Satellite Receiver Research Articles

Multivariate Analysis on the Ionospheric Responses to Planetary Waves During the 2019 Antarctic SSW Event

AbstractA rare minor sudden stratospheric warming is observed in the Antarctic polar region during September 2019, which results in the enhancement of a westward wavenumber 1 quasi‐6‐day wave (Q6DW) in the mesopause region. The impacts of this Q6DW event to the ionosphere are then comparatively investigated with multiple data sets, including the ground‐based total electron content (TEC) from geostationary BeiDou satellite receivers and F2 layer maximum frequency (foF2) from ionosondes ranging from 20 to 40°N over eastern Asia. Besides, the global TEC maps from the International Global Navigation Satellite Systems Service (IGS) are also utilized to study the longitudinal variations. The ground‐based TEC and foF2 observations clearly shows planetary wave (PW) signals with a similar period as those in the mesosphere, which are further verified to be westward with zonal wavenumber 1 by IGS TEC maps. The ground‐based TEC and foF2 also show that the peak of the ionospheric response is at around 1,200–1,400 LT and 25°N over eastern Asia with maximum amplitudes of ∼9 TECU and ∼1.5 MHz, respectively, which are also well captured by IGS TEC maps. Nevertheless, the wave amplitudes exhibited by ground‐based TEC are 2–3 times larger than that in IGS TEC. Besides, the IGS TEC map shows that the ionospheric oscillations at different longitudes peak in the equatorial ionospheric anomaly crest region at similar solar local time, but with significant variabilities in their amplitude. Our analysis shows that the ground‐based ionospheric observations and IGS TEC maps generally exhibit consistent latitudinal structures on the neutral‐ion coupling through PWs.

Teachers’ Perception towards Online English Learning Using Distance Education System at Rural Schools Area, Thailand

Due to the pandemic situation, the online learning process is really not easy for the teachers, especially for schools that are still located in rural areas. Besides the location, they also lack educators in English Subjects. Since the establishment of online learning, the Ministry of Education in Thailand has a program where the program can be an additional learning process for schools experiencing critical learning problems during the pandemic. This program is called educational TV channels which use a satellite receiver. Although the teachers at these schools have implemented this program to carry out the English learning process for their students, they also have to measure how useful this program is in providing understanding especially in English material to their students. Thus, this research aims to find out the teachers' perception on online English learning towards Educational TV Channels to accommodate the online English learning process in rural schools area, Thailand. Here, the researcher decides to use a mixed methodology. Based on the interview data, it can be concluded that learning through TV Channel, besides that students are more happy and interested when learning through TV Channel, the TV Channel education program is very interesting in the form of pictures, music and animation. And based on the questionnaire analysis, it was found that 40% and 60% of students agreed with the learning using TV Channels. Meanwhile, in the interview analysis, it was found that learning to use Educational TV Channels was very fun because the views, videos and TV Channels season were very interesting.

Investigation of the influence of surfaces between basic stations and satisfactory recognition on the accuracy of coordinating definitions

The distance between different base stations and the mobile receiver, as well as errors of coordinate definitions at different distances between the base station and the mobile receiver are investigated. For realization of the set tasks the following methods of research were applied: field measurements, mathematical modeling method and methods of mathematical statistics for the processing of experimental data. The degree of influence of distances between the base station and the satellite receiver on accuracy of coordinate definitions in RTK-mode is established.

Performance of the DBS Satellite Receiver under the Impact of Rainfall and Terrestrial Interference

This article presents a new study on the feasibility of operating a direct broadcasting satellite (DBS) system under the effect of both precipitation and interference from a fixed service (FS) at K‐band in a semiarid region. The carrier‐to‐noise plus interference ratio (CNIR) as a protection criterion has been adopted to make sure that the receiver of the DBS system operates with an acceptable performance under rainfall and interference from FS. Various measured data for rainfall in different areas have been utilized to investigate different rain rate exceedance percentages. Results have been shown that areas with high rain rates have a small CNIR at the DBS receiver and require large protection distances compared to low‐rain rate areas and vice versa. Some mitigation techniques have been suggested to alleviate the effect of rain and terrestrial interference on the DBS receiver performance.

An Improved Long-Period Precise Time-Relative Positioning Method Based on RTS Data.

