Dynamic Modelling of Zenith Wet Delay in GNSS Measurements

Proper modelling of the temporal correlations of the zenith wet delay (ZWD) is important in some of the Global Navigation Satellite Systems (GNSS) applications such as estimation of the Perceptible Water Vapour (PWV), and methods such as Precise Point Positioning (PPP). The random walk (RW) and the first-order Gauss- Markov (GM) autocorrelation model are commonly used for the dynamic modelling of ZWD in Kalman filtering of GNSS measurements. However, it was found that the GM model consistently underestimates the temporal correlations that exist among the ZWD estimates. Therefore, a new autocorrelation dynamic model is proposed in a form similar to that of a hyperbolic function. The impact of the proposed dynamic model on the near-real time estimation of the ZWD was tested and its results were compared to that of the GM model as well as the RW model. In this test, GPS dual-frequency data collected on the 25th Jan 2010 at two Western Australian IGS stations, namely, Yarragadee and Karratha, were used. Results showed that the proposed model outperformed the GM model, and when added to hydrostatic models were able to provide near real-time (with 30 seconds intervals) ZTD estimates to within a few cm accuracy

On the Maximum Nonlinearity of De Bruijn Sequence Feedback Function

The nonlinearity of Boolean function is an important cryptographic criteria in the Best Affine Attack approach. In this paper, based on the definition of nonlinearity, we propose a new design index of nonlinear feedback shift registers. Using the index and the correlative necessary conditions of de Bruijn sequence feedback function, we prove that when $n \ge 9$, the maximum nonlinearity $Nl{(f)_{\max }}$ of arbitrary $n -$order de Bruijn sequence feedback function $f$ satisfies $3 \cdot {2^{n - 3}} - ({Z_n} + 1) < Nl{(f)_{\max }} \le {2^{n - 1}} - {2^{\frac{{n - 1}}{2}}}$ and the nonlinearity of de Bruijn sequence feedback function, based on the spanning tree of adjacency graph of affine shift registers, has a fixed value. At the same time, this paper gives the correlation analysis and practical application of the index

Further on the Construction of Feedback Shift Registers with Maximum Strong Linear Complexity

In this paper, we present the more accurate definition of strong linear complexity of feedback shift registers based on Boolean algebraic than before, and analyze the bound of strong linear complexity by the fixed feedback function. Furthermore, the feedback shift registers with maximum strong linear complexity are constructed, whose feedback functions require the least number of monomials. We also show that the conclusions provide particular ideas and criteria for the design of feedback shift registers

A WiFi Indoor Location Tracking Algorithm Based on Improved Weighted K Nearest Neighbors and Kalman Filter

The weighted $K$ -nearest neighbors (WKNN) algorithm is a widely adopted lightweight methodology for indoor WiFi positioning based on location fingerprinting. Nonetheless, it suffers from the disadvantage of a fixed $K$ value and susceptibility to incorrect reference point matching. To address this issue, we present a novel algorithm in this paper, referred to as static continuous statistical characteristics-soft range limited-self-adaptive WKNN (SCSC-SRL-SAWKNN). Our algorithm not only takes into account location tracking in the motion state but also exploits the continuous statistical features of extended periods of inactivity to enhance localization. In the motion state, we initially employ the self-adaptive WKNN (SAWKNN) algorithm to determine the optimal $K$ value, followed by the employment of the soft range limited KNN (SRL-KNN) algorithm to identify the correct reference point and ultimately estimate the position. When a prolonged stationary state is detected, we first utilize the moving window method to obtain a more stable position fingerprint, and then proceed with the positioning process in the same motion state. Ultimately, we use Kalman filter to generate the location trajectory. Our experimental findings demonstrate that the proposed SCSC-SRL-SAWKNN algorithm outperforms traditional WKNN, SAWKNN, and SRL-KNN techniques in terms of localization accuracy and location trajectory. Specifically, the localization accuracy of our algorithm is 56.7&#x0025; and 36.6&#x0025; higher than that of traditional WKNN in the static state and overall situation, respectively

Single Frequency PPP Using Real-Time Regional Broadcast Corrections via NTRIP for the Australian GDA94 Datum

The possibility of Real-Time Precise Point Positioning directly in the Australian GDA94 datum has become possible through the availability of Real-Time Broadcast Corrections (BCs) provided by the IGS Real-Time Pilot-Project. Generation of BCs for the GDA94 datum has some pitfalls which are identified in this contribution. It is shown that it is impossible to obtain identical positioning results using either the BCs in ITRF or BCs in GDA94 due to scale differences between both systems. A new user-friendly RBC-approach is introduced, which deals with the scale-induced biases in the current approach. The user-friendly RBC-approach eliminates the user-need of having to apply the ITRF-to-GDA94 transformation, while still giving correct horizontal PPP positions in GDA94. For users that additionally require precise height information in GDA94 as well, a simple constant height-correction, valid for the complete Australian continent, is all that is needed to obtain the correct full 3D PPP position

Performance of Real-Time Precise Point Positioning

The IGS Real-time Pilot Project (IGS-RTPP) provides real-time precise orbits and clocks, which support real-time positioning for single stations over large areas using the Precise Point Positioning (PPP) technique. This paper investigates the impact of real-time orbits, network configuration, and analysis strategies on real-time PPP implementation and demonstrates the real-time PPP performance. One month of data from the IGS network is analyzed in a real-time simulation mode. Results reveal the following: (1) In clock estimation, differential approaches are much more efficient than the zero-differenced approach. (2) The precision of IGS Ultra rapid (IGU) orbits could meet the IGS-RTPP requirement for precise clock estimation and PPP positioning. (3) Considering efficiency and precision, a network with 50 stations is recommended for the IGS-RTPP. It is demonstrated that the real-time satellite clock precision is 0.1ns supporting hourly static PPP with a mean precision of 23cm in the North component and 34cm in the other components. Kinematic PPP assessed with onboard GPS data collected from a buoy provided mean coordinate precision of 2.2, 4.2, 6.1cm in the North, East and Up directions, compared to the RTK solutions

Trace metals, organic carbon and nutrients in the Beidagang Wetland Nature Reserve, northern China.

This study aimed to determine sediment contamination in the Beidagang Wetland Nature Reserve to describe atmospheric deposition of trace metals. We analyzed Hg, Cd, Pb, TOC, TN, TP, δ13C, and δ15N, and studied their variations in surface sediments and in the vertical profiles of sediment cores collected from the reserve. Evaluation of environmental trace metal contamination using sediment quality guidelines and geochemical background values indicated that the risk of metal pollution in the reserve sediments was relatively low. Concentrations of Hg, Cd, and Pb in the sediments were much lower than concentrations in sediment samples from Bohai Bay and polluted rivers in Tianjin. Enrichment factors indicate that samples are moderately contaminated with Hg, Cd, and Pb; whereas the geo-accumulation index results classify the sediments as uncontaminated to moderately contaminated with Hg, Cd, and Pb. The distribution patterns of trace metal concentrations in the three core samples were uniform. δ13C and δ15N were used to track the sources of TOC and TN in sediments. Results show that TOC mainly originated from the residue and decaying matter of aquatic plants (e.g., algae, reeds, and Typha), while TN was derived from soil N and elevated atmospheric N deposition. Because domestic and industrial waste is not discharged into the Beidagang Wetland Nature Reserve, trace metals found in sediments mainly originate from atmospheric deposition. The results provide baseline data for analysis of trace metal accumulation in Beijing-Tianjin-Hebei, a region subject to atmospheric deposition in northern China