Single-frequency Global Positioning System Research Articles

The capability of Artificial Neural Networks as a Model for Predicting Total Electron Content (TEC): A Review

The results of investigations from a complete analysis of ANN application on Total Electron Content (TEC) prediction are presented in this paper. TEC is important in defining the ionosphere and has many everyday applications, for example, satellite navigation, time delay and range error corrections for single frequency Global Positioning System (GPS) satellite signal receivers. The total electron content (TEC) in the ionosphere has been measured using GPS. GPS are not installed in every point on the earth to make global TEC measurements possible. As a result, it is crucial to have certain models that can aid to get data from places where there is not any in order to comprehend the global behavior of TEC. Neural Network (NN) models have been shown to accurately anticipate data patterns, including TEC. The capacity of neural networks to represent both linear and nonlinear relationships directly from the data being modeled is what makes them so powerful. The survey from literature reveals that, Levenberg-Marquardt algorithm is preferred and used mostly because of its speed and efficiency during learning process, and that ANN showed a good prediction of TEC compared to the IRI model. As a result, NNs are suitable for forecasting GPS TEC values at various locations if the model's input parameters are well specified.

Statistical validation of ionospheric electron density profiles retrievals from GOES geosynchronous satellites

In this paper, we discuss a novel retrieval of ionospheric electron density profiles using the Radio Occultation (RO) technique applied to measurements captured by the Global Positioning System (GPS) receivers onboard two Geostationary Operational Environmental Satellites (GOES). The GOES satellites operate at ~35,800 km altitude and are primarily weather satellites that operationally contribute continuous remote-sensing data for real-time weather forecasting, as well as near-Earth environment monitoring and Sun observations. The GPS receivers onboard GOES-16 and GOES-17 satellites can track GPS signals propagated through the Earth’s atmosphere, and although the receivers are primarily designed for navigation and station-keeping maneuvers, these GPS measurements that traverse the Earth’s atmosphere can be used to retrieve the ionospheric electron density profiles. This process poses a range of technical challenges. GOES RO links are different from the traditional low Earth orbit (LEO) RO geometry since the receiver is located in an orbit that is higher in altitude than the GPS constellation of transmitters. Additionally, the GPS receivers onboard GOES satellites provide only single-frequency GPS L1 observations and have clocks much less stable than those typically used for RO measurements. The geographical distribution of the retrieved GEO-based RO profiles was found to be uniquely constrained and repeatable based on the relative geostationary fixed positions in the Earth-Centered Earth Fixed reference frame with respect to the GPS constellation orbiting at lower altitude, and significantly different from the coverage patterns of LEO-based RO missions. We demonstrate the successful application of the proposed RO profiling technique with a statistically significant set of GPS observations from GOES-16 and GOES-17 satellites over several years of data collection. This enabled us to retrieve more than 10,000 ionospheric electron density profiles with a maximum altitude of up to 1000–2000 km, much higher than any existing LEO-based RO mission. We demonstrate good performance of GEO-based RO measurements for properly specifying the vertical distribution of ionospheric plasma density by comparing the profiles dataset from the GOES RO experiment with independent reference observations – ground-based ionosondes and LEO-based RO missions, as well as model simulation results provided by the empirical International Reference Ionosphere model. Over multiple years of observations, statistical analysis of discrepancies between the ionospheric F2 layer peak parameters (peak density and height) derived from geosynchronous GOES observations and reference measurements was conducted. This analysis reveals a very good agreement between GOES RO electron density profiles and independent types of measurements in both the F2 peak and the profile shape.

Cost-Effective, Single-Frequency GPS Network as a Tool for Landslide Monitoring.

