OFDM Diversity Receiver based on Reactance-domain Signal Processing

正交频分复用技术（OFDM）是一种有效的技术，能够减少多径环境下由于延迟扩散而导致的性能下降，并作为地面数字电视广播和无线局域网（LAN）的传输技术，但它不能改善由于衰落而导致的性能下降。为了克服衰落问题，我们必须使用空间分集。然而，它需要大量的计算成本。特别是对于结合分集的后DFT（离散傅里叶变换），它需要与分集分支相同数量的射频前端块和DFT处理器。为了在不需要庞大硬件的情况下实现空间分集接收机，本课题提出了电抗域信号处理方法，将靠近主天线单元的寄生天线用可变电抗端接。通过控制可变电抗，可以实现一个射频前端接一个OFDM接收机的分集效果。在本项目中，我们通过评估测试，确认了提出的基于电抗域信号处理的分集作为分集天线进行。根据实验结果，考虑到手持终端的尺寸限制，对天线的形状进行了优化。为了设计更具体的电抗域信号处理接收机，我们开发了地面数字电视广播移动接收模拟器。结果表明，即使在手持终端上安装小型化天线，该电抗域信号处理接收机也能获得分集效应。

Although OFDM(Orthogonal Frequency Division Multiplex) is an efficient technique capable of reducing the performance degradation due to delay spreading in multipath environment and employed as a transmission technique for terrestrial digital television broadcasting and wireless LAN(local area network), it is not capable of improving the degradation due to fading. In order to overcome the fading problem, we have to use space diversity. However, it requires huge amount of computational cost. Especially, in case of post DFT(discrete Fourier transformation) combining diversity, it requires the same number of RF(radio frequency) front-end blocks and DFT processors as of diversity branches.In order to achieve the space diversity receiver without huge hardware, this research project has proposed the reactance-domain signal processing, where the parasitic antenna close to the main antenna element is terminated with the variable reactance. By controlling the variable reactance, we can get the diversity effect with only one RF front-end followed by one OFDM receiver.In this project, we have confirmed that the proposed diversity based on reactance-domain signal processing is performed as a diversity antenna by carrying out the evaluation test. According to the result, we have optimized the shape of antennas where the limitation in size of handheld terminal is taken into account. In order to design the more specific receiver with reactance-domain signal processing, we have developed the simulator for mobile reception of terrestrial digital television broadcasting. We have shown that the proposed reactance domain signal processing receiver is capable of obtaining diversity effect even in case of miniaturized antenna installed onto handheld terminals.