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Measuring steering wheel angle in real-time normally requires accurate installation and reliability in a typical auto-pilot sensor system for agricultural machinery. There are mainly three types of steering wheel angle measurement at present. In the first type, the displacement sensors are widely used to measure the stroke of the steering cylinder, thereby indirectly obtaining the steering angle. In the second type, the resistive or magnetic angle sensors (hall-type) are used to measure the kingpin rotation angle, and then geometric relations are used to calculate the steering angle. In the third type, a gyroscope was selected to measure the angular rate of the steering axle for the angle increment. Nevertheless, all these types need to be updated, when connecting to the navigation controller of a tractor. The first type requires easy installation and high reliability. The second type has high detection accuracy, but also needs easy installation. Since the third type is simple to install, the angle accuracy depends mainly on the gyro’s zero drift, random drift and cumulative error. In this study, a measuring system of steering wheel angle was proposed using the combination of GNSS attitude and motor encoder. In this system, there was no need to install sensors on the steering wheels, or connect to the navigation controller. Firstly, the tractor attitude and ground speed were captured with a high precise GNSS terminal (MC4), and then the reference point of the vehicle precisely compensated the ground speed under the lever arm compensation with the roll and heading of a tractor. A dynamic motion model was selected to roughly calculate the wheel steering angle of the vehicle using the measuring system of steering angle. Secondly, a transfer model was established to real-time measure the steering wheel angle rate using the encoder of the electric wheel, thereby obtaining the steering axle angle rate, particularly considering the linear features of full hydraulic steering gear and the noise of hydraulic leakage. Thirdly, a Kalman filter was used to obtain a highly accurate steering wheel angle, where the rough angle was selected as the observed value, whereas, the steering axle angle rate was used to estimate the steering angle. A static hydraulic steering experiment was conducted to identify the transfer model of the steering wheel, where the LX1204’s transfer coefficient of hydraulic steering was 0.046 542. The field tests included dynamic steering and path tracking. A fixed motor and a ping-pong tuning wheel were used for driving in the dynamic steering tests with the specific speed of 5, 10, 15 and 20 r/min. The results showed that the standard deviation of output angle in the Kalman filter was less than 1°, compared with the angle sensor in the hall effect. Path tracking experiments included 3 times straight-line steering in mid-/high-speed, and 4 times curve path steering. Specifically, the standard deviation was less than 0.91°, while the deviation was 2.56° in the curve path tracking, and the largest measuring error was about 5° during the tractor wheel angle beyond ±20°. It inferred that the measuring system presented a better accuracy, when driving in a straight line, compared with the hall effect angle sensor. The navigation error of the auto-pilot system was less than 2.5 cm in the straight-line steering, while the navigation error was about 9.0 cm in the curve path tracking. Consequently, this angle measuring system can be used in the straight-line steering for the field work, or auto headland turn and harrowing in modern agriculture. [ABSTRACT FROM AUTHOR]

As essential specifications of correlation domain for signal quality evaluation, distortions of the S-curve, including bias and slope distortions of the zero-crossing point, are usually selected as indicators of optimisation in the process of designing the channels of receivers or navigation satellites. Focusing on this issue, we present a detailed analysis of slope distortion in the presence of group delay and amplitude distortions. After validating the theoretical results, we present further discussions about the impacts of different group delay terms on slope distortions. The results indicate that both the odd-order and the even-order terms have impacts on the slope distortion, and higher odd-order terms have less slope distortion compared with the lower odd-order terms. These results are useful for evaluating the slope distortion from the group delay and guiding improvement in design of the channel. [ABSTRACT FROM AUTHOR]

