• Cell phone service blocker,signal blockers for cell phones,Where Are We Now, and Where Are We Going? In this month’s column, we travel along the road of PPP development, examine its current status and look at where it might go in the near future By Sunil...

Cell phone service blocker | signal blockers for cell phones

Cell phone service blocker | signal blockers for cell phones


  • 2021/06/05
Where Are We Now, and Where Are We Going? In this month’s column, we travel along the road of PPP development, examine its current status and look at where it might go in the near future By Sunil Bisnath, John Aggrey, Garrett Seepersad and Maninder Gill Innovation Insights with Richard Langley PPP. It’s one of the many acronyms (or initialisms, if you prefer) associated with the uses of global navigation satellite systems. It stands for precise point positioning. But what is that? Isn’t all GNSS positioning precise? Well, it’s a matter of degree. Take GPS, for example. The most common kind of GPS signal use, that implemented in vehicle “satnav” units; mobile phones; and hiking, golfing and fitness receivers, is to employ the L1 C/A-code pseudorange (code) measurements along with the broadcast satellite orbit and clock information to produce a point position. Officially, this is termed use of the GPS Standard Positioning Service (SPS). It is capable of meter-level positioning accuracy under the best conditions. There is a second official service based on L1 and L2 P-code measurements and broadcast data called the Precise Positioning Service (PPS). In principle, because the P-code provides somewhat higher precision code measurements and the use of dual-frequency data removes virtually all of the ionospheric effect, PPS is capable of slightly more precise (and accurate) positioning. But because the P-code is encrypted, PPS is only available to so-called authorized users. While meter-level positioning accuracy is sufficient for many, if not most applications, there are many uses of GNSS such as machine control, surveying and various scientific tasks, where accuracies better than 10 centimeters or even 1 centimeter are needed. Positioning accuracies at this level can’t be provided by pseudoranges alone and the use of carrier-phase measurements is required. Phase measurements are much more precise than code measurements although they are ambiguous and this ambiguity must be estimated and possibly resolved to the correct integer value. Traditionally, phase measurements (typically dual-frequency) made by a potentially moving user receiver have been combined with those from a reference receiver at a well-known position to produce very precise (and accurate) positions. If done in real time (through use of a radio link of some kind), this technique is referred to as real-time kinematic or RTK. A disadvantage of RTK positioning is that it requires reference station infrastructure including a radio link (such as mobile phone communications) for real-time results. Is there another way? Yes, and that’s PPP. PPP uses the more precise phase measurements (along with code measurements initially) on at least two carrier frequencies (typically) from the user’s receiver along with precise satellite orbit and clock data derived, by a supplier, from a global network. Precision, in this case, means a horizontal position accuracy of 10 centimeters or better. In this month’s column, we travel along the road of PPP development, examine its current status, and look at where it might go in the near future. In a 2009 GPS World “Innovation” article co-authored by Sunil Bisnath, the performance and technical limitations at the time of the precise point positioning (PPP) GPS measurement processing technique were described and a set of questions asked about the potential of PPP, especially with regard to the real-time kinematic (RTK) measurement processing technique. Since the 2009 article, we’ve seen a significant amount of research and development (R&D) activity in this area. Many scientific papers discuss PPP and making use of PPP — a search on Google Scholar for “GNSS PPP” delivers nearly 7,000 results, and for “GPS PPP” more than 15,000 results! Will PPP eventually overtake RTK as the de facto standard for precise (that is, few centimeter-level) positioning? Or, in light of PPP R&D developments, should we be asking different questions, such as will multiple precise GNSS positioning techniques compete or complement each other or perhaps result in a hybrid approach? In almost a decade, have we seen much in the way of positioning performance improvement, where “performance” can refer to positioning precision, accuracy, availability and integrity? Or, to some users, has the Achilles’ heel of PPP — the initial position solution convergence period — only been reduced from, for example, 20 minutes to 19 minutes? From such a perspective, all of this PPP research might not appear to have produced much tangible benefit. Advances have been made from this research and we will explore them here. Also, aside from many researchers