GNSS spoofing detection for single antenna receivers via CNR variation monitoring

In this paper,a method for spoofing detection based on the variation of the signal’s carrier-to-noise ratio(CNR)is proposed.This method leverages the directionality of the antenna to induce varying gain changes in the signals across different incident directions,resulting in distinct CNR variations for each signal.A model is developed to calculate the variation value of the signal CNR based on the antenna gain pattern.This model enables the differentiation of the variation values of the CNR for authentic satellite signals and spoofing signals,thereby facilitating spoofing detection.The proposed method is capable of detecting spoofing signals with power and CNR similar to those of authentic satellite signals.The accuracy of the signal CNR variation value calculation model and the effectiveness of the spoofing detection method are verified through a series of experiments.In addition,the proposed spoofing detection method works not only for a single spoofing source but also for distributed spoofing sources.

基于载噪比模型加权的GNSS双频载波和差联合跟踪算法优化与分析

前期发展的全球导航卫星系统(global navigation satellite system,GNSS)双频载波和差联合跟踪算法存在双频信号载噪比不一致情况下双频信号跟踪稳定度和跟踪精度较差问题,对此提出了优化改进的算法。针对实际应用中共星双频信号存在的信号载噪比不同情况,优化原有双频载波和差联合跟踪环路结构,基于载噪比模型计算GNSS双频信号在双频载波和差联合跟踪环路中的加权值,利用该加权值实现共星双频信号的载波和差联合跟踪。算法理论分析和仿真结果表明,优化后的基于载噪比模型加权的GNSS双频载波联合跟踪算法更加适用于实际应用条件,能够提高原有算法在双频信号载噪比不一致情况下共星双频信号跟踪稳定性和跟踪精度。

基于图像加权的多能光子计数X线CT全能谱图像重建改进方法

为了提高基于图像加权的多能光子计数X线CT全能谱重建图像的质量,提出了一种图像重建改进方法.首先,对每个能量段的投影数据采用最大后验概率(MAP)统计重建算法进行图像重建;然后,对各能量段图像进行优化加权求和,获得全能谱图像.仿真实验结果表明,MAP统计重建算法可显著提高全能谱重建图像的对比噪声比(CNR).与滤波反投影算法相比,当能量段数分别为2,4,6,9时,MAP统计重建算法使得钙图像的CNR分别提高659.7%,643.4%,621.2%,586.1%,碘图像的CNR分别提高663.8%,648.6%,635.1%,600.9%,软组织图像的CNR分别提高596.2%,638.5%,592.6%,596.3%;与能量积分法相比,当能量段数分别为2,4,6,9时,M AP统计重建算法使得钙图像的CNR分别提高43.3%,49.1%,49.3%,44.5%,碘图像的CNR分别提高43.2%,45.7%,45.7%,40.2%,软组织图像的CNR分别提高21.5%,28.9%,25.5%,26.2%.

1．5TMR不同b值的扩散加权成像（DWI）在肺内实性病变鉴别中的优化

目的探讨MR扩散加权成像（DWI）中不同b值在肺内实性病变鉴别诊断中的应用及优化。方法收集我院肺内病变60例。其中恶性病变32例，良性病变28例。应用呼吸门控技术，在相同扫描参数下，激励次数（NEX）8次，采用三组不同b值分别等于（500s／mm2；800s／mm2；1000s／mm2）进行胸部DWI序列扫描。测量并分析三组ADC值特点及不同b值对影像质量、信噪比（SNR）、对比噪声比（CNR）的影响。结果在复杂的肺内病变影像中，采用不同b值时，ADC值测量结果呈现出逐步下降趋势，影像质量、信噪比、对比噪声比存在差异，ADC值测量结果均具有诊断价值。其中选择b=1000s／mm2时，最具有临床诊断意义。结论在1．5T场强下，应用上述参数及呼吸门控技术，在激励次数为8次，b=1000s／mm2时，操作特征（ROC）曲线下面积最大为0．636，其敏感度为61．5％，特异度为71．9％，最具有临床诊断意义，优于其它两种方案，未产生严重的磁敏感性伪影，但信噪比有所下降，仍可以清晰显示感兴趣区域的组织及病变形态。

Influence of double Rayleigh backscatter in CATV systems with Raman amplifiers

The double Rayleigh backscatter （DRB） effect in long distance CATV systems using fiber Raman amplifiers （FRAs） is investigated theoretically in the paper. As a comparison, performance of a system with erbium doped fiber amplifier （EDFA） is also evaluated. According to the simulation results, it is found that, in case of FRA, the increase of carrier-to-noise ratio （CNR） due to the DRB effect will not impair the performance more than that using EDFA.