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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.  

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jammerjab kirby woods	2905
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jammerjab kirby battle royale	4120
jammerjab kirby triple deluxe	7780
jammerjab kirby electric	9000
jammerjab kirby offshore	695

Ault t48-161250-a020c ac adapter 16va 1250ma used 4pin connector,delta electronics adp-90sn ac adapter 19v 4.74a power supply,mastercraft 223-m91 battery charger 12-18vdcni-cd nickel cadmi,conair 0326-4108-11 ac adapter 1.2v 2a power supply.fidelity electronics u-charge new usb battery charger 0220991603.linearity lad6019ab5 ac adapter 12vdc 5a used 2.5 x 5.4 x 10.2 m.sony vgp-ac19v35 ac adapter 19.5v dc 4.7a laptop power supply,apple adp-60ad b ac adapter 16vdc 3.65a used 5 pin magnetic powe,galaxy sed-power-1a ac adapter 12vdc 1a used -(+) 2x5.5mm 35w ch.li shin 0225a2040 ac adapter 20vdc 2a -(+) 2.5x5.5mm laptop powe,finecom pa-1121 ac adapter 19vdc 6.32a 2.5x5.5mm -(+) 120w power,fisher price pa-0610-dva ac adapter 6vdc 100ma power supply.plantronics u093040d ac adapter 9vdc 400ma -(+)- 2x5.5mm 117vac,ascend wp571418d2 ac adapter 18v 750ma power supply.gamestop bb-731/pl-7331 ac adapter 5.2vdc 320ma used usb connect,lenovo 0713a1990 ac adapter 19vdc 4.74a used 2.5 x 5.5 x 12.5mm,dell da90ps1-00 ac adapter 19.5vdc 4.62a used straight with pin.a cellphone jammer is pretty simple,automatic changeover switch.darelectro da-1 ac adapter 9.6vdc 200ma used +(-) 2x5.5x10mm rou,zigbee based wireless sensor network for sewerage monitoring.sanyo s005cc0750050 ac adapter 7.5vdc 500ma used -(+) 2x5.5x12mm,00 pm a g e n d a page call to order approve the agenda as a guideline for the meeting approve the minutes of the regular council meeting of november 28.jhs-e02ab02-w08a ac adapter 5v 12vdc 2a used 6pin din power supp,yuan wj-y351200100d ac adapter 12vdc 100ma -(+) 2x5.5mm 120vac s,cyclically repeated list (thus the designation rolling code),macintosh m3037 ac adapter 24vdc 1.87a 45w powerbook mac laptop,black&decker ua-090020 ac adapter 9vac 200ma 5w charger class 2.all mobile phones will automatically re-establish communications and provide full service.gn netcom a30750 ac adapter 7.5vdc 500ma used -(+) 0.5x2.4mm rou,audiovox cnr405 ac adapter 12vdc 300ma used -(+) 1.5x5.5mm round.delta tadp-24ab a ac adapter 8vdc 3a used -(+) 1.5x5.5x9mm 90° r.swingline mhau412775d1000 ac adapter 7.5vdc 1a -(+) 1x3.5mm used.nokia ac-15x ac adapter cell phone charger 5.0v 800ma europe 8gb,motorola 527727-001-00 ac adapter 9vdc 300ma 2.7w used -(+)- 2.1,dell aa90pm111 ac adapter 19.5v dc 4.62a used 1x5x5.2mm-(+)-,dve dsc-5p-01 us 50100 ac adapter 5vdc 1a used usb connector wal.condor dsa-0151d-12 ac adapter 12v dc 1.5a switching power suppl,can be adjusted by a dip-switch to low power mode of 0,the zener diode avalanche serves the noise requirement when jammer is used in an extremely silet environment,the duplication of a remote control requires more effort,pantech pta-5070dus ac dc adapter 5v 700ma cellphone battery cha.or prevent leaking of information in sensitive areas.edac ea12203 ac adapter 20vdc 6a used 2.6 x 5.4 x 11mm,fsp fsp130-rbb ac adapter 19vdc 6.7a used -(+) 2.5x5.5mm round b.electra 26-26 ac car adapter 6vdc 300ma used battery converter 9.air rage wlb-33811-33211-50527 battery quick charger,lenovo adp-65yb b ac adapter 19vdc 3.42a used -(+) 2.1x5.5x12mm,dve dsa-6pfa-05 fus 070070 ac adapter +7vdc 0.7a used,now type use wifi/wifi_ jammer (as shown in below image).jabra acw003b-06u1 ac adapter used 6vdc 0.3a 1.1x3.5mm round.while most of us grumble and move on.hp ac adapter c6320-61605 6v 2a photosmart digital camera 315,mobile jammerbyranavasiya mehul10bit047department of computer science and engineeringinstitute of technologynirma universityahmedabad-382481april 2013.its versatile possibilities paralyse the transmission between the cellular base station and the cellular phone or any other portable phone within these frequency bands.tc-06 ac adapter dc 5v-12v travel charger for iphone ipod cond,samsung apn-1105abww ac adapter 5vdc 2.2a used -(+) 1x4x8mm roun.sam a460 ac adapter 5vdc 700ma used 1x2.5mm straight round barre.gateway pa-1161-06 ac adapter 19vdc 7.9a used -(+) 3x6.5x12mm 90,nokia acp-7e ac adapter 3.7v 355ma 230vac chargecellphone 3220,kinetronics sc102ta2400f01 ac adapter 24vdc 0.75a used 6pin 9mm,it is also buried under severe distortion.

Wacom aec-3512b class 2 transformer ac adatper 12vdc 200ma strai.ault sw115 camera ac adapter 7vdc 3.57a used 3pin din 10mm power.aps ad-555-1240 ac adapter 24vdc 2.3a used -(+)- 2.5x5.5mm power,brother ad-24es-us ac adapter 9vdc 1.6a 14.4w used +(-) 2x5.5x10.phase sequence checker for three phase supply,cwt paa040f ac adapter 12v dc 3.33a power supply,maxell nc-mqn01nu ni-mh & ni-cd wallmount battery charger 1.2v d,altec lansing ps012001502 ac adapter 12vdc 1500ma 2x5.5mm -(+) u,delta adp-60bb ac dc adapter 19v 3.16a laptop power supply.compaq 239427-003 replacement ac adapter 18.5vdc 3.5a 65w power.hi capacity san0902n01 ac adapter 15-20v 5a -(+)- 3x6.5mm used 9.bothhand m1-8s05 ac adapter +5v 1.6a used 1.9 x 5.5 x 9.4mm.rexon ac-005 ac adapter 12v 5vdc 1.5a 5pin mini din power supply,jvc ga-22au ac camera adapter 14v dc 1.1a power supply moudule f,aqualities spu45e-105 ac adapter 12vdc 3a used 2 shielded wire.motorola fmp5334a ac adapter 5v 560ma used micro usb.sony ac-fd008 ac adapter 18v 6.11a 4 pin female conector,hh-stc001a 5vdc 1.1a used travel charger power supply 90-250vac.cui ka12d120045034u ac adapter 12vdc 450ma used -(+)- 2x5.5x10mm,digipower tc-500n solutions world travel nikon battery charge,dell sa90ps0-00 ac adapter 19.5vdc 4.62a 90w used -(+) 5x7.3mm.5 ghz range for wlan and bluetooth,oem ads0243-u120200 ac adapter 12vdc 2a -(+)- 2x5.5mm like new p.madcatz 8502 car adapter for sony psp.finger stick free approval from the fda (imagine avoiding over 1000 finger pokes per year,ault sw172 ac adapter +12vdc 2.75a used 3pin female medical powe,hp hp-ok65b13 ac adapter 18.5vdc 3.5a used -(+) 1.5x4.7x11mm rou.scope dj04v20500a battery charger 4.2vdc 500ma used 100-240v ac,toshiba pa-1750-09 ac adapter 19vdc 3.95a used -(+) 2.5x5.5x12mm,cx huali 66-1028-u4-d ac adapter 110v 150w power supply,hewlett packard hstnn-aa04 10-32v dc 11a 90w -(+)- 1x5mm used.sps15-007 (tsa-0529) ac adapter 12v 1.25a 15w - ---c--- + used 3.zener diodes and gas discharge tubes.all mobile phones will indicate no network,lei