L1 Band Research Articles

Inverting COSMIC-2 Phase Data to Bending Angle and Refractivity Profiles Using the Full Spectrum Inversion Method

The radio occultation technique provides stable atmospheric measurements that can work as a benchmark for calibrating and validating satellite-sounding data. Launched on 25 June 2019, the Constellation Observing System for Meteorology, Ionosphere, and Climate 2 and Formosa Satellite Mission 7 (COSMIC-2/FORMOSAT-7) are expected to produce about 5000 high-quality RO observations daily over the tropics and subtropics. COSMIC-2 constellation consists of 6 Low Earth Orbit (LEO) satellites in 24° inclination orbits at 720 km altitude and distributed mainly between 45°N to 45°S. The COSMIC-2 observations have uniform temporal coverage between 30°N to 30°S. This paper presents an independent inversion algorithm to invert COSMIC-2 geometry and phase data to bending angle and refractivity. We also investigate the quality of Global Navigation Satellite System (GNSS) and LEO position vectors derived from the UCAR COSMIC Data Analysis and Archive Center (CDAAC). The GNSS and LEO position vectors are stable with LEO position variations < 1.4 mm/s. The signal-to-noise ratio (SNR) on the L1 band ranges from 300–2600 v/v with a mean of 1600 v/v. The inversion algorithm developed at NOAA Center for Satellite Applications and Research (STAR) uses the Full Spectrum Inversion (FSI) method to invert COSMIC-2 geometry and phase data to bending angle and refractivity profiles. The STAR COSMIC-2 bending angle and refractivity profiles are compared with in situ radiosonde, the current COSMIC-2 products derived from CDAAC, and the collocated European Center for Medium-Range Weather Forecasts (ECMWF) climate reanalysis data ERA5. The mean bias at 8–40 km altitude among the UCAR, ERA5, and STAR is <0.1% for both bending and refractivity, with a standard deviation in the range of 1.4–2.3 and 0.9–1.1% for bending angles refractivity, respectively. In the lowest 2 km, the RO bias relative to ERA-5 shows a strong latitudinal and SNR dependence.

A Compact Cavity-Backed Tri-Band Antenna Design for Flush Mount GNSS (L1/L5) and SDARS Operations

This letter presents a unique compact cavity-backed tri-band antenna design for supporting simultaneous Global Navigation Satellite System (GNSS) ( L 1/ L 5) and Satellite Digital Audio Radio Service (SDARS) operations in a rooftop flush mount configuration. The cavity dimensions are 100 mm in diameter and only 9.35 mm in depth to meet a specific automobile manufacturer's physical dimension requirement. The achieved half-power realized gain bandwidths at L1, L5, and SDARS bands are 85, 54, and 250 MHz, respectively. This design consists of a bottom feeding board, a top GNSS board, and a middle SDARS board. All three boards are connected using vertical wires. The left-hand circular polarization (LHCP) SDARS element is a C-line coupled circular patch element that is excited via a novel traveling-wave proximity-coupling method that maximizes the passage of the out-of-band signals. The right-hand circular polarization (RHCP) dual-ring GNSS element is excited after the SDARS element using two orthogonal tapered-width proximity probes which are connected to two microstrip lines with different lengths for producing 90° phase difference at 1.4 GHz. The entire antenna assembly is connected to a single subminiature version A (SMA) connector. The design specifications and operating principles of the proposed antenna are discussed along with comparisons between the simulation and measurement performance obtained from a fabricated prototype.

Compact polarization diversity patch antenna in L and WiMAX bands for IoT applications

A miniaturized stacked patch antenna with circular polarization in GPS L1 band and dual linear polarization in WiMAX band for IoT (Internet of Things) applications is proposed. A novel technique has been introduced to enhance a second mode in dual-band patch antenna, by adding pi shaped slots and stacking another reflective patch, with shorting pins in between. The upper patch, thus, acts as an independent receiver in WiMAX band using enhanced second mode of the lower patch. At GPS L1 frequency of 1.575 GHz, the compact antenna of volume 0.13 λ0 × 0.13 λ0 × 0.067 λ0 (λ0 is the free-space wavelength at 1.575 GHz) achieves a wide half-power beamwidth of 104 ± 5°. The measured results exhibit an impedance bandwidth of 5.71% in WiMAX (3.4 GHz–3.6 GHz) band along with symmetrical radiation patterns for both horizontal and vertical polarizations of the transmitter. The fabricated prototype, with a radiation efficiency greater than 85%, proves to be highly efficient in portable devices for multipath spaces in IoT.

