Global Positioning System L1 Frequency Research Articles

SBAS-based navigation system for precision approach in CAT II LVC

Due to lack of advanced navigation systems, secondary airports are normally unable to support instrument approaches in low visibility conditions (LVC) more adverse than Category (CAT) I, making them inaccessible during such conditions. Incoming flights are then delayed, diverted to adjacent airports, or cancelled before take-off. This paper presents an onboard navigation solution, under development in scope of SESAR 2020 Solution PJ02-W2- 17.2, which focuses on technology development to mitigate these traffic disruptions by enabling instrument approaches in CAT II LVC with minimum airport and air navigation service provider investments. The concept builds upon global navigation satellite systems (Global Positioning System L1 frequency – GPS L1, satellite-based augmentation system), which currently enables Localizer Performance with Vertical guidance (LPV) operation down to LPV 200 minima. The designed system includes radio altimeter-based aiding and innovative integrity algorithm to improve navigation performance in support of operations below 200ft down to CAT II / LPV 100 minima. As no such requirements have yet been officially published, authors also defined sets of candidates based on Instrument Landing System Collision Risk Model and other sources. The team developed and verified a Monte-Carlo fast-time simulation toolset to enable representative and statistically significant evaluation of the concept feasibility via its availability throughout Europe, as well as sensitivity to proposed sets of alert limits. Also, flight data collection and a developed software prototype allow for further validations. Simulations demonstrated over 95% average availability with the best results achieving level of 99% depending on used set of requirements. The solution enabling operations in LVC allows unlocking various benefits to business/airline operators (e.g., avoided extra costs, increased predictability), passengers (avoided opportunity loss) and airports (retained profit from flights, less traffic at diversion airports). Technology development also marks an important step towards gate-to-gate autonomous operations.

Experimental Evaluation of the Impact of Different Types of Jamming Signals on Commercial GNSS Receivers

The received global navigation satellite system (GNSS) signal has a very low power due to traveling a very long distance and to the nature of the signal’s propagation medium. Thus, GNSS signals are easily susceptible to signal interference. Signal interference can cause severe degradation or interruption in GNSS position, navigation, and timing (PNT) services which could be very critical, especially in safety-critical applications. The objective of this paper is to evaluate the impact of the presence of jamming signals on a high-end GNSS receiver and investigate the benefits of using a multi-constellation system under such circumstances. Several jamming signals are considered in this research, including narrowband and wideband signals that are located on GPS L1 or GLONASS L1 frequency bands. Quasi-real dynamic trajectories are generated using the Spirent™ GSS6700 GNSS signal simulator combined with an interference signal generator through a Spirent™ GSS8366 unit. The performance evaluation was carried out using several evaluation metrics, including signal power degradation, navigation solution availability, dilution of precision (DOP), and positioning accuracy. The multi-constellation system presented better performance over the global positioning system (GPS)-only constellation in most cases. Moreover, jamming the GPS band caused more critical effects than jamming the GLONASS band.

A statistical approach to estimate Global Navigation Satellite Systems (GNSS) receiver signal tracking performance in the presence of ionospheric scintillation

Ionospheric scintillation can seriously impair the Global Navigation Satellite Systems (GNSS) receiver signal tracking performance, thus affecting the required levels of availability, accuracy and integrity of positioning that supports modern day GNSS based applications. We present results from the research work carried out under the Horizon 2020 European Commission (EC) funded Ionospheric Prediction Service (IPS) project. The statistical models developed to estimate the standard deviation of the receiver Phase Locked Loop (PLL) tracking jitter on the Global Positioning System (GPS) L1 frequency as a function of scintillation levels are presented. The models were developed following the statistical approach of generalized linear modelling on data recorded by networks in operation at high and low latitudes during the years of 2012–2015. The developed models were validated using data from different stations over varying latitudes, which yielded promising results. In the case of mid-latitudes, as the occurrence of strong scintillation is absent, an attempt to develop a dedicated model proved fruitless and, therefore, the models developed for the high and low latitudes were tested for two mid-latitude stations. The developed statistical models can be used to generate receiver tracking jitter maps over a region, providing users with the expected tracking conditions. The approach followed for the development of these models for the GPS L1 frequency can be used as a blueprint for the development of similar models for other GNSS frequencies, which will be the subject of follow on research.

A cavity‐backed spiral slot antenna with wide axial ratio beamwidth for GPS system

AbstractA monofilar spiral slot antenna with a cavity‐backed reflector is presented, which can achieve the performance of the wide axial ratio beamwave for global positioning system (GPS) system. It comprises an arrangement of a single printed spiral slots fed by a 50‐Ω microstrip line. By using cavity‐backed covering the slot structure, a wide axial ratio beamwidth performance is achieved in the GPS L1 frequency. The angle with less than 3‐dB axial ratio at 1.575 GHz in the YoZ plane is about 215°. The measured results show that the HPBW beamwidths at 1.575 GHz are 100° in the YoZ plane, respectively. The peak gain is 5.5 dBic. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1050–1054, 2014

A metamaterial-inspired, electrically small rectenna for high-efficiency, low power harvesting and scavenging at the global positioning system L1 frequency

An electrically small rectenna was designed and tested at the global positioning system (GPS) L1 frequency (1.5754 GHz). The metamaterial-inspired near-field resonant parasitic antenna size (ka ∼ 0.467) and its direct match to the input impedance of the rectifying circuit decreased the whole size of the rectenna (ka ∼ 0.611). The simulated and measured rectifying efficiencies were, respectively, 75.7% and 79.6% when the input power to the rectifying circuit was 0.0 dBm (1 mW). The highest rectifying efficiency, 84.7%, was achieved at the GPS L1 frequency for a 3.0 dBm input power. The simulated and measured results are in good agreement.

