超宽带信号在运动人体下阴影衰落对 通信性能的影响

超宽带信号在人体通信技术中具有低功耗、抗衰减等优势。针对人体信道建模工作中阴影衰落与运动状态关联性的问题,文章基于人体不同运动姿态与组织电磁特性建立人体模型,分析超宽带信号下的动态人体信道阴影衰落特性。首先,通过建立80条数据传播链路分析人体不同状态下的体表传播特性,给出了一种体表传播距离与路径损耗的二阶指数衰减关系。其次,分析了动态模型组织电特性变化对路径损耗的影响情况。最后,使用平均误码率研究了UWB系统在动态阴影衰落下的性能差异。结果表明,在动态人体模型下UWB频段的抗损耗性能优于HBC频段,其阴影衰落强度受运动状态影响程度强于HBC频段。研究对超宽带信号在人体通信的建模、应用工作中提供了动态人体阴影衰落强度分布的理论基础。     

28V低压直流载波通信系统的增益特性研究及系统实现

重点分析了搭载通信节点的直流信道的高频传输特性与阻抗特性,指出实际物理传输信道的特性是影响信号传输增益、有效传输距离及可靠性的关键,并利用信道结构的电路解析模型推导给出了不同通信节点配置情况下的高频信号传输增益计算式.在此基础上,搭建了总传输距离为8m的多节点直流载波通信实验平台,分别在1 MHz双节点与2 MHz多节...     

低压电力线通信信道模型

利用低压配电线进行高速数据通信，所使用的频段一般在1．6～30MHz之间。根据我国低压配电网的结构，对这个频段内低压电力线通信的信道模型进行了研究，包括单相传输部分和三相传输部分。     

水下回路通信电信号传输特性仿真研究

利用缆道与水体组成回路进行信号传输是实现水下至水上跨介质通信的有效方法,但此通信方式通信质量差且易受环境因素影响.为提升通信质量,对电信号在钢缆与水体形成的回路中的传输特性与影响因素进行研究.根据水体特性提出通信信道等效电路,通过有限元仿真分析电信号传输路径及电场分布,并且仿真计算通信距离、极板人水深度、水体宽度、极板...     

船舶超短波对空电台信道分析与使用策略研究

针对船舶在某海域航行中出现的通信距离无法提前判定的问题,在分析超短波传播特性的基础上,建立不同场景下的超短波无线信道模型,包括大尺度衰落的自由空间路径损耗模型、对数距离路径损耗模型和对数正态阴影路径损耗模型,该模型考虑到小尺度衰落的多普勒效应影响,并利用MATLAB软件仿真计算了各模型场景下对电台功率路径损耗的影响。在此基础上,提出计算链路预算方法,依此测算船舶超短波对空电台与飞机进行通信距离的方法以及优化通信链路预算的策略。     

基于人体通信的生物特征身份识别方法研究

由于人体通信技术发展迅速且应用前景广阔,提出一种基于人体通信技术的生物特征身份识别方法。在适合人体通信的UWB频段和HBC频段下,将人体通信链路的路径损耗作为生物特征。首先根据不同链路的测量值,使用支持向量机进行身份识别;再使用带有不同核函数的C-SVM和Nu-SVM方法在11条链路的数据集下进行身份识别;最后选取8～10 GHz的UWB子频段进行识别提高计算速度。结果表明,链路通信距离越长,识别率越高。带高斯核的C-SVM在UWB频段下的识别效果最好,识别率达96.41%、AUC为0.999 1以及0.017 2%的EER。通过选取子频段将计算时间降低到0.142 s,速度得到明显提高。     

39.5 GHz室内走廊环境毫米波MIMO信道特性研究

目前5 G采用毫米波通信系统,其中39.5 GHz频段为其中关键使用频段需要研究其MIMO信道特性。采用射线跟踪法预测在走廊环境下的39.5 GHz毫米波MIMO信道特性,通过对比仿真和实测结果验证了射线跟踪法的可行性。发现路径损耗斜率较小,说明该环境下毫米波传输较远。同时发现了沿走廊纵向方向收发距离较近时,以直射径为主,LOS分量大,距离较远时有效反射次数较少,角度扩展小相关性强,LOS分量也大,而沿纵向方向中间处具有丰富的散射,NLOS分量增大,所以容量会出现峰值。在此基础上预测了走廊环境下不同区域的2×2、4×4 MIMO以及4×64 Massive MIMO信道容量变化,发现了走廊中间的信道容量高于走廊壁两侧,同时发现采用4×64 Massive MIMO相较于4×4 MIMO可以获得一定的容量增益,但是不会有巨大的提升。     

有线电视电缆干线的调试与维护

1.电缆传输干线(1)放大器的间距电缆传输干线一般由干线放大器和同轴电缆串接而成。放大器的主要作用是补偿同轴电缆对信号的损耗,即放大器的增益等于同轴电缆的损耗。放大器间隔的距离由系统传输的带宽、选用电缆的质量和放大器的增益决定。     