working diligently on their own PPP software, there are now a number of well-established PPP-based commercial services — a number that has grown and been affected by the wave of GNSS industry consolidation over the decade. Consequently, there is much more to this story. This month’s article summarizes the current status of PPP performance and R&D, and discusses the potential future of the technique. In the first part of the article, we will present brief explanations of conventional dual-frequency PPP, recent research and implementations, and application of the evolved technique to low-cost hardware. We will conclude the article with a rather dangerous attempt at near-term extrapolation of potential upcoming developments and conceivable implications. Conventional PPP The concept of PPP is based on standard, single-receiver, single-frequency point positioning using pseudorange (code) measurements, but with the meter-level satellite broadcast orbit and clock information replaced with centimeter-level precise orbit and clock information, along with additional error modeling and (typically) dual-frequency code and phase measurement filtering. Back in 1995, researchers at Natural Resources Canada were able to reduce GPS horizontal positioning error from tens of meters to the few-meter level with code measurements and precise orbits and clocks in the presence of Selective Availability (SA). Subsequently, the Jet Propulsion Laboratory introduced PPP as a method to greatly reduce GPS measurement processing time for large static networks. When SA was turned off in May 2000 and GPS satellite clock estimates could then be more readily interpolated, the PPP technique became scientifically and commercially popular for certain precise applications. Unlike static relative positioning and RTK, conventional PPP does not make use of double-differencing, which is the mathematical differencing of simultaneous code and phase measurements from reference and remote receivers to greatly reduce or eliminate many error sources. Rather, PPP applies precise satellite orbit and clock corrections estimated from a sparse global network of satellite tracking stations in a state-space version of a Hatch filter (in which the noisy, but unambiguous, code measurements are filtered with the precise, but ambiguous, phase measurements). This filtering is illustrated in FIGURE 1, where measurements are continually added in time in the range domain, and errors are modeled and filtered in the position domain, resulting in reduced position error in time. FIGURE 1. Illustration of conventional PPP measurement and error modeling in state-space Hatch filter, resulting in reduced position error in time. The result is the characteristic PPP initial convergence period seen in FIGURE 2, where the position solution is initialized as a sub-meter, dual-frequency code point positioning solution, quickly converging to the decimeter-level in something like 5 to 20 minutes, and a few centimeters after ~20 minutes when geodetic-grade equipment is used (at station ALGO, Algonquin Park, Canada, on Jan. 2, 2017). For static geodetic data, daily solutions are typically at the few millimeter-level of accuracy in each Cartesian component. FIGURE 2. Conventional geodetic GPS PPP positioning performance characteristics of initial convergence period and steady state for station ALGO, Algonquin Park, Canada, on Jan. 2, 2017. The primary benefit of conventional PPP is that with the use of state-space corrections from a sparse global network, there is the appearance of precise positioning from only a single geodetic receiver. Therefore, baseline or network RTK limitations are removed in geographically challenging areas, such as offshore, far from population centers, in the air, in low Earth orbit, and so on, and without the need for the requisite terrestrial hardware and software infrastructure. PPP is now the de facto standard for precise positioning in remote areas or regions of low economic density, which limit or prevent the use of relative GNSS, RTK or network RTK, but allow for continuous satellite tracking. These benefits translate into the main commercial applications of offshore positioning, precision agriculture, geodetic surveys and airborne mapping, which also are not operationally bothered by initial convergence periods of tens of minutes. For urban and suburban applications, RTK and especially network RTK allow for near-instantaneous, few-centimeter-level positioning with the use of reference stations and regional satellite (orbit and clock) and atmospheric corrections. The use of double-differencing and these local or regional corrections allows sufficient measurement error mitigation to resolve double-differenced phase ambiguities. All of this additional information is not available to conventional PPP, limiting its precise positioning performance, but which is considered in PPP enhancements. Progress on PPP Convergence Limitations Over the past decade or so, PPP R&D activity can be categorized as follows: Integration of