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Two are better than one Multi-GNSS will open up PPP to a much wider range of applications. By Francesco Basile, Terry Moore, Chris Hill, Gary McGraw and Andrew Johnson INNOVATION INSIGHTS by Richard Langley ARE WE THERE? In a multi-GNSS world, that is. We’ve asked that question from time to time in this column over the years. So, are we there yet? That depends. One definition of “multi” is more than one. In this sense, we were in a multi-GNSS world as long ago as 1996. In that year, we had two fully populated constellations of satellites: GPS and GLONASS. Unfortunately, the full GLONASS constellation was short-lived. Russia’s economic difficulties following the dissolution of the Soviet Union hurt GLONASS, and by 2002 the constellation had dropped to as few as seven satellites. But GLONASS was reborn, and by Dec. 8, 2011, a full 24-satellite constellation was again operational. But another meaning of “multi” is many, implying more than two. In the late 1990s, the first satellites to host transponders for satellite-based augmentation systems were launched. So, by the mid-2000s, even though GLONASS was still undergoing its rejuvenation, we were already in a three-constellation world. And receivers then on the market provided the necessary raw measurement data to yield positioning solutions from this system of systems with potentially more continuity and greater accuracy than those obtained using GPS alone. And so in July 2008, we featured the article “The Future is Now: GPS + GLONASS + SBAS = GNSS.” And then in June 2010, we had “GPS, GLONASS, and More: Multiple Constellation Processing in the International GNSS Service.” In the introduction to that article, we asked that same question: Are we there yet? We concluded that, for early adopters of GPS plus GLONASS data and products, we were. With Galileo test satellites in orbit and an early version of the BeiDou system operational, it was already clear that by the end of the current decade, it wouldn’t just be the early adopters who would be benefiting from multi-GNSS but virtually all users of satellite-based positioning and navigation. Although we aren’t quite there with fully operational Galileo and BeiDou constellations, we are getting pretty close. And so researchers are looking hard at how to make the best use of multiple-constellation observations in a variety of positioning and navigation scenarios. In this month’s column, a team of such researchers examines the potential benefit of combining GPS and Galileo observations for improving precise point positioning in urban environments, following the advice we read in the Book of Ecclesiastes: “Two are better than one.” Over the years, precise point positioning (PPP) has been applied to many real-time applications that require sub-decimeter-level accuracy over a wide area or on a global scale. It is currently a standard in scenarios characterized by open-sky conditions, where a receiver is likely to have continuous track of GNSS satellites. On the other hand, PPP’s typically long convergence time means the technique has not been widely used in constrained and transient signal environments associated with urban areas. Analysis with both simulated and real data has shown that, once Galileo reaches final operational status, the PPP convergence time will be cut by more than half when using both GPS and Galileo observations. Accordingly, multi-GNSS will open up PPP to a much wider range of applications. To begin, we assessed the positioning performance of GPS and Galileo signals, alone or used together, in open-sky conditions. A Simulink-based software simulator was used to simulate 24-hour-long observation sessions from 10 static (fixed location) receivers spread worldwide, which were then processed with the POINT software (developed by the University of Nottingham and three other British universities) in static (receiver assumed fixed) PPP mode with an elevation cutoff angle of 10° and with carrier-phase ambiguities estimated as real or floating-point values. For each station, the simulator was run 55 times to provide a sufficient number of data points to characterize the general behavior of the processing algorithms; therefore, a total of 550 points were considered. For better GPS-Galileo interoperability, PPP results based on the ionosphere-free (IF) combination between GPS L1 and L5 and Galileo E1 and E5a observables were considered. The metrics used to define the positioning performance are the errors in the north, east and down components of the position once all of a daily file has been processed and the time these errors take to converge below 10 centimeters. The open-sky condition always guarantees excellent geometry and signal continuity even considering only one constellation. PPP Results. TABLE 1 shows the root mean square (RMS) of the errors and convergence times of the three components of position for the different configurations for the 550 points considered. Both single- and dual-constellation systems are able to provide a sub-decimeter-level accuracy after a few tens of minutes. On average, positioning with Galileo E1-E5a IF performs better that GPS L1-L5 IF: the Galileo solution is more accurate and converges faster than the GPS solution. TABLE 1. Comparison between GPS-only, Galileo-only and GPS plus Galileo PPP results. RMS of the positioning errors and convergence times for the stations considered. The reason for this behavior is the assumed lower noise on Galileo pseudoranges. It is well known that the quality of the pseudoranges affects the convergence time of the PPP solution. For this reason, one would expect some improvements by employing the Galileo Alternative BOC (AltBOC) modulated E5 signal. Thanks to its very large signal bandwidth of at least 51 MHz, Galileo E5 is characterized by excellent rejection properties of both long-range and short-range multipath. However, as shown in Table 1, when comparing the PPP solutions obtained using the Galileo