Accuracy, integrity, continuity and availability are the basic quality parameters extremely important in satellite navigation. The article presents results of research using the European Geostationary Navigation Overlay Service (EGNOS) that belongs to the group of Satellite Based Augmentation Systems (SBAS). The measurement data adopted for analysis were recorded in years: 2012, 2014, 2015, 2017 and 2018 in the north-eastern Poland. Results of the analysis showed a significant reduction in the maximum GPS / EGNOS positioning error values from 2014 onwards (compared to results from 2012). In general, values of parameters characterizing accuracy, integrity and availability meet the requirements for EGNOS applications in APV-1 and LPV-200 aviation procedures. It the case of continuity the requirements are not met. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Precise point positioning (PPP) has been well established for retrieving the precipitable water vapor (PWV) in the static model.Yet it is not always suitable for static PPP PWV retrieving,for an instance,the GNSS antenna keeps moving.Position and zenith total delay (ZTD) are coinstantaneously estimated in dynamic PPP model,which is an option for the PWV retrieving in dynamic scenario.GNSS data over 3. 5 hours have been gathered from the Continuously Operating Reference Stations (CORS).Both static and dynamic PPPs have been applied for the CORS data processing.The result reveals that the maximum difference is 6. 6 mm,and dynamic PPP PWV graduate movement agrees in magnitude with that from static PPP PWV.A rotation arm has been designed for GNSS receiver gathering data in dynamic scenario.PPP in dynamic model can retrieve the rotation arm PWV,which makes sense to the one from CORS PWV,but lose the capacity of detecting the PWV changes.GNSS station can have dis-placement in a short term in the earthquake event.Both static PPP and dynamic PPP have been assessed for this scenario.The result reveals that displacement due to the earthquake does not make an evident effect on the PWV retrieving both in static PPP and dynamic PPP.The static PPP is still recommended for the PWV retrieving over the earthquake period. [ABSTRACT FROM AUTHOR]

Vapor-cell devices based on microwave interrogation provide a stable frequency reference with a compact and robust setup. Further miniaturization must focus on optimizing the physics package, containing the microwave cavity and atomic reservoir. In this article, we present a compact cavity-cell assembly based on a dielectric-loaded cylindrical resonator. The loaded cavity resonating at 6.83 GHz has an external volume of only 35 cm3 and accommodates a vapor cell with 0.9-cm3 inner volume. The proposed design aims at strongly reducing the core of the atomic clock, maintaining, at the same time, high-performing short-term stability ($\sigma _{y}{(}\tau {)} \leq {5}\times {10}^{-{13}} \,\tau ^{-{1}/{2}}$ standard Allan deviation). The proposed structure is characterized in terms of microwave field uniformity and atom-field coupling with the aid of finite-element calculations. The thermal sensitivity is also analyzed and experimentally characterized. We present preliminary spectroscopy results by integrating the compact cavity within a rubidium clock setup based on the pulsed optically pumping technique. The obtained clock signals are compatible with the targeted performances. The loaded-cavity approach is, thus, a viable design option for miniaturized microwave clocks. [ABSTRACT FROM AUTHOR]

This article presents a system of precise navigation for a visually impaired person which uses GPS navigation and an infrared sensor in the form of an infrared matrix. The presented system allows determining the orientation and distance of a blind person relative to a selected object, e.g. a wall or road edge. The application of the above solution facilitates a significant increase in the accuracy of determining the position of a blind person compared to the accuracy offered by commonly used ground satellite devices. The system uses thermal energy accumulated in the environment without the need to generate additional signals. The main parts of the system are a simple infrared matrix, data processing system and vibrating wristband. Messages and navigation warnings are sent to a blind person in the form of a vibration code. The article describes the method of determining the path of a specified width and distance from the wall of a building, curb, etc., along which a blind person should move. The article additionally describes the method of determining the orientation of a blind person depending on the selected object. Such a method facilitates verifying whether the visually impaired person is moving according to the indicated direction. The method can also be used to navigate mobile robots. Due to the use of natural energy for data registration and processing, the mobile navigation system can be operated for a long time without the need to recharge the battery.

The global navigation satellite system has achieved great success in the civil and military fields and is an important resource for space-time information services. However, spoof interference has always been one of the main threats to the application security of satellite navigation receivers. In order to further improve the application security of satellite navigation receivers, this paper focuses on the application scenarios where narrowband and spoofing interference exist at the same time, studies the problem of spoofing interference detection under mixed interference conditions, then proposes a spoofing interference detection method based on the tracking loop identification curve. This method can effectively deal with the detection of spoofing interference under the conditions of narrowband interference and, at the same time, it can effectively detect the spoofing interference of gradual deviation. Simulation experiments verify the effectiveness of the spoofing interference detection method, based on the tracking loop discrimination curve. In typical jamming and spoofing scenarios, when the spoofing signal is about 7.5 m away from the real signal, the method used in this paper can achieve effective detection. The proposed detection method is of great significance for improving the anti-spoofing capability of satellite navigation receivers.

