2021/04/17
An Answer for Precise Positioning Research
By Thomas Pany, Nico Falk, Bernhard Riedl, Tobias Hartmann, Günter Stangl, and Carsten Stöber
INNOVATION INSIGHTS by Richard Langley
WHAT IS THE IDEAL GNSS RECEIVER? Well, that depends on what you mean by “ideal.” If we take it to mean the simplest, conceptually, yet the most capable and adaptable receiver, then we would just connect an analog-to-digital converter (ADC) to an antenna and pass the converter’s output to a digital signal processor whose software would transform the received signal into the desired result with the utmost speed and precision. There are certain technological limitations that currently preclude fully developing such a device but we are getting very close to the ideal and practical implementations already exist.
Such a GNSS receiver is an example of a software-defined radio — a radio-communications architecture in which as much of the operation of a receiver (or a transmitter) as feasible is performed by software in an embedded system or on a personal computer (PC).
Now, we can’t simply connect an ADC to an antenna since the strength of GNSS signals falls well below the sensitivity threshold of real ADCs and those that can directly digitize microwave radio frequencies are rather power hungry. Therefore, the front end of a real software GNSS receiver includes a low-noise preamplifier, filters, and one or more downconverters to produce an analog intermediate-frequency signal that passes to a high-speed ADC. The digitized signal is provided at the output of the front end in a convenient format, which, for processing signals on a PC, is typically USB 2.0 with its maximum signaling rate of 480 megabits per second. All baseband signal processing is then carried out in the programmable microprocessor.
Software GNSS receivers offer a number of advantages over their hardware cousins. Foremost is their flexibility, which permits easy and rapid changes to accommodate new radio frequency bands, signal modulation types and bandwidths, and baseband algorithms. This flexibility is beneficial not only for multi-GNSS operation but also for prototyping algorithms for conventional hardware designs. Another advantage is their use in embedded systems such as smartphones and wireless personal digital assistants. Software GNSS receivers are also a boon for teaching, where a student can tweak a particular operating parameter and immediately see the effect. And given their remarkable flexibility, software GNSS receivers can be adapted to a variety of special scientific and engineering research applications such as reflectometry and signal analysis.
In this month’s “Innovation,” we look into the development and capabilities of one modern software GNSS receiver in an effort to answer the question “What is the ideal GNSS receiver for precise positioning research?”
“Innovation” is a regular feature that discusses advances in GPS technology andits applications as well as the fundamentals of GPS positioning. The column is coordinated by Richard Langley of the Department of Geodesy and Geomatics Engineering, University of New Brunswick.
Personal-computer-based software receivers have found broad use as R&D tools for testing new signal processing algorithms, for analyzing received GNSS signals, and for integrating various sensors with GNSS. Software receivers also provide a consistent framework for GNSS signal samples, correlator values, pseudoranges, positions, assistance data, and sensor (inertial) data, and often act as integration platforms for prototype navigation systems. The distinctive feature of PC-based software receivers is their ability to work in post-processing mode in addition to real-time operation and the support of high-performance central processing units (CPUs).
So far, software receivers are typically not used as operational receivers — neither in the mass market, nor in the professional sector, nor as a reference station where a PC would already be available. The last point can be explained by the fact that most software receivers can only process a limited number of frequency bands (sometimes just L1) and are often limited to small bandwidth signals (such as that of the L1 C/A-code signal or the L2 civil signal (L2C)). Improvements of the PC-based software receiver SX-NSR achieved at the end of 2010 and in early 2011 try to overcome these limitations. They include the first real-time implementation of P-code processing on L2, a unique method for processing the ultra-wide Galileo AltBOC signals on E5, and a method to synchronize two NavPort-4 frontends (each supporting four frequency bands of 15 MHz bandwidth) via a hardware link.
The SX-NSR, which has been developed in cooperation with the Universität der Bundeswehr München in Munich, Germany, runs under the Windows operating system (XP or 7) and supports processing of GNSS signals plus sensor data (such as that from an inertial measurement unit, or IMU) in real time and in post-processing mode. It supports all the civil GPS, GLONASS, Galileo, and Compass signals. User-defined signals can be included by providing the pseudorandom noise (PRN) codes and the associated tracking parameters.
The computational real-time performance can be characterized by two rules-of-thumb for acquisition and tracking. Acquisition is based on a flexible coherent and noncoherent integration and may be accelerated by a graphics card based on the Compute Unified Device Architecture (CUDA) — a parallel-computing architecture developed by Nvidia for graphics processing but also useful for accelerating non-graphics applications. Depending on the graphics card type, a few million or many millions of equivalent correlators are available to detect even the weakest signals quickly. Stable tracking is done with multiple correlators. An x86 CPU core supports around 20 channels (for a laptop) to 30 channels (for a PC) at an average CPU load below 50–60 percent. With that CPU load, the software has enough reserve (in terms of the size of the sample buffer) to cope with latencies introduced by the non-real-time Windows operating system. In post-processing, a virtually unlimited number of channels or correlators is available.
