scholarly journals An Improved Ambiguity-Free Method for Precise GNSS Positioning with Utilizing Single Frequency Receivers

Sensors ◽  
2020 ◽  
Vol 20 (3) ◽  
pp. 856 ◽  
Author(s):  
Wenhao Yang ◽  
Yue Liu ◽  
Fanming Liu
Keyword(s):  
Global Optimum ◽  
Ambiguity Function ◽  
Single Frequency ◽  
Density Estimator ◽  
New Approach ◽  
Gnss Positioning ◽  
Cycle Slips ◽  
Computation Efficiency ◽  
Ambiguity Fixing ◽  
Computation Load

The solution of carrier phase ambiguity is essential for precise global navigation satellite system (GNSS) positioning. Methods of searching in the coordinate domain show their advantage over the methods based on ambiguity fixing, for example, immune to cycle slips, far fewer epochs taken for obtaining the precise solution. However, there are still some drawbacks via using the Ambiguity Function Method (AFM), such as low computation efficiency and the existence of a false global optimum. The false global optimum is a situation where the Least Square (LS) criterion achieves minimum in another place than the point of the actual position, which restricts the application of this method to single-frequency receivers. The numerical search approach derived in this paper is based on the Modified Ambiguity Function Approach (MAFA). It focuses on eliminating the false optimum solution and reducing the computation load by utilizing single-frequency receivers without solving the ambiguity fixing problem. An improved segmented simulated annealing method is used to decrease the computation load while the Kernel Density Estimator (KDE) method is used to filter out the false optimum candidates. Static experiments were carried out to evaluate the performance of the new approach. It is shown that a precise result can be obtained by handling two epochs of data with z coordinate fixed to the referenced value. Meanwhile, the new approach can achieve a millimeter level of position accuracy after dealing with nineteen epochs of observations data when searching in x , y , z domain. The new approach shows its robustness even if the search region is broad, and the prior position is several meters away from the referenced value.

scholarly journals Multi-GNSS Relative Positioning with Fixed Inter-System Ambiguity

2019 ◽  
Vol 11 (4) ◽  
pp. 454 ◽  
Author(s):  
Hua Chen ◽  
Weiping Jiang ◽  
Jiancheng Li
Keyword(s):  
Double Difference ◽  
Relative Positioning ◽  
New Approach ◽  
Gnss Positioning ◽  
Ambiguity Fixing ◽  
Single Difference ◽  
Phase Bias ◽  
System Phase

In multi-GNSS cases, two types of Double Difference (DD) ambiguity could be formed including an intra-system ambiguity and an inter-system ambiguity, which are identified as the DD ambiguity between satellites from the same and from different GNSS systems, respectively. We studied the relative positioning methods using intra-system DD observations and using Un-Difference (UD) observations, and developed a frequency-free approach for fixing inter-system ambiguity based on UD observations for multi-GNSS positioning, where the inter-system phase bias is calculated with the help of a fixed Single-Difference (SD) ambiguity. The consistency between the receiver-end uncalibrated phase delays (RUPD) and the SD ambiguity were investigated and the positioning performance of this new approach was assessed. The results show that RUPD could be modeled as a constant if the receiver were tracking satellites continuously. Furthermore, compared to the method using DD observations with only an intra-system DD ambiguity fixed, the new ambiguity fixing approach has a better performance, especially in hard environments with a large cut-off angle or serve signal obstructions.

scholarly journals An Improved Single-Epoch Attitude Determination Method for Low-Cost Single-Frequency GNSS Receivers

2021 ◽  
Vol 13 (14) ◽  
pp. 2746
Author(s):  
Xinzhe Wang ◽  
Yinbin Yao ◽  
Chaoqian Xu ◽  
Yinzhi Zhao ◽  
Huan Zhang
Keyword(s):  
Degrees Of Freedom ◽  
High Efficiency ◽  
Attitude Determination ◽  
Search Algorithm ◽  
Low Cost ◽  
Single Frequency ◽  
Baseline Length ◽  
Short Baseline ◽  
Cycle Slips ◽  
Ambiguity Fixing