Frequency-domain anti-jamming technology is a common anti-jamming method for satellite navigation receivers. 1/2 overlapping windowing can effectively solve the spectrum leakage in the frequency domain conversion process, but the traditional window function will cause the loss of signal energy. This paper proposes a window function design method with no loss of signal energy, which can effectively solve the signal energy loss caused by the window function. The feasibility of the proposed method is theoretically deduced, and the effectiveness of the proposed method is verified by simulation and measured data. Compared with the traditional window function, the signal-to-noise ratio improvement of the method proposed in this paper is better than 0.5 dB. The frequency domain anti-jamming processing is optimized, the signal-to-noise ratio loss caused by the anti-jamming processing is reduced, and the anti-jamming performance is indirectly improved. This plays an important role in the performance optimization of satellite navigation system links.

Today, a substantial portion of global trade is carried by sea. Consequently, the reliance on Global Navigation Satellite System (GNSS)-based navigation in the oceans and inland waterways has been rapidly growing. GNSS is vulnerable to various radio frequency interference. The objective of this research is to propose a resilient Multi-Frequency, Multi-Constellation (MFMC) receiver in the context of maritime navigation to identify any GNSS signal jamming incident and switch to a jamming-free signal immediately. With that goal in mind, the authors implemented a jamming event detector that can identify the start, end, and total duration of the detected jamming event on any of the impacted GNSS signal(s). By utilizing a jamming event detector, the proposed resilient MFMC receiver indeed provides a seamless positioning solution in the event of single-frequency jamming on either the lower or upper L-band. In addition, this manuscript also contains positioning performance analysis of GPS-L5-only, Galileo-E5a-only, and Galileo-E5b-only signals and their multi-GNSS combinations in a maritime operational environment in the Gulf of Finland. The positioning performance of lower L-band GNSS signals in a maritime environment has not been thoroughly investigated as per the authors’ knowledge.

Recently, the Korean government has announced a plan to develop a satellite-based navigation system called the Korean Positioning System (KPS). When designing a new Radio Navigation Satellite Service (RNSS) signal, the use of the S-band has emerged as an alternative to avoiding signal congestion in the L-bands, and South Korea is considering using the S-band with the L-bands. Therefore, this study proposed possible S-band signal candidates and evaluated their performance, such as the radio frequency (RF) compatibility, spectral efficiency, ranging performance, and receiver complexity. Several figures-of-merit (FoMs) were introduced for quantitative performance evaluation for each candidate. Each FoM was calculated using an analytical equation by considering the signal design parameters, such as the center frequency, modulation scheme, and chip rate. The results showed that the outstanding candidate signal was different depending on the signal performance of interest and the reception environments. Therefore, we discuss and summarize the signal performance analysis results considering the whole FoMs together. Under the assumptions given in this paper, the binary phase shift keying (BPSK)(1), sine-phased binary offset carrier (BOCs)(5,2), and BPSK signals were superior for the spectral efficiency, ranging performance, and receiver complexity, respectively.

This article presents a system of precise navigation for a visually impaired person which uses GPS navigation and an infrared sensor in the form of an infrared matrix. The presented system allows determining the orientation and distance of a blind person relative to a selected object, e.g. a wall or road edge. The application of the above solution facilitates a significant increase in the accuracy of determining the position of a blind person compared to the accuracy offered by commonly used ground satellite devices. The system uses thermal energy accumulated in the environment without the need to generate additional signals. The main parts of the system are a simple infrared matrix, data processing system and vibrating wristband. Messages and navigation warnings are sent to a blind person in the form of a vibration code. The article describes the method of determining the path of a specified width and distance from the wall of a building, curb, etc., along which a blind person should move. The article additionally describes the method of determining the orientation of a blind person depending on the selected object. Such a method facilitates verifying whether the visually impaired person is moving according to the indicated direction. The method can also be used to navigate mobile robots. Due to the use of natural energy for data registration and processing, the mobile navigation system can be operated for a long time without the need to recharge the battery. [ABSTRACT FROM AUTHOR]