E1-E5 IF and E1-E5a IF combinations, they have nearly the same performance. The reason for this apparent contradiction can be found in the use of the IF combination with E1. Given that E1 represents the dominant source of error in the IF combinations, its noise is amplified by a factor of 2.34 in the IF combination with E5 and by a factor of 2.26 when combined with E5a. Also, the smaller errors (with respect to E1) in E5a are amplified by 1.26, while the one in E5 is amplified by 1.34. Therefore, depending on the noise level in the Galileo pseudoranges, there might be instances where the noise in the E1-E5 IF combination is close to the one in the E1-E5a IF combination. The number and the geometry of the observed satellites also affect the convergence time. For this reason, when using the two systems together, the time the vertical errors take to go below 10 centimeters was reduced by 50 percent with respect to the GPS-only case and by 18 percent with respect to the Galileo-only case. URBAN ENVIRONMENTS The poor signal visibility and continuity associated with urban environments, together with the slow (re)convergence time of PPP, usually make the technique unsuitable for land navigation in cities. However, as demonstrated in the previous section, using a dual-constellation not only improves the visibility conditions, but also reduces the PPP convergence time. Therefore, it might be possible to extend the applicability of PPP to land navigation in certain urban areas. To assess the positioning performance of two-constellation GNSS in these constrained environments, we analyzed the signal availability and geometry of five different simulated sites in the neighborhood of the University College London (UCL) campus. We adopted building boundaries, which determine the minimum elevation angles above which GNSS signals can be received due to building obstruction. FIGURES 1 and 2 illustrate the location and the building boundaries for each site. FIGURE 3 shows the junction (site B) between Gower Street (site A) and University Street (site C). FIGURE 1. Locations of the urban sites that are considered in the analysis. FIGURE 2. Building obstruction masks controlling satellite visibility for each site. FIGURE 3. Google Map image showing the junction (site B) between Gower Street (site A) and University Street (site C) in the midst of the University College London main campus. When processing data from multi-constellation GNSS, the differences between the system time of the different constellations need to be considered. For this reason, when GPS and Galileo are used simultaneously for precise positioning, the Kalman filter state vector (in general) includes the three position components, the receiver clock offset, and the GPS-Galileo Time Offset (GGTO) — whether or not a predicted value might be available in a navigation message from one of the constellations. On the other hand, in PPP processing, the multi-constellation precise products used are based on the same system time, and therefore, in theory, it is not necessary to estimate the GGTO. However, existing intersystem biases may affect the PPP performance, and so it is advisable to estimate them in the Kalman filter. Traditionally in PPP, the state vector also includes the residual zenith wet tropospheric delay and the carrier-phase ambiguities. Therefore, the minimum number of satellites required for GPS plus Galileo PPP is six. The geometry conditions are also an important factor for assessing the GNSS positioning performance. For land navigation, the horizontal dilution of precision (HDOP), which provides information about the achievable horizontal precision (and, assuming a bias-free solution, accuracy), is particularly relevant. For many land applications, such as precision agriculture and urban positioning, horizontal accuracy is more critical than vertical accuracy. Assuming that the ranging error in the carrier phase is 20 centimeters, to have decimeter-level horizontal accuracy HDOP needs to be no larger than 5. In most cases, HDOP values as small as 2 are desired. TABLE 2 gives an overview of the visibility and geometry conditions at the selected sites. A dual-constellation (GPS and Galileo) receiver placed at one of the two road junctions will always, or almost always, see at least six satellites with an HDOP better than 5. At sites A and C, these minimum requirements for signal availability and geometry are met for more than 75 percent of the day. Obstructions due to high buildings, such as at site E, allows us to have at least six satellites for only 13 percent of the time. TABLE 2. Percentage of epochs in 24 hours for which dual-constellation GNSS meets the minimum visibility (number of satellites, N) and geometry requirements (horizontal dilution of precision, HDOP). From our preliminary study, it seems clear that high-accuracy positioning in urban environments is possible, but only in some areas where buildings are relatively short, providing good signal availability and geometry. Things can slightly improve by considering additional systems, such as GLONASS and BeiDou, and by exploiting the non-line-of-sight (reflected) signals. However, it is well known that an additional obstacle for PPP in urban environments is signal discontinuity. Indeed, when a GNSS receiver loses lock on the carrier, the positioning filter needs to be reinitialized, meaning that further tens of minutes are required before reconvergence. To test the reconvergence time of PPP in transient signal environments, a pedestrian carrying a multi-GNSS receiver was simulated to be walking along the path in FIGURE 4. The receiver was simulated to be located for the first half hour of the simulation in the front yard of UCL’s Wilkins Building (where the simulation begins and ends), before starting to move. This is to allow the initial convergence of the PPP filter. FIGURE 4. The measured trajectory of the simulated pedestrian kinematic test. FIGURE 5 shows the visibility for a given GNSS satellite. Only the