Passive location estimation using scatterer information for non-line-of-sight environments

In order to improve the performance of the traditional hybrid time-of-arrival（TOA）/angle-of-arrival（AOA）location algorithm in non-line-of-sight（NLOS）environments,a new hybrid TOA/AOA location estimation algorithm by utilizing scatterer information is proposed.The linearized region of the mobile station（MS）is obtained according to the base station（BS）coordinates and the TOA measurements.The candidate points（CPs）of the MS are generated from this region.Then,using the measured TOA and AOA measurements,the radius of each scatterer is computed.Compared with the prior scatterer information,true CPs are obtained among all the CPs.The adaptive fuzzy clustering（AFC）technology is adopted to estimate the position of the MS with true CPs.Finally,simulations are conducted to evaluate the performance of the algorithm.The results demonstrate that the proposed location algorithm can significantly mitigate the NLOS effect and efficiently estimate the MS position.

Review of Ultraviolet Non-Line-of-Sight Communication

With rapid advances of solar blind ultraviolet LED and ultraviolet detecting technology in recent years, ultraviolet communication gradually becomes a research hotspot due to its inherent advantages: low solar background noise, non-line-of-sight(NLOS) and good secrecy. The strong scattering characteristics in atmospheric render ultraviolet waveband the ideal choice for achieving NLOS optical communication. This paper reviews the research history and status of ultraviolet communication both in China and abroad, and especially introduces three main issues of ultraviolet communication: channel model, system analysis and design, light sources and detectors. For each aspect, current open issues and prospective research directions are analyzed.

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.

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.

Passive non-line-of-sight imaging for moving targets with an event camera

Non-line-of-sight[NLOS]imaging is an emerging technique for detecting objects behind obstacles or around corners.Recent studies on passive NLOS mainly focus on steady-state measurement and reconstruction methods,which show limitations in recognition of moving targets.To the best of our knowledge,we propose a novel event-based passive NLOS imaging method.We acquire asynchronous event-based data of the diffusion spot on the relay surface,which contains detailed dynamic information of the NLOS target,and efficiently ease the degradation caused by target movement.In addition,we demonstrate the event-based cues based on the derivation of an event-NLOS forward model.Furthermore,we propose the first event-based NLOS imaging data set,EM-NLOS,and the movement feature is extracted by time-surface representation.We compare the reconstructions through event-based data with frame-based data.The event-based method performs well on peak signal-to-noise ratio and learned perceptual image patch similarity,which is 20%and 10%better than the frame-based method.

Non-Line-of-Sight Multipath Detection Method for BDS/GPS Fusion System Based on Deep Learning

Non-line-of-sight(NLOS)multipath effect is the main factor that restricts the application of global navigation satellite system(GNSS)in complex environments,especially in urban canyon.The effective avoidance of NLOS signals can significantly improve the positioning performance of GNSS receiver.In this paper,an NLOS/LOS classification model based on recurrent neural network is proposed to classify satellite signals received in urban canyon environments.The accuracy of classification is 91%,and the recognition rate of NLOS is 89%;the classification performance is better than that of traditional machine learning classification models such as support vector machine.For BeiDou navigation satellite system/global positioning system(BDS/GPS)fusion system,the least square algorithm and extended Kalman filter are used to estimate the position.The experimental results show that the three-dimensional positioning accuracy after NLOS recognition is improved about 60%on average compared with the traditional methods,and the positioning stability is also improved significantly.

Non-LOS target localization via millimeter-wave automotive radar

This paper considers the non-line-of-sight(NLOS)vehicle localization problem by using millimeter-wave(MMW)automotive radar.Several preliminary attempts for NLOS vehicle detection are carried out and achieve good results.Firstly,an electromagnetic(EM)wave NLOS multipath propagation model for vehicle scene is established.Subsequently,with the help of available multipath echoes,a complete NLOS vehicle localiza-tion algorithm is proposed.Finally,simulation and experimental results validate the effectiveness of the established EM wave propagation model and the proposed NLOS vehicle localization algorithm.