Performance of global navigation satellite systems (GNSSs) mounted on aerial platforms could be degraded by the presence of jamming or spoofing threats. Detection of jamming and spoofing is essential considering practical applications of satellite navigation in passenger aircrafts, unmanned aerial vehicles (UAVs), helicopters and fighters. Different algorithms and methods have been proposed for detection of these threats; however, their usage has many limitations because of their demanding weight, size and computational complexity, when embedded on aerial systems. In this study, the authors develop a theoretical framework to detect the presence of the threat of UAVs. The idea is based on the fact that, due to the UAV motion, the samples of received signal power from a fixed threat and from a GNSS satellite have different empirical probability density functions. Moreover, by using two antennas (an omnidirectional and a down‐tilted‐directional), they introduce a new method to distinguish between aerial and ground‐based threats. The proposed algorithms have a low‐computational burden and can consider the fading loss as well. Simulation results show the superior performance of the proposed methods, in terms of detection and false alarm probability, compared to the existing methods. [ABSTRACT FROM AUTHOR]

Space–time adaptive processor based on power inversion (PI) criterion can effectively suppress interference for the global navigation satellite system (GNSS) receiver when the steering vector of the GNSS signal is unknown. However, existing space–time PI processing methods will introduce meter‐level pseudo‐code tracking biases into the GNSS receiver measurements which cause several meter‐level position errors. A distortionless pseudo‐code tracking space–time PI algorithm is proposed. It could not only suppress interference, but also introduce no pseudo‐code tracking biases. The major novelty of the proposed method is ensuring the symmetry of the output signal's cross‐correlation function by constraining coefficients. Several experiments are implemented to test the performance of the proposed algorithm. For comparison, the results of the PI algorithm and the minimum variance distortionless response (MVDR) algorithm are also shown. Results show that for the PI algorithm and the MVDR algorithm, pseudo‐code tracking biases are introduced in different experiments; however, for the proposed algorithm, there are no pseudo‐code tracking biases in those experiments. As a result, the effectiveness of the proposed method is verified. [ABSTRACT FROM AUTHOR]

By forging global navigation satellite system (GNSS) signals similar to authentic ones, a spoofer can make receivers track forged signals (spoofing signals) and generate wrong position, velocity and time results. Receiver autonomous integrity monitoring (RAIM) can be extended to the field of spoofing detection and exclusion (SDE). However, it is well known that when there are six or more signals and only one spoofing signal among them, RAIM can effectively exclude the spoofing signal. In this study, based on maximum likelihood estimation (MLE) theory and the idea of the traverse, one‐dimensional traversal MLE‐RAIM (TMRAIM) is proposed, which can exclude multiple spoofing signals. Theoretically, the influence of spoofing biases will be reflected in pseudorange residuals, and then affect the probability distribution of the parity vector. Through MLE deduction, the authors can find corresponding spoofing signals which are relevant with the maximum probability of the parity vector only once under the supposed number of spoofing signals. By just traversing the number of spoofing signals, TMRAIM can run effectively on real‐time GNSS receivers with low complexity. The SDE ability and time complexity are analysed in detail and two field experiments are constructed. Experimental results demonstrate the method is feasible and effective for anti‐spoofing applications. [ABSTRACT FROM AUTHOR]

Aiming at the problem that the satellite navigation system of the unmanned aerial vehicle (UAV) is vulnerable to electromagnetic interference during the flight, the injection experiment of the continuous wave (CW) interference is carried out with the navigation receiver of a certain UAV type. Through the experiments, the in-band electromagnetic sensitivity curves of the different types of satellites are obtained, and the relationship between the initial carrier-to-noise ratio with the electromagnetic sensitivity threshold and interference signal ratio (ISR) is studied. Then, the sensitive frequency band of the navigation receiver is obtained, when positioning fails. Through the qualitative experiment analysis, the main reasons for the navigation receiver's positioning failure is the co-channel interference and the mixer sub channel interference. According to the above conclusion, a feasibility method for electromagnetic interference prediction of UAV satellite navigation system is given, which is of great significance for improving the safety situation of UAV in complex electromagnetic environment. [ABSTRACT FROM AUTHOR]

