An Effective GNSS/PDR Fusion Positioning Algorithm on Smartphones for Challenging Scenarios.

The location-based smartphone service brings new development opportunities for seamless indoor/outdoor positioning. However, in complex scenarios such as cities, tunnels, overpasses, forests, etc., using only GNSS on smartphones cannot provide stable and reliable positioning results. Usually, additional sensors are needed to assist GNSS. This paper investigates the GNSS positioning algorithm assisted by pedestrian dead reckoning (PDR) in complex scenarios. First, we introduce a step detection algorithm based on the peak-valley of acceleration modulus, and the Weinberg model and the Mahony algorithm in PDR are used to estimate step length and heading. On this basis, we evaluated the performance of GNSS/PDR fusion positioning in an open scenario, a semiopen scenario, and a blocked scenario, respectively. Finally, we develop a GNSS/PDR real-time positioning software, called China University of Mining and Technology-POSitioning (CUMT-POS) version 1.0, on the Android 10 platform. By comparing GNSS solutions, PDR solutions, GNSS/PDR solutions, and real-time kinematic (RTK) solutions, we verify the potential auxiliary ability of PDR for GNSS positioning in complex environments, proving that multisource sensor fusion positioning significantly improves reliability and stability. Our research can help the realization of urban informatization and smart cities.

Switchable optical vortex beam generator based on an all-dielectric metasurface governed by merging bound states in the continuum.

The polarization topology around the bound states in continuum (BIC) affects the optical vortex (OV) beam generation. We propose a cross-cross-shaped resonator based on a THz metasurface to realize an OV beam generator in real space by exploiting the inherent winding topology around the BIC. The BIC merging at the point Γ is achieved by tuning the width of the cross resonator, which significantly improves the Q factor and enhances the field localization. Furthermore, the switching between the high-order OV beam generator governed by the merged BIC and the low-order OV beam generator is realized. This extends the application of BIC in modulating orbital angular momentum.

Dirac semimetal and an all dielectric based tunable ultrasensitive terahertz sensor with multiple bound states in the continuum.

Herein, we propose an all dielectric, open-slit, U-shaped resonant arm-based metasurface that achieves three bound states in the continuum (BIC) in the high-frequency terahertz band whose quasi-BIC (QBIC) states can achieve Q factor of the magnitude order of 104. The maximum sensitivities of accidental QBIC and the figure-of-merit were respectively equal to 1717 GHz/RIU and 16670. Furthermore, the dependencies of the three QBICs on the THz incidence angle were different. Finally, the tunable sensor based on the Dirac semimetal metasurface achieves active tuning of the sensitivity and sensing range. This overcomes the shortcomings of the fixed structure without tuning capabilities, and provides a broad applicability platform for THz sensors.

Dynamic switching between bound states in the continuum (BIC) and quasi-BIC based on a Dirac semimetal terahertz metasurface.

To synthesize dynamically tunable bound states in the continuum (BIC) metasurfaces in the terahertz (THz) band, in this study, a Dirac semimetal metasurface was designed for dynamic switching between THz-band BIC and quasi-BIC. We have simulated the designed metasurface, a symmetry-protected BIC with a quality factor (Q-factor) of 147 was achieved by breaking the symmetry of the structure, the variation law of the Q-factor with the asymmetry parameter was investigated, and the physical mechanism of quasi-BIC generation was determined by analyzing the surface electric field and surface current. Notably, the dynamic transition from BIC to quasi-BIC was achieved by varying the Fermi level of the Dirac semi-metal, with the maximum transmission difference of 0.61 and an almost constant resonant frequency for Fermi levels ranging from 2-20 meV. In addition, we fabricated and demonstrated a dynamic near-field display array, wherein different content is dynamically displayed by successively applying different gate voltages. This paper presents a novel design concept for dynamic switching between BIC and quasi-BIC on a metasurface and promotes the practical application of BIC metasurfaces.

Dust Removal from 3D Point Cloud Data in Mine Plane Areas Based on Orthogonal Total Least Squares Fitting and GA-TELM.

With the further development of the construction of "smart mine," the establishment of three-dimensional (3D) point cloud models of mines has become very common. However, the truck operation caused the 3D point cloud model of the mining area to contain dust points, and the 3D point cloud model established by the Context Capture modeling software is a hollow structure. The previous point cloud denoising algorithms caused holes in the model. In view of the above problems, this paper proposes the point cloud denoising method based on orthogonal total least squares fitting and two-layer extreme learning machine improved by genetic algorithm (GA-TELM). The steps are to separate dust points and ground points by orthogonal total least squares fitting and use GA-TELM to repair holes. The advantages of the proposed method are listed as follows. First, this method could denoise without generating holes, which solves engineering problems. Second, GA-TELM has a better effect in repairing holes compared with the other methods considered in this paper. Finally, this method starts from actual problems and could be used in mining areas with the same problems. Experimental results demonstrate that it can remove dust spots in the flat area of the mine effectively and ensure the integrity of the model.

Research on Remote GPS Common-View Precise Time Transfer Based on Different Ionosphere Disturbances.

Propagation path delays are a major error for the remote precise time transfer of common view; these path delays contain the ionosphere and troposphere impact, while the contributions of the ionosphere and the troposphere from common-view satellites to receivers on the ground tend to become uncorrelated when the distance between these receivers increases. In order to select the appropriate ionospheric correction method for common view under different distances between receivers, a detailed test using multi-source data under different ionosphere disturbances are carried out in this paper. Here, we choose three different ionosphere disturbance methods and analyze the advantages and disadvantages of these methods for common-view time transfer and time comparison. At last, we put forward a suitable ionospheric correction method for different distances common view. The RMS shows that the method proposed for 3000 km remote common view can achieve 2.5 ns.

A Vondrak low pass filter for IMU sensor initial alignment on a disturbed base.

The initial alignment of the Inertial Measurement Unit (IMU) is an important process of INS to determine the coordinate transformation matrix which is used in the integration of Global Positioning Systems (GPS) with Inertial Navigation Systems (INS). In this paper a novel alignment method for a disturbed base, such as a vehicle disturbed by wind outdoors, implemented with the aid of a Vondrak low pass filter, is proposed. The basic principle of initial alignment including coarse alignment and fine alignment is introduced first. The spectral analysis is processed to compare the differences between the characteristic error of INS force observation on a stationary base and on disturbed bases. In order to reduce the high frequency noise in the force observation more accurately and more easily, a Vondrak low pass filter is constructed based on the spectral analysis result. The genetic algorithms method is introduced to choose the smoothing factor in the Vondrak filter and the corresponding objective condition is built. The architecture of the proposed alignment method with the Vondrak low pass filter is shown. Furthermore, simulated experiments and actual experiments were performed to validate the new algorithm. The results indicate that, compared with the conventional alignment method, the Vondrak filter could eliminate the high frequency noise in the force observation and the proposed alignment method could improve the attitude accuracy. At the same time, only one parameter needs to be set, which makes the proposed method easier to implement than other low-pass filter methods.