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Although originally developed for the military, the Global
Positioning System (GPS) has proven invaluable for a multitude of
civilian applications. Each application demands specific performance
from the GPS receiver and the associated requirements often vary widely.
This paper describes the architectures and functions of civilian GPS
receivers and...
Contexts in source publication
Context 1
... , , , , , and are defined in Fig. 7; sign is the sign of the navigation message data bit. As indicated in Fig. 7, , and denote correlation with early, late, and prompt versions of the locally generated prn code. The three discriminator functions are plotted in Fig. ...
Context 2
... , , , , , and are defined in Fig. 7; sign is the sign of the navigation message data bit. As indicated in Fig. 7, , and denote correlation with early, late, and prompt versions of the locally generated prn code. The three discriminator functions are plotted in Fig. ...
Context 3
... Degradation Due to Finite-Bit Quantization in the A/D Converter tracking. The digitized samples are mixed with in-phase and quadrature outputs of the so-called carrier numerically controlled oscillator (NCO) to produce the and data streams (Fig. 7). A feedback loop is used to ensure the NCO matches the phase or frequency of the received signal. This carrier NCO output also is accumulated to form the delta range and accumulated delta-range ...
Context 4
... discriminator output is formed in the microprocessor and then filtered and scaled before being fed back to the code NCO (Fig. 7). Similarly, the 's and 's are processed in the software PLL or FLL to demodulate the navigation data bits and provide feedback to the carrier NCO to maintain phase or frequency ...
Citations
... where the brackets indicate ensemble average, which is replaced by the time average in the present study, and SI is the detrended signal intensity. We used the receiver's carrier-to-noise-density (C/N0) measurements for SI (Braasch & van Dierendonck, 1999). We converted C/N0 in dB-Hz units to the linear form before detrending (Van Dierendonck, 1999). ...
Ionospheric density structures at low latitudes range in size from thousands of kilometers down to a few meters. Radio frequency (RF) signals, such as those from global navigation satellite systems, that propagate through irregularities suffer from rapid fluctuations in phase and intensity, known as scintillations. In this study, we use the high‐sample‐rate measurements of the Swarm Echo (CASSIOPE/e‐POP) satellite's GPS Occultation (GAP‐O) receiver taken after its antenna was re‐oriented to vertical‐pointing, simultaneously with e‐POP Ion Mass Spectrometer surface current observations as a proxy for plasma density, to obtain the spectral characteristics of GPS signal intensity and in‐situ irregularities at altitudes from 350 to 1,280 km. We show that the power spectra of both measurements can generally be characterized by a power law. In the case of density irregularities, the spectral index with the highest occurrence rate is around 1.7, which is consistent with previous studies. Also, all the power spectra of GPS signal intensity in this study show a single spectral index near 2. Moreover, roll‐off frequencies estimated in this work range from 0.4 to 2.5 Hz, which is significantly higher than Fresnel frequencies calculated from ground GPS receivers at low latitudes (between 0.2 and 0.45 Hz). Part of this increase is due to the 8 km/s orbital velocity of Swarm Echo near perigee. Another key difference is that variations in the GPS signals in this study are dominated by the topside ionosphere, whereas GPS signals received from ground are affected mostly by the relatively dense F‐region plasma in the 250–350 km altitudinal range.
... The Doppler shift impacts the frequency received by the GNSS receiver, primarily due to the relative motion between the receiver and the satellite. This shift leads to a variation in the received frequency (f RX ) concerning the transmitted one (f T X ), it can be described as (Braasch and van Dierendonck, 1999): ...
Recent research into state estimation algorithms for Low Earth Orbit (LEO) satellites, driven in part by the emergence of broadband LEO constellations, has stimulated interest in their application to Position, Navigation and Timing (PNT). This study investigates the effectiveness of Doppler measurements as a complementary solution for positioning and compares them with conventional pseudorange-based methods in Global Navigation Satellite Systems (GNSSs). The study highlights a limitation in Maximum Likelihood (ML) estimators, especially Least Squares (LS), which affect the convergence of positioning algorithms, especially when dealing with satellites in the LEO region. To analyse this problem, we developed a theoretical framework called ”satellite scale-down”. We then used Monte Carlo simulations to investigate the relationship between the initialisation point of the algorithm and orbital altitude. We also examined the algorithm’s performance with satellites positioned at different orbital altitudes. The results indicate that decreasing the orbital radius enhances the performance of the Doppler-based positioning algorithm; however, it makes the LS positioning algorithm more sensitive to the initialisation point. In fact, without any a priori data on the receiver, the algorithm fails to converge. Therefore, it is necessary to make a trade-off between the achievable performance and the available information about the receiver.