In this paper, a large gain variable range, high linearity, low noise, low DC offset VGAs with a simple gain-dB variable circuit are introduced. In the VGAs chain, the last and the first VGAs employ Bipolar transistors, to improve the linearity and noise characteristics. And the middle three stages VGAs employ MOS transistors. The whole circuitry is designed in 0.35um BiCMOS process, including variable gain amplifiers (VGAs) , fixed gain amplifiers , gain control and DC offset cancellation parts. The automatic gain control loop (AGC) provides a process independent gain variable range of 60dB (including 50dB gain-dB-linearity variable range), with a 200us loop lock time, the VGAs provide a 73dB largest gain, the THD is less than 1% at a 1V(P-P) output level; the equivalent output integral noise is 0.011v/√hz@20MHz bandwidth. The whole area is 1173um*494 um, and the power is 7.1mA at 3.3V signal supply voltage.

Global navigation satellite systems (GNSS) have a wide range of applications in forest industry, including forest inventory. In this study, the horizontal accuracy of 45 inventory plots in different forest environments and 5 inventory plots under open sky conditions were examined. The inventory plots were located using a mapping-grade GNSS receiver during leaf-on season in 2017. True coordinates of the plot centres were acquired using a survey-grade GNSS receiver during leaf-off season in 2018. A study was conducted across a range of forest conditions in the forest unit Vígľaš, which is located in Slovakia (Central Europe). Root mean square error of horizontal accuracies was 8.45 m in the plots under forest canopy and 6.61 m under open sky conditions. We note decreased positional errors in coniferous forests as well as in younger forests. However, results showed that there is no statistically significant effect of tree species composition and stand age on horizontal accuracy.

Owing to the existence of non-line-of-sight (NLOS) signals in global navigation satellite system (GNSS) challenged environment, the real-time kinematic (RTK) position precision is seriously damaged. In order to improve the position accuracy, the authors propose a robust positioning method which tackles this problem by detecting the NLOS through a decision tree and estimating the double-differenced multipath errors in real time. The NLOS detection performance of the proposed method is 95.64%. The field experiment shows that the ambiguity fixing rate has improved by 43% in the instantaneous mode, and the 3D position accuracy is about 81.77% higher better than that of normal RTK method which is implemented by using RTKLIB software. [ABSTRACT FROM AUTHOR]

This work addresses the problem of integrating a new signal in the Galileo E1 band. Thus, the arising question is how the existing multiplexing methods can be efficiently used or modified to integrate a new binary signal in the Galileo E1 band with the existing Galileo E1 signals. To this end, in this study, the authors first select three efficient multiplexing methods from the state of the art (i.e. interplexing, POCET and CEMIC methods) to multiplex a new Galileo signal along with the Galileo E1 legacy signals in a constant envelope modulation. Moreover, they evaluate their performance and main advantages and drawbacks. Secondly, in order to improve both performance and flexibility/adaptability of the multiplexing method, a modified CEMIC method, called ACEMIC, is proposed. This method allows to design modulations which maximise the power efficiency with respect to a given peak‐to‐average‐power‐ratio constraint. Finally, they compare the previous multiplexing methods in terms of power signal distribution, constant envelope fluctuation and power efficiency. [ABSTRACT FROM AUTHOR]

The state of the signal in space (SIS) broadcasted by the broadcast ephemeris will affect the reliability and safety of the user navigation and positioning. Understanding the SIS anomaly of a satellite is conducive to fault allocation in advanced receiver autonomous integrity monitoring. In this study, precise ephemeris was used to calculate the SIS error of all healthy Galileo satellites from 2017 to 2018, the detection thresholds were obtained through statistics of SIS error, and the satellite SIS anomalies for two years were detected. Results show that the SIS anomalies of Galileo satellites are primarily caused by satellite clock error, the scale of which can sometimes reach tens or even hundreds of metres. Except for E24 satellite, the annual accumulation of anomalies for Galileo satellites was <∼7 h, and the average annual accumulation of anomalies is ∼2.5 h. The accumulation of anomalies for E24 in 2017 was ∼50 h∼50 h, but this decreased to 4.5 h in 2018, indicating that its stability improved. Overall, the SIS stability in 2018 was improved compared with 2017. In addition, as the serious missing of broadcast ephemeris of Galileo satellites, it is not conducive to the continuity and reliability of the user's navigation and positioning. [ABSTRACT FROM AUTHOR]