基于230MHz电力专用频谱的载波聚合技术

无线专网通信技术是中低压通信接入网络中的重要组成部分,但频谱资源的有限性是制约电力无线专网技术发展的重要因素。目前电力专用230MHz频谱只能支持很低的传输速率和频谱效率,为了提高频谱效率,承载更高传输速率的业务,文中提出了在该频段上使用载波聚合技术。结合230MHz频段特点,设计出载波聚合的数字电路。为验证载波聚合的实现效果,对230MHz频谱上使用载波聚合后的传输速率进行估算,并在新型电力无线宽带系统中进行实验验证。计算和实验结果都表明:通过载波聚合技术,该频段的频谱效率有显著提高。     

低压电力线载波信道阻抗测试终端的设计与应用

依据自由坐标轴阻抗测试原理,设计了低压电力线载波信道阻抗测试终端,实现了载波信道阻抗模值和阻抗相位的实时测量、数据远程传输以及主站监控计算机对信道阻抗特性的远程监控。阻抗测试终端依据主站监控计算机的控制命令,能够实现在100～500kHz频率范围内的任意5个载波频率点或单一载波频率点处,同时对A、B、C三相或某一相的循环阻抗测试,且载波频率点间的最小间隔为0.1kHz。阻抗测试范围与精度可达到(5～10Ω)±10%、(10～500Ω)±5%。本文分析了公用建筑不同季节和住宅小区冬季载波通信性能较差情况下的电力线信道阻抗测量结果,为电力线阻抗监测及改善电力线载波系统通信性能提供有力手段。     

农村10 kV配电线路高频信道特性测试及分析

利用中压电力线实现高速数据通信,目前在国内尚属一项空白。如果能够充分运用农村高覆盖率的中压配电网,进行远距离PLC高速通信,将推进农村信息化建设和开创电力工业新的经济增长点。文章对中压(10 kV)配电线路的高频信道特性进行了测试研究,并以河北省某乡一座35 kV变电站的10 kV出线为测试对象,自行搭建测试系统,进行了噪声特性、衰减特性、阻抗特性方面的测试,掌握了相应数据资料。笔者通过分析,提出了选用2~12 MHz作为实现中压PLC远距离高速数据传输工作频段的建议。     

A low‐power,area‐efficient multichannel receiver for micro MRI

A new integrated, low‐noise, low‐power, and area‐efficient multichannel receiver for magnetic resonance imaging (MRI) is described. The proposed receiver presents an alternative technique to overcome the use of multiple receiver front‐ends in parallel MRI. The receiver consists of three main stages: low‐noise pre‐amplifier, quadrature down‐converter, and a band pass filter (BPF). These components are used to receive the nuclear magnetic resonance signals from a 3 × 3 array of micro coils. These signals are combined using frequency domain multiplexing (FDM) method in the pre‐amplifier and BPF stages, then amplified and filtered to remove any out‐of‐band noise before providing it to an analog‐to‐digital converter at the low intermediate frequency stage. The receiver is designed using a 90 nm CMOS technology to operate at the main B₀ magnetic field of 9.4 T, which corresponds to 400 MHz. The receiver has an input referred noise voltage of 1.1 nV/√Hz, a total voltage gain of 87 dB, a power consumption of 69 mA from a 1 V supply voltage, and an area of 305 µm × 530 µm including the reference current and bias voltage circuits. Copyright © 2013 John Wiley & Sons, Ltd.     

A Tunable Active Phase Shifter Using a Thin Film Ferroelectric Capacitor

This paper describes an active phase shifter with a large amount of variable phase. We propose a design that has second-order all-pass network characteristics and that uses a tunable ferroelectric capacitor. The transmitted phase is changed by varying the capacitance of a ferroelectric capacitor. A computer simulation is presented that shows that the network, even with markedly non-ideal transistors, can provide a true all-pass response over the frequency band of interest (100 MHz–400 MHz). These simulated results demonstrate an analog tunability of about 200° with a gain variation of about 3 dB at 300 MHz—when using a Ba_0.96Ca_0.04Ti_0.84Zr_0.16O₃ (BCTZ) capacitor with a tunability of 2:1. The simulation performed at 300 MHz because the physical layout of the real life circuit will be done mostly with the discrete components. As the self resonance frequency of most of the discrete components lies in the few hundreds of MHz range, our preferred frequency is a practical one to deal with. The simulation also predicts a flat band gain of approximately 10 dB with ± 2 dB of gain ripple.     