GNSS attitude determination has been widely used in various navigation and positioning applications, due to its advantages of low cost and high efficiency. The navigation positioning and attitude determination modules in the consumer market mostly use low-cost receivers and face many problems such as large multipath effects, frequent cycle slips and even loss of locks. Ambiguity fixing is the key to GNSS attitude determination and will face more challenges in the complex urban environment. Based on the CLAMBDA algorithm, this paper proposes a CLAMBDA-search algorithm based on the multi-baseline GNSS model. This algorithm improves the existing CLAMBDA method through a fixed geometry constraint among baselines in the vehicle coordinate system. A fixed single-baseline solution reduces two degrees of freedom of vehicle rigid body, and a global minimization search for the ambiguity objective function in the other degree of freedom is conducted to calculate the baseline vector and its Euler angles. In addition, in order to make up for the shortcomings of short baseline ambiguity in complex environments, this paper proposes different validation strategies. Using three low-cost receivers (ublox M8T) and patch antennas, static and dynamic on-board experiments with different baseline length set-ups were carried out in different environments. Both the experiments prove that the method proposed in this paper has greatly improved the ambiguity fixing performance and also the Euler angle calculation accuracy, with an acceptable calculation burden. It is a practical vehicle-mounted attitude determination algorithm.

Estimation of the Linearized Damping Coefficients of a Squeeze-Film Vibration Isolator

1987 ◽  
Vol 201 (3) ◽  
pp. 181-191 ◽  
Author(s):  
R Stanway ◽  
R Firoozian ◽  
J E Mottershead
Keyword(s):  
Single Frequency ◽  
Squeeze Film ◽  
Experimental Facility ◽  
Vibration Isolator ◽  
New Approach ◽  
Filtering Algorithm ◽  
Damping Coefficients ◽  
Performance Predictions ◽  
Frequency Excitation ◽  
Extract Information

In this paper the authors present experimental confirmation of the feasibility of a new approach to the estimation of the four damping coefficients associated with a squeeze-film vibration isolator. The design and construction of the experimental facility is described in detail. A time-domain filtering algorithm is applied to process the displacement responses to single-frequency excitation and thus extract information on the linearized dynamics of the squeeze-film. The estimated coefficients are validated by comparing performance predictions with those obtained from spectrum analysis and from short-bearing theory. The significance of the results is discussed and suggestions are made for further work in this area.

scholarly journals Investigation of Tightly Combined Single-Frequency and Single-Epoch Precise Positioning Using Multi-GNSS Data

2020 ◽  
Vol 12 (2) ◽  
pp. 285
Author(s):  
Chenlong Deng ◽  
Qian Liu ◽  
Xuan Zou ◽  
Weiming Tang ◽  
Jianhui Cui ◽  
...  
Keyword(s):  
Satellite System ◽  
Position Estimation ◽  
Single Frequency ◽  
Navigation Satellite ◽  
Typical Situation ◽  
Practical Algorithms ◽  
Ambiguity Fixing ◽  
Global Navigation ◽  
Global Navigation Satellite ◽  
Tc Model

The loose combination (LC) and the tight combination (TC) are two different models in the combined processing of four global navigation satellite systems (GNSSs). The former is easy to implement but may be unusable with few satellites, while the latter should cope with the inter-system bias (ISB) and is applicable for few tracked satellites. Furthermore, in both models, the inter-frequency bias (IFB) in the GLObal NAvigation Satellite System (GLONASS) system should also be removed. In this study, we aimed to investigate the performance difference of ambiguity resolution and position estimation between these two models simultaneously using the single-frequency data of all four systems (GPS + GLONASS + Galileo + BeiDou Navigation Satellite System (BDS)) in three different environments, i.e., in an open area, with surrounding high buildings, and under a block of high buildings. For this purpose, we first provide the definition of ISB and IFB from the perspective of the hardware delays, and then propose practical algorithms to estimate the IFB rate and ISB. Thereafter, a comprehensive performance comparison was made between the TC and LC models. Experiments were conducted to simulate the above three observation environments: the typical situation and situations suffering from signal obstruction with high elevation angles and limited azimuths, respectively. The results show that in a typical situation, the TC and LC models achieve a similar performance. However, when the satellite signals are severely obstructed and few satellites are tracked, the float solution and ambiguity fixing rates in the LC model are dramatically decreased, while in the TC model, there are only minor declines and the difference in the ambiguity fixing rates can be as large as 30%. The correctly fixed ambiguity rates in the TC model also had an improvement of around 10%. Once the ambiguity was fixed, both models achieved a similar positioning accuracy.