The derivation of tight estimation lower bounds is a key tool to design and assess the performance of new estimators. In this contribution, first, the authors derive a new compact Cramér–Rao bound (CRB) for the conditional signal model, where the deterministic parameter's vector includes a real positive amplitude and the signal phase. Then, the resulting CRB is particularised to the delay, Doppler, phase, and amplitude estimation for band‐limited narrowband signals, which are found in a plethora of applications, making such CRB a key tool of broad interest. This new CRB expression is particularly easy to evaluate because it only depends on the signal samples, then being straightforward to evaluate independently of the particular baseband signal considered. They exploit this CRB to properly characterise the achievable performance of satellite‐based navigation systems and the so‐called real‐time kinematics (RTK) solution. To the best of the authors' knowledge, this is the first time these techniques are theoretically characterised from the baseband delay/phase estimation processing to position computation, in terms of the CRB and maximum‐likelihood estimation. [ABSTRACT FROM AUTHOR]

Integration of global navigation satellite system (GNSS) and strap‐down inertial navigation system (SINS) in pseudo‐range and pseudo‐range rate measurements level has been demonstrated as an effective way to provide more reliable navigation solutions. Under this condition, the dimension of measurements matrix of the integration filter increases dramatically along with more GNSSs included in the integration, traditional centralized integration filter processing method cannot address the computational load well. In this study, a distributed integration filter processing method is proposed for the integration of multiple GNSSs and SINS using the pseudo‐range and pseudo‐range rates as the measurements. Measurement difference inner a same satellite constellation is conducted to remove the clock related variables, which reduces the dimension of the state vector. Secondly, a federated Kalman filter is employed to obtain global optimal estimation of the state variables, which reduces the measurement vector dimension. Mathematical model of the distributed processing model with the simplified integration filter scheme is given in detail. Through the simulation based on a dynamic trajectory, the performance of the proposed method is investigated and compared with the centralized integration processing method. Results show that new method has analogous position and velocity accuracy with better computation efficiency. [ABSTRACT FROM AUTHOR]

In order to use a stand‐alone global navigation satellite system (GNSS) receiver to determine the stable instantaneous velocity, a new hybrid GNSS velocimetry approach combining carrier phase and Doppler measurements is proposed. This is a data fusion problem. The problem is expressed as a state‐space model, in which the deviation between the average velocity determined by the time difference carrier phase approach and the instantaneous velocity is represented by the uncertainty of the state model. In kinematic applications, this uncertainty is often variant and hard to be known in advance, a predefined process noise level of the state model is often not sufficiently accurate in the whole working time. Here, an adaptive Kalman filtering approach is employed to fix this problem. To verify the proposed approach, one static experiment and two dynamic experiments with different sampling intervals are performed, separately. All results demonstrate the validity and stability of the proposed approach. [ABSTRACT FROM AUTHOR]

Convex relaxation methods are commonly used to solve nonconvex mathematical optimization problems. These methods transform the original nonconvex problem in such a way that effective methods of solving convex optimization problems become applicable. Thus, a convex problem giving the approximate solution of the original task can be solved instead of the original computationally complex problem. Presented is the application of semidefinite relaxation to the task of determining the optimal set of Global navigation satellite systems signals that are selected for processing while solving the positioning problem. The need for signals set optimization is due to large number of navigation satellites accessible for the customers on the ground level. This binary optimization problem is hard to solve in real time. Two approaches are proposed to reduce the initial problem to the convex problem allowing the effective solution. [ABSTRACT FROM AUTHOR]