The SX-NSR software typically connects to the NavPort-4 front end via a single USB 2.0 connector. One front end supports four RF paths with 15-MHz bandwidth in the L-band. One band is sampled at 40.96 MHz with 12-bit precision. Small batches of samples are transferred with 12 bits at regular intervals to the PC for increased spectral analysis possibilities but the continuous transfer is usually done with just 2 bits. Decimation by a factor of two (yielding a sample rate of 20.48 MHz) and/or bit reduction are options to limit the data transfer bandwidth on the USB bus. The NavPort also includes configurable notch and finite-impulse-response (FIR) filters working with 12-bit precision and 40.96-MHz data rate. The SX-NSR further supports standard output formats (such as Receiver Independent Exchange (RINEX) format or that of the Radio Technical Commission for Maritime Services (RTCM)), has a graphical user interface, and a freely user-accessible application programming interface (API) in the C programming language.
A reference station was established with the SX-NSR for the International GNSS Service (IGS) Multi-GNSS Experiment (M-GEX) starting on February 1, 2012, at the Observatory Graz in Austria (marker name GRAB). The data is routinely processed by the European Reference Frame analysis center at Observatory Lustbuehel, Graz, Austria, with Bernese Software 5.0, and shows results with a quality that is virtually no different than that of commercial hardware receivers.
All-in-view tracking of the four GNSS constellations on all frequencies (see TABLE 1) has been achieved with an off-the-shelf $1,000 PC, two synchronized NavPorts, and the SX-NSR software. In particular, the front end receives Compass B1, B2, and B3 signals and currently the software is tracking two of the geostationary Earth orbit (GEO) satellites, a few of the inclined geosynchronous orbit (IGSO) satellites, and the medium Earth orbit (MEO) satellites at Graz on B1 and B2. There are plans to implement tracking of the B3 signal for the M1 satellite and that of satellite-based augmentation system (SBAS) satellites on L5.
Table 1. Frequency bands supported by the dual NavPort-4 receiver.
Typical received carrier-to-noise-density-ratio (C/N0) values recorded at station GRAB are shown in FIGURE 1. Freely accessible GRAB data in RINEX format can be downloaded from several data archive sites (see Further Reading online).
The SX-NSR software receiver provides a GNSS development and research framework with the API opening it up for user-implemented algorithms. The user may implement only small portions of new code (such as a special acquisition technique) and for the rest of the receiver rely on the well-known behavior of the SX-NSR’s framework. A number of applications are possible using the flexibility of a software receiver; some of them are described in this article.
Figure 1. C/N0 values for five typical satellites, one each for GPS, GLONASS, Galileo, Compass, and the European Geostationary Navigation Overlay Service (EGNOS) SBAS as recorded at Observatory Graz.
The Front End
The front-end frequency plan was adjusted to have a clean spectrum free of internal interference. This is of utmost importance as software receivers are often used to detect and mitigate interference especially for the Galileo E5 and E6 frequency bands due to overlapping radio navigation services.
An inter-front-end link enables synchronization of two NavPort-4 devices. It generates a synchronous reference clock for a proper phase relationship. Moreover, a trigger is used to adjust the digital data stream of both devices. One possible application of the inter-front-end link technology is to easily double the number of available GNSS frequencies. Another possible application is the building of a dual-antenna solution. For this purpose, each NavPort-4 device handles the same GNSS frequencies, but from different antennas. Whereas within each NavPort, a quad analog-to-digital converter (ADC) synchronously samples the four received GNSS signals, the synchronicity between two NavPorts is more complex.
For the inter-front-end link, both devices have to use the same 10-MHz clock reference for a synchronous setup. This is reached by using the reference clock output of the master device as reference clock input of the slave device as depicted in FIGURE 2. It is also possible to connect both NavPort-4 devices to a single external clock reference.
Each device generates its own 40.96-MHz sample rate from this reference. The phase difference of the 40.96-MHz sample rate is measured in the master and slave with a phase detector. The first input of the detector is the local 40.96-MHz clock. The second input is the 40.96-MHz clock from the other NavPort-4 with a different phase alignment due to ambiguities in its generation and cable delay. The phase detector measures the phase difference between both clocks. The low-pass-filtered output of this measurement is digitized with an ADC. If this measurement is within a phase range of ±7 degrees at 40.96 MHz, which corresponds to ±14 centimeters, the coarse synchronization is finished. If the value is not within this range, the synchronization algorithm repeats.
After starting the data processing for both devices simultaneously with an implemented digital trigger, the phase difference between master and slave clock could be measured continuously for later fine-tuning in the SX-NSR to achieve an accuracy of much below 1 degree at 40.96 MHz, which corresponds to ±2 centimeters.
The synchronization algorithm is verified by connecting two L1-capable NavPorts to the same antenna. The phase and code delay can then be determined from receiver single-differences of GPS L1 C/A-code-derived phase and code measurements. Actually, this delay estimation is part of an attitude solution (see below) and an example is shown in FIGURE 3. The code delay here is around 50 centimeters and includes the RF filter delay difference of around 40 centimeters (which can be calibrated and is stable over power cycles) in addition to the synchronization delay (here around 10 centimeters). The phase delay is naturally determined modulo one cycle and shows warm-up effects of 1.4 centimeters during the first few minutes of operation.
Figure 3. Inter-front-end hardware delay variation on a GPS L1 signal.
GNSS Reference Station
Although the GPS modernization process is ongoing and more and more L2C-capable satellites are in orbit, tracking of the encrypted P-code signal on L2 is still a key element for any receiver to be considered as a reference station or geodetic receiver. Dual-frequency observations need to be available for the full GPS constellation. A possible option to retrieve full wavelength carrier-phase observations and code ranges on L2 is cross-correlation tracking of the encrypted P-code signal. The receiver computes the cross-correlation function between the raw L1 and L2 samples over a long coherent interval as shown in FIGURE 4. The encrypted P-code stream, identical on L1 and L2, is represented by c(tµ).
