Real-time ray-based channel generation and emulation for UAV communications

A real-time ray-based hardware emulator for Unmanned Aerial Vehicle (UAV) communication channels which suits for the Three-Dimensional (3D) dynamic scenarios and considers the movements of both terminals is developed in this paper. The time-variant channel parameters, i.e., ray delay, ray gain, and ray Doppler frequency are precalculated in the host by using the Ray Tracing (RT) method. Meanwhile, RT simulation dramatically increases the number of valid rays. To address the problem of resource limitation and huge computational burden in the implementation, an efficient ray coefficients generation method based on iteration is proposed and implemented. With the advantages of low cost and high flexibility, a Software Defined Radio (SDR) hardware platform is used to emulate the ray-based UAV channels by utilizing the compact architecture including the Time-Division (TD) scheme and Tapped-Delay Line (TDL) for channel convolution. Finally, hardware measurement results demonstrate that the properties of emulated channel, i.e., Power Delay Profile (PDP) and Doppler Power Spectrum Density (DPSD) consist with the simulated ones, which verifies the correctness of hardware implementation. The proposed channel emulator provides an efficient way for optimization, verification, and evaluation of UAV communication systems.     

轴流压气机特性计算及激波模型研究

为快速准确预估轴流压气机特性和激波损失,基于轴流压气机S2流面流线曲率法,分别采用正激波模型和改进的双激波模型,对某型2级跨声速风扇特性进行数值模拟计算,得到了100%设计转速近设计点与99.76%设计转速近堵塞点的总体性能和气动参数,以及95%、100%和110%设计转速的特性曲线。通过将计算结果与试验数据进行对比,分析研究了各激波损失模型在激波损失预估和风扇/压气机特性计算方面的差异。分析结果表明:在跨声速风扇/压气机近设计点激波损失和特性参数的计算中,正激波模型损失径向分布计算结果接近试验值,总压比和总效率计算值分别较试验值约低1.96%和2.54%,模型能够满足工程需要。而在近堵塞点,改进的双激波模型总损失计算值更接近试验值,总压比计算值和试验值很吻合,总效率计算值比试验值约高7.28%。改进双激波模型的不同转速线效率特性曲线也明显更接近试验值,模型能够较准确地预测远离设计点激波损失和特性参数。