Observation Quality Assessment and Performance of GNSS Standalone Positioning with Code Pseudoranges of Dual-Frequency Android Smartphones.

The new generation of Android smartphones is equipped with GNSS chips capable of tracking multi-frequency and multi-constellation data. In this work, we evaluate the positioning performance and analyze the quality of observations collected by three recent smartphones, namely Xiaomi Mi 8, Xiaomi Mi 9, and Huawei P30 pro that take advantage of such chips. The analysis of the GNSS observation quality implies that the commonly employed elevation-dependent function is not optimal for smartphone GNSS observation weighting and suggests an application of the -dependent one. Regarding smartphone code signals on L5 and E5a frequency bands, we found that they are characterized with noticeably lower noise as compared to E1 and L1 ones. The single point positioning results confirm an improvement in the performance when the weights are a function of the -rather than those dependent on the satellite elevation and that a smartphone positioning with E5a code observations significantly outperforms that with E1 signals. The latter is expressed by a drop of the horizontal RMS from 8.44 m to 3.17 m for Galileo E1 and E5a solutions of Xiaomi Mi 9 P30, respectively. The best positioning accuracy of multi-GNSS single-frequency (L1/E1/B1/G1) solution was obtained by Huawei P30 with a horizontal RMS of 3.24 m. Xiaomi Mi 8 and Xiaomi Mi 9 show a horizontal RMS error of 4.14 m and 4.90 m, respectively.

Co-Site Interference Study and Mitigation Onboard a Submarine Between Communication and Positioning Systems at L Band

This letter focuses on modeling and studying the RF interference between a civilian Inmarsat FB emitter at 1627 MHz (culprit) and a GPS L1 band maritime system at 1575 MHz (victim) on close antennas proximity onboard a submarine. Once predicted the RFI, we propose the design of an adequate mitigation for it. The chosen platform to host this study is a 3D model of the U.S. Navy retired Los Angeles SSN-688 original class submarine. The proposed methodology consists on calculating through numerical 3D electromagnetic simulation the electromagnetic decoupling between culprit and victim’s antennas on different antenna placement scenarios onboard the SSN-688’s masts; modeling a typical GPS front-end receiver simultaneously excited with both the interferer signal after decoupling, and the GPS weak signal reception; to observe the RFI effects on the modeled receiver circuit; and to finally propose and design an adequate filter to control and mitigate the interference. The result is a pre-filter, to be connected to the GPS receiver front-end before the GPS’s low noise amplifier, which attenuates the Inmarsat signal on the rejection band below the RFI threshold level and inserts a low insertion loss on GPS pass band.

Single-Pass Soil Moisture Retrieval Using GNSS-R at L1 and L5 Bands: Results from Airborne Experiment

Global Navigation Satellite System—Reflectometry (GNSS-R) has already proven its potential for retrieving a number of geophysical parameters, including soil moisture. However, single-pass GNSS-R soil moisture retrieval is still a challenge. This study presents a comparison of two different data sets acquired with the Microwave Interferometer Reflectometer (MIR), an airborne-based dual-band (L1/E1 and L5/E5a), multiconstellation (GPS and Galileo) GNSS-R instrument with two 19-element antenna arrays with four electronically steered beams each. The instrument was flown twice over the OzNet soil moisture monitoring network in southern New South Wales (Australia): the first flight was performed after a long period without rain, and the second one just after a rain event. In this work, the impact of surface roughness and vegetation attenuation in the reflectivity of the GNSS-R signal is assessed at both L1 and L5 bands. The work analyzes the reflectivity at different integration times, and finally, an artificial neural network is used to retrieve soil moisture from the reflectivity values. The algorithm is trained and compared to a 20-m resolution downscaled soil moisture estimate derived from SMOS soil moisture, Sentinel-2 normalized difference vegetation index (NDVI) data, and ECMWF Land Surface Temperature.