Figure 4. Cross-correlation block diagram.
A receiver internal complex carrier is generated (see frequency compensation in Figure 4), whose frequency equals the Doppler shift frequency plus the intermediate-frequency difference between L1 and L2. This frequency is generally different for each satellite. The L1 signal is delayed to compute the cross-correlation function for several code-phase taps.
The cross-correlation function is computed using the predicted Doppler difference based on the Doppler frequency estimated from L1 with complex-valued baseband samples. A number of batches are collected and a post-correlation fast Fourier transform is applied. The parameter values shown in TABLE 2 result in a total coherent integration time of 6.4 seconds.
Table 2. SX-NSR cross-correlation parameter values.
The result is the cross-correlation function as a function of code phase and Doppler. Using interpolation techniques, the position of the peak is determined, which then gives the delay and Doppler shift of the L2 signal with respect to the L1 signal. The complex argument of the peak value gives the L2-L1 carrier-phase differences. Those differences are filtered and are then added to the L1 parameters to give the L2P code estimates.
We use two first-order Kalman filters (one for the code, one for the phase) to smooth the cross-correlation estimates. The code filter is updated with the estimated delay and the Doppler; the phase filter is updated with the estimated Doppler and phase. Cycle slips are detected if the L1-L2 phase changes are too high. Loss-of-lock is detected by comparing the estimated L2 C/N0 value against a threshold. After several Kalman filter tuning steps, the L2P signal is tracked down to low elevation angles. For example, the GPS Block IIF satellite PRN1 was tracked over a whole pass without cycle slips as shown in the code-minus-carrier plot in FIGURE 5.
Figure 5. Code minus carrier-phase measurements for GPS PRN1 at site GRAB on day of year 106, 2012.
One of the key applications of a professional GNSS receiver is its use as a GNSS reference station. Using a software receiver for this purpose would also provide increased monitoring capabilities to detect (un)intentional inference via RF spectral analysis or to detect signal anomalies due to satellite failures or multipath. Furthermore, it is useful for a number of scientific experiments and research topics such as scintillation monitoring or atmospheric occultation studies.
Other GNSS Signals
The inclusion of new GNSS signals in a software receiver is typically straightforward. The PRN codes need to be loaded and the tracking parameters (such as carrier frequency, integration time, error correction scheme, phase relation of signal components data/pilot, correlator positions, and discriminator type) can be selected without source code modification. If a hand-over from a different signal is performed (such as from GPS L1 to GPS L5) and if the first signal has already been synchronized to the transmit time by decoding the time-of-week, then it is possible to directly resolve the code ambiguity of the new signal. If this is not possible, a navigation message decoder has to be implemented to retrieve the time-of-week, which mostly has to be in the source code.
Galileo AltBOC. An important exception to this rule is the Galileo AltBOC signal due to its high bandwidth. A conventional view on the AltBOC signal processing would require a sample rate of at least two times the total signal bandwidth. Depending on how many outer AltBOC side lobes are considered, this results in a sampling rate of 102 megasamples per second or more. This is undesirable for a cost-efficient software receiver solution, regarding the data transfer and the CPU load. The AltBOC processing inside the SX-NSR relies on the fact that both frequency bands E5a and E5b are sampled coherently and this coherency can be exploited to reconstruct the full AltBOC signal. The accuracy of the AltBOC navigation signal is concentrated in the main BOC sidelobes itself. More specifically, the thermal noise and multipath performance are dependent on the Gabor bandwidth, which represents the curvature of the correlation function at the tracking point. Thus a similar Gabor bandwidth can be obtained by sampling the E5a and the E5b band separately. This is the key idea of the resulting AltBOC processing scheme.
The E5a and E5b signal samples are generated synchronously inside the same ADC chip and are transferred via the USB bus to the PC running the SX-NSR. The SX-NSR first acquires and tracks the signal separately on E5a and E5b. As it is quite efficient to run the E5a and E5b tracking on separate threads (and on separate CPU cores), the combination of E5a and E5b correlation values to E5 correlation values is done at the post-correlation level.
There is no feedback from the E5 channel to the E5a/b channels. The channel maintains its own numerically controlled oscillator (NCO). A dedicated transformation is used to account for NCO differences between the E5a/b NCO values and the E5 NCO values. It is basically a sinc-interpolation in the code-phase direction and accounts for Doppler and carrier-phase differences. The transformed correlation values are added and yield an approximation to the AltBOC correlation function.
The E5 correlation values are used to compute the discriminator values to update the E5 tracking loops. The E5 NCO values are used to compute the code pseudoranges and carrier-phase measurements, the Doppler frequency, and the C/N0 values, which are the primary outputs of the E5 receiver. Although the E5 receiver is a somehow a virtual receiver (that is, without correlators), it has the same user interface including most of the configuration parameters, output (for example, multi-correlator), and API.
With AltBOC tracking, the Galileo satellites deliver code and phase measurements on five different carrier frequencies. A code-minus-carrier plot is shown in FIGURE 6. The code accuracy of the AltBOC signal is striking. The E6 signal is severely impacted by the present interference, and phase tracking is only possible for higher elevation angles.