The constant monitoring of active landslides, particularly those located in the proximity of populated areas or touristic places, is crucial for early warning and risk-management purposes. The commonly used techniques deploy expensive instrumentation that can be hardly afforded, especially by small mountain communities in which landslide events often occur repeatedly. In recent years, the scientific community, as well as the private sector, have devoted growing effort to reducing the costs of monitoring systems. In this work, we present a monitoring network based on single-frequency Global Positioning System (GPS) sensors that have been activated to monitor an active landslide in the Carnic Alps, North-Eastern Italy. The system, which was composed of 12 single-frequency GPS stations, one seismometric station coupled with a single-frequency GPS instrument for real-time monitoring, and one permanent dual-frequency GPS station located in a stable area, provided daily reports of the landslide motion to the local authorities and administration. We show that this system is a valuable, flexible, and cost-effective tool for quick landslide characterization, and has high potential to be used as a landslide early warning system in case of emergency situations.

Field Testing and Evaluation of Single-Receiver GPS Odometry for Use in Robotic Navigation

Mobile robots rely on odometry to navigate in areas where localization fails. Visual odometry (VO), for instance, is a common solution for obtaining robust and consistent relative motion estimates of the vehicle frame. In contrast, Global Positioning System (GPS) measurements are typically used for absolute positioning and localization. However, when the constraint on absolute accuracy is relaxed, accurate relative position estimates can be found with one single-frequency GPS receiver by using time-differenced carrier phase (TDCP) measurements. In this paper, we implement and field test a single-receiver GPS odometry algorithm based on the existing theory of TDCP. We tailor our method for use on an unmanned ground vehicle (UGV) by incorporating proven robotics tools such as a vehicle motion model and robust cost functions. In the first half of our experiments, we evaluate our odometry on its own via a comparison with VO on the same test trajectories. After 4.3 km of testing, the results show our GPS odometry method has a 79% lower drift rate than a proven stereo VO method while maintaining a smooth error signal despite varying satellite availability. GPS odometry can also make robots more robust to catastrophic failures of their primary sensor when added to existing navigation pipelines. To prove this, we integrate our GPS odometry solution into Visual Teach and Repeat (VT&R), an established visual, path-following navigation framework. We perform further testing to show it can maintain accurate path following and prevent failures in challenging conditions including full camera dropouts. Code is available at https://github.com/utiasASRL/cpo.

Testing Patch, Helix and Vertical Dipole GPS Antennas with without Choke Ring Frame

Abstract: The antenna is the connecting part between Global Positioning System (GPS) satellite and receiver, and it works on transferring the satellite signal propagation to the receiver with minimum interruption. This is beside the main role that GPS antenna can play for accurate and precise positioning. High quality GPS antennas have high gain, systematic radiation pattern, Right Hand Circular Polarization (RHCP), and low directivity. Multipath error is a principal error source connected with GPS positioning and it can be mitigated using better antenna design. GPS antennas tend to be provided with choke ring frame for protection from the reflected RHCP electromagnetic waves. In this paper, the performance of three different types of GPS antenna, namely: Microstrip Patch Antenna (MPA), Helix antenna (HA), and Vertical Dipole antenna (VDA), with and without choke ring frame, has been investigated using single frequency GPS receiver. The antennas have been examined under the same GPS environment, including satellites constellation, geometry, and surroundings, with different heights from the ground reflector surface for multipath evaluation. Short base-line kinematic differential code GPS (DGPS) technique has been used for removing and mitigating the main GPS error sources and focusing on multipath effect. Satellite residuals and the quality of the obtained positioning have been considered for evaluating the performance of each antenna. The results have reflected the ability of choke ring frames to improve the performance of the three GPS antennas with different rates in multipath areas, and illustrate the advantages and limitations of each antenna. Keywords: Micro-strip, Patch, Helix, Vertical Dipole, GPS, Choke Ring Antenna, Multipath.