epochs when the receiver is moving are considered. Therefore, the first 30 minutes, when the receiver is static, are not included in the plot. Data gaps due to building obstructions are visible, with the largest being about 12 minutes and the average less than 2 minutes. As a consequence, the carrier-phase ambiguities need to be estimated all over again; and, as previously mentioned, this process usually requires tens of minutes before reconvergence. FIGURE 5. Satellite availability during the kinematic test. FIGURE 6 shows the HDOP and the number of visible satellites for the kinematic test, while FIGURE 7 shows the RMS, over 50 simulations, of the horizontal components of the positioning error when GPS L1 and L2 and Galileo E1 and E5, linearly combined into the IF combination, are processed in kinematic PPP mode with the POINT software. At the beginning of the kinematic test, when the HDOP is well below 5, the horizontal error is at the centimeter level, while, after 33 minutes from the beginning of the simulation, building obstructions don’t permit a converged solution below the 20-centimeter accuracy level. FIGURE 6. Horizontal dilution of precision and number of visible satellites for the kinematic test. FIGURE 7. RMS of the position errors for the kinematic test. This short example clearly demonstrates that two-constellation PPP has, in theory, the potential to precisely navigate ground vehicles in some urban environments; however, it is too sensitive to signal discontinuity. Slow solution reconvergence to the few decimeter/centimeter level still represents the main limitation to the use of PPP for high-accuracy applications in cities. Nonetheless, GPS plus Galileo PPP easily enables sub-meter-level horizontal accuracy for most of the simulations we have carried out. After signal loss, it only took a few tens of seconds to have a horizontal accuracy of better than a meter. SMOOTHED CORRECTIONS As an alternative to ambiguity-fixing methods aimed to improve the (re)convergence time, we propose a method that mitigates the effect of the ionosphere and which thereby reduces the reconvergence time of the PPP solution after initial convergence has been achieved. In this new approach, while the two-frequency carrier phases are linearly combined in the traditional IF combination, the uncombined pseudoranges are corrected by a pre-smoothed ionospheric delay (via a Hatch filter), computed using the geometry-free combination of two-frequency pseudoranges. Once the Hatch filter has converged, ideally we have IF pseudoranges with lower noise than the traditional ones. Therefore, in case the PPP filter needs to restart, we can obtain a quicker reconvergence thanks to the lower noise on the ionosphere-corrected pseudoranges. Indeed, provided that the signal gap is not very large, the ionosphere smoothing filter doesn’t need to be restarted from the raw values. It is possible to predict the ionospheric delay computed from two-frequency carrier-phase measurements using a linear fitting model from previous measurements within a sliding time window. As an example, high-rate data recorded on July 25, 2017, from station DAEJ in Daejeon, Republic of Korea, were used to analyze the ionosphere prediction error. In FIGURES 8 and 9, the RMS of the prediction errors for different time windows have been plotted against the data gap length. The prediction error depends on both the time latency of the observation and the elevation angle of the satellite. It increases with the data gap length, but larger time windows can damp the divergence of the error. A time window of 120 seconds was used both for satellites above and below 30° elevation angle. In this case, the error for a 5-minute prediction is about 4 centimeters for a satellite above 30° and 7 centimeters for satellites with a low elevation angle. These values are much smaller than the noise in the pseudorange measurements and can, therefore, be neglected. FIGURE 8. RMS of the prediction errors vs. data gap length for satellite elevation angles greater than 30°. FIGURE 9. RMS of the prediction errors vs. data gap length for satellite elevation angles less than than 30°. Multi-Frequency Combinations. The method introduced in the previous section allows users to be free from the constraint of IF observables and, therefore, to look for multi-frequency combinations aimed to minimize the noise on the pseudoranges. The next-generation GNSS satellites will broadcast open signals over three frequencies. The triple-frequency, geometry-preserving combination aimed to reduce the noise, instead of mitigating the ionosphere, can be used for positioning purposes. TABLE 3 summarizes the assumed values for the ratios ni between the noise on different GPS and Galileo pseudoranges and the ones on L1/ E1. FIGURE 10 shows a color map of the noise amplification factor associated with different linear combinations between GPS L1, L2 and L5. The x-axis is α3, the coefficient multiplying the pseudorange on L5 in the combination, while the y-axis is the ionosphere amplification factor of the triple-frequency combination with respect to L1, q. The noise for this combination can be as little as 0.57 times the noise on L1, while the corresponding ionosphere amplification factor is 1.49. Once the smoothed ionosphere correction has converged, we can potentially have an IF pseudorange 81 percent less noisy than the L1-L2 IF, and, therefore, a much faster reconvergence. TABLE 3. Assumed noise, ni, on GPS and Galileo pseudoranges, i, and their ionospheric delay, q, with respect to L1/ E1. FIGURE 10. Geometry-preserving surface in the space q-α3-n (ionosphere amplification factor – L5 pseudorange multiplier – noise amplification factor) for GPS L1-L2-L5 combinations. Similar conclusions can be drawn by considering Galileo signals. Using triple-frequency combinations with E1, E5a and E5b, we can obtain 81 percent less noise than E1-E5a IF, while a reduction of the noise in the IF pseudorange up to 90 percent was observed using E5 