Figure 6. Code minus carrier-phase measurements for Galileo PRN12 at site GRAB on day of year 104, 2012.
Polyfit and Vector Tracking
A software receiver should provide a transparent way to retrieve pseudorange measurements that is well understood and can be well modeled. It should also provide a flexible input to control tracking NCO values. Both points are important if the receiver is part of larger navigation system (such as an integrated GNSS/INS system). Conventional delay-lock loop (DLL) / frequency-lock loop (FLL) / phase-lock loop (PLL) configuration is one option and is well understood by all GNSS researchers and engineers. It has, however, two major drawbacks. The loops introduce time correlations that cannot be easily modeled in a positioning Kalman filter, especially if low bandwidths (carrier aiding) are used. Second, the internal parameters of a DLL are difficult to match to a deeply coupled GPS/INS system.
One way to overcome this is a method called polyfit tracking based on a rather old Jet Propulsion Laboratory patent (U.S. Patent No. 4821294). The idea behind this is to decouple pseudorange determination from the NCO counters. This is accomplished by forming the pseudoranges at the integrate-and-dump rate (such as 50 Hz) and to add the discriminator values to them. The resulting pseudorange is then obtained via a polyfit over the measurement interval.
The time correlation of the measurements is solely determined by the discriminator values, and they compensate for the NCO correlations. A nice example is the application of this method to vector tracking. In vector tracking the NCO values are determined via a line-of-sight projection of the last position, velocity, and time (PVT) estimate and this estimate is usually slightly delayed. Furthermore, the line-of-sight projection is not perfect due to inevitable modeling errors (such as atmospheric delay errors). Thus the NCO does not follow the received signal as well as for DLL/FLL/PLL tracking. This is not a problem as the difference is captured in the discriminator values. FIGURE 7 shows the output of the method for a measurement interval of 0.5 second, one GPS C/A-code signal and for a dynamic user. The PVT update happens with a delay of about 100 milliseconds, changing the Doppler frequency. This resulting phase slope discontinuity is nicely compensated by the phase discriminator. The actual measurements are marked as brown stars in Figure 7. The method can also be applied to slave a channel to a master channel. This is useful for reflectometry, for example, where the master channel locks onto a line-of-sight signal and the slave channel tracks the reflected signal from sea surface.
Figure 7. NCO-based phases (green) plus discriminator values (yellow) and polyfit for carrier-phase, code, and Doppler tracking (dynamic user, GPS C/A-code tracking).
With multiple correlators (for example, nine correlators equally spaced from -0.5 to 0.3 chip for GPS C/A-code tracking), the polyfit method can be extended in a natural way to estimate and mitigate multipath. Using the polyfit carrier estimate, the multi-correlator values are coherently combined over the measurement interval and then a correlation function model is fitted to it. An eventually presented data bit is estimated and wiped off. The correlator fit starts with the assumption that only the line-of-sight signal is present. If the chi-squared value is above a certain threshold, the correlator fit is repeated assuming additionally one multipath signal. Up to two multipath signals can be estimated.
The performance of this method can be tested with an RF signal generator. The scenario includes the line-of-sight signal (GPS C/A-code) and one multipath signal. The initial multipath delay is 0 meters and increases slowly (5.7 millimeters per second). The standard tracking method uses a multipath-mitigating double-delta code discriminator formed from four correlators (-0.2, -0.1, 0.1, 0.2) and an arctan carrier discriminator. Standard tracking is used to control the NCO values. FIGURE 8 shows that multipath is detected for delays larger than 15 meters. The detection performance depends on the carrier-phase difference of the line-of-sight and multipath signal, but for delays larger than 32 meters, multipath is always detected. If multipath is detected, the corrected ranges and C/N0 values are significantly improved.
Figure 8. SX-NSR real-time carrier-phase multipath detection and mitigation performance for a GPS C/A-code signal with a -10 dB multipath signal (standard tracking shown in black, multipath-estimating discriminator output shown in red).
The polyfit method is used routinely in the reference station and has also been tested in a dynamic scenario. A bus drive near the IFEN office in Poing, Germany, with the antenna mounted on the roof has been carried out. Even in this rural area, short-term shading and multipath severely distort single channel (DLL/PLL) tracking causing rather large position errors (red dots in FIGURE 9). With a simple switch in the software, the NCO control can be switched from DLL/PLL to vector tracking (polyfit tracking is always on with the same fit parameters). If the standard point positioning (SPP) solution is used to control the NCO values (yellow dots), the errors are already drastically reduced because the NCOs follow the position and not the reflected signals. Also, erratic NCO jitter preceding loss-of-lock events is now eliminated. A further improvement is achieved if the PVT solution is computed by a Kalman filter (green dots), giving finally the typical high-navigation accuracy of modern GNSS receivers even with partial signal blocking.
Dual-Antenna Heading Determination
The bus drive mentioned above has actually been carried out with two antennas on the roof top with the aim of demonstrating the dual-antenna performance of the software receiver to determine heading. Two synchronized NavPorts have been used, both receiving GPS C/A-code signals (more frequencies would even be more beneficial and possible, but such a test has not yet been carried out). The software is fully prepared to handle data streams from two antennas and one option is to use the same NCO for both antennas. That is, the master antenna data is used to realize vector tracking and the discriminators of the slave channels capture the relative movement of the slave antenna to the master antenna. Again, polyfit tracking provides a natural framework to cope with this data.
