中频软件无线电接收机的设计与实现

文章通过对软件无线电基本理论的研究,得出一种多相滤波数字正交变换的中频软件无线电结构,A/D的采样频率只有原采样频率的一半,这样就降低了对采样器件的要求。为了降低后续DSP处理速度需求压力,文中利用FPGA实现了多相滤波数字正交变换结构的延迟滤波,证明了这种结构的正确性和可行性。     

Oblique-incidence ionospheric soundings over Central Europe and their application for testing now casting and long term prediction models

After a first oblique-incidence ionospheric sounding campaign over Central Europe performed during the period 2003–2004 over the radio links between Inskip (UK, 53.5°N, 2.5°W) and Rome (Italy, 41.8°N, 12.5°E) and between Inskip and Chania (Crete, 35.7°N, 24.0°E), new and more extensive analysis of systematic MUF measurements from January 2005 to December 2006 have been performed. MUF measurements collected during moderately disturbed days (17 ? Ap ? 32), disturbed days (32 < Ap ? 50) and very disturbed days (Ap > 50), have been used to test the long term prediction models (ASAPS, ICEPAC and SIRM&LKW), and the now casting models (SIRMUP&LKW and ISWIRM&LKW). The performances of the different prediction methods in terms of r.m.s are shown for selected range of geomagnetic activity and for each season.     

Gradient pattern analysis of short solar radio bursts

We analyze the weak component of the localized temporal pattern variability of 3 GHz solar burst observed by the Ondrejov radiospectrograph. A complex, short and weak impulsive sample from the time series was analyzed by applying a method based on the gradient pattern analysis and discrete wavelet decomposition. By analyzing canonical temporal variability patterns we show that the new method can reliably characterize the phenomenological dynamical process of short time series (N ? 10³ measurements) as the radio burst addressed here. In the narrowest sense, by estimating the mutual information distance in the gradient spectra, we show that the fluctuation pattern of the short and weak 3 GHz impulsive solar burst, with energetic amplitudes <350 SFU, is closer to the intermittent and strong MHD turbulent variability pattern.     

Multi-scale reconnections in a complex CME

A series of three flares of GOES class M, M and C, and a CME were observed on 20 January 2004 occurring in close succession in NOAA 10540. Types II, III, and N radio bursts were associated. We use the combined observations from TRACE, EIT, Hα images from Kwasan Observatory, MDI magnetograms, GOES, and radio observations from Culgoora and Wind/ WAVES to understand the complex development of this event. We reach three main conclusions. First, we link the first two impulsive flares to tether-cutting reconnections and the launch of the CME. This complex observation shows that impulsive quadrupolar flares can be eruptive. Second, we relate the last of the flares, an LDE, to the relaxation phase following forced reconnections between the erupting flux rope and neighbouring magnetic field lines, when reconnection reverses and restores some of the pre-eruption magnetic connectivities. Finally, we show that reconnection with the magnetic structure of a previous CME launched about 8 h earlier injects electrons into open field lines having a local dip and apex (located at about six solar radii height). This is observed as an N-burst at decametre radio wavelengths. The dipped shape of these field lines is due to large-scale magnetic reconnection between expanding magnetic loops and open field lines of a neighbouring streamer. This particular situation explains why this is the first N-burst ever observed at long radio wavelengths.     

HPM对伪码脉冲无线电引信的压制干扰效应仿真

为了对高功率微波作用于伪码脉冲无线电引信的干扰效果进行分析,建立了引信信号处理模型并进行了计算机仿真。仿真结果表明,在频率对准的情况下,当 HPM进入引信距离门对回波信号造成压制时,由于 HPM的信号频带较宽,覆盖了多普勒滤波器带宽,多普勒滤波器的输出信号幅度仍可达到启动门限电平,压制干扰无效。     

水下单信标导航航路规划和最优航路接近方法

相比于传统的长基线和超短基线等导航方式，水下单信标导航具有布放简单的优点，但其导航精度有待进一步提高。为此，提出了单信标导航的航路规划方案，通过泰勒级数展开推导了水平位置精度因子的表达式，并分析了导航点和声信标的相对几何位置关系对导航精度的影响，最终提出了航路规划方案。在此基础上，还提出了自主水下航行器(autonomous underwater vehicle，AUV)从其他位置接近最优航路的方法，包括两部分：一是建立以时延为观测量的滤波模型，利用滤波算法实时获取AUV的位置估计值；二是基于可观测度分析结果对最优航路接近过程的轨迹进行了设计。二者的结合使得AUV高效率且高精度地逼近最优航路。仿真证明了采用所提出的航路规划方案和最优航路接近方法可以提高导航精度，航路规划方案使得AUV位置估计的均方根误差近似为2 m。     

雷达遥感卫星频率分配与射频干扰抑制:机遇与挑战

雷达遥感卫星作为一种重要的民用空间基础设施，能够实现全天时、全天候的高分辨对地观测，对推动科学进步、促进经济发展和维护国家安全具有重大战略意义。但随着全域无线电业务的快速增长，频率共享导致的兼容冲突日益加剧，衍生出的射频干扰已成为困扰定量化精确遥感探测性能的共性难题。本文系统地梳理了典型波段的对地观测业务频率分配现状，介绍了射频干扰的定义和影响机理，提出了模型数据混合驱动的干扰抑制新思路，并对面临的机遇与挑战进行了归纳总结，为新一代雷达遥感卫星的频率优化设计提供知识依据，进而保障其在复杂电磁环境的对地观测效能。     

一种瞬时大带宽DRFM系统的信道化设计

为实现宽带雷达回波信号的模拟生成,通常采用基于信道化技术的射频存储(DRFM)系统。在信道化DRFM系统中,不合理的信道划分方案和多相滤波器设计会导致频谱混叠、频谱分量缺失和幅度失真。文章提出了一种相邻信道频谱有50%交叠的信道划分方法,并对信道化滤波器组进行了优化设计。在此基础上,给出了一种瞬时大带宽DRFM系统的实现方案。仿真结果表明,文章提出的设计方案可以实现Nyquist采样带宽内雷达信号的射频存储和模拟转发,且具有较小的幅度失真,可以满足瞬时大带宽雷达回波信号的模拟需求。     

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.     

一种多源测距与视觉惯性融合的月球车定位方法

针对月球车月面探测活动任务中对高精度定位的需求,当前视觉惯性定位方法存在误差累积,并且在缺乏先验环境信息时无法消除,基于三角测量原理的无线电定位方法可以通过测量接收端到至少三个不同发射端的距离来确定目标物体位置,但需要架设三台以上基站,因此难以满足月面环境下大范围定位的需求。文章提出了一种基于基站无线测距和视觉惯性里程计融合定位方法,以解决上述定位手段存在的问题。该方法首先利用视觉惯性里程计构建的环境模型将WIFI、UHF和UWB三类无线电基站测距信息进行融合,然后将测距结果和视觉IMU信息进行位置联合解算来确定月球车位置,最后在Matlab和Gazebo软件平台上进行仿真验证,在距离基站最远行进1500米的条件下实现了0.92米定位误差。实验结果表明,该方法能够在满足月面探测任务对于精准定位的需求。