A new method to determine the gravity field of small bodies from line-of-sight acceleration data

We present a new method to derive line-of-sight acceleration observables from spacecraft radio tracking data. The observables can be used to estimate the mass and gravity of a natural satellite as a spacecraft flyby. The corresponding observation model adapts to one-way and two/three-way tracking modes. As a test case for method validation and application, we estimated the mass and degree two gravity field for the Martian moon Phobos using simulated tracking data when the spacecraft Mars Express flew by Phobos on 2013 December 29. We have a few real tracking data during flyby and they will be used to confirm raw data simulation. The main purpose of this paper is to demonstrate the method of line-of-sight acceleration reduction from raw tracking data and the feasibility to estimate mass and gravity of a natural satellite using this type of observable. This novel method is potentially applicable to planet and asteroid gravity field studies combined with Doppler tracking data.

Comparison of visual effects of FS-LASIK for myopia centered on the coaxially sighted corneal light reflex or the line of sight

AIM：To compare visual quality after femtosecond laser in situ keratomileusis（FS-LASIK）,between the coaxially sighted corneal light reflex（CSCLR） group and conventional ablation line of sight（LOS） group.METHODS：In total,243 eyes（122 patients） were treated with centration on the CSCLR（visual axis） and 238 eyes（119 patients） treated with centration on the pupil center（LOS）.Postoperative outcomes [uncorrected visual acuity（UCVA）,best spectacle-corrected visual acuity（BSCVA）],safety index,efficacy index,refractive outcome,ablation center distance from the visual axis,corneal high-order aberrations,subjective discomfort glare and shadowing incidence rate,and contrast sensitivity at 1,3,and 6mo were measured and compared.RESULTS：The mean age was 27.77±7.1y in the CSCLR group and 26.03±7.70 y in the LOS group.Preoperatively,the manifest refraction spherical equivalent（MRSE） was-6.68±2.60 D in the CSCLR group and-6.65±2.68 D in the LOS group.The postoperative UCVA,BSCVA,MRSE（-0.03±0.263 D in the CSCLR group,-0.05±0.265 D in the LOS group）,efficacy index（1.04,1.03）,and safety index（1.09,1.08） were not significantly different between the groups（all P〉0.05）.In total,3% lost one line and more of BSCVA in the CSCLR group,as 9% in the LOS group postoperatively（P〈0.05）.The ablation center deviation was 0.20±0.15 mm from the visual axis（Pentacam system default setting;range,0-0.75 mm） in the CSCLR group,and 0.43±0.22 mm（range,0-1.32 mm） in the LOS group（P〈0.0001）.Statistically significant greater augmentationof total corneal higher-order aberrations（0.15±0.10 μm and 0.20±0.12 μm respectively,P=0.03） and vertical and horizontal coma（P〈0.0001） were noted in the LOS group.Subjective discomfort glare and shadowing incidence rates were 8.59% and 17.5% in the CSCLR and LOS groups,respectively（P〈0.05）.The 1-month postoperative contrast sensitivity visual acuity in the CSCLR group was significantly higher than that in the LOS group on contrast（100%,25%,10%） with a dark background,but there was no significant difference between the groups at 3 or 6m.CONCLUSION：Myopic LASIK centered on the CSCLR achieves significantly lower induction of loss of BSCVA,corneal high-order aberrations,and lower risk of subjective discomfort glare and shadowing,and lower decline in early contrast sensitivity by comparison with centration on the LOS,giving advantages in visual quality postoperatively.

Efficiency Effect of Obstacle Margin on Line-of-Sight in Wireless Networks

Line-of-sight clarity and assurance are essential because they are considered the golden rule in wireless network planning,allowing the direct propagation path to connect the transmitter and receiver and retain the strength of the signal to be received.Despite the increasing literature on the line of sight with different scenarios,no comprehensive study focuses on the multiplicity of parameters and basic concepts that must be taken into account when studying such a topic as it affects the results and their accuracy.Therefore,this research aims to find limited values that ensure that the signal reaches the future efficiently and enhances the accuracy of these values’results.We have designed MATLAB simulation and programming programs by Visual Basic.NET for a semi-realistic communication system.It includes all the basic parameters of this system,taking into account the environment’s diversity and the characteristics of the obstacle between the transmitting station and the receiving station.Then we verified the correctness of the system’s work.Moreover,we begin by analyzing and studying multiple and branching cases to achieve the goal.We get several values from the results,which are finite values,which are a useful reference for engineers and designers of wireless networks.