The Advantages and Limitations of Low-Cost Single Frequency GPS/MEMS-Based INS Integration

Global Positioning System (GPS) provides a method for directly obtaining instantaneous position and velocity estimates using satellites-based passive range measurements. GPS is a whole day, all-weather, passive, satellite positioning system. Inertial Navigation System (INS) is a navigation aid system that uses a computer and Inertial Measurement Unite (IMU). IMU includes motion sensors and rotation sensors to continuously calculate relative position, orientation, and velocity. The integration of GPS/INS can help to overcome the limitations of the two systems providing integrated system better than either on a stand-alone basis. The integration of low-cost INS with dual frequency GPS has been widely studied and the same for the integration of tactical grid INS with low-cost GPS. However, during the last a few years, a number of low-cost GPS\low-cost INS integrated systems have been introduced and become popular in various engineering applications. However, reliable investigations into the advantages, limitations and quality of such integration level are still needed and more efforts are required, which will be the focus of this paper. The methodology followed in this paper for evaluating the integration of low-cost GPS/INS sensors depends on evaluating the two sensors individually and comparing the results with the integrated system. The results show that low-cost single frequency GPS receivers are able to provide a comparable accuracy level in both static and kinematic carrier phase differential GPS (DGPS). As for low-cost Micro-Electro-Mechanical System (MEMS)-based IMU, the accelerometers have provided instability comparing to gyros. The performance of gyros can be improved based on modelling the nearly-linear behaviour of the gyro drift. Tests show that the integration of low-cost GPS sensors with MEMS-based INS degrades the quality of gyro measurements and may not add any improvements to the quality of the individual GPS positioning.

Characterizing the accuracy of Global Positioning System for single point positioning at African low-latitude region

ABSTRACT This paper examines the accuracy of the Global Positioning System (GPS) within the African low-latitude sector. We evaluated the vertical and horizontal of the single-point positioning (SPP) accuracy of GPS and critically analysed the effects of the equatorial ionospheric anomaly (EIA) over the region of study. Our results imply that using single-frequency GPS for any application could give a positioning error up to 45.00 m vertically and ~25.00 m horizontally. The study revealed that 54% of GNSS positioning errors during the night-time could be linked to ionospheric plasma irregularities. Also, positioning errors are higher in western Africa than in the eastern region. The influence of geomagnetic activities is not consistent with GPS positioning accuracy. However, positioning errors are lower during geomagnetically disturbed conditions in comparison to quiet conditions. The unique phenomena of the EIA can severely limit GPS services at night-time for positioning in the study area.

Predicting total electron content in ionosphere using vector autoregression model during geomagnetic storm

Abstract The ionospheric total electron content (TEC) severely impacts the positional accuracy of a single frequency Global Positioning System (GPS) receiver at the equatorial latitudes. The ionosphere causes a frequency-dependent group delay in the GPS-ranging signals, which reduces the receiver’s accuracy. Further, the variations in TEC due to various space weather phenomena make the ionosphere’s behaviour nonhomogeneous and complex. Hence, developing an accurate forecast model that can track the dynamic behaviour of the ionosphere remains a challenge. However, advances in emerging data-driven algorithms have been found helpful in tracking non-stationary behavior in TEC. These models help forecast the delays in advance. The multivariate Vector Autoregression model (VAR) predicts the Ionospheric TEC in the proposed model. The prediction model uses input data compiled in real-time from the lag values of incoming TEC data and features extracted from TEC. The TEC is predicted in real-time and tested for different prediction intervals. The metrics – Mean Percentage Error (MAPE), Mean Absolute Error (MAE), and Root Mean Square Error (RMSE) are used for testing and validating the accuracy of the model statistically. Testing the predicted output accuracy is also done with the dynamic time warping (DTW) algorithm by comparing it with the actual value obtained from the dual-frequency receiver. The model is tested for storm days of the year 2015 for Bangalore and Hyderabad stations and found to be reliable and accurate. A prediction interval of twenty-minute shows the highest accuracy with an error within 10 TECU for all the storm days.