Advanced architectures for real-time Delay-Doppler Map GNSS-reflectometers: The GPS reflectometer instrument for PAU (griPAU)

In recent years Global Navigation Satellite System’s signals Reflectometry (GNSS-R) has stood as a potential powerful remote sensing technique to derive scientifically relevant geophysical parameters such as ocean altimetry, sea state or soil moisture. This has brought out the need of designing and implementing appropriate receivers in order to track and process this kind of signals in real-time to avoid the storage of huge volumes of raw data. This paper presents the architecture and performance of the Global Positioning System (GPS) Reflectometer Instrument for PAU (griPAU), a real-time high resolution Delay-Doppler Map reflectometer, operating at the GPS L1 frequency with the C/A codes. The griPAU instrument computes 24 × 32 complex points DDMs with configurable resolution (Δ f Dmin = 20 Hz, Δ τ min = 0.05 chips) and selectable coherent (minimum = 1 ms, maximum = 100 ms for correlation loss Δ ρ < 90%) and incoherent integration times (minimum of one coherent integration period and maximum not limited but typically <1 s). A high sensitivity (DDM peak relative error = 0.9% and DDM volume relative error = 0.03% @ T i = 1 s) and stability (Δ ρ/Δ t = −1 s −1) have been achieved by means of advanced digital design techniques.

Details of an Imaging System Based on Reflected GPS Signals and Utilizing SAR Techniques

This research endeavor reveals a method for utilizing reflected Global Positioning System (GPS) signals to form an image of targets within a region of interest. The principle is based upon a type of bistatic synthetic aperture radar (SAR) in which a matched filter technique is employed to perform the image reconstruction. A major challenge was the appalling signal to noise ratio associated with the received reflected GPS signals. Moreover, the reconstruction method resulted in an undesirable point spread function (PSF) which degraded the reconstructed image. The entire GPS signal generation and image reconstruction process was simulated as faithfully as possible and it has been demonstrated that a spatial resolution of the order of the GPS L1 frequency (wavelength of 19 cm) is possible. The smeared image obtained due to poor quality PSF was improved by means of a Wiener filter based deconvolution method. An imaging system based on a stationary receiver has been practically demonstrated with the successful identification of a 0.5 m 2 spherical target.

Coherent GPS Reflections From the Sea Surface

In this letter, we explore a method to obtain accurate ocean heights using measurements of the global positioning system (GPS) carrier phase after reflection on the sea surface. A carrier tracking algorithm is employed in measuring travel path differences between GPS direct and reflected signals collected from antennas suspended over a marine estuary, when roughness guarantees partially coherent reflections at the GPS L1 frequency. This technique proves to be sensitive to surface roughness and able to follow tide variations with a precision better than 5 cm (1-sigma) for sea states with significant wave heights below 10 cm. It is expected that this technique could be further extended to rougher sea states using GPS frequency combinations with longer synthetic wavelengths.

Evaluation of solar radio bursts' effect on GPS receiver signal tracking within International GPS Service network

The direct interference from solar radio bursts (SRB) has not usually been considered as a potential threat to global positioning system (GPS) signal tracking, since the flux densities of most bursts are below 40,000 solar flux units (sfu), a threat threshold to GPS L1 frequency proposed by Klobuchar et al. (1999). Recent analysis indicated that a much lower threshold should be adopted for codeless or semicodeless dual‐frequency GPS receivers. In this investigation, severe signal corruptions were found at dayside International GPS Service GPS receiver stations during a large solar radio burst that accompanied the super flare of 28 October 2003. Almost no GPS L2 signals were tracked during the solar flux peak time for areas near the subsolar point. Correlation analysis was performed between the rate of loss of lock on GPS L2 frequency and solar radio flux density at different bands, and a correlation index as high as 0.75 is revealed in the 1415 MHz solar radiation band, which is located between the two GPS operating frequencies L2 (1227.60 MHz) and L1 (1575.42 MHz). The correlation analysis indicates that GPS signal losses of lock were primarily caused by microwave in‐band interference and that the threat threshold of SRB effects on the GPS system should be re‐evaluated, since the flux density of the burst at 1415 MHz was just 4,000–12,000 sfu, which is far below the previously proposed threat threshold. The signal‐tracking performance of different types of GPS receivers during such a super flare event is also presented.