The high precision positioning can be easily achieved by using real-time kinematic (RTK) and precise point positioning (PPP) or their augmented techniques, such as network RTK (NRTK) and PPP-RTK, even if they also have their own shortfalls. A reference station and datalink are required for RTK or NRTK. Though the PPP technique can provide high accuracy position data, it needs an initialisation time of 10–30 min. The time-relative positioning method estimates the difference between positions at two epochs by means of a single receiver, which can overcome these issues within short period to some degree. The positioning error significantly increases for long-period precise positioning as consequence of the variation of various errors in GNSS (Global Navigation Satellite System) measurements over time. Furthermore, the accuracy of traditional time-relative positioning is very sensitive to the initial positioning error. In order to overcome these issues, an improved time-relative positioning algorithm is proposed in this paper. The improved time-relative positioning method employs PPP model to estimate the parameters of current epoch including position vector, float ionosphere-free (IF) ambiguities, so that these estimated float IF ambiguities are used as a constraint of the base epoch. Thus, the position of the base epoch can be estimated by means of a robust Kalman filter, so that the position of the current epoch with reference to the base epoch can be obtained by differencing the position vectors between the base epoch and the current one. The numerical results obtained during static and dynamic tests show that the proposed positioning algorithm can achieve a positioning accuracy of a few centimetres in one hour. As expected, the positioning accuracy is highly improved by combining GPS, BeiDou and Galileo as a consequence of a higher amount of used satellites and a more uniform geometrical distribution of the satellites themselves. Furthermore, the positioning accuracy achieved by using the positioning algorithm here described is not affected by the initial positioning error, because there is no approximation similar to that of the traditional time-relative positioning. The improved time-relative positioning method can be used to provide long-period high precision positioning by using a single dual-frequency (L1/L2) satellite receiver.

Small Scale Rain Field Sensing and Tomographic Reconstruction with Passive Geostationary Satellite Receivers

Sensing of the rain rate and the movement of the rain field over a relatively small geographical area may often be necessary for agricultural purposes, water management objectives or transport management in airports or harbors. In this paper, an entirely passive method is suggested to sense rainfall rate and extension of a rain field, with reconstruction in two dimensions using a tomographic method. In order to achieve this goal, multiple colocated satellite receivers are proposed to measure the beacon signal levels of geostationary satellites received at different azimuth angles. The tomographic reconstruction of the rain field takes the advantage of the dis-placement of the rain field due to the movement of air masses, while the rain intensity along the receiving path is estimated by the attenuation of the radio signal between the satellite and the ground receiver. To realize the proposed system, a complete receiver setup and an existing, operational group of satellites are selected. A widely known rain field modeling method is applied to generate test data and evaluate the system. The feasibility of a technically realizable system is provided, and its capabilities are compared with a hypothetical, ideal system. The methods and algorithms are tested on an existing geographical location, simulating a real operating environment.

AN ATTEMPT TO USE GOOGLE EARTH PRO IMAGES FOR SELECTED GEODETIC WORKS − FOR EXAMPLE OF WOLNOŚCI SQUARE IN POZNAŃ (POLAND)

The article concerns issues pertaining to satellite geodesy and the possibilities of using the available source materials such as high-resolution satellite maps for selected works which require a high degree of accuracy in determining the location of topographic objects. The purpose of the work was to indicate the potential use of Google Earth maps for selected geodetic works (preparing topographic descriptions, sketch maps) in order to facilitate and accelerate the process. Works were carried out in an urban area, Wolności Square in Poznań (Poland) where 58 checkpoints were located. In order to design them, maps from the Google system from four periods were used. The research used the Global Navigation Satellite Systems set consisting of a Leica GS08 + satellite receiver and a Leica CS15 controller, geodetic software for work design (Trimble GNSS Planning Online) and calculations (C-Geo 8) as well as cartographic materials and data obtained from the Municipal Center of Geodetic and Cartographic Documentation in Poznań: the master map, catalog data and topographic descriptions of the reference points. The results show that the accuracy of the location of points offered by Google is greater than declared by the system operators. However, it is not sufficient for applications in the assumed geodetic works.