Positioning accuracy improvement in high‐speed GPS receivers using sequential extended Kalman filter

It is well known that in high-speed movements, the positioning accuracy of global positioning system (GPS) receivers decreases drastically. The models presented so far to describe high-speed motion do not represent the state of the system precisely, so positioning accuracy with the methods based on these models is not appropriate. Here, a comprehensive method is proposed to solve the accuracy issue of the single-frequency GPS receiver at high-speed motions without increasing the computational complexity. Suitable modelling of the GPS receivers at high-speed motion, using the sequential extended Kalman filter, correct determination of the process noise covariance matrix and accurately estimating the variance of the observations are the basics of the proposed approach. Simulations with different data and motion scenarios (at speeds from 100 to 7300 m/s) show that the proposed method, while not increasing the computational cost, improves the accuracy of positioning more than 70% when compared to the conventional methods.

Design and Implementation of GPS RTK Positioning Using Carrier Phase Measurement on an Embedded Board

The Global Positioning System (GPS) is currently used in many geodetic applications to obtain precise positions within a centimeter, or even within a millimeter. Generally, such a level of accuracy can be obtained by performing complex processing on expensive receivers and antennas. Such high-cost devices can be replaced by low-cost, single-frequency GPS receivers to obtain precise positions. To do so, in this paper, Carrier Phase (CP)-based relative algorithms are successfully implemented on a CUDA-enabled embedded board (the Jetson TK1) with two low-cost GNNS receivers. A CUDA-enabled graphics processing unit (GPU) is a highly parallel structure that makes efficient and faster CP-based algorithms and that can process large blocks of data in parallel. Our results from field measurements clearly show that the positioning performance of a Rover with respect to the Base receiver reached the centimeter level. Therefore, this work shows the possibility of accurately estimating the position of a receiver using low-cost hardware-based RTK algorithms.

Xiaomi Mi 8 smartphone GNSS data quality analysis and single‐frequency RTK positioning performance evaluation

In this study, the authors mainly explore the relationship between the data quality of smartphones equipped with global navigation satellite system (GNSS) modules and the accuracy and reliability of single-frequency real-time kinematic (RTK) positioning. Specifically, the visible satellite number, code minus carrier and the signal-to-noise ratio of the GNSS raw observations were evaluated through static experiments and dynamic experiments, and the performance difference between single-frequency global positioning system (GPS) RTK and single-frequency BeiDou Navigation Satellite System (BDS) RTK positioning was compared and analysed. In the static experiment, the average values of visible satellites of BDS and GPS in Xiaomi Mi 8 smartphone are 7.4 and 8.4, respectively. The average code minus carrier error of GPS is 5.234 m, the BDS is 5.518 m, and the average signal-to-noise ratio of GPS is ~29.092 dB Hz and the BDS is ~28.718 dB Hz. The data quality of the dynamic experiment is similar to the static experimental result. The positioning accuracy obtained by the static experiment from the single-frequency GPS RTK and single-frequency BDS RTK in the east/north/up (E/N/U) directions is 0.146/0.555/0.464 m and 0.843/0.287/0.317 m, respectively. The instability of BDS-locked satellite in dynamic experiment results the positioning accuracy of BDS RTK is lower than that of GPS.

Low Latitude Ionosphere Error Correction Algorithms for Global Navigation Satellite System

The ionospheric errors occur due to loss of data in ionospheric region. Low latitudinal regions are the most affected regions due to ionospheric errors and also causes loss of signal or data for space based augmentation system(SBAS) such as aircraft. So to reduce these ionospheric errors in low latitude regions of Global Navigation Satellite System(GNSS) Klobuchar algorithm is used which mitigates the errors occurring in low latitude regions and is used as a standard algorithm in US Global Positioning System(GPS) till now; however, this model can reduce the ionospheric error by approximately 50-60% Root Mean Square(RMS) error in low-latitudes. So in order to increase the percentage deviation of errors in low-latitude regions, Enhanced Klobuchar algorithm is proposed which enhances the correction of low-latitude ionospheric errors approximately up to 80% RMS for a single frequency GPS user. In this paper error correction algorithms are performed over International GPS Service(IGS) data was collected using Hyderabad station receiver, Telangana (latitude- 17.41728°, longitude-78.55088°) in southern part of India during year 2016.