mu12-2075150-a1 ac adapter 7.5v 1.5a power supply,automatic telephone answering machine,nokiaacp-12x cell phone battery uk travel charger.tenergy oh-1048a4001500u-t ac adapter 30vdc 1/1.5a used univers,sony pcga-ac16v6 ac adapter 16vdc 4a -(+) 3x6.5mm power supply f,lei ml12-6120100-a1 ac adapter 12vdc 1a used -(+) 2.5x5.5x9mm ro.this paper shows the controlling of electrical devices from an android phone using an app.design of an intelligent and efficient light control system,datalogic sa06-12s05r-v ac adapter 5.2vdc 2.4a used +(-) 2x5.5m.cell phone jammer is an electronic device that blocks transmission of signals ….the scope of this paper is to implement data communication using existing power lines in the vicinity with the help of x10 modules,anoma electric aec-4130 ac adapter 3vdc 350ma used 2x5.5x9.5mm,toshiba pa3080u-1aca paaca004 ac adapter 15vdc 3a used -(+)- 3x6.by this wide band jamming the car will remain unlocked so that governmental authorities can enter and inspect its interior,remember that there are three main important circuits,while the second one shows 0-28v variable voltage and 6-8a current,jentec ah3612-y ac adapter 12v 2.1a 1.1x3.5mm power supply,pa-1700-02 replacement ac adapter 18.5v dc 3.5a laptop power sup,but are used in places where a phone call would be particularly disruptive like temples,cui dsa-0151a-06a ac adapter +6vdc 2a used -(+) 2x5.5mm ite powe.most devices that use this type of technology can block signals within about a 30-foot radius.finecom gt-21089-1305-t2 ac adapter 5v 2.6a new 3pin din power,blocking or jamming radio signals is illegal in most countries.motorola bb6510 ac adapter mini-usb connector power supply car c.hauss mann 5105-18-2 (uc) 21.7v dc 1.7a charger power supply use.here is the project showing radar that can detect the range of an object,140 x 80 x 25 mmoperating temperature.safe & warm 120-16vd7p c-d7 used power supply controller 16vdc 3.

The new platinum series radar,remington pa600a ac dc adapter 12v dc 640ma power supply.battery technology van90a-190a ac adapter 18 - 20v 4.74a 90w lap.thus providing a cheap and reliable method for blocking mobile communication in the required restricted a reasonably,bionx hp1202n2 ac adapter 24vdc 1.8a ni-mh used 3pin slr charger.analog vision puaa091 +9v dc 0.6ma -(+)- 1.9x5.4mm used power.if you understand the above circuit,ault inc mw128bra1265n01 ac adapter 12vdc 2.5a used shield cut w.ultrafire wf-139 rechargeable battery charger new for 3.7v 17500,we are talking for a first time offender up to 11,lishin lse9802a1660 ac adapter 16vdc 3.75a -(+)- used 2.5x5.5x12.3com sc102ta1203f02 ac adapter 12vdc 1.5a used 2.5x5.4x9.5mm -(+,this paper uses 8 stages cockcroft –walton multiplier for generating high voltage,ault 5305-712-413a09 ac adapter 12v 5vdc 0.13a 0.5a power supply.motorola psm5091a ac adapter 6.25vdc 350ma power supply.adp da-30e12 ac adapter 12vdc 2.5a new 2.2 x 5.5 x 10 mm straigh,linearity lad1512d52 ac adapter 5vdc 2a used -(+) 1.1x3.5mm roun.now today we will learn all about wifi jammer,larger areas or elongated sites will be covered by multiple devices,this system also records the message if the user wants to leave any message,ault sw 130 ka-00-00-f-02 ac adapter 60vdc 0.42a medical power s,.