Simultaneous estimation of GPS P1-P2 differential code biases using low earth orbit satellites data from two different orbit heights

Global navigation satellite system (GNSS) differential code bias (DCB) is a significant error source in ionosphere modeling that uses GNSS observation data. Given that the orbit altitudes of low earth orbit (LEO) satellites are above the F layer of ionosphere, ionized electrons come from the upper ionosphere or plasmasphere, so observations suffer from small signal delays. DCBs can be estimated using LEO data instead of that from ground stations. In most studies, LEO-based DCB estimation employs onboard data from either a single LEO or from two that are at the same orbit height. In our study, we applied four LEO satellites data from two different orbit heights to estimate GPS satellite DCBs, receiver DCBs and LEO-based vertical total electron content (VTEC) parameters simultaneously. Before DCB estimation, a data preprocessing strategy suitable for LEO onboard data was applied to obtain clear pseudorange data. We developed a processing method for the upper ionosphere using LEO onboard data from different orbit heights, by introducing LEO-based VTEC models in advance to remove its effects; two introduced VTEC models were derived from modeling results using paired data from the same orbital height, respectively. We draw some conclusions as follows. For the LEO satellites at different orbit heights, the more the number of LEO satellites involved, the more stable estimation results achieved. We also noted that the GPS satellite DCBs stability and accuracy with established LEO-based VTEC models, using multi-LEOs data from different orbit heights, were better than the achievable results using onboard data from the same orbital height or using single LEO satellite schemes. Compared with the estimation results of single LEO solutions, the monthly stabilities and accuracies for multi-LEOs solutions from different orbit heights are improved by 25–35% approximately. Among all the tested schemes, superior stability derived from simultaneous estimation using four LEO data at different orbit heights is 0.064 ns; the optimal accuracies for DCB estimation for different GPS satellites are the scheme GRACE-A and JASON-2 (two LEOs) of 0.146 ns, approximately, compared with Center of Orbit Determination of Europe products, respectively. The stability and accuracy of LEO-based DCB estimations were approximately similar to those achieved using ground solutions.

Influence of dense wavelength division multiplexing (DWDM) technique on the low earth orbit intersatellite systems performance

Abstract This work discusses the effect of wavelength division multiplexing on performance of intersatellite link. Intersatellite optical wireless communication (IsOWC) system is simulated by using OptiSystem software. Number of multiplexing channels involve on system performance. Bit rate is an operating parameter that determines the quality of the signal. Also, wavelength and distance between satellite transmitter and satellite receiver determine the system performance. In this article, the max Q factor, received power, and optical signal/noise ratio are the major leading performance parameters.

An Improved Weight Optimization AAIM Method Aided by Barometric Altimeter

Aiming at the problem of insufficient availability in the satellite receiver autonomous integrity monitoring (RAIM) method, an improved aircraft autonomous integrity monitoring (AAIM) method aided by barometric altimeter based on weight optimization is proposed under the actual configuration of the airborne navigation system. The information of satellite navigation system and barometric altimeter is used to establish the observation equation of the integrated system. The algorithm for integrity monitoring and protection-level calculation is derived based on multiple solution separation, and a weight optimization is adopted to achieve a trade-off between position accuracy and integrity, which can improve the availability of AAIM method. The simulation experiment shows that when the number of visible stars is 5, the traditional method cannot effectively detect the satellite fault, and the positioning error is 43.65 m. The improved algorithm can effectively isolate the fault and reduce the positioning error to 0.37 m. Compared with the traditional RAIM algorithm and the Baro-aided AAIM algorithm, the proposed algorithm has a lower vertical protection threshold. Therefore, the algorithm in this paper improves the performance of satellite navigation system integrity monitoring and ensure the accuracy and reliability of the satellite navigation system.

ELF/VLF Communication Experiment by Modulated Heating of Ionospheric Auroral Electrojet at EISCAT