Link Budget Design for RF Line-of-Sight via Theoretical Propagation Prediction

Line-of-sight (LOS) link planning condition has been observed to have effects on the atmospheric factor which cause crucial signal loss. The main objective of the planning was to improve a set of a link using point to point condition to assist the performance in emerging its strategy for handling the fixed WLAN service. The purpose of this paper is to provide a quick description of various propagation loss mechanisms on Link Budget Tool (LBT). LBT is customized to create point to point link for local area network (LAN) through radio frequency range operating between 2.400 GHz and 5.800 GHz. This software is able to define the effect of signal loss and expected performances according to the distances between link propagation conditions based on a number of system parameters.

Calculation of Probability of Cloud-Free Lines-of-Sightat Given Heights in Foshan, China

Based on Lund and Shanklin’s work (1972), methods of calculating Probability of Cloud-Free Lines-of-Sight (PCFLOS), Persistence Probability of Cloud-Free Lines-of-Sight (PPCFLOS) and Recurrence Probability of Cloud-free Lines-of-Sight (RPCFLOS) at given heights are presented. PCFLOS, PPCFLOS and RPCFLOS are calculated in Foshan, China by conventional observation data from 1961 to 1990. The conclusions are: (1) The higher the elevations, the smaller the PCFLOS and the larger the view angles, the larger the PCFLOS. (2) PPCFLOS and RPCFLOS decrease with the increase of elevation and the delay of time. (3) RPCFLOS is always equal to or larger than PPCFLOS at lag times.

Line-of-Sight MIMO for Next-Generation Microwave Transmission Systems

Line-of-sight MIMQ （LoS MIMO） is not applicable in scattering wireless transmission scenarios, but it may be applied in LoS microwave transmission scenarios if antenna spacing （within transmit and/or receive arrays） is suitable and there is one hop distance. LoS MIMQ can improve channel capacity and performance of a transmission system. In this paper, we discuss factors affecting channel capacity and performance in LoS MIMO. We also discuss the feasibility LoS MIMO applications.

Disparity-Based Generation of Line-of-Sight DSM for Image-Elevation Co-Registration to Support Building Detection in Off-Nadir VHR Satellite Images

The integration of optical images and elevation data is of great importance for 3D-assisted mapping applications. Very high resolution (VHR) satellite images provide ideal geo-data for mapping building information. Since buildings are inherently elevated objects, these images need to be co-registered with their elevation data for reliable building detection results. However, accurate co-registration is extremely difficult for off-nadir VHR images acquired over dense urban areas. Therefore, this research proposes a Disparity-Based Elevation Co-Registration (DECR) method for generating a Line-of-Sight Digital Surface Model (LoS-DSM) to efficiently achieve image-elevation data co-registration with pixel-level accuracy. Relative to the traditional photogrammetric approach, the RMSE value of the derived elevations is found to be less than 2 pixels. The applicability of the DECR method is demonstrated through elevation-based building detection (EBD) in a challenging dense urban area. The quality of the detection result is found to be more than 90%. Additionally, the detected objects were geo-referenced successfully to their correct ground locations to allow direct integration with other maps. In comparison to the original LoS-DSM development algorithm, the DECR algorithm is more efficient by reducing the calculation steps, preserving the co-registration accuracy, and minimizing the need for elevation normalization in dense urban areas.

Netro-非视距(Non Line Of Sight)固定无线架构的灵活性

成功地部署一个固定宽带无线(FBW)网络取决于两个关键因素：射频网络规划的灵活性和视距(LOS)／非视距(NLOS)情况。因为在视距(LOS)情况下要求在发射机和接收器之间没有阻挡，运营商在规划和部署一个视距(LOS)的固定宽带无线(FBW)网络时，需面对许多技术和业务上的困难；事实上第……

Characterization of Blue-Green Light Non-Line-of-Sight Transmission in Seawater

The blue-green light in the 450 nm to 550 nm band is usually used in underwater wireless optical communication (UWOC). The blue-green light transmission in seawater is scattered by the seawater effect and can achieve communication in non-line-of-sight (NLOS) transmission mode. Compared to line-of-sight (LOS) transmission, NLOS transmission does not require alignment and can be adapted to various underwater environments. The scattering coefficients of seawater at different depths are different, which makes the scattering of light in different depths of seawater different. In this paper, the received optical power and bit error rate (BER) of the photodetector (PD) were calculated when the scattering coefficients of blue-green light in seawater vary from large to small with increasing depth for NLOS transmission. The results show that blue-green light in different depths of seawater in the same way NLOS communication at the same distance, the received optical power and BER at the receiver are different, and the received optical power of green light is greater than that of blue light. Increasing the forward scattering coverage of the laser will suppress the received optical power of the PD, so when performing NLOS communication, appropriate trade-offs should be made between the forward scattering coverage of the laser and the received optical power.