measurements from multiple GNSS constellations, transitioning from GPS PPP to GNSS PPP; Resolution of carrier-phase ambiguities in PPP user algorithms — in an effort to increase positional accuracy and solution stability, but foremost in an effort to reduce the initial convergence period; and Use of a priori information to reduce the initial convergence and re-convergence periods and improve solution stability, making use of available GNSS error modeling approaches. Unlike relative positioning, which makes use of measurements from the user receiver as well as the reference receiver, PPP only relies on measurements from the user site. This situation results in weaker initial geometric strength, and so the addition of more unique measurements is welcome. To make use of measurements from all four GNSS constellations (GPS, GLONASS, Galileo and BeiDou), user-processing engines must account for differences in spatial and temporal reference systems between constellations and numerous equipment delays between frequencies and modulations. The former can be done so that any number of measurements from any number of constellations can be processed to produce one unique PPP position solution. The latter requires a great deal of calibration, especially for heterogeneous tracking networks and user equipment (antenna, receiver and receiver firmware), most notably for the current frequency division multiple access GLONASS constellation. FIGURE 3 shows typical multi-GNSS float (non-ambiguity-fixed) horizontal positioning performance at multi-GNSS station GMSD in Nakatane, Japan, on March 24, 2017. As with all modes of GNSS data processing, more significant improvement with additional constellations can be seen in sky-obstructed situations. FIGURE 3. Typical conventional multi-GNSS PPP float horizontal positioning accuracy for station GMSD, Nakatane, Japan, March 24, 2017 (G: GPS, R: GLONASS, E: Galileo and C: BeiDou). Related to multi-constellation processing is triple-frequency processing afforded by the latest generation of GPS satellites and the Galileo and BeiDou constellations. More frequencies mean more measurements, although with the same satellite-to-receiver measurement geometry as dual-frequency measurements. Again, additional signals require additional equipment delay modeling, in this case especially for the processing of GPS L1, L2 and L5 observables. For processing of four-constellation data available from 20 global stations in early 2016, FIGURE 4 shows the average reduction of float (non-ambiguity-fixed) horizontal error from dual- to triple-frequency processing of approximately 40% after the first five minutes of measurement processing. In terms of positioning, this result, for this time period with a limited number of triple-frequency measurements, means a reduction in average horizontal positioning error from 43 to 26 centimeters within the first five minutes of data collection. FIGURE 4. Average dual- and triple-frequency static, float PPP horizontal solution accuracy for 20 global stations. Data collected from tracked GPS, GLONASS, Galileo and BeiDou satellites in early 2016. PPP with ambiguity resolution, or PPP-AR, was seen as a potential solution to the PPP initial solution convergence “problem” analogous to AR in RTK. Various researchers put forward methods, in the form of expanded measurement models, to isolate pseudorange and carrier-phase equipment delays to estimate carrier-phase ambiguities. These methods remove receiver equipment delays through implicit or explicit between-satellite single-differencing and estimate satellite equipment delays in the network product solution either as fractional cycle phase biases or altered clock products. FIGURE 5 illustrates the difference between a typical GPS float and fixed solution (for station CEDU, Ceduna, Australia, on June 28, 2017). Initial solution convergence time is reduced, and stable few-centimeter-level solutions are reached sooner. For lower quality data, ambiguity fixing does not provide such quick initial solution convergence. Fixing is dependent on the quality of the float solution; and, for PPP, the latter requires time to reach acceptable levels of accuracy. Therefore, depending on the application, PPP-AR may or may not be helpful. FIGURE 5. Typical float (red) and fixed (pink) GPS PPP horizontal solution error at geodetic station CEDU, Ceduna, Australia, on June 28, 2017. To consistently reduce the initial solution convergence period, PPP processing requires additional information, as is the case for network RTK, in which interpolated satellite orbit, ionospheric and tropospheric corrections are needed since double-differenced RTK baselines over 10 to 15 kilometers in length contain residual atmospheric errors too large to effectively and safely resolve phase integer ambiguities. For PPP, uncombining the ionospheric-free code and phase measurements from the conventional model is required, to directly estimate slant ionosphere propagation terms in the filter state. In this form, the model can allow for very