Amplitude modulation high-frequency (HF) radio waves at extremely low frequencies (ELF, 0.3-3 kHz) or very low frequencies (VLF, 3-30 kHz), heating the ionosphere, can nonlinearly modulate the auroral electrojet to produce ELF/VLF waves for long-distance communication. This article presents the results of the first ELF/VLF communication experiments being conducted at Tromsø, where the European Incoherent Scatter Scientific Association (EISCAT) HF facility is located. The ELF/VLF waves from the ionosphere are modulated by quaternary phase shift keying (QPSK) and used for communication. The ELF signals of 2017 Hz at 20 and 100 b/s, as well as VLF signals of 3517 Hz at 20, 100, and 400 b/s, received by a ground-based receiver (15 km away from the heater) were decoded, albeit with a high bit error rate (BER) for 3517 Hz at 20 b/s. With the decoding principle of QPSK, we attempted to find a solution to reduce the BER for future communication experiments. Based on the results of the ground experiment, the transmitted signals of 2017 Hz at 20 b/s were selected in the China Seismo-Electromagnetic Satellite (CSES) reception experiments. In a first, we demonstrate that ELF communication signals generated by the amplitude modulation heating of the ionosphere have been successfully received by the satellite and the ground-based receiver. These experimental results confirm that the ELF/VLF waves radiated by amplitude modulation heating of the auroral electrojet can be used for long-distance communication in future.

Investigating the Benefits of Vector-Based GNSS Receivers for Autonomous Vehicles under Challenging Navigation Environments

There is a growing demand for robust and accurate positioning information for various applications, including the self-driving car industry. Such applications rely mainly on the Global Navigation Satellite System (GNSS), including the Global Positioning System (GPS). However, GPS positioning accuracy relies on several factors, such as satellite geometry, receiver architecture, and navigation environment, to name a few. In urban canyons in which there is a significant probability of signal blockage of one or more satellites and/or interference, the positioning accuracy of scalar-based GPS receivers drastically deteriorates. On the other hand, vector-based GPS receivers exhibit some immunity to momentary outages and interference. Therefore, it is becoming necessary to consider vector-based GPS receivers for several applications, especially safety-critical applications, including next-generation navigation technologies for autonomous vehicles. This paper investigates a vector-based receiver’s performance and compares it to its scalar counterpart in signal degraded conditions. The realistic simulation experiments in this paper are conducted on GPS L1 C/A signals generated using the SpirentTM simulation system to create a fully controlled environment to examine and validate the performance. The results show that the vector tracking system outperforms the scalar tracking in terms of position and velocity estimation accuracy in signal-degraded environments.

Secure Beamforming and Jamming for Multibeam Satellite Systems With Correlated Wiretap Channels

Multibeam satellite communication plays an important role in future integrated satellite-terrestrial communication systems. However, the large area covered by the satellite beams makes itself vulnerable to be wiretapped, especially for the cases that eavesdroppers are located near the legitimate receivers. In this paper, cooperative jamming from both satellite and full-duplex receivers are investigated where we aim to minimize the power consumed by a multibeam satellite system with secrecy outage probability constraints. To tackle this problem, an algorithm of joint beamforming and power allocation via alternating optimization (JBFPA-AO) is proposed. Specifically, a feasible solution is first obtained by transforming the original non-convex problem into a semi-definitive programming (SDP) problem with relaxed constraints. And then, alternating optimization is adopted to find better solutions iteratively. Convergence of the proposed JBFPA-AO is proved, and simulation results show its effectiveness to reduce the power utilized by the satellite.

A Large Doppler Weak Direct Spread Signal Acquisition Algorithm and Optimization Method

For satellite receivers, on the one hand, large Doppler frequency will cause accumulation loss for a long-term accumulation acquisition algorithm, which leads to the problem of correlation peak broadening; on the other hand, searching within a larger Doppler uncertainty range will consume more logic resources. Thus, this paper first analyses the impact of large Doppler frequency on coherent accumulation and non-coherent accumulation based on the traditional Double Block Zero Padding (DBZP) algorithm. Secondly, an improved DBZP algorithm is designed in combination with the Keystone transform of the transform domain, and simplify the variable-scale DFT to reduce the amount of calculation. Then, the key parameters of the algorithm are extracted to establish the optimization objective function, the algorithm parameters are optimized through genetic algorithm without reducing the performance of the algorithm. Finally, the simulation verifies that the optimized and improved DBZP algorithm can effectively solve the problem of code phase walking.

Simulation Platform for SINS/GPS Integrated Navigation System of Hypersonic Vehicles Based on Flight Mechanics.