Analysis of Amplitude Scintillation and Positioning Error of IRNSS/GPS/SBAS Receiver for Heavy Rainy Days

Indian Regional Navigation Satellite System (IRNSS) was developed for providing positioning, velocity and timing information to Indian users within the error of 10 m. Amplitude scintillation is the rapid fluctuations in amplitude of navigation signal due to small scale irregularities in electron density presents in ionosphere. Strong scintillation can degrade the accuracy of navigation system and generate the errors in precise positioning services. S4 index is the statistical measurement of amplitude scintillation which reflects scintillation event. The characteristics of amplitude scintillation on IRNSS/SBAS/GPS receiver with all seven satellites during heavy rainy days at the low altitude station IITRAM, Ahmedabad are investigated. The raw data are collected from the IRNSS/GPS/SBAS receiver with L1, L5 and S band at the Ahmedabad city with average altitude of 53 m in Gujarat. Here, real time monitoring system for amplitude scintillation and positioning error is designed for all three bands. S4 values for three bands are calculated and analyzed to define the scintillation event for the period of 14 days. The position errors of heavy rainy days are also found. This study also focuses on time duration over which the carrier to noise ratio acquires zero value, effect of elevation angle of satellite on carrier to noise ratio and ionospheric delay. We found that L1 band suffers more from scintillation compare to L5 and S band. Day to day investigation of amplitude scintillation is carried out here. The results of this investigation would be utilized for understanding of amplitude scintillation effect during rainy weather condition in low altitude station.

Design narrow-band frequency amplifier (1.5GHz -1.6GHz) based on InGaP Heterojunction Bipolar Transistor (HBT) and GaAs HBT

The research aims to design a narrow-band frequency drive amplifier (1.5GHz -1.6GHz), which is used to boost the transmitter amplifier's input signal or amplify the GPS, GlONASS signals at the L1 band.
 The Power Amplifier printed circuit board (PCB) prototype was designed using InGaP HBT homogeneous technology transistor and GaAs Heterojunction Bipolar Transistor (HBT) transistor. Two models have been compared; one of the models gave 16dB gain, and the other gave 23dB when using an input power signal (-15dBm). The PCB consumes 2.4W of power and has a physical dimension of 11 x 4 cm.

Performance of 6 Different Global Navigation Satellite System Receivers at Low Latitude Under Moderate and Strong Scintillation

AbstractAfter sunset, in the equatorial regions ionospheric plasma irregularities are generated due to the generalized Rayleigh‐Taylor instability. Under favorable conditions these irregularities develop in the equatorial region while mapping along the magnetic field lines giving rise to large plasma depletion structures called Equatorial Plasma Bubbles with embedded smaller structures on their walls. The global navigation satellite system (GNSS) L1 band frequency is sensitive to irregularities of the size of 300–400 m in the first Fresnel zone, which cause scattering and diffraction of the signal and produce amplitude and/or phase scintillation. Severe scintillation of GNSS signals can in turn cause loss of lock of the receiver code and/or carrier loops. As a result, GNSS navigation and positioning solution can be adversely affected by the ionospheric scintillation. There are multiple GNSS receivers designed to monitor scintillations. These receivers are based on different hardware designs and use different methodologies to process the raw data. When using simultaneous data from different GNSS scintillation monitors it is important to evaluate and compare their performances under similar scintillation conditions. The scintillation monitoring techniques may be useful for many applications that use GNSS signal. The aim of this work is to evaluate the performance of six different GNSS receivers located at São José dos Campos (23.1°S, 45.8°W, dip latitude 17.3°S) during moderate and strong scintillation activity. The amplitude (S4) and phase (σϕ) scintillation indexes from these receivers were analyzed and compared for the nights February 20–21 and November 27–28, 2013.