... The triple frequency IRNSS receiver being unequipped to provide S 4 , it was calculated from C/N O using 60 samples, each collected every second, using the following equation (Braasch & Van Dierendonck, 1999;Chakraborty et al., 2017;Dey et al., 2021). ...
This paper reports observation of moderate to intense scintillations, at S band of Indian Regional Navigation Satellite System (IRNSS). During current solar cycle 25, these occurrences are probably being reported for the first time, from a low‐latitude station Calcutta (22.58°N, 88.38°E geographic; magnetic dip 34.54°), located near the northern crest of Equatorial Ionization Anomaly. Efforts have been made to analyze irregularity dynamics at IRNSS S band, along with a comparative study at GNSS L1 to characterize occurrence and evolution of multiscale irregularity structures. Power spectral analysis technique has been applied on recorded C/NO, during scintillation patches, to measure east‐west zonal drift velocity. Efforts are also made to study intensity of signal perturbation at L5 frequency of IRNSS, compared to S band, when observed simultaneously, during period of ionospheric scintillation. Concurrent irregularity dynamics at L1, L5, and S band, particularly from a low‐latitude station, has not been extensively reported earlier. Data is recorded during vernal equinox (February–April 2022) of current solar cycle. Results of this study show occurrence of simultaneous night‐time scintillation at L1, L5, and S band. East‐west zonal drift velocity of irregularity, obtained from S band observations are found to decrease with the progress of time during 20–23 LT having a maximum value of 125 m/s. At GNSS L1, hourly average value of the velocity, is observed to maximize during 20–21 LT. Simultaneous observation of scintillation effects at L5 and S band of IRNSS led to loss‐of‐lock at L5, while no such occurrence was noted at S band.
... The Doppler effect is caused by the relative movement between the transmitter and receiver and can be described as (Braasch and Dierendonck 1999): where D is Doppler frequency shift; f R and f T are the received and transmitted frequencies, respectively; c is the velocity of light; f T is the wavelength of the transmitted signal; and v los is the relative velocity magnitude between transmitter (e.g., satellite) and receiver in line-of-sight (LOS) direction. The Doppler shift is positive if the transmitter and receiver are moving toward, while it is negative if they are moving away. ...
... The Doppler shift is positive if the transmitter and receiver are moving toward, while it is negative if they are moving away. v los is also referred to as the pseudorange rate (Braasch and Dierendonck 1999): ...
Recently, the Doppler shifts from Low Earth Orbit (LEO) satellites have been used to augment GNSS and provide navigation services. We propose a Doppler-only point-solution algorithm for GNSS-like navigation systems operated in LEO. The proposed algorithm can simultaneously estimate the receiver clock drift, position and velocity. Then, we analyze the main error sources in Doppler positioning. To achieve the meter-level positioning accuracy, the satellite position and velocity errors should be within several meters and several centimeters per second, respectively. The ionospheric delay rates of C-band signal will cause about 1 m error in Doppler positioning, which can be eliminated using the ionosphere-free combination. The Doppler positioning accuracy will deteriorate sharply by dozens of meters if there are no corrections for the tropospheric errors. Subsequently, we analyze the Doppler positioning performance. The undifferenced Doppler positioning accuracy is at meter level, which is comparable with the pseudorange-based positioning in GNSS. To ensure convergence in the LEO-based Doppler positioning, the initial receiver position error should be less than 300 km when the satellites orbit is at an altitude of 550 km.
... The parameter ò is the correlator spacing for the delay lock loop-the circuit that attempts to phase up the satellites matched code with the received signal. GNSS applications have to filter for radio frequency interference and this generally restricts ò > 0.1 (Misra & Enge 2012), but it is likely in our case that smaller ò may be achievable with the absolute minimum being ( ) » -BT c 1 (Braasch & van Dierendonck 1999). 9 The above is for ranging using the lowfrequency code. ...