Scintillations observed at Tucuman as observed from GPS signals. First results

The occurrence of ionospheric irregularities was studied using Global Positioning System (GPS) measurements at Tucumán (26.9° S, 294.6° E; geomag. lat.: −15.5), a station placed near the souther peak of the equatorial anomaly. Radio scintillations at the GPS L1 frequency (1.575 GHz) were monitored using the GPS receiver installed at the mentioned station. The considered measurements were obtained during September 1998 – April 1999 period. The results show that amplitude scintillations frequently occur between 21 and 02 LT. Scintillations are more frequent when the satellites are in the northwest — northeast sector of Tucumán's sky. Strong scintillations were observed in about 40% of the nights.

First in situ observations of equatorial ionospheric bubbles by Indian satellite SROSS‐C2 and simultaneous multisatellite scintillations

The first observation of equatorial ionospheric irregularities by RPA probe of the Indian low Earth orbiting satellite SROSS‐C2 is presented in this paper. Amplitude scintillations of medium Earth orbiting Global Positioning System (GPS) satellites and geostationary FLEETSATCOM (244 MHz, 73°E) and INMARSAT (1.5 GHz, 65°E) signals recorded simultaneously at Calcutta (lat: 22.97° N, long: 88.50°E geographic; dip: 32°N) are used for a coordinated study of equatorial F region irregularities in the Indian zone. Cases of ionospheric irregularities identified from the SROSS‐C2 records obtained during the initial one‐and‐a‐half years since its launch in May 1994 have been analyzed. Some events of in situ ion density irregularities are compared with scintillations simultaneously observed on the transionospheric satellite links. Intense bite‐outs of ion density (maximum relative irregularity amplitude ΔN/N ∼ 65%) were detected on one occasion (October 29, 1994) coupled with deep fadings (S4 ∼ 1 at VHF, ∼0.52 at L‐band, and ∼0.69 at GPS L1 frequency) on ground‐based satellite links. An estimate of scintillation indices from the observed in situ density deviations compares well with the ground‐based measurements. The development of intense equatorial bubbles even on a day like October 29, 1994, under low solar activity conditions, may be attributed to a prompt penetration of magnetospheric electric field equatorwards during the main phase of a magnetic storm in progress [maximum negative excursion of Dst ∼ −127 nT at 1600UT (2100MLT) with a dDst/dt rate −37 nT/hr at 1300–1400UT (1800–1900MLT)]. The drift velocity and spatial extent of these irregularities have been estimated from ground‐based observations.

Ionospheric specification algorithms for precise GPS‐based aircraft navigation

The Federal Aviation Administration (FAA) is implementing an aircraft navigation scheme for the United States using the Global Positioning System (GPS) L1 signal (1575.42 MHz). To achieve position accuracies of a few meters, sufficient to allow precision airfield approaches, it will be necessary to broadcast corrections to the direct GPS signal. A significant component of these corrections is the delay in the GPS signal introduced by its propagation through the ionosphere. Ionospheric delay corrections will be derived using a ground network of at least 24 dual‐frequency GPS receivers distributed across the continental United States. This network is part of the FAA's wide area augmentation system (WAAS) and will provide real‐time total electron content (TEC) measurements. We present a technique for converting these TECs into gridded vertical delay corrections at the GPS L1 frequency, which will be broadcast to users every 5 min via geosynchronous satellite. Users will convert these delays to slant corrections for their own particular lines of sight to GPS satellites. To preserve user safety, estimates of the error in the user delay corrections will also be broadcast. However, the error algorithm must not resort to excessive safety margins as this reduces the expected accuracy, and thus utility, of the navigation system. Here we describe an error algorithm and its dependence on various factors, such as user location with respect to the WAAS ground network and ionospheric conditions.

Global Positioning System measurements of the ionospheric zonal apparent velocity at Cachoeira Paulista in Brazil

Ionospheric irregularities and their zonal apparent drift were studied using Global Positioning System (GPS) measurements at Cachoeira Paulista (22.41°S, 45.00°W, −26° dip angle) in Brazil during November 6–19, 1998. Radio scintillations at the GPS L1 frequency (1.575 GHz) were monitored using four GPS receivers spaced geomagnetically east–west and north–south. Total electron content (TEC) was measured through the ionospheric advance of the GPS L1 and L2 (1.227 GHz) phases. Strong amplitude scintillations coincided with TEC fluctuations associated with spread F bubbles elongated along the magnetic field. Movement of the Presnel‐scale (400 m) ionospheric irregularity layers caused the scintillation to drift, and their zonal apparent drift velocities were measured using a cross‐correlation technique. Our measurements show that the apparent eastward velocity varies from 200 m/s to 150 m/s at 2000 LT, and then it decreases to 100–50 m/s at midnight. On a magnetically disturbed day, reversal of the zonal apparent drift was observed just after midnight, and the apparent westward velocities observed at early in the morning showed large variations with location in the sky. From the receivers spaced in the geomagnetic north–south direction we measured near‐zero time shifts, from which we conclude that the correlation length of several‐hundred‐meter‐scale irregularities is much larger than 70‐m separation between the north and south receivers.