Experimental Research on Narrowband Interference Suppression of GNSS Signals

The navigation satellites are running at a high altitude of 20000 km from the ground, and the satellite signals arriving at the ground are very weak, such as the C/A code on the L1 band, which is only ‐160 dBW. In complex urban environments, especially when there is an occlusion, the signal power will be even lower. Low power causes the signal to be easily disturbed, where suppressed interference is the most common method of interference. The purpose of this paper is to experiment with the BPSK and BOC signal system to do the narrowband suppression of interference analysis and set up the actual test environment, based on the commonly used LMS algorithm for the two systems of narrowband interference performance contrast analysis, and throughout the simulation, it can be seen that the two improved algorithms can effectively suppress narrowband interference, thus improving the anti‐interference performance of satellite navigation receiver.

Метод раскрытияфазовых неоднозначностей, использующий обработку псевдодальностей по коду и фазе несущей в фильтре калмановского типа

The main problem of implementing high-precision pseudoranges by carrier phase lies in their ambiguity associated with the ambiguity of the phase measurements of the navigation receiver. Thus, the development of new methods for phase ambiguity resolution becomes a very important element of high-precision positioning. The paper considers relative methods for estimating the coordinates of a stationary object that involve the use of both user and base (network in the case of a network of base receivers) receivers with precisely known coordinates located at a distance of several thousand kilometers from each other. We propose an algorithm for phase ambiguity resolution (integer type) based on the use of a Kalman-type filter (KTF), which receives ionosphere-free combinations of code and carrier phase pseudoranges. It is shown that traditional methods of ambiguity resolution require a significant observation period (about 2,000 seconds). We propose a method for evaluating the linear combination of phase ambiguities in the L1 and L2 bands obtained from instantaneous phase measurements. Its application along with the estimation of KTF parameters makes it possible to resolve phase ambiguities from as early as 50 seconds of observation. Set forth are the results of an experiment, in which code pseudorange measurements are used prior to the resolution of phase ambiguities and carrier phase pseudorange measurements are used after ambiguity resolution.

Applications of Ground-Based Multipath Reflectometry Based on Combinations of Pseudorange and Carrier Phase Observations of Multi-GNSS Dual-Frequency Signals

Measurements from a geodetic global navigation satellite system (GNSS) setup can be deployed to retrieve geophysics parameters, because coherent reflections from the surrounding environment enter the antenna along with direct signals. Previous GNSS multipath studies of snow depth and sea level were mainly based on signals-to-noise ratio (SNR) measurements. In this article, two new methods based on combinations of pseudorange and carrier phase observations from multi-GNSS dual-frequency signals are proposed, which can be used as substitutes for the SNR method when there are no SNR observations. The first method is based on the combination of dual-frequency pseudorange, which is geometry-free, and avoids any consideration of the influence of ambiguity and cycle slip of carrier phase observations. The second method is based on the combination of dual-frequency pseudorange and carrier phase. This, too, is geometry-free, and is not affected by ionospheric delays. To test these two methods, parameter retrievals using multi-GNSS observations reflected from different surface materials were applied. The derived snow depth series over a 256-day period from SG27 station showed an optimal RMSE of 8 cm with respect to in situ data for both methods by using the combination of observations from GPS L2 and L5 frequency bands. In addition, in a separate 365-day experiment at AT01 station, sea levels were estimated using the proposed methods with optimal RMSE of 21 cm when compared with tide gauge measurements. All these results indicate that the two proposed methods can be seen as supplements to the applications of ground-based multipath reflectometry.

