链路增益平坦度对OTA测试准确性的影响分析

空口(OTA)测试已广泛应用在无线通信领域,提高测试结果的准确性是OTA测试当前急需解决的问题.文章从影响OTA测试结果准确性的因素链路增益平坦度入手,使用衰减器对测试链路进行增益削剪,分析测试了不同链路增益平坦度对被测件的EVM(误差矢量幅度)、BER(误码率)、TIS(总全向灵敏度)三项性能指标的测试误差与测试不确定度的影响.测试结果表明,增大链路增益平坦度会导致EVM、BER参数发生偏移,降低测试系统的通信质量;当系统的链路增益平坦度为1.82 dB时,测试误差与不确定度接近CTIA测试标准中规定值.最后,提出一种使用增益均衡器降低链路增益平坦度的方法,在链路增益平坦度为3.25 dB的测试系统中可将其控制在0.5dB以内.     

基于DF中继协作的车联网安全传输性能研究

5G时代的到来加快了以车路协同为核心的车联网技术的发展脚步。高效，可靠，安全的通信质量将是实现智能交通管理系统，完善智慧出行的基本要求。因此，针对存在信息窃取者的车联网中继协作传输场景，利用机会式中继选择策略与最大比合并技术设计了直接传输链路与多跳中继转发链路共存的安全传输方案，旨在提高信息传输的可靠性及安全性。同时，在获得信道概率密度函数及累积分布函数的基础上，利用全概率公式等方法推导出基于DF(Decode-Forward)中继协作传输的车联网系统安全中断概率的闭合表达式，其中涉及的信息传输信道均服从Nakagami-m分布，提高了理论推导的难度。最终的仿真实验证实了理论推导的准确性及本方案的可行性。      

雾天多次散射对激光透射仪能见度测量的影响

为了分析雾天多次散射引起的激光透射仪能见度测量误差，结合激光大气透射仪的系统参量，基于平流雾和辐射雾分布模型，采用蒙特卡洛法对激光在雾中的传输特性进行了理论分析和数值模拟，获得了雾天透过率数据，并计算得到了多次散射引起的能见度误差。结果表明，在雾天气下随着空气中含水量的增多，多次散射越明显，透过率测量误差越大，辐射雾的透过率相对误差高达116.76%；同等条件下，当接收机直径为100cm时，辐射雾多次散射引起的能见度测量误差为19.30%；同时选取较小的接收机直径可以减小多次散射引起的能见度测量误差。因此, 在雾天应用激光透射仪进行能见度测量时，需考虑多次散射的影响。此研究结果对实际雾天气下激光大气透射仪能见度的测量具有重要的指导意义。     

Crystal-Plasticity-Based Dynamic Constitutive Model of AZ31B Magnesium Alloy at Elevated Temperature and with Explicit Plastic-Strain-Rate Control

In this study,a series of experiments were carried out on the AZ31B magnesium alloy,including both a macro-experiment(mechanical experiment)and a micro-experiment(dislocation observation).Next,based on the consideration of the deformation mechanism of magnesium alloys(dislocation slip and twinning),a dynamic constitutive model of the magnesium alloy was established.In the developed model,the strain-rate-sensitivity control and the effect of temperature on the dynamic mechanical performance of the alloy were also investigated.The model parameters were determined by fitting the macroscopic experimental results.Next,the evolution of the micro-deformation mechanism was calculated by the developed model,and the trend of macro-mechanical behavior was also discussed.     

Health Monitoring of Long-Haul Fiber Communication System Using Chaotic OTDR

A novel chaotic optical time-domain reflectometry(OTDR)-based approach was proposed for monitoring long-haul fiber communication systems with multiple fiber segments. The self-phase modulation and group velocity dispersion effects of the optical cable was considered in demonstrating the proof-of-concept experiment and simulation. In experiments, the correlation peaks are clearly obtained from the correlation trace between the reference and reflected(or scattered) light signals propagating in three optical-fiber segments. The technique affords a high spatial resolution of 2 m, and further long-haul fiber simulations indicate that the sensing distance can be more than 3300 km. Thus, the new proposed technique can be effectively applied for health monitoring of long-haul fiber communication systems.