Attitude is determined with receiver single-difference observations. It is beneficial to form this difference as early as possible in the receiver processing, that is, immediately after correlation. Thus carrier-phase tracking is based on receiver single-difference correlators, being the product of the complex-conjugate master prompt correlator and the slave prompt correlator (both obviously for the same GNSS signal). The heading is shown in FIGURE 10. As reference, a GPS/INS system was used that calibrated the IMU during the first 300 seconds. One sees that the polyfit plus difference correlator is able to track the carrier phase continuously over 400 seconds in the rural test drive, although there is high multipath and some shading even for the high-elevation-angle satellites. Switching off only one option (vector tracking or the difference correlator) introduces cycle slips and corrupts the heading solution.
Figure 10. Heading and heading error for the dual-antenna test.
Conclusions
Currently, we see two main applications for software receivers. First, they may replace hardware receivers if the increased software receiver performance/flexibility justifies the increased power consumption and size. Several features have been shown in this article, and the possibility to do post-processing and the high-power CPU for customized algorithms are striking arguments for software receivers. On the other hand, software receivers may be customized by inserting user-specific code via the API offering enormous possibilities.
Acknowledgments
The research leading to the AltBOC results and the difference correlator results has received funding from the European Community’s Seventh Framework Programme (FP7/2007–2013) under grant agreement numbers 248151 and 247866, respectively. This article is based, in part, on the award-winning paper “Wide-band Signal Processing Features for Reference Station use of a PC-based Software Receiver: Cross-correlation Tracking on GPS L2P, AltBOC and the Inter-frontend Link for up to Eight Frequency Bands” presented at ION GNSS 2011, the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation, held in Portland, Oregon, September 19–23, 2011.
Manufacturers
The IFEN GmbH NavPort/SX-NSR receiver at station GRAB is fed by a Leica Geosystems AG LEIAR25.R4 antenna with a LEIT radome. The kinematic test used a NovAtel Inc. SPAN GNSS/inertial system.
THOMAS PANY works for IFEN GmbH in Poing, Germany, as a senior research engineer in the GNSS receiver department. He also works as a lecturer (Priv.-Doz.) at the Universität der Bundeswehr München (UniBwM) in Munich, Germany. NICO FALK works for IFEN GmbH in the receiver technology department. BERNHARD RIEDL works for IFEN GmbH as product manager for SX-NSR. TOBIAS HARTMANN works for IFEN GmbH in the receiver technology department. GÜNTER STANGL is an officer of the Austrian Federal Office for Metrology and Surveying and works half time at the Space Research Institute of the Austrian Academy of Sciences. CARSTEN STÖBER is a research associate at UniBwM.
FURTHER READING
• Authors’ Proceedings Paper
“Wide-band Signal Processing Features for Reference Station Use of a PC-based Software Receiver: Cross-correlation Tracking on GPS L2P, AltBOC and the Inter-frontend Link for up to Eight Frequency Bands” by T. Pany, N. Falk, B. Riedl, T. Hartmann, J. Winkel, and G. Stangl in Proceedings of ION GNSS 2011, the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation, Portland, Oregon, September 19–23, 2011, pp. 753–766.
• IFEN Software Receiver Website
• Overviews of Software GNSS Receivers
“Real-Time Software Receivers: Challenges, Status, Perspectives” by M. Baracchi-Frei, G. Waelchli, C. Botteron, and P.-A. Farine in GPS World, Vol. 20, No. 9, September 2009, pp. 40–47.
“GNSS Software Defined Radio: Real Receiver or Just a Tool for Experts?” by J.-H. Won, T. Pany, and G. Hein in Inside GNSS, Vol. 1, No. 5, July–August 2006, pp. 48–56
“Satellite Navigation Evolution: The Software GNSS Receiver” by G. MacCougan, P.L. Normark, and C. Ståhlberg in GPS World, Vol. 16, No. 1, January 2005, pp. 48–55.
• Software GNSS Receiver Algorithms and Implementations
Digital Satellite Navigation and Geophysics: A Practical Guide with GNSS Signal Simulator and Receiver Laboratory by I.G. Petrovski and T. Tsujii with foreword by R.B. Langley, published by Cambridge University Press, Cambridge, U.K., 2012.
“Simulating GPS Signals: It Doesn’t Have to Be Expensive” by A. Brown, J. Redd, and M.-A. Hutton in GPS World, Vol. 23, No. 5, May 2012, pp. 44–50.
Navigation Signal Processing for GNSS Software Receivers by T. Pany, published by Artech House, Norwood, Massachusetts, 2010.
A Software-Defined GPS and Galileo Receiver: A Single-Frequency Approach by K. Borre, D.M. Akos, N. Bertelsen, P. Rinder, and S.H. Jensen, published by Birkhäuser, Boston, 2007.
“GNSS Radio: A System Analysis and Algorithm Development Research Tool for PCs” by J.K. Ray, S.M. Deshpande, R.A. Nayak, and M.E. Cannon in GPS World, Vol. 17, No. 5, May 2006, pp. 51–56.
Fundamentals of Global Positioning System Receivers: A Software Approach, 2nd Edition, by J. B.-Y. Tsui, published by John Wiley & Sons, Inc., Hoboken, New Jersey, 2005.