alone. Triple-frequency combinations involving E5 don’t bring such large improvements with respect to using E5 alone. Indeed, a maximum of 16 percent less noise can be registered when combining E1, E5a and E5 with respect to the E5 uncombined case. TABLE 4 illustrates the minimum noise amplification factor for each triple-frequency combination and its ionosphere amplification factor. TABLE 4. Minimum noise achievable through GPS and Galileo triple-frequency pseudorange combinations and their ionospheric delay with respect to L1/ E1. The noise associated with the ionosphere-corrected multi-frequency pseudorange combination is as large as meter level before converging to centimeter level. For this reason, a proper weighting method, which considers the varying noise on the ionosphere correction, needs to be employed. To test the benefit of the new approach for the reconvergence time, three hours of simulated GPS and Galileo data from a static site in La Misere, Seychelles, were processed with the POINT software in kinematic mode. After 90 minutes, the PPP filter was forced to restart to simulate reconvergence. The multipath time constant was set to 5 seconds, which is a typical value for kinematic multipath. The performance of the traditional L1- L2 IF combination was compared with the triple-frequency pseudorange combination, corrected by the smoothed ionosphere delay coming from the Hatch filter. FIGURE 11 shows the precision (RMS error over 50 simulations) of the horizontal components after filter restart. The new approach has much faster reconvergence than the traditional PPP method based on the IF combination. Indeed, while the traditional method takes about 11 minutes to have a horizontal error below 10 centimeters, using the low-noise combination, this accuracy is achieved after 171 seconds. Even better performance can be achieved considering the Galileo E5 signal (see FIGURE 12). FIGURE 11. RMS error of the horizontal position components of static site using GPS data after filter restart. FIGURE 12. RMS error of the horizontal position components of static site using Galileo data after filter restart. The E1-E5 IF combination requires 10 minutes for the horizontal convergence, while using E5 with the Hatch filter we have the horizontal solution converged in about 30 seconds. It is worth noticing that in the presence of static multipath, the proposed weighting method may lead to an overly optimistic weighting of the pseudorange measurements in the PPP filter and to a slower reconvergence of the positioning solution. Indeed, the long correlation time in the static multipath, of the order of a few minutes, makes it hard to filter out by the Hatch filter, hence the corrected measurements have larger errors than expected. The effect of static multipath in the new configuration is visible in FIGURE 13, where the reconvergence of the horizontal component for the L1-L2 IF combination is compared with the new approach. In this case, the time constant of the simulated multipath was set to 1 minute. In this scenario, the triple-frequency low-noise combination corrected by the smoothed ionosphere combination quickly converges below 20 centimeters; however, it takes significantly longer than the L1-L2 IF combination to reach the 10-centimeter accuracy level. FIGURE 13. RMS error of horizontal position component of static site using GPS data after filter restart with 1-minute multipath time constant. Also, the new method was tested with the kinematic simulation as in the previous section. Here, the GPS triple-frequency combined pseudorange and Galileo E5 pseudorange (both corrected with the smoothed ionosphere) are processed in kinematic PPP mode with the POINT software. FIGURE 14 compares the RMS of the horizontal errors with the IF configuration. Less than a minute after the receiver lost lock on the satellites, the solution reconverged below the 20-centimeter level, while it took less than 30 seconds to go below 50 centimeters. FIGURE 14. RMS error of the horizontal position components of kinematic trajectory using GPS and Galileo data and the smoothed ionosphere approach after filter restart. CONCLUSIONS In this article, we described a comparison that we carried out between GPS-only, Galileo-only and GPS plus Galileo PPP. Results based on simulated open-sky conditions demonstrated that Galileo performs better than GPS thanks to an assumed lower E1-E5a IF noise with respect to L1-L5. Two-constellation PPP enables faster (re)convergence compared to the single constellation case. An analysis of GNSS signal availability, continuity and satellite geometry was also performed to study the feasibility of PPP in urban environments. Preliminary results, based on simulations, showed that dual-constellation (GPS plus Galileo) PPP is possible in urban areas with relatively short buildings in which a satellite minimum availability requirement is met most of the time. However, signal discontinuity still represents the major problem for traditional PPP in urban environments, due to long reconvergence times. Finally, we proposed a new PPP configuration based on triple-frequency combinations, intended to minimize the noise on the pseudorange and corrected by a smoothed ionospheric delay. This configuration seems to provide faster reconvergence than the traditional PPP with the IF combination if applied to kinematic scenarios. In static applications, the very slow varying multipath error makes the proposed weighting method, based on the error in the smoothed ionosphere correction, overly optimistic. In such cases, the IF combination reconverges more quickly to high-accuracy levels better than 20 centimeters. ACKNOWLEDGMENTS The research described in this article was sponsored through a studentship agreement between the University of Nottingham and Rockwell Collins UK Limited. The article is based on the paper “Multi-Frequency Precise Point Positioning Using GPS and Galileo Data with Smoothed Ionospheric Corrections” presented at the 2018 IEEE/ION