Structural Design of High-precision Positioning System in Weak Signal Environment Based on UWB and IMU Fusion

Aiming at the problem that indoor positioning technology based on wireless ultra-wideband pulse technology is susceptible to non-line-of-sight effects and multipath effects in confined spaces and weak signal environments,a high-precision positioning system based on UWB and IMU in a confined environment is designed.The STM32 chip is used as the main control,and the data information of IMU and UWB is fused by the fusion filtering algorithm.Finally,the real-time information of the positioning is transmitted to the host computer and the cloud.The experimental results show that the positioning accuracy and positioning stability of the system have been improved in the non-line-of-sight case of closed environment.The system has high positioning accuracy in a closed environment,and the components used are consumer-grade,which has strong practicability.

NLOS环境下基于信号检测的单次与二次散射路径识别

针对NLOS(Non-Line-of-Sight)传播环境中单次与多次散射路径的识别问题,本文基于单次散射圆环模型建立了一种二次散射圆环模型,对该模型的统计特征进行了分析。同时,基于信号统计检测理论建立了一种单次与二次散射路径检测模型,然后根据是否已知先验概率两种情况,分别采用广义似然比和奈曼皮尔逊准则来检测识别两种散射路径。仿真结果表明:本文提出的检测识别方法在NLOS环境下能有效识别两种散射路径,相对于LPMD(Line of Possible Mobile Device)算法具有更高的识别率以及更小的虚警概率和漏警概率,且时间开销小,具有一定的应用价值。

Ultraviolet communication technique and its application

With recent developments of deep ultraviolet(DUV)light-emitting diodes and solar-blind detectors,UV communication(UVC)shows great potential in replacing traditional wireless communication in more and more scenarios.Based on the atmospheric scattering of UV radiation,UVC has gained considerable attention due to its non-line-of-sight ability,omnidirectional communication links and low background noise.These advantages make UVC an ideal option for covert secure communication,especially for military communication.In this review,we present the history and working principle of UVC with a special focus on its light sources and detectors.Comprehensive comparison and application of its light sources and detectors are provided to the best of our knowledge.We further discuss the future application and outlook of UVC.Hopefully,this review will offer valuable insights into the future development of UVC.

NBP-based localization algorithm for wireless sensor networks in NLOS environments

To mitigate the impacts of non-line-of-sight（NLOS） errors on location accuracy, a non-parametric belief propagation（NBP）-based localization algorithm in the NLOS environment for wireless sensor networks is proposed.According to the amount of prior information known about the probabilities and distribution parameters of the NLOS error distribution, three different cases of the maximum a posterior（MAP） localization problems are introduced. The first case is the idealized case, i. e., the range measurements in the NLOS conditions and the corresponding distribution parameters of the NLOS errors are known. The probability of a communication of a pair of nodes in the NLOS conditions and the corresponding distribution parameters of the NLOS errors are known in the second case. The third case is the worst case, in which only knowledge about noise measurement power is obtained. The proposed algorithm is compared with the maximum likelihood-simulated annealing（ML-SA）-based localization algorithm. Simulation results demonstrate that the proposed algorithm provides good location accuracy and considerably outperforms the ML-SA-based localization algorithm for every case. The root mean square error（RMSE）of the location estimate of the NBP-based localization algorithm is reduced by about 1. 6 m in Case 1, 1. 8 m in Case 2 and 2. 3 m in Case 3 compared with the ML-SA-based localization algorithm. Therefore, in the NLOS environments,the localization algorithms can obtain the location estimates with high accuracy by using the NBP method.

Impacts of Transceiver Configuration on Ultraviolet Communication

In the channel estimation for ultraviolet communication, the single scattering power is usually used to approximate the received total power. This approximation error is affected by the transceiver configuration. Here, we employ the proportion of received single scattering power in received total power to indicate the approximation error of the single scattering model in different configurations. This is useful for reducing the approximation error by selecting a more appropriate transceiver configuration.