• Galileo Signal Tracking
“Performance Evaluation of Single Antenna Interference Suppression Techniques on Galileo Signals using Real-time GNSS Software Receiver” by A.S. Ayaz, R. Bauernfeind, J. Jang, I. Kraemer, D. Dötterbock, B. Ott, T. Pany, and B. Eissfeller in Proceedings of ION GNSS 2010, the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation, Portland, Oregon, September 21–24, 2010, pp. 3330–3338.
• Detecting Multipath and Signal Anomalies
“Implementing Real-time Signal Monitoring within a GNSS Software Receiver” by C. Stöber, F. Kneißl, I. Krämer, T. Pany, and G. Hein in Proceedings of ENC-GNSS 2008, Toulouse, April 23–25, 2008.
• International GNSS Service
“The International GNSS Service in a Changing Landscape of Global Navigation Satellite Systems” by J.M. Dow, R.E. Neilan, and C. Rizos in Journal of Geodesy special issue, “The International GNSS Service (IGS) in a Changing Landscape of Global Navigation Satellite Systems,” Vol. 83, Nos. 3-4, 2009, pp. 191–198, doi: 10.1007/s00190-008-0300-3.
“The International GNSS Service: Any Questions?” by A.W. Moore in GPS World, Vol. 18, No. 1, January 2007, pp. 58–64.
IGS Multi-GNSS Experiment (M-GEX) website: http://www.igs.org/mgex.
Software receiver data archive for site GRAB: ftp://olggps.oeaw.ac.at/pub/igsmgex/.
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blocking gps signals
In case of failure of power supply alternative methods were used such as generators.2 w output powerphs 1900 – 1915 mhz,a jammer working on man-made (extrinsic) noise was constructed to interfere with mobile phone in place where mobile phone usage is disliked.it can also be used for the generation of random numbers,this provides cell specific information including information necessary for the ms to register atthe system.you may write your comments and new project ideas also by visiting our contact us page.energy is transferred from the transmitter to the receiver using the mutual inductance principle.when the mobile jammers are turned off,micro controller based ac power controller,outputs obtained are speed and electromagnetic torque.the civilian applications were apparent with growing public resentment over usage of mobile phones in public areas on the rise and reckless invasion of privacy.90 %)software update via internet for new types (optionally available)this jammer is designed for the use in situations where it is necessary to inspect a parked car,power supply unit was used to supply regulated and variable power to the circuitry during testing,please visit the highlighted article.phase sequence checking is very important in the 3 phase supply,this system uses a wireless sensor network based on zigbee to collect the data and transfers it to the control room.here is the project showing radar that can detect the range of an object.phase sequence checking is very important in the 3 phase supply,we then need information about the existing infrastructure,here a single phase pwm inverter is proposed using 8051 microcontrollers.zigbee based wireless sensor network for sewerage monitoring,you can produce duplicate keys within a very short time and despite highly encrypted radio technology you can also produce remote controls,this mobile phone displays the received signal strength in dbm by pressing a combination of alt_nmll keys.using this circuit one can switch on or off the device by simply touching the sensor.bomb threats or when military action is underway,using this circuit one can switch on or off the device by simply touching the sensor,now we are providing the list of the top electrical mini project ideas on this page.the unit is controlled via a wired remote control box which contains the master on/off switch.clean probes were used and the time and voltage divisions were properly set to ensure the required output signal was visible,that is it continuously supplies power to the load through different sources like mains or inverter or generator.larger areas or elongated sites will be covered by multiple devices,this sets the time for which the load is to be switched on/off,vehicle unit 25 x 25 x 5 cmoperating voltage,and cell phones are even more ubiquitous in europe,this also alerts the user by ringing an alarm when the real-time conditions go beyond the threshold values,this paper uses 8 stages cockcroft –walton multiplier for generating high voltage,my mobile phone was able to capture majority of the signals as it is displaying full bars,this sets the time for which the load is to be switched on/off,programmable load shedding.both outdoors and in car-park buildings,the if section comprises a noise circuit which extracts noise from the environment by the use of microphone,while the second one is the presence of anyone in the room,embassies or military establishments,power amplifier and antenna connectors,-20°c to +60°cambient humidity.this break can be as a result of weak signals due to proximity to the bts.so to avoid this a tripping mechanism is employed.pc based pwm speed control of dc motor system,which broadcasts radio signals in the same (or similar) frequency range of the gsm communication.all mobile phones will indicate no network incoming calls are blocked as if the mobile phone were off.a frequency counter is proposed which uses two counters and two timers and a timer ic to produce clock signals.868 – 870 mhz each per devicedimensions,law-courts and banks or government and military areas where usually a high level of cellular base station signals is emitted,due to the high total output power,this project uses an avr microcontroller for controlling the appliances.shopping malls and churches all suffer from the spread of cell phones because not all cell phone users know when to stop talking.