Accuracy analysis of GNSS-IR snow depth inversion algorithms

In recent years, with the continuous development of Global Navigation Satellite System (GNSS), it has been applied not only to navigation and positioning, but also to Earth surface environment monitoring. At present, when performing GNSS-IR (GNSS Interferometric Reflectometry) snow depth inversion, Lomb-Scargle Periodogram (LSP) spectrum analysis is mainly used to calculate the vertical height from the antenna phase center to the reflection surface. However, it has the problem of low identification of power spectrum analysis, which may lead to frequency leakage. Therefore, Fast Fourier Transform (FFT) spectrum analysis and Nonlinear Least Square Fitting (NLSF) are introduced to calculate the vertical height in this paper. The GNSS-IR snow depth inversion experiment is carried out by using the observation data of P351 station in PBO (Plate Boundary Observatory) network of the United States from 2013 to 2016. Three algorithms are used to invert the snow depth and compared with the actual snow depth provided by the station 490 in the SNOTEL network. The observations data of L1 and L2 bands are respectively used to find the optimal combination between different algorithms further to improve the accuracy of GNSS-IR snow depth inversion. For L1 band, different snow depths correspond to different optimal algorithms. When the snow depth is less than 0.8 m, the inversion accuracy of NLSF algorithm is the highest. When the snow depth is greater than 0.8 m, the inversion accuracy of FFT algorithm is higher. Therefore, according to the different snow depth, a combined algorithm of NLSF + FFT is proposed for GNSS-IR snow depth inversion. Compared with the traditional LSP algorithm, the inversion accuracy of the combined algorithm is improved by 10%. For L2 band data, the results show that the accuracy of snow depth inversion of various algorithms do not change with the variations of snow depth. Among the three single algorithms, the inversion accuracy of FFT algorithm is better than that of LSP and NLSF algorithms.

Analytical Computation of the Spatial Resolution in GNSS-R and Experimental Validation at L1 and L5

Global navigation satellite systems reflectometry (GNSS-R) is a relatively novel remote sensing technique, but it can be understood as a multi-static radar using satellite navigation signals as signals of opportunity. The scattered signals over sea ice, flooded areas, and even under dense vegetation show a detectable coherent component that can be separated from the incoherent component and processed accordingly. This work derives an analytical formulation of the response of a GNSS-R instrument to a step function in the reflectivity using well-known principles of electromagnetic theory. The evaluation of the spatial resolution then requires a numerical evaluation of the proposed equations, as the width of the transition depends on the reflectivity values of two regions. However, it is found that results are fairly constant over a wide range of reflectivities, and they only vary faster for very high or very low reflectivity gradients. The predicted step response is then satisfactorily compared to airborne experimental results at L1 (1575.42 MHz) and L5 (1176.45 MHz) bands, acquired over a water reservoir south of Melbourne, in terms of width and ringing, and several examples are provided when the transition occurs from land to a rough ocean surface, where the coherent scattering component is no longer dominant.

Design of single‐fed spiral‐shaped slotted planar antenna for GPS L2 and L5 applications

An innovative design of a right hand circularly polarised (RHCP) antenna at two different resonant frequencies that is GPS (global positioning system) L2 and L5 has been proposed in this study. The proposed design comprised the concept of slotted radiator excited with a coaxial probe. Two asymmetric spiral slots were incorporated in a rectangular radiator to realise size miniaturisation, the axial ratio bandwidth and beamwidth at L2 (1.22760 GHz) and L5 (1.17645 GHz) frequencies of GPS applications. The proposed design has accomplished an excellent axial ratio bandwidth and beamwidth at both GPS L2 and L5 bands. The size of the designed antenna has been , which makes it attractive for the consumer market. Measured and simulated results achieved that the antenna conquered RHCP radiation at two separate operating bands, i.e. GPS L2 and L5.

The Design and Simulation of Dual-band Beidou Navigation Receiver LNA

The Beidou satellite navigation receiver requires receiving multi-band signals to ensure more accurate and reliable positioning and navigation. According to the working frequency bands B3I and L1 of the system, we propose a low-noise amplifier which is based on Infineon’s BFP740FESD transistor. We employ the ADS software to simulate and optimize the low-noise amplifier input, and adopt the conjugate matching two-stage amplifier circuit. The simulation results show that the gain Gain ≧ 30dB in the L1 and B3 dual frequency band, the input and output standing wave ratio VSWR < 1.5, the noise coefficient < 1.0dB, and the out-of-band suppression is more than -40dB, which effectively reduces the out-of-band noise interference.