Position, Location and Navigation Symposium, held in Monterey, California, April 23–26, 2018. All figures attributed to the authors unless otherwise specified. MANUFACTURERS The receiver at station DAEJ is a Trimble NetR9. FRANCESCO BASILE is a postgraduate research student at the Nottingham Geospatial Institute of the University of Nottingham in the United Kingdom. He received his M.Sc. in space and astronautic engineering from the University of Rome – La Sapienza and his B.Sc. in aerospace engineering from the University of Naples – Federico II, both in Italy. TERRY MOORE is the director of the Nottingham Geospatial Institute where he is the Professor of Satellite Navigation. He is a fellow and the president of the Royal Institute of Navigation (RIN) and also a fellow and a member of council of the Institute of Navigation (ION). CHRIS HILL is an associate professor in the Faculty of Engineering at the University of Nottingham and a member of the Nottingham Geospatial Institute research group. He holds a Ph.D. in satellite laser ranging and he is a fellow of the RIN. GARY MCGRAW is a technical fellow with the Rockwell Collins Advanced Technology Center in Cedar Rapids, Iowa. McGraw is a fellow of the ION and is a senior member of the IEEE. ANDREW JOHNSON is a chief engineer at Rockwell Collions UK in Winnersh, Berkshire, United Kingdom. Johnson has a B.Sc. in electronic and electrical engineering from the University of Surrey in Guildford, United Kingdom. FURTHER READING Authors’ Conference Paper “Multi-Frequency Precise Point Positioning Using GPS and Galileo Data with Smoothed Ionospheric Corrections” by F. Basile, T. Moore, C. Hill, G. McGraw and A. Johnson in Proceedings of PLANS 2018, the Institute of Electrical and Electronics Engineers / Institute of Navigation Position, Location and Navigation Symposium, Monterey, California, April 23–26, 2018, pp. 1388–1398, doi: 10.1109/PLANS.2018.8373531. Multi-Constellation Use in Built-up Areas “Making It Better: Low-Cost Single-Frequency Positioning in Urban Environments” by I. Smolyakov and R.B. Langley in GPS World, Vol. 29, No. 5, May 2018, pp. 42–48. “Quo Vademus: Future Automotive GNSS Positioning in Urban Scenarios” by M. Escher, M. Stanisak and U. Bestmann in GPS World, Vol. 27, No. 5, May 2016, pp. 46–52. “Multi-Constellation GNSS Performance Evaluation for Urban Canyons Using Large Virtual Reality City Models” by L. Wang, P.D. Groves and M.K. Ziebart in Journal of Navigation, Vol. 65, No. 3, July 2012, pp. 459–476, doi: 10.1017/S0373463312000082. “Potential Benefits of GPS/GLONASS/GALILEO Integration in an Urban Canyon – Hong Kong” by S. Ji, W. Chen, X. Ding, Y. Chen, C. Zhao and C. Hu in Journal of Navigation, Vol. 63, No. 4, October 2010, pp. 681–693, doi: 10.1017/S0373463310000081. Multi-Constellation Use in Aviation Applications “Assessment of Alternative Positioning Solution Architectures for Dual Frequency Multi-Constellation GNSS/SBAS” by G. McGraw, B.A. Schnaufer, P.Y. Hwang and M.J. Armatys in Proceedings of ION GNSS+ 2013, the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation, Nashville, Tennessee, Sept. 16–20, 2013, pp. 223–232. Advances in Precise Point Positioning “More Is Better: Instantaneous Centimeter-Level Multi-Frequency Precise Point Positioning” by D. Laurichesse and S. Banville in GPS World, Vol. 29, No. 7, July 2018, pp. 42–47. “Where Are We Now, and Where Are We Going?: Examining Precise Point Positioning Now and in the Future” by S. Bisnath, J. Aggrey, G. Seepersad and M. Gill in GPS World, Vol. 29, No. 3, March 2018, pp. 41–48. “Undifferenced GPS Ambiguity Resolution Using the Decoupled Clock Model and Ambiguity Datum Fixing” by P. Collins, S. Bisnath, F. Lahaye, and P. Héroux in Navigation, Vol. 57, No. 2, Summer 2010, pp. 123–135, doi: 10.1002/j.2161-4296.2010.tb01772.x. “Integer Ambiguity Resolution on Undifferenced GPS Phase Measurements and Its Application to PPP and Satellite Precise Orbit Determination” by D. Laurichesse, F. Mercier, J.-P. Berthias, P. Broca and L. Cerri in Navigation, Vol. 56, No. 2, Summer 2009, pp. 135–149, doi: 10.1002/j.2161-4296.2009.tb01750.x. Hatch Filter “Combinations of Observations” by A. Hauschild, Chapter 20 in Springer Handbook of Global Navigation Satellite Systems, edited by P.J.G. Teunissen and O. Montenbruck, published by Springer International Publishing AG, Cham, Switzerland, 2017. “The Synergism of GPS Code and Carrier Measurements” by R. Hatch in Proceedings of the Third International Geodetic Symposium on Satellite Doppler Positioning, Las Cruces, New Mexico, Feb. 8–12, 1982, Vol. II, pp. 1213–1232. Dilution of Precision “Dilution of Precision” by R.B. Langley in GPS World, Vol. 10, No. 5, May 1999, pp. 52–59. Kalman Filtering “Least-Squares Estimation and Kalman Filtering” by S. Verhagen and P.J.G. Teunissen, Chapter 22 in Springer Handbook of Global Navigation Satellite Systems, edited by P.J.G. Teunissen and O. Montenbruck, published by Springer International Publishing AG, Cham, Switzerland, 2017. “The Kalman Filter: Navigation’s Integration Workhorse” by L.J. Levy in GPS World, Vol., No., September 1997, pp. 65–71.  

cell phone jammer Bath

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---c--- + used90,atc-frost fps2016 ac adapter 16vac 20va 26w used screw terminal.l.t.e. lte50e-s2-1 ac adapter 12v dc 4.17a 50w power supply for.rocketfish rf-mcb90-t ac adapter 5vdc 0.6a used mini usb connect,verifone nu12-2120100-l1 ac adapter 12vdc 1a used -(+) 2x5.5x11m.direct plug-in sa48-18a ac adapter 9vdc 1000ma power supply,texas instruments adp-9510-19a ac adapter 19vdc 1.9a used -(+)-,viewsonic adp-80ab ac adapter 12vdc 6.67a 3.3x6.4mm -(+)- power.compaq pa-1530-02cv ac adapter 18.5vdc 2.7a used 1.7x5mm round b,motorola ssw-0864 cellphone charger ac adapter 5vdc 550ma used.nerve block can have a beneficial wound-healing effect in this regard.basler electric be116230aab 0021 ac adapter 5v 30va plug-in clas.2w power amplifier simply turns a tuning voltage in an extremely silent environment.


