Help from space: grant-free massive access for satellite-based IoT in the 6G era

The Sixth-Generation (6G) standard for wireless communications is expected to realize ubiquitous coverage for massive Internet of Things (IoT) networks by 2030. Satellite-based communications are recognized as a highly promising technical enabler to satisfy IoT service requirements in the 6G era. This study analyzes multiple access technologies, which are essential for the effective deployment of satellite-based IoT. First, we thoroughly investigate the existing research related to massive access, including information-theory considerations as well as Non-Orthogonal Multiple Access (NOMA) and Random Access (RA) technologies.Then, we explore the influence of the satellite transmission environment on multiple access technologies. Based on this study, a Non-orthogonal Massive Grant-Free Access (NoMaGFA) scheme, which reaps the joint benefits of RA and NOMA, is proposed for asynchronous transmissions in satellite-based IoT to achieve improved system throughput and enhance the system robustness under varying traffics. Finally, we identify some important and interesting future developments for satellite-based IoT, including waveform design, transceiver design, resource allocation, and artificial intelligence-enhanced design.     

Unprovability of a “precognition” effect in quantum mechanics

It is shown that nonlocality gives rise to an undecidable proposition, meaning it cannot be proved true nor proved false from the usual assumptions, but is independent of them. A variation on the usual thought experiment is considered in which the observers are timelike separated, but the nonlocality fails to become a precognition effect because of this independence result.     

对星载SAR压制式干扰的作战使用问题

压制式干扰是对抗星载SAR的重要手段，目前对星载SAR实施压制式干扰的方法可分为直达波压制干扰和间接波压制干扰。本文针对星载SAR的作战使用特点，在分析压制式干扰技术的基础上，重点对星载SAR压制式干扰的战术使用问题进行了研究，并且将压制干扰与间接波压制干扰的作战使用作了比较。研究结果表明：间接波干扰更有利于干扰设备作战效能的发挥，在对抗星载SAR的过程中有直达波干扰无法比拟的优势。     

三值双传输管电路的通用综合方法

提出采用双传管逻辑设计三值电路的方法,对每个MOS管的逻辑功能均采用传输运算予以表示以实现有效综合.建立了三值双传输管电路的反演法则和对偶法则.新提出的三值双传输管逻辑电路具有完全基于标准CMOS工艺,无需对MOS管作任何阈值调整,结构简单、规则,输入信号负载对称性好,逻辑摆幅完整以及无直流功耗等特点.采用TSMC 0.25μm工艺参数和最高电压为3V的HSPICE模拟结果验证了所提出综合方法的正确性.     

贝叶斯融合在SAR图像分类中的应用

本文研究将数据融合理论用于SAR图像分类.通过贝叶斯理论进行多通道SAR图像测量级数据融合,充分利用像素的从属信息并获得单通道分类无法获取的分类结果,有效保留各通道有用信息并抑制图像中的斑点噪声;针对贝叶斯融合涉及到的先验概率的问题采用两种方式进行先验概率估计,对估计引起的马赛克现象提出了三种解决方法;并提出三种先验概率融合方法,比较得出相对最优的SAR图像多通道分类方案.     

亚马逊热带雨林星载SAR辐射定标算法

天线外定标是实现星载SAR天线方向图在轨测试的主要手段。天线方向图的准确测量,对星载SAR图像的应用具有重要作用。分布目标辐射定标在星载SAR天线方向图测试中受到广泛重视。亚马逊热带雨林的后向散射系数呈现大面积的均匀性和稳定性,故成为分布目标定标最主要的定标场。该文在分布目标定标原理的基础上,对基于亚马逊热带雨林的星载SAR天线方向图测量算法进行了研究,提出了采用K．Pearson统计量非参数假设检验的一致性处理算法,并采用Levenberg-Marquard算法（LM算法）估计俯仰向天线方向图模型参数。仿真数据验证了算法的可靠性和准确性。     

基于电磁特性SAR图像目标识别模板的建立

针对SAR图像目标识别过程中识别模板形成的缺点和难点,提出了基于电磁散射特性SAR图像目标识别模板的数学模型和成像原理。采用一种混合算法计算了复杂目标的雷达截面(RCS),由目标的散射系数σ或RCS值,通过宽带合成孔径原理求出物体散射特性的空间分布,建立了SAR图像目标识别模板。实验验证了其正确性、有效性,以及具有近实时性、目标姿态连续性和精确性等特点,为快速准确地获取SAR图像中的目标信息提供技术支持。     

基于单片机和CPLD的控制系统设计

给出了控制系统的设计框图,对每一个模块的功能进行了分析,利用单片机、CPLD和数字化技术完成了系统设计,最后给出了分析结果.     

SAR stereo imaging algorithm based on Capon spectrum estimation

This letter presents a novel approach for the Synthetic Aperture Radar （SAR） stereo imaging based on the Capon spectrum estimation technique. In order to deal with nonuniform sampling space and lead to super resolution in the elevation direction, Capon approach is used to focus the SAR data on a certain height. Results obtained on simulated data demonstrate the feasibility of the Capon based algorithm. Compared with the classical Fast Fourier Transform （FFT）, the Capon based algorithm shows better resolution quality.     

一种1.8 V低功耗2 GHz预分频电路的设计

描述了一个应用于高集成度2 GHz频率综合器的预分频电路的设计,预分频电路中D触发器采用了源极耦合逻辑电路结构,可以提高电路工作频率,同时有效减小开关噪声和电路功耗.预分频电路采用TSMC 0.25 μm IPSM CMOS工艺实现,Spectre仿真表明,在1.8 V的电源电压下,经过优化的预分频电路能够在各种工艺条件和温度下正常工作,整体功耗为6.2 mw(单个D触发器功耗仅为1.8 mW),满足手持设备的要求.