In this study, a simulation platform for an integrated navigation algorithm for hypersonic vehicles based on flight mechanics is designed. In addition, the generation method of inertial measurement unit data and satellite receiver data is introduced. First, the interface relationship between a high-precision six-degree-of-freedom (6DoF) model and the simulation platform in the launch-centered Earth-fixed frame is introduced. Three-axis theoretical specific force and angular velocity are output by the 6DoF model. Accelerometer and gyroscope error models are added, and integral processing of the specific force and angular velocity is performed to obtain velocity increment of the accelerometer and the angular increment of the gyroscope. These data are quantified to obtain the accelerometer and gyroscope pulses. The satellite’s pseudo-range and pseudo-range rate as well as its position and velocity are obtained from the theoretical position, velocity, the attitude of the hypersonic vehicle’s 6DoF model output, and the global positioning system (GPS) satellite broadcast ephemeris. The simulation data can be used for the verification of the loose and tight coupling integrated navigation algorithms. The simulation test verifies the accuracy of the designed method.

Implementation of fast independent component analysis on field‐programmable gate array for resolving the slot collision issue in the space‐based automatic identification system

SummaryThe space‐based automatic identification system (S‐AIS) is a maritime safety and vessel monitoring system used to broadcast the ship position and other telemetry every few seconds in short bursts. A satellite‐based AIS receiver is of interest to defense community as it provides global or wide‐area coverage. However, when the satellite passes regions with elevated traffic density, a major challenge is to overcome the message or signal interference at the satellite receiver. This paper mainly focuses on developing a novel AIS satellite receiver that uses fast independent component analysis (FastICA) blind source separation technique to resolve the overlapped signals at the satellite. We propose an architecture to realize FastICA algorithm on hardware. In addition to this, we present Gaussian minimum shift keying modulator and demodulator design schemes used by the S‐AIS transponders. The proposed framework is realized on Virtex5‐xc5vlx110t field‐programmable gate array. The results obtained validate the effectiveness of the FastICA architecture realized by recovering the original ship data from the overlapped signals.

Space State Representation Product Evaluation in Satellite Position and Receiver Position Domain.

In Global Navigation Satellite Systems (GNSS) positioning, important terms in error budget are satellite orbits and satellite clocks correction errors. International services are developing and providing models and correction to minimize the influence of these errors both in post-processing and real-time applications. The International GNSS Service (IGS) Real-Time Service (RTS) provides real-time orbits and clock corrections for the broadcast ephemeris. Real-time products provided by IGS are generated by different analysis centres using different algorithms. In this paper, four RTS products—IGC01, CLK01, CLK50, and CLK90—were evaluated and analysed. To evaluate State Space Representation (SSR) products’ GPS satellites, the analyses were made in three variants. In the first approach, geocentric real-time Satellite Vehicle (SV) coordinates and clock corrections were calculated. The obtained results were compared with the final IGS, ESA, GFZ, and GRG ephemerides. The second approach was to use the corrected satellite positions and clock corrections to determine the Precise Point Position (PPP) of the receiver. In the third analysis, the impact of SSR corrections on receiver Single Point Position (SPP) was evaluated. The first part of the research showed that accuracy of the satellite position is better than 10 cm (average 3 to 5 cm), while in the case of clock corrections, mean residuals range from 2 cm to 17 cm. It should be noted that the errors of the satellites positions obtained from one stream differ depending on the reference data used. This shows the need for an evaluation of correction streams in the domain of the receiver position. In the case of PPP in a kinematic mode, the tests allowed to determine the impact that the use of different streams has on the final positioning results. These studies showed differences between specific streams, which could not be seen in the first study. The best results (3D RMS at 0.13 m level) were obtained for the CLK90 stream, while for IGC01, the results were three times worse. The SPP tests clearly indicate that regardless of the selected SSR stream, one can see a significant improvement in positioning accuracy as compared to positioning results using only broadcast ephemeris.