The light from an extragalactic source at a distance d will arrive at detectors separated by 100 au at times that differ by as much as 120( d /100 Mpc) ⁻¹ nanoseconds because of the curvature of the wave front. At gigahertz frequencies, the arrival time difference of a point source can be determined to better than a nanosecond with interferometry. If the spacetime positions of the detectors are known to a few centimeters, comparable to the accuracy to which very long baseline interferometry baselines and global navigation satellite systems (GNSS) geolocations are constrained, nanosecond timing would allow competitive cosmological constraints. We show that a four-detector constellation at Solar radii of ≳10 au could measure geometric distances to individual sources with subpercent precision. The precision increases quadratically with baseline length. Fast radio bursts (FRBs) are the only known bright extragalactic radio source that are sufficiently point-like for this experiment, and the simplest approach would target the population of repeating FRBs. Galactic scattering limits the timing precision at ≲3 GHz, whereas at higher frequencies the precision is set by removing the differential dispersion between the detectors. Furthermore, for baselines greater than 100 au, Shapiro time delays limit the precision, but their effect can be cleaned at the cost of two additional detectors. Outer solar system accelerations that result in ∼1 cm uncertainty in detector positions could be corrected for with weekly GNSS-like trilaterations between members of the constellation. The proposed interferometer would not only provide a geometric constraint on the Hubble constant, but also could advance solar system, pulsar, and gravitational wave science.
... One of the parameters used to define the performance of the Costas loop is the estimated phase error variance (σ φ 2 ). For the Costas loop working with a conventional discriminator (CC), this variance is given by [17] 2 0 ...
... The positioning module is integrated into the smartphone chips. It is known that the structural design and phase-locked loop (PLL) regulated by the chipsets of smartphones would be different from the geodetic GNSS receivers [6]- [8]. This causes new characteristics of the smartphone GNSS observations. ...
... However, the smartphone positioning algorithm is basically inherited from the models generated with the geodetic receivers. Considering the differences in their received signals [8], the models would be far from suitable for smartphones. To obtain high-precision positioning, specific GNSS models for smartphones should be further studied. ...
The emerging Internet of Things (IoT) applications, such as intelligent transportation based on vehicular-lane accurate positioning, have a growing demand for precise and reliable positioning with Global Navigation Satellite Systems (GNSSs). It is desirable to use GNSS modules in smartphones to achieve high-precision positioning. The GNSS modules in some brands of smartphones thus far are able to track the new L5 signals of GPS and QZSS, E5a signals of Galileo and B2a signals of BeiDou-3. The L5/E5a/B2a signals have higher quality due to their signal structure, which provides an important potential for high-precision positioning in smartphones. In this paper, we will study the quality of L5/E5a/B2a signals, and their superiorities in integer ambiguity resolution (IAR) and precise positioning with respect to the L1/E1/B1 signals from GPS, QZSS, Galileo and Beidou-2/3 satellites. The signal quality is evaluated in terms of observation precision, multipath, double-differenced ambiguity fractions and ambiguity dilution of precision (ADOP). In addition, we propose a new weighting model that takes into account the variation range of carrier-to-noise density ratio (C/N0). The results indicate that the Beidou-3 B2a signal has comparable quality to L5/E5a signals of other systems, and all of them are better than the L1/E1/B1 signals. However, the ambiguity fractions of B2a signals diverge abruptly in some periods, resulting in the unsuccessful ambiguity fixing. The L5/E5a/B2a signals can generally obtain higher IAR fix-rate and positioning accuracies than the L1/E1/B1 signals. The new weighting model can capture the smartphone noise characteristics better than the traditional weighting model, thus improving the positioning accuracy.
... The Global Positioning System (GPS) is used in various applications for positioning navigation systems because of its exclusivity characteristics. Although its development was initially for military purposes, its usage has expanded in various aspects [1]. Aircraft, marine fleets, and modern vehicles use the GPS receiver for high-level accuracy in navigation operations [1,2]. ...
... Although its development was initially for military purposes, its usage has expanded in various aspects [1]. Aircraft, marine fleets, and modern vehicles use the GPS receiver for high-level accuracy in navigation operations [1,2]. In recent years, other aspects of GPS have been employed as well. ...