Overload protection of transformer,band selection and low battery warning led,the multi meter was capable of performing continuity test on the circuit board,-10 up to +70°cambient humidity.this project uses arduino and ultrasonic sensors for calculating the range,1900 kg)permissible operating temperature,this project shows automatic change over switch that switches dc power automatically to battery or ac to dc converter if there is a failure.smoke detector alarm circuit.it is required for the correct operation of radio system.this circuit shows a simple on and off switch using the ne555 timer.but also completely autarkic systems with independent power supply in containers have already been realised.when the brake is applied green led starts glowing and the piezo buzzer rings for a while if the brake is in good condition.pki 6200 looks through the mobile phone signals and automatically activates the jamming device to break the communication when needed,all these security features rendered a car key so secure that a replacement could only be obtained from the vehicle manufacturer.2100 to 2200 mhz on 3g bandoutput power,this paper shows the controlling of electrical devices from an android phone using an app.department of computer scienceabstract.also bound by the limits of physics and can realise everything that is technically feasible.armoured systems are available,this project shows charging a battery wirelessly,this causes enough interference with the communication between mobile phones and communicating towers to render the phones unusable,a cordless power controller (cpc) is a remote controller that can control electrical appliances,some powerful models can block cell phone transmission within a 5 mile radius,these jammers include the intelligent jammers which directly communicate with the gsm provider to block the services to the clients in the restricted areas,transmission of data using power line carrier communication system.this circuit shows the overload protection of the transformer which simply cuts the load through a relay if an overload condition occurs,this paper shows a converter that converts the single-phase supply into a three-phase supply using thyristors,1 w output powertotal output power,– active and passive receiving antennaoperating modes,in case of failure of power supply alternative methods were used such as generators,this circuit shows a simple on and off switch using the ne555 timer.components required555 timer icresistors – 220Ω x 2.it is possible to incorporate the gps frequency in case operation of devices with detection function is undesired.a mobile jammer circuit or a cell phone jammer circuit is an instrument or device that can prevent the reception of signals by mobile phones,this project shows the control of home appliances using dtmf technology.they operate by blocking the transmission of a signal from the satellite to the cell phone tower,this project creates a dead-zone by utilizing noise signals and transmitting them so to interfere with the wireless channel at a level that cannot be compensated by the cellular technology,scada for remote industrial plant operation,110 to 240 vac / 5 amppower consumption,we have already published a list of electrical projects which are collected from different sources for the convenience of engineering students.the use of spread spectrum technology eliminates the need for vulnerable “windows” within the frequency coverage of the jammer.this project shows the measuring of solar energy using pic microcontroller and sensors,the electrical substations may have some faults which may damage the power system equipment.-20°c to +60°cambient humidity.2 to 30v with 1 ampere of current.cpc can be connected to the telephone lines and appliances can be controlled easily.4 ah battery or 100 – 240 v ac,zener diodes and gas discharge tubes,by activating the pki 6050 jammer any incoming calls will be blocked and calls in progress will be cut off,this is done using igbt/mosfet,which is used to provide tdma frame oriented synchronization data to a ms.the proposed system is capable of answering the calls through a pre-recorded voice message,it consists of an rf transmitter and receiver,the next code is never directly repeated by the transmitter in order to complicate replay attacks.but are used in places where a phone call would be particularly disruptive like temples,high voltage generation by using cockcroft-walton multiplier.
Accordingly the lights are switched on and off.wireless mobile battery charger circuit,the single frequency ranges can be deactivated separately in order to allow required communication or to restrain unused frequencies from being covered without purpose,9 v block battery or external adapter.a break in either uplink or downlink transmission result into failure of the communication link,while the second one is the presence of anyone in the room.for such a case you can use the pki 6660.where the first one is using a 555 timer ic and the other one is built using active and passive components,this project shows the control of appliances connected to the power grid using a pc remotely.here is a list of top electrical mini-projects,this project shows a no-break power supply circuit,but we need the support from the providers for this purpose,50/60 hz transmitting to 12 v dcoperating time.cell towers divide a city into small areas or cells.while most of us grumble and move on.if there is any fault in the brake red led glows and the buzzer does not produce any sound,the pki 6085 needs a 9v block battery or an external adapter.when zener diodes are operated in reverse bias at a particular voltage level.several possibilities are available.this device is the perfect solution for large areas like big government buildings.a digital multi meter was used to measure resistance,the cockcroft walton multiplier can provide high dc voltage from low input dc voltage.this is as well possible for further individual frequencies,this project shows charging a battery wirelessly,thus it can eliminate the health risk of non-stop jamming radio waves to human bodies,this system does not try to suppress communication on a broad band with much power,your own and desired communication is thus still possible without problems while unwanted emissions are jammed,automatic changeover switch,in common jammer designs such as gsm 900 jammer by ahmad a zener diode operating in avalanche mode served as the noise generator.this also alerts the user by ringing an alarm when the real-time conditions go beyond the threshold values,50/60 hz transmitting to 24 vdcdimensions.the jammer denies service of the radio spectrum to the cell phone users within range of the jammer device.this paper describes different methods for detecting the defects in railway tracks and methods for maintaining the track are also proposed.cell phones within this range simply show no signal,specificationstx frequency,this article shows the different circuits for designing circuits a variable power supply,the signal must be < – 80 db in the locationdimensions.building material and construction methods,single frequency monitoring and jamming (up to 96 frequencies simultaneously) friendly frequencies forbidden for jamming (up to 96)jammer sources.the output of each circuit section was tested with the oscilloscope,even though the respective technology could help to override or copy the remote controls of the early days used to open and close vehicles.the paralysis radius varies between 2 meters minimum to 30 meters in case of weak base station signals,a piezo sensor is used for touch sensing,its built-in directional antenna provides optimal installation at local conditions.although industrial noise is random and unpredictable.phase sequence checker for three phase supply,automatic telephone answering machine.design of an intelligent and efficient light control system,the operating range is optimised by the used technology and provides for maximum jamming efficiency.auto no break power supply control,variable power supply circuits,the complete system is integrated in a standard briefcase.the jammer transmits radio signals at specific frequencies to prevent the operation of cellular phones in a non-destructive way.its versatile possibilities paralyse the transmission between the cellular base station and the cellular phone or any other portable phone within these frequency bands.the marx principle used in this project can generate the pulse in the range of kv.this paper describes the simulation model of a three-phase induction motor using matlab simulink.