Robust location algorithm for NLOS environments

One of the main problems facing accurate location in wireless communication systems is non-line-of- sight （NLOS） propagation. Traditional location algorithms are based on classical techniques under minimizing a least-squares objective function and it loses optimality when the NLOS error distribution deviates from Gaussian distribution. An effective location algorithm based on a robust objective function is proposed to mitigate NLOS errors. The proposed method does not require the prior knowledge of the NLOS error distribution and can give a closed-form solution. A comparison is performed in different NLOS environments between the proposed algorithm and two additional ones （LS method and Chan＇s method with an NLOS correction）. The proposed algorithm clearly outperforms the other two.

The realization of a wide-angle voice transmission non-line-ofsight ultraviolet communication system

A 300 kbps wide-angle non-line-of-sight ultraviolet communication system with voice transmission function is designed here.Based on Poisson distribution theory,we design the symbol detecting method for the receiving discrete photon signals.Using 272 nm LED array as the light source and PMT as the detector,the voice transceiver is integrated into the carriable size of 200×90×65 mm^(3).An outfield test shows the system obtains the BER of 0.88% under 200 m.Under 10°wide-angle deviation of the transmitter,a BER below 1.33% is achieved.

TOA-BASED ROBUST LOCATION ALGORITHMS FOR WIRELESS CELLULAR NETWORKS

Caused by Non-Line-Of-Sight (NLOS) propagation effect, the non-symmetric contamination of measured Time Of Arrival (TOA) data leads to high inaccuracies of the conventional TOA based mobile location techniques. Robust position estimation method based on bootstrapping M-estimation and Huber estimator are proposed to mitigate the effects of NLOS propagation on the location error. Simulation results show the improvement over traditional Least-Square (LS)algorithm on location accuracy under different channel environments.

Lens-free wavefront shaping method for a diffuse non-lineof-sight link in visible light communication

In this Letter,we propose and experimentally demonstrate a lens-free wavefront shaping method that utilizes synchronized signal block beam alignment and a genetic algorithm(SSBGA)for a diffuse non-line-of-sight(NLOS)visible light communication(VLC)system.The proposed method effectively controls the position and mobility of visible light beams by partitioning spatial light modulator pixels and manipulating beams to converge at distinct spatial positions,thereby enhancing wavefront shaping efficiency,which achieves a significant 23.9 dB optical power enhancement at+2 mm offset,surpassing the lens-based continuous sequence(CS)scheme by 21.7 dB.At+40°angle,the improvement reaches up to 11.8 dB and 16.8 dB compared to the results with and without lens-based CS,respectively.A maximum rate of 5.16 Gbps is successfully achieved using bit-power loading discrete multi-tone(DMT)modulation and the proposed SSBGA in an NLOS VLC system,which outperforms the lens-based CS by 1.07 Gbps and obtains a power saving of 55.6%during the transmission at4 Gbps.To the best of our knowledge,this is the first time that high-speed communication has been realized in an NLOS VLC system without a lens.

A robust vector tracking loop structure based on potential bias analysis

This paper proposes a robust vector tracking loop structure based on potential bias analysis. The influence of four kinds of biases on the existing two implementations of Vector Tracking Loops(VTLs) is illustrated by theoretical analysis and numerical simulations, and the following findings are obtained. Firstly, the initial user state bias leads to steady navigation solution bias in the relative VTL, while new measurements can eliminate it in the absolute VTL. Secondly, the initial code phase bias is transferred to the following navigation solutions in the relative VTL, while new measurements can eliminate it in the absolute VTL. Thirdly, the user state bias induced by erroneous navigation solution of VTLs can be eliminated by both of the two VTLs. Fourthly,the multipath/NLOS likely affects the two VTLs, and the induced tracking bias in the duration of the multipath/NLOS would decrease the performance of VTLs. Based on the above analysis,a robust VTL structure is proposed, where the absolute VTL is selected for its robustness to the two kinds of initialization biases;meanwhile, the instant bias detection and correction method is used to improve the performance of VTLs in the duration of the multipath/NLOS. Numerical simulations and experimental results verify the effectiveness of the proposed robust VTL structure.