... After that, the value of the count is compared to the MinPts stored in another register. If it satisfies the necessary condition (see Sect. 4. 1 Step 2), the union of the value of local_neighbor_shadow and local_neighbors is calculated and transmitted to the local_neighbors register. When all the calculation is done, local_db_cluster, using a multiplexer, assigns related clusters to each data point. ...
GPS receivers have a wide range of applications, but are not always secure. A spoofing attack is one source of conscious errors in which the counterfeit signal overcomes the authentic GPS signal and takes control of the receiver’s operation. Recently, GPS spoofing attack detection based on computational algorithms, such as machine learning, classification, wavelet transform and clustering, has been developing. This paper proposes multiple clustering algorithms for accurately clustering the authentic and spoofing signals, called subtractive, FCM and DBSCAN clustering. The spoofing attack is recognized using two distinct features: moving phase detector variance and norms of correlators. Spoofing and authentic signals have different patterns in the proposed features. According to the Dunn and Silhouette indexes, the validation of the results is investigated. The Dunn values for the proposed approaches are 0.8592, 0.5285 and 0.6039 for DBSCAN, FCM and subtractive clustering, respectively. Also, the DBSCAN algorithm is implemented at the RTL level because of its highest value for the Dunn index and algorithm verifiability. Using the Vivado tools, this algorithm is implemented and designed on a Xilinx Virtex 7 xc7vx690tffg1930-3 hardware device for two-dimensional data with 32-bit accuracy and 130 data points.
... • α: the multipath-to-direct signal strength ratio (M/D ratio) As is observed from Eq. 11 and discussed in [25], both the upper bound and lower bound of the envelope consist of four segments: the first segments are slopes, which are functions of M/D ratio and extra path delay, independent of correlator spacing and PRN chipping rate. In extreme case of materials of reflector, i.e. α → 1, the lower slope will be infinitely close to vertical. ...
... Due to the single-frequency observation, the fix rate is greatly reduced, and the fix time is much elongated for low-cost receivers under mobile and multipath environments. (Braasch and Van Dierendonck, 1999) Figure 4.1 illustrates the architecture of the GPS receivers. Various grades of receivers may adopt different designs resulting in a quality difference in different modules. ...
... Compared to low-cost receivers, surveygrade receivers usually adopt high-quality designs for noise, multipath, and interference reduction. For example, for survey-grade receivers, generally Front ends are characterised by the lower noise The A/D (analog to digital) converters are multi-bit instead of single-bit The DSPs are high speed with more channels available Dual frequencies observations are tracked Low and narrow bandwidths are adopted in the carrier phase tracking loop (Braasch and Van Dierendonck, 1999). ...
Current deformation monitoring applications adopting GNSS technology are usually conducted with high-grade GNSS sensors, consisting of both geodetic receiver and geodetic antenna. However, the high-cost feature of the equipment constrains its broader application. With the development of state-of-art low-cost GNSS receivers/antennas in recent years, especially those with multi-GNSS precise carrier phase measurement, the potential for its application in deformation monitoring is expected. However, compared to conventionally adopted survey-grade equipment, most low-cost receivers have the major drawback of single-frequency and larger background noise in the signal processing phase, and the patch antennas have the major disadvantage of the less gain, less multipath suppression, etc. Despite the comparatively poorer quality, empirical research has demonstrated its feasibility in landslide monitoring within centimetre level of accuracy. To test the feasibility and accuracy of the low-cost equipment in other deformation applications, a systematic approach is adopted by carrying out several experiments. Experiments are conducted sequentially from zero-baseline test for internal receiver noise evaluation, short baseline static test to identify and mitigate the practical GNSS monitoring errors majorly consisted of multipath, short baseline dynamic test to determine the precision of low-cost equipment in dynamic monitoring scenario, and finally, the low-cost equipment is tested on a real bridge monitoring project to assess its feasibility and evaluate its accuracy. It is concluded that the modal frequencies from deformation monitoring could be revealed from measurements of a single low-cost rover, and with proper multipath mitigation technique, displacement amplitude could be obtained within centimetre accuracy by a closely-spaced dual low-cost system. The difference of low-cost rover measurement is quantified to be within around 3mm compared to geodetic GNSS sensors. This finding is quite promising for low-cost GNSS deformation monitoring applications. However, future investigation still needs to be carried out with a calibrated patch antenna or with a geodetic antenna to examine further improvement and possibly explore the potential of applying it in real-time.