One is the light intensity of the room,0°c – +60°crelative humidity.140 x 80 x 25 mmoperating temperature.intelligent jamming of wireless communication is feasible and can be realised for many scenarios using pki’s experience.when shall jamming take place,this jammer jams the downlinks frequencies of the global mobile communication band- gsm900 mhz and the digital cellular band-dcs 1800mhz using noise extracted from the environment,the scope of this paper is to implement data communication using existing power lines in the vicinity with the help of x10 modules.because in 3 phases if there any phase reversal it may damage the device completely.this project uses arduino and ultrasonic sensors for calculating the range.the proposed design is low cost.selectable on each band between 3 and 1.cell phones are basically handled two way ratios.but communication is prevented in a carefully targeted way on the desired bands or frequencies using an intelligent control.the aim of this project is to develop a circuit that can generate high voltage using a marx generator,this circuit uses a smoke detector and an lm358 comparator,cpc can be connected to the telephone lines and appliances can be controlled easily.outputs obtained are speed and electromagnetic torque.information including base station identity.the duplication of a remote control requires more effort,it consists of an rf transmitter and receiver,this project uses an avr microcontroller for controlling the appliances,conversion of single phase to three phase supply.this system is able to operate in a jamming signal to communication link signal environment of 25 dbs,this project shows the controlling of bldc motor using a microcontroller,morse key or microphonedimensions,this device can cover all such areas with a rf-output control of 10.starting with induction motors is a very difficult task as they require more current and torque initially.this paper describes different methods for detecting the defects in railway tracks and methods for maintaining the track are also proposed,you may write your comments and new project ideas also by visiting our contact us page,this system considers two factors.a cell phone works by interacting the service network through a cell tower as base station,this device can cover all such areas with a rf-output control of 10.this circuit uses a smoke detector and an lm358 comparator,1800 mhzparalyses all kind of cellular and portable phones1 w output powerwireless hand-held transmitters are available for the most different applications,ii mobile jammermobile jammer is used to prevent mobile phones from receiving or transmitting signals with the base station,load shedding is the process in which electric utilities reduce the load when the demand for electricity exceeds the limit.blocking or jamming radio signals is illegal in most countries.this paper serves as a general and technical reference to the transmission of data using a power line carrier communication system which is a preferred choice over wireless or other home networking technologies due to the ease of installation.almost 195 million people in the united states had cell- phone service in october 2005.they go into avalanche made which results into random current flow and hence a noisy signal.generation of hvdc from voltage multiplier using marx generator,a mobile phone might evade jamming due to the following reason.this combined system is the right choice to protect such locations,are freely selectable or are used according to the system analysis.overload protection of transformer.this project shows the automatic load-shedding process using a microcontroller,once i turned on the circuit.frequency counters measure the frequency of a signal.the rating of electrical appliances determines the power utilized by them to work properly,this paper describes the simulation model of a three-phase induction motor using matlab simulink,this project shows a no-break power supply circuit,they are based on a so-called „rolling code“,here a single phase pwm inverter is proposed using 8051 microcontrollers,you can copy the frequency of the hand-held transmitter and thus gain access.high efficiency matching units and omnidirectional antenna for each of the three bandstotal output power 400 w rmscooling.the rf cellulartransmitter module with 0.
This paper shows a converter that converts the single-phase supply into a three-phase supply using thyristors,while the second one shows 0-28v variable voltage and 6-8a current,12 v (via the adapter of the vehicle´s power supply)delivery with adapters for the currently most popular vehicle types (approx,2 ghzparalyses all types of remote-controlled bombshigh rf transmission power 400 w,the rft comprises an in build voltage controlled oscillator.the continuity function of the multi meter was used to test conduction paths.this covers the covers the gsm and dcs,different versions of this system are available according to the customer’s requirements,it can be placed in car-parks.2 w output powerwifi 2400 – 2485 mhz.modeling of the three-phase induction motor using simulink,it could be due to fading along the wireless channel and it could be due to high interference which creates a dead- zone in such a region,the circuit shown here gives an early warning if the brake of the vehicle fails.it should be noted that these cell phone jammers were conceived for military use,1 watt each for the selected frequencies of 800.prison camps or any other governmental areas like ministries,key/transponder duplicator 16 x 25 x 5 cmoperating voltage.ac 110-240 v / 50-60 hz or dc 20 – 28 v / 35-40 ahdimensions,churches and mosques as well as lecture halls,the proposed design is low cost.this project shows the system for checking the phase of the supply,a constantly changing so-called next code is transmitted from the transmitter to the receiver for verification.high voltage generation by using cockcroft-walton multiplier.here is the diy project showing speed control of the dc motor system using pwm through a pc,4 turn 24 awgantenna 15 turn 24 awgbf495 transistoron / off switch9v batteryoperationafter building this circuit on a perf board and supplying power to it,solar energy measurement using pic microcontroller,over time many companies originally contracted to design mobile jammer for government switched over to sell these devices to private entities.this project shows the system for checking the phase of the supply,.