In this paper, the potentials of using Global Navigation Satellite System (GNSS) techniques in the complex calibration procedure of the tracking sensors for missile test range applications have been presented. The frequently used tracking sensors in test range applications are- electro-optical tracking stations (EOTS) and tracking radars. Over the years, the EOTS are used as the reference for bias estimation of the radars. With the introduction of GPS in test range applications, especially the DGPS, the reference for bias estimation got shifted to DGPS from the EOTS. However, the achievable position solution accuracy is limited to the order of a few meters for DGPS, EOTS, and Radars. With the evolution of Multi-constellation GNSS and carrier-phase based measurement techniques in satellite navigation, achievable position solution accuracies may be improved to sub-meter level. New navigation techniques like real time kinematic (RTK) and precise point positioning have the potentials for use in the calibration procedures of the missile test ranges to the accuracies of centimeter-level. Moreover, because of the availability of a large number of navigation signals over the Indian region, multi-constellation GNSS receivers can enhance signal availability, reliability, and accuracies during the calibration of missile test ranges. Currently available compact, low-cost GNSS modules also offer the possibilities of using these for cost-effective, networked RTK for dynamic calibration of test ranges reducing cost and resource requirements. [ABSTRACT FROM AUTHOR]

As Global Navigation Satellite System (GNSS) spoofing techniques are highly stealthy and pose a tremendous risk to targets using GNSS technology, studies on GNSS spoofing techniques have been in the spotlight. If the accurate position and velocity of the target receiver can be obtained, the target receiver can be covertly spoofed during the signal tracking stage using synchronous lift-off spoofing. However, it is often difficult to accurately obtain the position and velocity of a target in real GNSS spoofing scenarios. To address this problem, To study the effects of spoofing signals’ power (relative to the real signal), code pulling rate, carrier Doppler shift, initial code phase difference, and carrier phase difference on the efficacy of spoofing, the intrusion of receiver’s signal tracking loop by spoofing signals is mathematically modeled. Based on the model, an asynchronous lift-off spoofing for GNSS receivers in the signal tracking stage is proposed. Theoretical analysis and experimental results show that the new method resulted in stable Doppler frequency variations, short fluctuations in carrier-to-noise ratio (C/N) and signal lock time, and gentle changes to the receiver’s 3D Earth-Centered Earth Fixed (ECEF) coordinates, when the target’s position and velocity were approximately known during the intrusion period. The proposed spoofing method is highly feasible and could expand the scope of applicability of lift-off spoofing. [ABSTRACT FROM AUTHOR]

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With more and more missions around the Moon, a communication/navigation constellation around the Moon is necessary. Halo orbits, due to their unique geometry, are extensively studied by researchers for this purpose. A dedicated survey is carried out in this work to analyse the coverage ability of halo orbits. It is found that a two-satellite constellation is enough for continuous one-fold coverage of the north or the south polar regions but never both. A three-satellite constellation is enough for continuous one-fold coverage of both north and south polar regions. A four-satellite constellation can cover nearly 100% of the whole lunar surface. In addition, the coverage ability of another special orbit – distant retrograde orbit (DRO) – is analysed for the first time in this study. It is found that three satellites on DROs can cover 99·8% of the lunar surface, with coverage gaps at polar caps. A four-satellite constellation moving on spatial DROs can cover nearly the whole lunar surface. By combining halo orbits and DROs, we design a five-satellite constellation composed of three halo orbit satellites and two DRO satellites. This constellation can provide 100% continuous one-fold coverage of the whole lunar surface. [ABSTRACT FROM AUTHOR]

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Instrumental Landing System (ILS) system has been used for decades as an irreplaceable navigation aid at most international airports worldwide. Older radio navigation aids are very reliable, and still in use, although are very complex with high maintenance and installation costs. Due to increased traffic and limited peak hour capacity, the need for new technological solutions arises. Global Navigation Satellite System (GNSS) based navigation is already widely used in the aviation sector. This paper will provide decision-makers, involved in the development strategy for Sarajevo International Airport, a clear insight into the benefits of Ground Based Augmentation System (GBAS) over the classic ILS system. Besides, it describes several essential steps to research before implementing GBAS Category (CAT) II / III system. Sarajevo Airport has many limiting factors regarding the installation of a higher ILS category system, so this article proposes a solution in the form of a GBAS system, and analyse how it will affect the Sarajevo airport operations, especially in low visibility conditions. [ABSTRACT FROM AUTHOR]