Absorption of decimetre radio waves in the Earth’s high-latitude ionosphere during a geomagnetic storm in June 2015

We have analyzed the radio occultation (RO) results of ∼100 sounding sessions of the high-latitude (>65°N) lower ionosphere of the Earth’s northern hemisphere, which were carried out on 22–23 June 2015 at the GPS-frequency of 1545.42 MHz (L1 band) in the FORMOSAT-3/COSMIC experiment. Coronal plasma ejections that reached the Earth in this period provoked a class G4 magnetic storm (strong geomagnetic storm with planetary Kp-index equal to 8), which in turn caused significant ionospheric fluctuations of radio waves on the sounding paths: navigation (GPS) satellites – low-orbit (FORMOSAT-3/COSMIC) satellites. For the first time, the analysis of FORMOSAT-3/COSMIC radio frequency measurements revealed the absorption of L1 radio waves in the lower high-latitude ionosphere of the Earth. The absorption value is ∼3 dB in the range of 60-90 km and in some cases reaches ∼10 dB at altitudes from 90 to 95 km. It is shown that it is possible to obtain the absorption coefficient of GPS-frequency radio waves in the Earth’s ionosphere at these altitudes from experimental data of FORMOSAT-3/COSMIC.

A Metamaterial based Monopole antenna for Satellite based Navigation Applications

A metamaterial-based monopole antenna which resonates at L (L1 and L5) and S band for the IRNSS applications is described. The antenna has a low profile and is nearly is four times smaller in size than a conventional patch antenna. The multifrequency behavior is realized using a reactively loaded structure for the monopole antenna resulting in operation at both monopole and dipole modes. The monopole resonates at S Band and the dipolar mode resonance at L5 band. The novelty of the configuration is in realizing an additional band by introducing small square slot in the loaded structure. Copper wires are used to balance the current between the two ground at the antenna and the CPW feed line. The performance of the antenna is evaluated using ANSYS HFSS.

A Metamaterial based Monopole antenna for Satellite based Navigation Applications

A metamaterial-based monopole antenna which resonates at L (L1 and L5) and S band for the IRNSS applications is described. The antenna has a low profile and is nearly is four times smaller in size than a conventional patch antenna. The multifrequency behavior is realized using a reactively loaded structure for the monopole antenna resulting in operation at both monopole and dipole modes. The monopole resonates at S Band and the dipolar mode resonance at L5 band. The novelty of the configuration is in realizing an additional band by introducing small square slot in the loaded structure. Copper wires are used to balance the current between the two ground at the antenna and the CPW feed line. The performance of the antenna is evaluated using ANSYS HFSS.

Application of GNSS Interferometric Reflectometry for the Estimation of Lake Ice Thickness

Lake ice thickness is a sensitive indicator of climate change largely through its dependency on near-surface air temperature and on-ice snow mass (depth and density). Monitoring of the seasonal variations and trends in ice thickness is also important for the operation of winter ice roads that northern communities rely on for the movement of goods as well as for cultural and leisure activities (e.g., snowmobiling). Therefore, consistent measurements of ice thickness over lakes is important; however, field measurements tend to be sparse in both space and time in many northern countries. Here, we present an application of L-band frequency Global Navigation Satellite System (GNSS) Interferometric Reflectometry (GNSS-IR) for the estimation of lake ice thickness. The proof of concept is demonstrated through the analysis of Signal-to-Noise Ratio (SNR) time series extracted from Global Positioning System (GPS) constellation L1 band raw data acquired between 8 and 22 March (2017 and 2019) at 14 lake ice sites located in the Northwest Territories, Canada. Dominant frequencies are extracted using Least Squares Harmonic Estimation (LS-HE) for the retrieval of ice thickness. Estimates compare favorably with in-situ measurements (mean absolute error = 0.05 m, mean bias error = −0.01 m, and root mean square error = 0.07 m). These results point to the potential of GPS/GNSS-IR as a complementary tool to traditional field measurements for obtaining consistent ice thickness estimates at many lake locations, given the relatively low cost of GNSS antennas/receivers.