful signal better than the traditional system in the fast time-varying frequency-selective deep fading channel environment and thus has better performance .