Improvement of Single-Frequency GPS Positioning Performance Based on EGNOS Corrections in Algeria

The main objective of the European Geostationary Navigation Overlay System (EGNOS) is to improve the positioning accuracy by correcting several error sources affecting the Global Positioning System (GPS) and to provide integrity information to GPS signals for users in real time. This research presents analysis used to investigate improvement in the performance of single-frequency GPS positioning using EGNOS corrections in Algeria. In this study, we performed position measurements with two calculation approaches, the first based on GPS single-point positioning and the second using EGNOS differential corrections. Positioning accuracy was determined by comparison with the known precise coordinates of the sites; and then the improved ionospheric correction using EGNOS was investigated. The results revealed that GPS + EGNOS performance was significantly improved compared with GPS alone, when measurements of horizontal and vertical accuracy were taken into account, and that the EGNOS corrections improved east and north components slightly, and the up component significantly.

Performance Analysis of Positioning Solution Using Low-Cost Single-Frequency U-Blox Receiver Based on Baseline Length Constraint.

With the rapid development of the satellite navigation industry, low-cost and high-precision Global Navigation Satellite System (GNSS) positioning has recently become a research hotspot. The traditional application of GNSS may be further extended thanks to the low cost of measuring instruments, but effective methods are also desperately needed due to the low quality of the data obtained using these instruments. Thus, in this paper, we propose the analysis and evaluation of the ambiguity fixed-rate and positioning accuracy of single-frequency Global Positioning System (GPS) and BeiDou Navigation Satellite System (BDS) data, collected from a low-cost u-blox receiver, based on the Constrained LAMBDA (CLAMBDA) method with a baseline length constraint, instead of the classical LAMBDA method. Three sets of experiments in different observation environments, including two sets of static short-baseline experiments and a set of dynamic vehicle experiments, are adopted in this paper. The experiment results show that, compared to classical LAMBDA method, the CLAMBDA method can significantly improve the success rate of the GNSS ambiguity resolution. When the ambiguity is fixed correctly, the baseline solution accuracy reaches 0.5 and 1 cm in a static scenario, and 1 and 2 cm on a dynamic platform.

Tightly combined GPS and GLONASS for RTK positioning with consideration of differential inter-system phase bias

A tightly combined inter-system model between two global navigation satellite systems can improve the performance of real-time kinematic (RTK) positioning, if the associated differential inter-system biases (DISBs) are processed well, especially for the severely obstructed environment. In recent years, tightly combined models among code division multiple access (CDMA) systems (e.g. Global Positioning System (GPS), BeiDou Navigation Satellite System (BDS), Quasi-Zenith Satellite System (QZSS)) have been extensively studied. However, when there is tightly combined use of CDMA systems and Global Navigation Satellite System (GLONASS), which adopts frequency-division multiple access (FDMA), we need to process not only the DISBs between systems, but the problem caused by the different wavelengths of the GLONASS satellites. In this paper, we propose a new model for the tight combination of GPS and GLONASS. First, we adopt the model with two reference satellites to maintain the integer ambiguity resolution of GLONASS. Then, an inter-system model between GPS and GLONASS is proposed with a total of three ‘reference satellites’ involved. Using several zero and ultra-short baselines, the stability of GPS and GLONASS differential inter-system phase biases (DISPBs) will be evaluated. The results indicated that the DISPBs between GPS and GLONASS are generally stable, although low-frequency variations may appear in the baselines with different receiver types. Using the stability of DISPBs, the combined GPS and GLONASS single-frequency RTK positioning performance is evaluated with simulated obstructed environments with no more than four GPS and four GLONASS satellites visible. It will be shown that compared with the intra-system model, the proposed inter-system model can improve the positioning accuracies by 13.5%, 15.0% and 46.2%, respectively, in three directions.