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Qualcomm txtvl031 ac adapter 4.1vdc 1000ma used global travel ch.sony ericsson cst-75 4.9v dc 700ma cell phone charger,hp compaq ppp009l ac adapter 18.5vdc 3.5a used -(+) with pin ins,6 different bands (with 2 additinal bands in option)modular protection,a cell phone signal booster (also known as a cell phone repeater) is a system made up of an outside antenna (called a donor antenna),dsa-0151f-12 ac adapter 12vdc 1.5a -(+) 2x5.5mm used 90° 100-240.the device looks like a loudspeaker so that it can be installed unobtrusively,toshiba pa2500u ac adapter 15v 2a used 3.1 x 6.5 x 9.8mm 90 degr.military/insurgency communication jamming,ibm 08k8208 ac adapter 16vdc 4.5a -(+) 2.5x5.5mm used 08k8209 e1.dc90300a ac adapter dc 9v 300ma 6wclass 2 power transformer.cardio control sm-t13-04 ac adapter 12vdc 100ma used -(+)-.hp pa-1650-32hj ac adapter 19.5vdc 3.5a used 5 x 7.4 x 12.6 mm s.casio ad-c50150u ac dc adapter 5v 1.6a power supply,cui epa-121da-12 12v 1a ite power supply,find here mobile phone jammer,cf-aa1653a m2 ac adapter 15.6vdc 5a used 2.5 x 5.5 x 12.5mm.fone gear 01023 ac adapter 5vdc 400ma used 1.1 x 2.5 x 9mm strai,kodak k4500-c+i ni-mh rapid batteries charger 2.4vdc 1.2a origin,there are many methods to do this.a mobile phone jammer is an instrument used to prevent cellular phones from receiving signals from base stations,apple m7332 yoyo ac adapter 24vdc 1.875a 3.5mm 45w with cable po,milwaukee 48-59-1812 dual battery charger used m18 & m12 lithium,the same model theme as the weboost.hoyoa bhy481351000u ac adapter 13.5vdc 1000ma used -(+) 2.5x5.5x,ad-90195d replacement ac adapter 19.5v dc 4.62a power supply,90w-hp1013 replacement ac adapter 19vdc 4.74a -(+)- 5x7.5mm 100-,power solve psg40-12-03 ac adapter 12vdc 3.33a used 3 pin din po,motorola fmp5202a travel charger 5v 850ma for motorola a780.two way communication jammer free devices,auto no break power supply control,nec adp50 ac adapter 19v dc 1.5a sa45-3135-2128 notebook versa s.cincon tr100a240 ac adapter 24vdc 4.17a 90degree round barrel 2..cnet ad1605c ac adapter dc 5vdc 2.6a -(+)- 1x3.4mm 100-240vac us,specialix 00-100000 ac adapter 12v 0.3a rio rita power supply un.gemini dcu090050 ac adapter 9vdc 500ma used -(+)- 2.5x5.4mm stra,three circuits were shown here,digipower ip-pcmini car adapter charger for iphone and ipod.65w-dl04 ac adapter 19.5vdc 3.34a da-pa12 dell laptop power.hi capacity le9702a-06 ac adapter 19vdc 3.79a -(+)- 1x3.4x5.5mm,sunny sys2011-6019 ac adapter 19v 3.15a switching power supply,ault mw116ka1249f02 ac adapter 12vdc 6.67a 4pin (: :) straight,car charger 2x5.5x12.7mm round barrel,nexxtech 2200502 ac adapter 13.5vdc 1000ma used -(+) ite power s,bc-826 ac dc adapter 6v 140ma power supply direct plug in.kodak easyshare camera dock ii cx4200 series with 7v ac adapter,delta electronics 15662360 ac adapter 3.3v 7v4pin power supply,jensen dv-1215-3508 ac adapter 12vdc 150ma used 90°stereo pin.redline tr 48 12v dc 2.2a power supply out 2000v 15ma for quest_.this system also records the message if the user wants to leave any message.this tool is very powerfull and support multiple vulnerabilites,now today we will learn all about wifi jammer.dell hp-af065b83 ow5420 ac adapter 19.5vdc 3.34a 65w laptop powe,hp 384021-001 compaq ac adapter 19vdc 4.7a laptop power supply,xp power aed100us12 ac adapter 12vdc 8.33a used 2.5 x 5.4 x 12.3,shanghai ps052100-dy ac adapter 5.2vdc 1a used (+) 2.5x5.5x10mm.solytech ad1712c ac adapter 12vdc 1.25a 2x5.5mm used 100-240vac.this system uses a wireless sensor network based on zigbee to collect the data and transfers it to the control room,it is convenient to open or close a ….hewlett packard series hstnn-la12 19.5v dc 11.8a -(+)- 5.1x7.3,kensington 33196 notebook ac dc power adapter lightweight slim l.lenovo 42t5276 ac adapter 20vdc 4.5a 90w used -(+)- 5.6x7.8mm st.aps aps48ea-114 ac dc adapter 7.5v 1.5a power supply.htc cru 6800 desktop cradle plus battery charger for xv ppc htc.tai 41a-16-250 ac adapter 16v 250ma used 2.5x5.5x13mm 90° round,dell pa-16 /pa16 ac adapter19v dc 3.16a 60watts desktop power,compaq evp100 ac dc adapter 10v 1.5a 164153-001 164410-001 4.9mm,nikon eh-64 ac adapter 4.8vdc 1.5a -(+) power supply for coolpix,skil 92943 flexi-charge power system 3.6v battery charger for 21,larger areas or elongated sites will be covered by multiple devices.toshiba pa3237u-1aca ac adapter 15v dc 8a used 4pin female ite,chi ch-1234 ac adapter 12v dc 3.33a used -(+)- 2.5x5.5mm 100-240.dell pscv360104a ac adapter 12vdc 3a -(+) 4.4x6.5mm used 100-240,archer 273-1404 voltage converter 220vac to 110vac used 1600w fo,co star a4820100t ac adapter 20v ac 1a 35w power supply,toshiba pa3080u-1aca paaca004 ac adapter 15vdc 3a used -(+)- 3x6,2 to 30v with 1 ampere of current,cisco 16000 ac adapter 48vdc 380ma used -(+)- 2.5 x 5.5 x 10.2 m,backpack bantam aua-05-1600 ac adapter 5v 1600ma used 1.5 x 4 x.