Copyright of Journal of National University of Defense Technology / Guofang Keji Daxue Xuebao is the property of NUDT Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Here, we introduce a low-cost airglow imaging system developed for observing plasma bubble signatures in 630.0-nm airglow emission from the F region of the ionosphere. The system is composed of a small camera, optical filter, and fish-eye lens, and is operated using free software that automatically records video from the camera. A pilot system was deployed in Ishigaki Island in the southern part of Japan (Lat 24.4, Lon 124.4, Mlat 19.6) and was operated for ~ 1.5 years from 2014 to 2016 corresponding to the recent solar maximum period. The pilot observations demonstrated that it was difficult to identify the plasma bubble signature in the raw image captured every 4 s. However, the quality of the image could be improved by reducing the random noise of instrumental origin through an integration of 30 consecutive raw images obtained in 2 min and further by subtracting the 1-h averaged background image. We compared the deviation images to those from a co-existing airglow imager of OMTIs, which is equipped with a back-illuminated cooled CCD camera with a high quantum efficiency of ~ 90%. It was confirmed that the low-cost airglow imager is capable of imaging the spatial structure of plasma bubbles, including their bifurcating traces. The results of these pilot observations in Ishigaki Island will allow us to distribute the low-cost imager in a wide area and construct a network for monitoring plasma bubbles and their space weather impacts on satellite navigation systems. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aiming at the long term and high-precision performance maintenance requirements of the satellite-borne four-axis redundant inertial measurement unit (IMU) in space, the satellite navigation velocity information, the attitude information provided by the star sensor and the redundant measurement output are used as references to derive the measurement model, including the star sensor installation error. Three rotation sequences of optimal observation, sub-optimal observation, and under-observation are designed and compared. The Kalman filter is used to calibrate the redundant IMU in the orbit. The numerical simulation shows that all three rotation sequences can calibrate more than 91% of the constant error, which meets the requirements of the use, and the calibration accuracy of the optimal rotation sequence is the highest. The ground repeatability calibration experiment is carried out 10 times for the optimal rotation sequence. The calibration results show that the range of all the error terms is less than its threshold, illustrating that the calibration result is stable and reliable. It is a real-time calibration method for all error terms on orbit, providing a reference method for the high-precision performance maintenance of the spacecraft integrated navigation system. [ABSTRACT FROM AUTHOR]

Global navigation satellite system (GNSS) is a key positioning system for intelligent transport systems (ITS). The GNSS receiver should be able to autonomously perform integrity monitoring, including detection of faulty observations. In this contribution, new models for fault detection in the position domain are presented that are tailored for ITS. The fault detection tests are parameterised for the track frame of the vehicle, and in a combined single test form. Another new form is presented where the detection testing is parameterised in the direction of the maximum possible error. The tests are formed where position errors are assumed to have a zero‐mean Gaussian distribution, which is a working hypothesis in the open environment. The case of positioning in the urban environment is also addressed using two approaches. The first is by using a logistic distribution that is found to empirically better fit a very large sample of position errors compared to the normal distribution in this environment. The second approach is to use of an overbounding Gaussian distribution. The protection levels (PLs) in the track frame are presented, and the advantage of expressing PL along the maximum direction is shown. The presented methods are experimentally demonstrated in practice through a kinematic test. [ABSTRACT FROM AUTHOR]

The space application task is to carry out various scientific experiments and applied research by using the ability of space experiment of spacecraft. In the past 20 years, >50 space application studies have been carried out in Chinese manned space flight application system, >500 units have been involved in the previous flight missions, and fruitful results have been achieved. The white paper 'Chinese spaceflight in 2016' pointed out that in the next 5 years, Chinese satellite system will enhance the level and basic ability to construct the satellite system. Chinese manned space station project is scheduled to be completed ∼2022 and it will plan to operate >10 years. The space station, based on the world-wide integrated information network, has a large number of payloads and will become a national space laboratory. Space activities are full of risks and challenges. On the basis of a great deal of literatures, the method of avoiding space risk in the field of spaceflight is discussed. Aiming at the fault diagnosis task for space utilisation, the intelligent methods of deep learning including deep belief network, convolutional neural network and generative adversarial network are discussed. [ABSTRACT FROM AUTHOR]