UAV color images for determination of citrus plant parameters

Unmanned aerial vehicles (UAVs) or drones are being studied for many agricultural applications. One application is plant phenotyping to reduce the time and effort required in collecting field data. This study aims to explore the use of a UAV, 4K-color camera and a commercial image analysis service to measure citrus plant parameters that are important to a crop scientist or grower with limited technical background and resources. Citrus spp. are important crops in Puerto Rico and the United States. Currently, the citrus industry is struggling to contain the devastating effects of citrus greening or Huanglongbing disease. The disease is associated with a phloem-limited bacteria, Candidatus Liberibacter asiaticus (CLAs), vectored by the Asian citrus psyllid (ACP), Diaphorina citri Kuwayama. The use of insecticides for vector control is the primary strategy used in nurseries and orchards. However, once the citrus plant is infected, there is no effective control available for the disease. In Puerto Rico this disease has reduced Citrus spp. yields by more than 50%; studies are underway to find effective control measures such as supplemental nutrients, vector management practices, planting disease-free vegetative material and protective screen structures. An experiment at the Fortuna Agricultural Experiment Substation, in Juana Díaz, Puerto Rico, was conducted to address the challenges posed by citrus greening. The experiment was established in a four-year-old grove of Tahiti lime (Citrus latifolia Tan.) on Cleopatra mandarin (Citrus reshni hort. ex Tanaka), naturally infected with Candidatus Liberibacter asiaticus. The experiment was arranged in a randomized complete block design with four replicates and three treatments: supplemental nutrients, supplemental nutrients + salicylic acid, and granular fertilization. Tree growth parameters were measured, and laboratory analyses were carried out to determine nutrient levels and disease severity levels from the leaf samples. The color camera, on board the UAV, was employed to acquire images of the experimental plot. Drone Deploy application was used for planning the UAV flights and image analysis. Field-measured plant height and canopy diameter compared well with the parameters determined from the color images. The average errors in measuring canopy diameter (14.5%) and plant height (22.4%) could be considered within an acceptable range, especially for comparing different treatments or crop varieties. However, the average errors in measuring canopy volume (47.5%) were high and can be considered unacceptable. It appears that the assumed conical shape of the trees could be one of the main reasons, besides the algorithms used in calculating plant volume, and built-in inaccuracies of the single frequency GPS (global positioning system) used in estimating altitude. Further studies could help in reducing errors and exploring other applications. The method used can be of importance in evaluating fruit trees.

Precise ionospheric electron content monitoring from single-frequency GPS receivers

The number of existing global positioning system (GPS) single-frequency receivers continues growing. More than 90% of GPS receivers are implemented as low-cost single-frequency chipsets embedded in smartphones. This provides new opportunities, in particular for ionospheric sounding. In this context, we present the new sidereal days ionospheric graphic (SIg) combination of single-frequency GNSS measurements. SIg is able to monitor, for each given GNSS transmitter–receiver pair, the vertical total electron content (VTEC) relative to the previous observation with the same or almost the same line-of-sight (LOS) vector. In such arrangements the SIg multipath error mostly cancels, thus increasing the accuracy of the ΔVTEC significantly. This happens for the GPS constellation after one sidereal day (about 23 h 56 m) and for Galileo after 10 sidereal days approximately. Moreover, we show that the required calibration of the corresponding carrier phase ambiguity can be accurately performed by means of VTEC global ionospheric maps (GIMs). The results appear almost as accurate as those based on the dual-frequency technique, i.e., about 1 TECU or better, and with much more precision and resolution than the GIM values in the ionospheric region sounded by each given single-frequency receiver. The performance is demonstrated using actual data from 9 permanent GPS receivers during a total solar eclipse on August 21, 2017 over North America, where the corresponding ionospheric footprint is clearly detected in agreement with the total solar eclipse predictions. The advantages of extending SIg to lower carrier frequencies and the feasibility of applying it to other global navigation satellite system (GNSS) systems are also studied. This is shown in terms of a fully consistent VTEC depletion signature of the same eclipse phenomena, obtained with Galileo-only data in North America at mid and low latitude. Finally the SIg feasibility, including the cycle slip detection, is shown as well with actual mass-market single frequency GPS receivers at mid and high latitude.