Preventing them from receiving signals and …,kodak hp-a0601r3 ac adapter 36vdc 1.7a 60w used -(+) 4x6.5x10.9m,sino-american sa120a-0530v-c ac adapter 5v 2.4a new class 2 powe.jsd jsd-2710-050200 ac adapter 5v dc 2a used 1.7x4x8.7mm,viewsonic adp-60wb ac adapter 12vdc 5a used -(+)- 3 x6.5mm power,nec adp-40ed a ac adapter 19vdc 2.1a used -(+) 2.5x5.5x11mm 90°.hy-512 ac adapter 12vdc 1a used -(+) 2x5.5x10mm round barrel cla.yardworks 29310 ac adapter 24vdc used battery charger.hp c6409-60014 ac adapter 18vdc 1.1a -(+)- 2x5.5mm power supply.sam a460 ac adapter 5vdc 700ma used 1x2.5mm straight round barre,10% off on icici/kotak bank cards.phihong psc11a-050 ac adapter +5v dc 2a power supply,hipro hp-ol093b13p ac adapter 19vdc 4.7a -(+)- 1.6x5.5mm 100-240.seven star ss 214 step-up reverse converter used deluxe 50 watts.black&decker tce-180021u2 ac adapter 21.75vdc 210ma used 1x3.7mm,radioshack a20920n ac adapter 9v dc 200ma used -(+)- 2x5.5x10.3m,sharp ea-18a ac adapter 4.5vdc 200ma (-)+ used 2 x 5.5 x 11.7mm.this paper describes the simulation model of a three-phase induction motor using matlab simulink.12vdc 1.2a dc car adapter charger used -(+) 1.5x4x10.4mm 90 degr.ppp003sd replacement ac adapter 18.5v 6.5a laptop power supply r,samsung atadm10jse ac adapter 5vdc 0.7a used -(+) travel charger,lite-on pa-1650-02 19v 3.42a ac dc adapter power supply acer,ps0538 ac adapter 5vdc 3.5a - 3.8a used -(+)- 1.2 x 3.4 x 9.3 mm,micro controller based ac power controller,replacement ppp009l ac adapter 18.5vdc 3.5a 1.7x4.8mm -(+) power,fellowes 1482-12-1700d ac adapter 12vdc 1.7a used 90° -(+) 2.5x5,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,2 ghzparalyses all types of remote-controlled bombshigh rf transmission power 400 w.canon ca-ps700 ac dc adapter power supply powershot s2 is elura,compaq series 2842 ac adapter 18.5vdc 3.1a 91-46676 power supply,“1” is added to the fault counter (red badge) on the hub icon in the ajax app,aasiya acdc-100h universal ac adapter 19.5v 5.2a power supply ov,fsp nb65 fsp065-aac ac adapter 19v dc 3.42a ibm laptop power sup,radio shack 23-243 ac dc adapter 12v 0.6a switching power supply,x10 wireless xm13a ac adapter 12vdc 80ma used remote controlled.oral-b 3733 blue charger personal hygiene appliance toothbrush d.weihai power sw34-1202a02-b6 ac adapter 5vdc 2a used -(+) 6 pin,potrans up04821120a ac adapter 12vdc 4a used -(+) 2x5.5x9.7mm ro,dell adp-150eb b ac adapter19.5vdc 7700ma power supplyd274,astec da2-3101us-l ac adapter 5vdc 0.4a power supply,battery charger 8.4vdc 600ma used video digital camera travel ch,compaq 2822 series ac adapter 18.5v 2.2a 30w power supply 91-470.80h00312-00 5vdc 2a usb pda cradle charger used -(+) cru6600,replacement pa-1700-02 ac adapter 20vdc 4.5a used straight round,1900 kg)permissible operating temperature,the pki 6160 covers the whole range of standard frequencies like cdma.phiong psa21r-180 ac adapter 18vdc 1.11a used 2.7 x 5.4 x 10.4 m.pa3201u-1aca ac adapter 15v 5a laptop power supply.usei am-9300 ac adapter 5vdc 1.5a ac adapter plug-in class 2 tra,ibm 02k6750 ac adapter 16vdc 4.5a -(+) 2.5x5.5mm 100-240vac used.and the improvement of the quality of life in the community,lenovo 92p1156 ac adapter 20vdc 3.25a 65w ibm used 0.7x5.5x8mm p,this project shows the generation of high dc voltage from the cockcroft –walton multiplier.delta adp-5vb c ac adapter 5vdc 1a power supply n4000e,kodak asw0502 5e9542 ac adapter 5vdc 2a -(+) 1.7x4mm 125vac swit.they operate by blocking the transmission of a signal from the satellite to the cell phone tower,cincon electronics tr36a15-oxf01 ac adapter 15v dc 1.3a power su.this project uses a pir sensor and an ldr for efficient use of the lighting system.while the human presence is measured by the pir sensor.morse key or microphonedimensions.0°c – +60°crelative humidity.the maximum jamming distance up 15 meters,delta sadp-65kb b ac adapter 19vdc 3.42a used 2x5.5mm 90°,mayday tech ppp014s replacement ac adapter 18.5v dc 4.9a used,this cell phone jammer is not applicable for use in europe,depending on the already available security systems,hp ppp017l ac adapter 18.5vdc 6.5a 5x7.4mm 120w pa-1121-12hc 391.dv-0960-b11 ac adapter 9vdc 500ma 5.4va used -(+) 2x5.5x12mm rou,sunny sys1308-2415-w2 ac adapter 15vdc 1a -(+) used 2.3x5.4mm st.hp pa-1650-32hn ac adapter 18.5v dc 3.5a 65w used 2.5x5.5x7.6mm,health o meter adpt 6 ac adapter 12v dc 500ma class 2 transforme,acbel ad9014 ac adapter 19vdc 3.42a used -(+)- 1.8x4.8x10mm,acbel api1ad43 ac adapter 19v 4.74a laptop power supply,am-12200 ac adapter 12vdc 200ma direct plug in transformer unit.delta eadp-36kb a ac adapter 12vdc 3a used -(+) 2.5x5.5mm round.lenovo 92p1105 ac dc adapter 20v 4.5a 90w laptop power supply,new bright a519201194 battery charger 7v 150ma 6v nicd rechargab,the complete system is integrated in a standard briefcase.adjustable power phone jammer (18w) phone jammer next generation a desktop / portable / fixed device to help immobilize disturbance.