Locating the position of objects in non-line-of-sight based on time delay estimation

Non-line-of-sight imaging detection is to detect hidden objects by indirect light and intermediary surface（diffuser）.It has very important significance in indirect access to an object or dangerous object detection, such as medical treatment and rescue. An approach to locating the positions of hidden objects is proposed based on time delay estimation. The time delays between the received signals and the source signal can be obtained by correlation analysis, and then the positions of hidden objects will be located. Compared with earlier systems and methods, the proposed approach has some modifications and provides significant improvements, such as quick data acquisition, simple system structure and low cost, and can locate the positions of hidden objects as well： this technology lays a good foundation for developing a practical system that can be used in real applications.

Application of the sun line-of-sight vector in the optimal attitude estimation of deep-space probe

This paper proposed an optimal algorithm using the sun line-of-sight vector to improve the probe attitude estimation accuracy in deep-space mission.Firstly,the elaborate analysis of the attitude estimation error from vector observations was done to demonstrate that the geometric relation between the reference vectors is an important factor which influences the accuracy of attitude estimation.Then,with introduction of the sun line-of-sight vector,the attitude quaternion obtained from the star-sensor was converted into a pair of mutually perpendicular reference vectors perpendicular to the sun vector.The normalized weights were calculated according to the accuracy of the sensors.Furthermore,the optimal attitude estimation in the least squares sense was achieved with the quaternion estimation method.Finally,the results of simulation demonstrated the validity of the proposed optimal algorithm based on the practical data of the Deep Impact mission.

基于CNN-LSTM的超宽带NLOS/LOS分类算法研究

超宽带(ultra-wideband,UWB)室内定位系统中,非视距(non-line-of-sight,NLOS)信号的识别与分类是影响定位精度的关键技术。为解决用于NLOS识别的信道冲激响应(Channel Impulse Response,CIR)中存在的噪声干扰问题以及传统NLOS识别方法多场景下阈值选取困难等问题,论文采用一种用于CIR数据去噪的可逆变换方法,并使用卷积神经网络(Convolutional Neural Network,CNN)结合长短期记忆网络(long short-term memory network,LSTM)的结构识别NLOS信号。采用开源数据集进行训练与验证,结果显示,CIR去噪后的CNN-LSTM分类精度最高可达90.62%。表明该方法可以有效提高NLOS信号分类精度。

基于TOF和自适应抗差卡尔曼滤波的UWB室内定位算法

为提高超宽带(UWB)定位系统在室内复杂环境下的定位精度,提出一种基于飞行时间(TOF)和自适应抗差卡尔曼滤波(ARKF)的改进定位算法。针对超低功耗宽带设备在复杂室内环境状态下易受周围干扰而存在标准时间偏差的问题,提出一种改进的TOF算法,同时进行测距标定,拟合数据;对室内存在非视距(NLOS)干扰的情形,提出一种ARKF算法,通过比较残差与3倍信息的方差来判断视距(LOS)与NLOS情形。实验结果显示:该算法可以在静态与动态定位实验中有效提高系统定位精度,降低定位误差,取得较好的定位效果。

An Optimization Approach of IoD Deployment for Optimal Coverage Based on Radio Frequency Model

Recently,Internet of Drones(IoD)has garnered significant attention due to its widespread applications.However,deploying IoD for area coverage poses numerous limitations and challenges.These include interference between neighboring drones,the need for directional antennas,and altitude restrictions for drones.These challenges necessitate the development of efficient solutions.This research paper presents a cooperative decision-making approach for an efficient IoDdeployment to address these challenges effectively.The primary objective of this study is to achieve an efficient IoDdeployment strategy thatmaximizes the coverage regionwhile minimizing interference between neighboring drones.In deployment problem,the interference increases as the number of deployed drones increases,resulting in bad quality of communication.On the other hand,deploying a few drones cannot satisfy the coverage demand.To accomplish this,an enhanced version of a concise population-based meta-heuristic algorithm,namely Improved Particle SwarmOptimization(IPSO),is applied.The objective function of IPSO is defined based on the coverage probability,which is primarily influenced by the characteristics of the antennas and drone altitude.A radio frequency(RF)model is derived to evaluate the coverage quality,considering both Line of Sight(LOS)and Non-Line of Sight(NLOS)down-link coverage probabilities for ground communication.It is assumed that each drone is equipped with a directional antenna to optimize coverage in a given region.Extensive simulations are conducted to assess the effectiveness of the proposed approach.Results demonstrate that the proposed method achieves maximum coverage with minimum transmission power.Furthermore,a comparison is made against Collaborative Visual Area Coverage Approach(CVACA),and a game-based approach in terms of coverage quality and convergence speed.The simulation results reveal that our approach outperforms both CVACA and the gamebased schemes in terms of coverage and convergence speed.Comparisons validate the superiority of our approach over existing methods.To assess the robustness of the proposed RFmodel,we have considered two distinct ranges of noise:range1 spanning from−120 to−90 dBm,and range2 spanning from−90 to−70 dBmfor different numbers of UAVs.In summary,this research presents a cooperative decision-making approach for efficient IoD deployment to address the challenges associatedwith area coverage and achieves an optimal coveragewithminimal interference.

