双选择性衰落信道下非相干OFDM检测技术研究

Radio channels of vehicle-ground wireless communication systems show rapidly time varying and multipath propagation because of the high mobility of the transmitter and receiver in complex terrain.The fading of the channel is composed of time selective fading and frequence selective fading at the same time. The estimation and tracking for rapidly time varying channel is the key problem for broadband wireless communication over doubly selective fading channels. Compared to coherent OFDM systems, noncoherent OFDM systems are suitable to communication over doubly selective channels for bypassing channel estimation, but higher signal to noise ratio is needed in order to obtain a satisfactory bit error rate performance. In this project, the detection of noncoherent OFDM over doubly selective fading channels is investigated and mechanism of using the signal processing methods to improve the noncoherent OFDM detection performance is explored based on characteristics of doubly selective channel and noncoherent OFDM signals. The main content of the project includes: Rubustness noncoherent modulation scheme against doubly selective fading, multipath diversity and Doppler diversity in noncoherent OFDM systems without channel state information and detection of noncoherent OFDM signal aided by imperfect channel state information. After finishing the theoretical analysis and experimental research, it is wished that the obtained results promote efficiently the resolution of the challenge for wideband wireless communications at high mobility scenarios, and thus, provide the key fundamentals to design the advanced equipments to improve the passenger safety and running security of vehicles.

在交通工具高速运行于多变地理环境时，其与地面间多径无线信道快速变化，呈现频率选择性衰落和时间选择性衰落，快变信道的估计与跟踪是宽带无线传输面临的主要难题。非相干OFDM技术在接收端无需进行信道估计，因而相较于相干OFDM更加适合于快变多径信道下传输，但其需要在较高的信噪比下才能获得满意的误码率性能。本项目拟展开快变多径衰落信道下非相干OFDM检测技术研究，根据传输信道双选择性衰落的特点及非相干OFDM信号自身的特点，探索利用信号处理方法提高非相干OFDM检测性能的机理。主要包括双选择性衰落信道下稳健的非相干OFDM调制方法研究、非相干OFDM分集接收技术研究和基于部分信道信息的非相干OFDM检测技术研究。完成有关理论推演和实验研究，期望有效促进高速移动环境下宽带无线传输技术难题的解决，为我国交通工具安全监测先进设备的研制提供技术基础。

高速移动环境下，无线信道呈现时间选择性衰落和频率选择性衰落，双选择性衰落严重恶化了无线通信系统性能。针对双选性衰落信道下的非相干OFDM系统，项目探索了利用信号处理手段提高非相干OFDM系统性能的方法。研究了双选择衰落信道稳健的非相干OFDM调制方案，提出了OFDM-(n+m)/MFSK调制方法、OFDM-ADQAM调制方案和基于分数阶小波变换的OFDM调制方案；研究了OFDM分集接收技术，提出了一种基于过采样的OFDM-MFSK分集接收方法、一种GLCP-OFDM过采样分集接收方法、一种基于球面共形阵的OFDM角度分集接收方法；研究了信道估计及基于部分信道信息的非相干OFDM检测方法，提出了一种基于ICI抵消的信道估计方法和一种部分相干OFDM-MFSK检测方法。从调制、分集接收和检测三个方面提高了双选信道下的OFDM通信系统性能。可为高速铁路、公路及飞机等高速移动场景下的宽带无线通信系统提供理论指导。