Indoor Power-Line Communications Channel Characterization up to 100 MHz—Part II: Time-Frequency Analysis

Estimations of coherence bandwidth and time-delay parameters from wideband channel sounding measurements made in the 30 kHz-100 MHz band in several indoor environments are described in and taken back in this paper. Powerline communications (PLC) modems rather see a channel which starts almost from 2 MHz . A comparison between coherence bandwidth and time-delay parameters estimated in both frequency bands 30 kHz-100 MHz and 2 MHz-100 MHz is elaborated in this paper. Results are intended for applications in high-capacity indoor power-line networks. The investigation is aimed to show that the PLC channel studies in a band starting from a frequency lower than 2 MHz distorts the real values that an implementer should take, as the PLC modem see only the frequencies from 2 MHz. The coherence bandwidth and the time delay parameters are estimated from measurements of the complex transfer functions of the PLC channels. For the 30 kHz-100 MHz frequency band, the 90 th percentile of the estimated coherence bandwidth at 0.9 correlation level stay above 65.5 kHz and below 691.5 kHz. It was observed to have a minimum value of 32.5 kHz. The maximum excess delay spread results show that 80% of the channels exhibit values between 0.6 s and 6.45 s. And a mean rms delay spread of 0.413 s is obtained. The passage to the 2 MHz-100 MHz frequency band induced an increase of the coherence bandwidth, whose min value is brought back to 43.5 kHz, and an important reduction of the time delay parameters: The min, max, mean, and standard deviation values of the maximum excess delay are almost divided by 2. For the twice frequency bands, this paper studies, also, the variability of the coherence bandwidth and time-delay spread parameters with the channel class , and thus with the location of the receiver with respect to the transmitter, and finally relates the rms delay spread to the coherence bandwidth.     

矢量调制在相干多通道信号发生中的应用研究

对基于相干体制的多通道电子系统如MIMO通信、相控阵雷达、多通道侦察接收机等进行性能评估与测试一直是一个复杂、昂贵的过程,因为难以产生符合测试要求的多路相干信号。提出了一种基于矢量调制技术的宽频带相干多通道信号发生方法,分析了矢量调制器的非理想特性对多通道相干信号发生的影响,给出了解决思路。该方法具有频率覆盖范围宽、相位控制范围大、精度高、调节分辨率精细等优点,为基于相干体制的多通道接收机测试提供了一种高效便捷的信号模拟方法。     

A −40-dB EVM 20-MHz subsampling multistandard receiver architecture with dynamic carrier detection,bandwidth estimation,and EVM optimization

In this work, a reconfigurable multistandard subsampling receiver with dynamic carrier frequency detection and system-level EVM optimizations is proposed. Ideal software defined radio (SDR) receivers promise complete flexibility at the expense of high-performance analog-to-digital converters (ADCs) that are challenging to implement in current technologies for low-power applications. This scenario leads to the research of digital intensive sampling receivers with discrete-time signal processing (DTSP) implemented in analog domain. This approach makes it feasible to move channel selection filtering and dynamic gain adaptability from analog to digital domain. The proposed receiver employs subsampling down-conversion along with subband filters to dynamically detect the carrier frequency of the incoming signal, estimate its bandwidth, and identify if the signal is present in one of the target standard bands. This carrier detection provides a unique capability to reconfigure the receiver dynamically. Additionally, in this work, system-level EVM optimization is proposed considering frequency synthesizer phase noise, IQ mismatch, sampling frequency selection and block-level gain, noise, and nonlinearity. The RF front end of the proposed receiver is modeled in Verilog-AMS whereas the digital signal processing is implemented in Simulink-Matlab. The complete receiver has been verified to detect and process three different bands belonging to three different standards (GSM, UMTS, and WLAN) with the carrier frequency ranging from 0.9 to 2.5 GHz. Test signals with 4-QAM modulation, maximum bandwidth of 20 MHz, and input-dynamic range from –109 to –20 dBm is utilized to demonstrate the receiver performance including an EVM of –40 dB.     

两通道多级信道化接收机的设计

为满足测向接收机对两个同时到达的不同带宽雷达信号的测量和跟踪需求,提出了一种双通道、多级信道化的高效宽带数字接收机结构,该接收机采用了宽窄两种带宽、奇偶两种信道排列形式,三级信道化结构的方案。经过三级的频带分割可提供多种频率分辨率,可以适应不同带宽信号的输入,改善了单级信道化同时处理窄带信号和宽带信号的性能局限性,并通过有效信道检测机制实现了对两个同时到达的不同带宽的雷达信号的接收跟踪。仿真结果表明,该双通道多级信道化接收机功能正确,具备硬件实现的可行性。     

Broadband transmission characteristics for power-line channels

Transmission properties of the power-line channels play a very important role in the reliability of signal propagations. This paper discusses the physical signal transmission property on the broadband power-line channels based on transmission-line theory, mode propagation theory and electromagnetic-field radiation theory. It also examines the carrier signal propagating through the multi-path line channel by empirical data. The correlations among the channel attenuation and frequency, length of the path, loads and branches are analyzed, respectively, and the path loss is calculated based on empirical data and linear regressive analysis. In the end, the impact of the radiation from carrier signals on the channel characteristic measurement is concluded.