Preliminary analysis of the quality and positioning performance of BDS-3 global interoperable signal B1C&B2a

BeiDou-3 Navigation Satellite System (BDS-3) satellites are equipped with the new generation GNSS signals B1C and B2a, which support the interoperability with GPS and Galileo systems. In this study, the pseudo-range multipath error and carrier phase observation noise of the BDS-3 B1C and B2a signals were evaluated based on zero baseline measurements from the day of year (DOY) 113 to 116, 2020. Further, the precision and performance of the single point positioning (SPP) and precise point positioning (PPP) are assessed at 9 stations. This assessment manifests that the standard deviations (STDs) of the pseudo-range multipath error are about 0.09 ~ 0.22 m, while STDs of the carrier phase observation noise are about 0.075 mm. For the single-frequency SPP, its positioning precision is about 2.03 ~ 4.85 m and 3.29 ~ 10.73 m at the 99.99% confidence level in horizontal and vertical directions, respectively, while the dual-frequency SPP precision is about 1.92 ~ 8.02 m and 4.81 ~ 12.77 m in horizontal and vertical directions, respectively. For the daily static PPP, the convergence time is about 20 ~ 30 min, while the daily positioning precision can reach 1.38 ~ 4.42 cm and -1.31 ~ 4.34 cm in horizontal and vertical directions, respectively. In general, the quality and the SPP and PPP performance of the BDS-3 B1C&B2a signals are comparable to the GPS and Galileo.     

The impact of different background errors in the assimilation of satellite radiances and in-situ observational data using WRFDA for three rainfall events over Iran

Satellite radiances and in-situ observations are assimilated through Weather Research and Forecasting Data Assimilation (WRFDA) system into Advanced Research WRF (ARW) model over Iran and its neighboring area. Domain specific background error based on x and y components of wind speed (UV) control variables is calculated for WRFDA system and some sensitivity experiments are carried out to compare the impact of global background error and the domain specific background errors, both on the precipitation and 2-m temperature forecasts over Iran. Three precipitation events that occurred over the country during January, September and October 2014 are simulated in three different experiments and the results for precipitation and 2-m temperature are verified against the verifying surface observations. Results show that using domain specific background error improves 2-m temperature and 24-h accumulated precipitation forecasts consistently, while global background error may even degrade the forecasts compared to the experiments without data assimilation. The improvement in 2-m temperature is more evident during the first forecast hours and decreases significantly as the forecast length increases.     

The connection between space weather and Single Event Upsets in polar low earth orbit satellites

Space weather is driven and modulated by the activity in the Sun. Space weather events have the potential to inflict critical damage to space systems. Nowadays, space assets are essential in our basic needs, such as communications, cell phone networks, navigation systems, television and internet. Hence, understanding space weather dynamics and its effects on spacecraft is crucial for satellites engineers and satellite operators, in order to prevent and mitigate its impacts.In the last decade our Sun has erupted several times causing dozens of space weather events. Some of these led to satellite malfunctions and outages lasting from mere hours, up to days and weeks. This research is focused on two different space weather events, March 7–8, 2012, and September 6–10, 2017, that occurred during the last ten years and caused satellite anomalies that are related to an increase in the single event upsets rate. Single event upset is a bit flip in a memory device due to high energy particle interaction with the device sensitive volume. During these two periods, Eros B, a low Earth orbiting polar satellite detected an increased rate of single event upsets on two of its processing computers when the high energy proton flux was elevated. On both occasions X-class flares were detected, and the increased single event upsets count rate in Eros B took place only after the 100 MeV protons flux was three orders of magnitude above the background levels. In this research, Israeli satellite anomalies that were detected are first demonstrated.     

陷波器对DLL的影响及其改进方法研究

陷波器被广泛应用于直接序列扩谱系统中滤除存在于系统工作频段内的干扰,分析 了陷波器对伪码跟踪环路的影响。针对陷波器引起的信号时延和畸变问题,提出对本地产 生的伪码也进行相应的陷波处理的方法来增加其与接收信号的相关性,同时针对信号畸变导 致的能量差值波动大的问题,提出增加能量积分时间的方法。在systemvue2006环境下对 提出的方法进行仿真验证,仿真结果表明这两种方法可以有效地削弱陷波器对伪码跟踪环 路的影响。
     

一种单子样旋转矢量姿态算法

旋转矢量姿态算法可有效抑制高动态环境下捷联惯导系统(SINS)产生的圆锥误差。当 直接应用多子样旋转矢量姿态算法时,会降低系统姿态更新频率;若要保持姿态更新频率, 则需要提高采样频率,从而增加了导航计算机的硬件负担,并导致量化误差突出。针对上述 不足,提出了一种利用当前及前N个姿态更新周期角增量的单子样旋转矢量姿态算 法,并在典型圆锥运动条件下推导了算法补偿项系数。此外,由于陀螺输出经过数字滤波处 理后其幅频特性的改变会影响圆锥误差的补偿效果,根据滤波器特性推导了单子样旋 转矢量姿态算法的修正算法,以便于在工程中推广应用。该算法在不降低姿态更新频率 的同时,可获得较高的解算精度,适于高动态环境应用,实验结果验证了上述算法的正确性 和有效性。
     

微弱GPS信号精捕获算法

为了解决微弱GPS信号比特/二次编码（Neumann\|Hoffman码）的同步以及频偏精细估计等问题,本文提出了对相关器输出数据进行精捕获的算法。通过对相关器输出数据进行二次变频,对不同频点的信号进行比特/二次编码位置的搜索,从而实现弱信号条件下比特/NH码的同步以及频偏的精捕获。精捕获后,使用频偏补偿后的数据进行频偏的再次精细估计。经过理论推导和仿真验证,在C/N0不低于20dB/Hz时,用1299个相关器输出数据进行精捕获时就有95%以上的检测概率,说明本方法适用于微弱GPS信号条件下比特/NH码的同步和频偏精细估计问题。
     

3GPP中TFCI编译码研究

在3GPP（第三代合作项目）协议中,为了提高传输格式组合指示（TFCI）的可靠性,对其采取了基于Reed-Muller码的超码编码。与经典RM编码相比,不但增加了码距,提高了纠错能力,而且可以利用快速哈达玛变换（FHT）提高译码速度。文章对协议中的编译码算法进行了研究,并对其纠错能力进行了仿真。     

吸收剂颗粒尺寸对吸波材料性能的影响

对最佳的吸收剂颗粒粒度进行数值计算和分析。从趋肤效应和单个磁畴颗粒大小两个角度,以纯铁粉为例对最佳的粒度做了分析,结果表明,对于2~18 GHz的雷达波,铁粉颗粒在16 nm~1μm为好。还分析了利用纳米颗粒的量子尺寸效应来吸收电磁波时颗粒的尺寸范围,计算结果表明,此时颗粒尺寸至少应小于22 nm。     

舰载机拦阻着舰动力学研究

舰载机拦阻着舰是舰载机有别于陆基飞机的主要特点,也是造成舰载机高事故率的主要原因。文章通过对舰载机着舰过程的分析建立了较完整的舰载机拦阻着舰动力学方程,并通过对拦阻力所在的拦阻平面研究,依据拦阻钩与拦阻索相对滑动所经历的时间进一步计算出舰载机撞索的安全范围。