带有NLOS误差补偿的UWB/INS室内融合定位算法研究

针对室内环境中超宽带(Ultra-Wideband,UWB)定位精度易受非视距影响,以及惯性导航系统(Inertial Navigation System,INS)误差随运行时间迅速累积的问题,在无迹卡尔曼滤波的基础上提出了一种带有非视距误差补偿的UWB/INS室内融合定位算法。该算法利用INS预测定位目标的位置信息;采用残差检验法对相邻时刻UWB测距结果进行非视距检测;利用INS预测信息设计了“近似补偿误差”,结合UWB测距信息实现对非视距测量值的误差补偿;利用无迹卡尔曼滤波算法以紧耦合方式融合UWB和INS定位信息,得到融合定位结果。实验结果表明,该算法既能抑制INS的误差累积,又能缓解非视距误差对UWB定位技术的影响,具有较好的定位精度和鲁棒性。

密集多径环境下UWB测距的NLOS误差减小方法

为减小密集多径环境下超宽带(UWB)测距结果中因为障碍物引起的非视距(NLOS)误差,提出了一种有效的NLOS误差减小方法.此方法考虑了NLOS误差的产生原理及特点,以信号传播的路径损耗模型为基础,通过对接收信号中不同时间到达单径的能量比较,实现了对NLOS误差的粗略估计,进而以此估计值对测距结果进行校正.在方法的具体实现上,给出了一种计算量较小、复杂度较低的单径检测算法.对实测数据的处理验证了方法的正确性,结果表明本文提出的NLOS误差减小方法使UWB测距精度有了较大提升.

基于高度的紫外光NLOS单次散射链路模型的研究

为了更精确、更全面地研究紫外光的通信性能,使之更适合于实际空间中的3维应用,在2维紫外光单次散射链路模型的基础上融入高度信息,并利用仿真计算了在添加高度信息与否的两种情况下接收功率误差的大小。结果表明,高度对于发射仰角和接收仰角潜在的影响直接引起接收功率的改变,甚至在某些情况下不能进行通信。高度信息的考虑对通信设备在实际空间中的应用给予了正确的指导。

两种NLOS误差消除及TOA定位算法

在蜂窝网络定位中,由于NLOS环境造成的附加时延(NLOS误差)是导致定位精度下降的主要原因,本文将NLOS误差与系统测量误差合成的噪声分为均值部分和随机部分,利用卡尔曼滤波算法输出与噪声方差无关的特性,无需得到全部噪声方差的准确值,只利用系统测量噪声的方差,用卡尔曼滤波算法除随机部分,再根据噪声均值部分与移动台到基站距离的关系,提出了一种简单的最小二乘(LS)定位算法,或利用最优化方法进行定位;利用仿真实验得到滤波距离——误差先验信息,基于先验信息提出了第二种NLOS误差消除算法,再利用所提的最小二乘定位算法进行定位。仿真结果表明,本文提出的算法能够有效消除NLOS误差带来的影响,具有更高的定位精度与稳健性。

IR-UWB测距中NLOS状态的鉴别

NLOS效应是IR-UWB测距定位系统中影响精度的主要因素之一。该文提出不依赖于信道估计,直接从接收信号采样序列中提取特征参量进行NLOS鉴别的方法,构造了采样序列的首均比与峰均比乘积作为鉴别参量,并与使用峭度和平均附加时延这两个参量的鉴别性能进行了对比。仿真结果表明:相干测距所对应的鉴别性能要好于非相干测距,原因是更为精确的DP检测结果及高采样速率使得参量提取值更能准确地反映信道状态信息;使用峭度和平均附加时延作为鉴别参量所能获得鉴别性能均不理想,而使用采样序列的首均比与峰均比乘积能使鉴别成功率提高10%左右。在定位模块中融入该文所获得的NLOS的鉴别结果将有助于定位精度的进一步提升。

基于神经网络的鲁棒NLOS误差抑制算法

提出一种基于Kalman滤波器和神经网络(NN)的非视距(NLOS)误差抑制算法。根据到达时间(TOA)测量值的特点和NLOS误差的统计特性,推导出Kalman滤波器输出无偏估计所需满足的条件,利用NN估计该条件中的环境参数,实现NLOS误差抑制。仿真结果表明,该算法在估计精度和算法鲁棒性方面均具有较好的性能。