Analysis and Assessment of BDS-2 and BDS-3 Broadcast Ephemeris: Accuracy, the Datum of Broadcast Clocks and Its Impact on Single Point Positioning

For the global ordinary users, the broadcast ephemeris plays important roles in positioning, navigation and timing (PNT) services. With the construction of a new generation of the BeiDou navigation satellite system (BDS), the development of BDS has entered the era of globalization. It is meaningful for global users to analyze and assess the BDS-2 and BDS-3 broadcast ephemeris. Therefore, the satellite orbits and clock offsets calculated by broadcast ephemeris are compared with the precise orbit and clock offset products provided by three analysis centers (i.e., Helmholtz Centre Potsdam German Research Center for Geosciences (GFZ), Wuhan University (WHU) and Shanghai Astronomical Observatory (SHA)), and the corresponding signal-in-space range error (SISRE) and the orbit-only SISRE are analyzed to assess the accuracy of BDS broadcast ephemeris. Due to the upgrade of BDS-3 satellite hardware technology and inter-satellite links payload and the development of satellite orbit determination algorithm, the accuracy of broadcast orbit and clock offsets has been greatly improved. The root mean square (RMS) of BDS-3 broadcast orbit errors is improved by 86.30%, 89.47% and 76.86%, and the standard deviation (STD) is improved by 79.41%, 77.00% and 76.78% compared with BDS-2 in the radial, along-track and cross-track directions. The corresponding RMS and STD of all BDS-3 satellite clock offsets are improved by 40.34% and 52.49% than that of BDS-2, respectively. Meanwhile, the mean RMS and STD are 1.78 m and 0.40 m for BDS-2 SISRE, 1.72 m and 0.34 m for BDS-2 orbit-only SISRE, 0.50 m and 0.14 m for BDS-3 SISRE, and 0.17 m and 0.04 m for BDS-3 orbit-only SISRE. It is noteworthy that the average broadcast-minus-precise (BMP) clock values of BDS-2 and BDS-3 are inconsistent, which can indirectly prove that the datum of broadcast clock offsets for BDS-2 and BDS-3 are inconsistent. The inconsistency of the datum of satellite clock offsets and receiver hardware delay bias between BDS-2 and BDS-3 will result in the inter-system bias (ISB) on the receiver segment. For JAVAD TRE_3 receivers, the ISB is relatively small and thus can be ignored. However, for the TRIMBLE ALLOY, SEPT POLARX5, CETC-54-GMR-4016, CETC-54-GMR-4011, GNSS-GGR and UB4B0-13478 receivers, estimating ISB can improve the positioning accuracy of single point positioning (SPP) by 20.15%, 19.81% and 12.76% in north, east and up directions, respectively.

Positioning Accuracy Comparison of GNSS Receivers Used for Mapping and Guidance of Agricultural Machines

Global Navigation Satellite Systems (GNSS) allow the determination of the 3D position of a point on the Earth’s surface by measuring the distance from the receiver antenna to the orbital position of at least four satellites. Selecting and buying a GNSS receiver, depending on farm needs, is the first step for implementing precision agriculture. The aim of this work is to compare the positioning accuracy of four GNSS receivers, different for technical features and working modes: L1/L2 frequency survey-grade Real-Time Kinematic (RTK)-capable Stonex S7-G (S7); L1 frequency RTK-capable Stonex S5 (S5); L1 frequency Thales MobileMapper Pro (TMMP); low-cost L1 frequency Quanum GPS Logger V2 (QLV2). In order to evaluate the positioning accuracy of these receivers, i.e., the distance of the determined points from a reference trajectory, different tests, distinguished by the use or not of Real-Time Kinematic (RTK) differential correction data and/or an external antenna, were carried out. The results show that all satellite receivers tested carried out with the external antenna had an improvement in positioning accuracy. The Thales MobileMapper Pro satellite receiver showed the worst positioning accuracy. The low-cost Quanum GPS Logger V2 receiver surprisingly showed an average positioning error of only 0.550 m. The positioning accuracy of the above-mentioned receiver was slightly worse than that obtained using Stonex S7-G without the external antenna and differential correction (maximum positioning error 0.749 m). However, this accuracy was even better than that recorded using Stonex S5 without differential correction, both with and without the external antenna (average positioning error of 0.962 m and 1.368 m).

Outage Performance of Uplink NOMA in Land Mobile Satellite Communications

Non-orthogonal multiple access (NOMA) can be efficiently used in land mobile satellite (LMS) communications in order to increase link availability, coverage and reliability. In this letter, we study -for first time in the literature- the outage performance of an uplink LMS system consisting of two terrestrial user nodes which perform NOMA in the uplink, with either successive interference cancellation or joint decoding at the satellite receiver. Closed-form expressions for the outage probability are derived for both cases assuming composite shadowed-Rician fading channels. Finally, numerical results and simulations validate the theoretical analysis.