Improvement of Indian-Regional Klobuchar Ionospheric Model Parameters for Single-Frequency GNSS Users

In general, global positioning system (GPS) ranging errors and positioning caused by the ionosphere can be corrected by the Klobuchar ionospheric model. GPS satellites broadcast the model coefficients to the single-frequency users based on the average solar flux and seasonal variations. In low-latitude regions, such as India and Brazil, correction of the ionospheric delay based on these coefficients is not accurate because of the large gradients and complex dynamic ionospheric behavior. The traditional employment of refining the ionospheric Klobuchar model parameters with single-shell approximation is inappropriate for the equatorial/low-latitude regions. In this letter, we propose a technique to determine the ionospheric delay by using the new Klobuchar parameters (coefficients) based on multishell-spherical harmonics function (MS-SHF) analysis. It has been reported that by using the MS-SHF model, the ionospheric delays can be modeled accurately in the low-latitude regions. Furthermore, the proposed model performance has been evaluated with the Denis Bouvet (2017) single-frequency ionospheric correction model. In the single-frequency usage, the proposed model can improve (62.69%/77.08%) during quiet/disturbed days. Preliminary results reveal that the refined Klobuchar model parameters impart enhanced ionospheric delay corrections to regional navigation satellite systems with single-frequency GPS receivers, such as the Indian Regional Navigation Satellite System.

Performance Evaluation of QZSS Augmenting GPS and BDS Single-Frequency Single-Epoch Positioning with Actual Data in Asia-Pacific Region

The Quasi-Zenith Satellite System (QZSS) service area covers the Asia-Pacific region and there are four quasi-zenith satellites (QZS) in orbit with three QZS in operation until March 2018. The QZSS is not required to work in a stand-alone mode, but the system can be used to enhance the Global Positioning System (GPS) or Beidou Satellite Navigation System (BDS). The availability, position dilution of precision (PDOP), ambiguity dilution of precision (ADOP), and success rate of GPS/QZSS and BDS/QZSS under different cut-off elevation angles were compared based on a simulation. Two sets of actual QZSS data were processed and analyzed for single-frequency single-epoch (SFSE) positioning together with GPS/BDS data in this paper. Different combination forms were executed to evaluate the positioning performance of GPS/QZSS and BDS/QZSS for two baseline cases. The results indicate that QZSS is able to increase the SFSE PDOP, ADOP, and success rate of the baseline resolution and decrease the position error for GPS or BDS, especially for longer GPS baseline data. The more QZS are used, the better the enhancement effect.

TEC Regional Modeling and prediction using ANN method and single frequency receiver over IRAN

In order to study in the field of the dynamics and continuous variations in the ionosphere, the ionospheric measurement tools such as ionosondes, incoherent scatter radars, satellites, and Global Positioning System (GPS) networks should be used. Total Electron Content (TEC) is a key parameter in the investigation and identification of ionosphere layer. From observations of dual frequency GPS receivers, the ionospheric TEC can be extracted. Global Ionospheric Maps (GIM) are auxiliary Maps for a study on ionosphere layer in around the world. It is necessary to produce the regional TEC map for precise studying of the ionospheric TEC. Bernese software is used to extract TEC by dual frequency GPS receivers. Regional modeling of ionospheric TEC by Artificial Neural Network (ANN) is a significant domain for prediction TEC at both single and double frequency GPS receivers. Five locations in Iran during the period of 2006-2010 were identified and used in the development of an input space and ANN architecture for the TEC modeling. The input space included the day number (seasonal variation), hour (diurnal variation), sunspot number (a measure of the solar activity) and magnetic index (a measure of magnetic activity). Based on the results, the ANN have capability and flexibility to model and to predict TEC. TEC predicted by ANN A (NN TEC) and TEC obtained from the IRI2007 version of the International Reference Ionosphere (IRI TEC) are compared during equinoxes and solstices. Results show that ANN predicts GPS TEC more accurately than the IRI over Iran. The IRI-2007 model is not a suitable method to produce TEC over IRAN.