scholarly journals Conductivity tomography at two frequencies

Geophysics ◽  
2003 ◽  
Vol 68 (2) ◽  
pp. 516-522 ◽  
Author(s):  
Junxing Cao ◽  
Zhenhua He ◽  
Jieshou Zhu ◽  
Peter K. Fullagar
Keyword(s):  
Single Frequency ◽  
Dual Frequency ◽  
Frequency Range ◽  
Frequency Method ◽  
New Approach ◽  
Electromagnetic Absorption ◽  
Universal Approach ◽  
Approximate Frequency ◽  
Transmitting Antenna

We present a new approach for crosshole radio tomography. Conductivity images of the investigated area are reconstructed from the ratio of the electric field intensities measured at two similar frequencies. The method largely avoids assumptions about the radiation pattern and in‐situ intensity of the transmitting antenna, which introduce errors in conventional single‐frequency crosshole electromagnetic‐absorption tomography. Application of the method to field data achieved an improvement in resolution of anomalies over traditional single‐frequency absorption tomography. The dual‐frequency method is not a universal approach; it is suitable for moderately conductive media (<0.01 S/m) over the approximate frequency range 1–100 MHz.

scholarly journals Improved Estimates of the Vertical Structures of Rain Using Single Frequency Doppler Radars

2021 ◽  
Author(s):  
A. R. Jameson ◽  
Michael Larsen ◽  
David Wolff
Keyword(s):  
Drop Size ◽  
Physical Structure ◽  
Single Frequency ◽  
Fall Rate ◽  
Size Distributions ◽  
New Approach ◽  
Rain Fall ◽  
Temporal And Spatial ◽  
Air Motion ◽  
Drop Size Distributions

It is important to understand the statistical-physical structure of the rain in the vertical so that observations aloft can be translated meaningfully into what will occur at the surface. In order to achieve this understanding, it is necessary to gather high temporal and spatial resolution observations of rain in the vertical. This can only be accomplished using radars. It can be achieved by translating radar Doppler spectra into drop size distributions which can then be integrated to calculate variables such as the rain fall rate. A long-standing difficulty in using such measurements, however, is the problem of vertical air motion which can shift the Doppler spectra, and, therefore, significantly alter the deduced drop size distributions and integrated variables. In this work, we illustrate the improvement in measured rain structures using a new approach for removing the effect of mean vertical air motion. It is demonstrated that the new approach proposed here not only produces what appear to be better estimates of the rainfall rates, but, also as a consequence, provides estimates of the temporal and spatial regionally coherent updraft and downdrafts occurring in the precipitation. Furthermore, the technique is readily applicable to other radars especially those operating at non-attenuating frequencies.

A New Cycle Slip Detection and Repair Method for Single-Frequency GNSS Data

2018 ◽  
Vol 71 (6) ◽  
pp. 1492-1510 ◽  
Author(s):  
Qusen Chen ◽  
Hua Chen ◽  
Weiping Jiang ◽  
Xiaohui Zhou ◽  
Peng Yuan
Keyword(s):  
Satellite System ◽  
Single Frequency ◽  
Half Cycle ◽  
Cycle Slip ◽  
Cycle Slips ◽  
Small Cycle ◽  
Cycle Slip Detection ◽  
Gnss Data ◽  
The Impact ◽  
Slip Detection

Cycle slip detection for single frequency Global Navigation Satellite System (GNSS) data is currently mainly based on measurement modelling or prediction, which cannot be effectively performed for kinematic applications and it is difficult to detect or repair small cycle slips such as half-cycle slips. In this paper, a new method that is based on the total differential of ambiguity and Least-Squares Adjustment (LSA) for cycle slip detection and repair is introduced and validated. This method utilises only carrier-phase observations to build an ambiguity function. LSA is then conducted for detecting and repairing cycle slips, where the coordinate and cycle slips are obtained successively. The performance of this method is assessed through processing short and long baselines in static and kinematic modes and the impact of linearization and atmospheric errors are analysed at the same time under a controlled variable method. The results indicate this method is very effective and reliable in detecting and repairing multiple cycle slips, especially small cycle slips.

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