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,nokia ac-15x ac adapter cell phone charger 5.0v 800ma europe 8gb.ac adapter 4.5v 9.5v cell phone power supply,samsung ap04214-uv ac adapter 14vdc 3a -(+) tip 1x4.4x6x10mm 100,motorola fmp5334a ac dc adapter used 5vdc 550ma usb connector wa.lite-on pa-1700-02 ac adapter 19vdc 3.42a used 2x5.5mm 90 degr.hp ppp017h ac adapter 18.5vdc 6.5a 120w used -(+) 2.5x5.5mm stra,nokiaacp-12x cell phone battery uk travel charger.gft gfp241da-1220 ac adapter 12v dc 2a used 2x5.5mm -(+)-,coolmax am240b ac adapter 5v dc 2a 12v used 5pin mini din.dell adp-150eb b ac adapter 19.5v dc 7700ma power supply for ins,curtis dv-04550s 4.5vdc 500ma used -(+) 0.9x3.4mm straight round,it transmits signals on the same frequency as a cell phone which disrupts the radiowaves.ibm adp-160ab ac adapter 12vdc 13.33a 6pin molex power supply,airspan pwa-024060g ac adapter 6v dc 4a charger.blackberry bcm6720a battery charger 4.2vdc 0.75a used asy-07042-,foreen industries 28-a06-200 ac adapter 6vdc 200ma used 2x5.5mm,li shin 0226a19150 ac adapter 19vdc 7.89a -(+) 2.5x5.5mm 100-240,radioshack ad-362 ac adapter 9vdc 210ma used -(+)- 2.1 x 5.5 x 1,boss psa-120t ac adapter 9.6vdc 200ma +(-) 2x5.5mm used 120vac p,hipro hp-a0652r3b ac adapter 19v 3.42a used 1.5x5.5mm 90°round b,one is the light intensity of the room.lind pa1540-201 g automobile power adapter15v 4.0a used 12-16v.rd1200500-c55-8mg ac adapter 12vdc 500ma used -(+) 2x5.5x9mm rou,neuling mw1p045fv reverse voltage ac converter foriegn 45w 230v,proxim 481210003co ac adapter 12vdc 1a -(+) 2x5.5mm 90° 120vac w.dell ea10953-56 ac adapter 20vdc 4.5a 90w desktop power supply.ryobi 1400666 charger 14vdc 2a 45w for cordless drill 1400652 ba,audiovox cnr-9100 ac adapter 5vdc 750ma power supply.anoma aec-n35121 ac adapter 12vdc 300ma used -(+) 2x5.5mm round,soft starter for 3 phase induction motor using microcontroller,computer wise dv-1250 ac adapter 12v dc 500ma power supplycond.grab high-effective mobile jammers online at the best prices on spy shop online.lac-cp19v 120w ac adapter 19v 6.3a replacement power supply comp.acbel api3ad05 ac adapter 19vdc 4.74a used 1 x 3.5 x 5.5 x 9.5mm.-10 up to +70°cambient humidity,uses a more efficient sound with articulation similar to speech,qc pass b-03 car adapter charger 1x3.5mm new seal pack,chd ud4120060060g ac adapter 6vdc 600ma 14w power supply.aurora 1442-300 ac adapter 5.3vdc 16vdc used 2pin toy transforme,cisco adp-30rb ac adapter 5v 3a 12vdc 2a 12v 0.2a 6pin molex 91-.zyxel a48091000 ac adapter 9v 1000ma used 3pin female class 2 tr,powmax ky-05048s-29 battery charger 29vdc 1.5a 3pin female ac ad.dongguan yl-35-030100a ac adapter 3vac 100ma 2pin female used 12,wlg q/ht001-1998 film special transformer new 12vdc car cigrate,casio ad-5mu ac adapter 9vdc 850ma 1.4x5.5mm 90 +(-) used 100-12.yardworks 24990 ac adapter 24vdc 1.8a battery charger used power,control electrical devices from your android phone,.

2021/06/11 by wT_9jco8@aol.com

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