quick re-initialization of short data gaps by using the pre-gap slant ionospheric (and zenith tropospheric) estimates as down-weighted a priori estimates post-gap — making these estimates bridging parameters in the estimation filter. Expanding this approach, external atmospheric models can be used to aid with initial solution convergence. FIGURE 6 illustrates, for a large dataset, that applying a spatially and temporally coarse global ionospheric map (GIM) to triple-frequency, four-constellation float processing can reduce one-sigma convergence time to 10 centimeters horizontal positioning error from 16 to 6 minutes. If local ionospheric (and tropospheric) corrections are available and AR is applied, PPP (sometimes now referred to as PPP-RTK) can produce RTK-like results with a few minutes of initial convergence to few-centimeter-level horizontal solutions. FIGURE 6. Averaged horizontal error from 70 global sites in mid-2016 using four-constellation, triple-frequency processing. PPP Processing with Low-Cost Hardware As the impetus for low-cost, precise positioning and navigation for autonomous and semi-autonomous platforms (such as land vehicles and drones) continues to grow, there is interest in processing such low-cost data with PPP algorithms. For example, it has been shown that with access to single-frequency code and phase measurements from a smartphone, short-baseline RTK positioning is possible. It has also been shown that similar smartphone data can be processed with the PPP approach. From the origins of PPP, it may be argued that single-frequency processing and many-decimeter-level positioning performance is not “precise.” But we will avoid such semantic arguments here (but see “Insights”), and focus on the use of high-performance measurement processing algorithms to new low-cost hardware. We are currently witnessing great changes in the GNSS chip market: single-frequency chips for tens-of-dollars or less; and boards with multi-frequency chips for hundreds-of-dollars. And these chips will continue to undergo downward price pressure with increases in capability, and be further enabled for raw measurement use in a wider range of applicable technology solutions. There are now a number of low-cost, dual-frequency, multi-constellation products on the market, with additional such products as well as smartphone chips coming soon. To process data from such products with a PPP engine, modifications are required to optimally account for single-frequency measurements in the estimation filter, optimize the measurement quality control functions for the much noisier code and phase measurements compared to data from geodetic receivers, and optimize the stochastic modeling for the much noisier code and phase measurements. The single-frequency measurement model can be modified to either make use of the Group and Phase Ionospheric Calibration linear combination (commonly referred to as GRAPHIC) or ingest data from an ionospheric model. Due to the use of low-cost antennas, as well as the low-cost chip signal processing hardware, code and phase measurements suffer from significant multipath and noise at lower signal strengths; therefore, outlier detection functions must be modified. Also, the relative weighting of code and phase measurements must be customized for more realistic low-cost data processing. FIGURE 7 compares the carrier-to-noise-density ratio (C/N0) values from ~1.5 hours of static GPS L1 signals collected from a geodetic receiver with a geodetic antenna, a low-cost receiver chip with a patch antenna, and a tablet chip and internal antenna, as a function of elevation angle. Received signal C/N0 values can be used as a proxy for signal precision. The three datasets were collected at the same time in mid-September 2017 in Toronto, Canada, with the receivers and antennas within a few meters of each other. The shading represents the raw estimates output from each receiver, while the solid lines are moving-average filtered results. FIGURE 7. Carrier-to-noise-density ratios of ~1.5 hour of static GPS L1 signals from a geodetic receiver with a geodetic antenna, a low-cost receiver chip with a patch antenna, and a tablet chip and internal antenna, as a function of elevation angle. Keeping in mind the log nature of C/N0, the high measurement quality of the geodetic antenna and receiver are clear. The low-cost chip and patch antenna signal strength structure is similar, but, on average, 3.5 dB-Hz lower. And the tablet received signal strength is lower still, on average a further 4.0 dB-Hz lower, with greater degradation at higher signal elevation angles and much greater signal strength variation. The PPP horizontal position uncertainty for these datasets is shown in FIGURE 8. Note that reference coordinates have been estimated from the datasets themselves, so potential biases, in especially the low-cost and tablet results, can make these results optimistic. Given that only single-frequency GPS code and phase measurements are being processed, initial convergence periods are short and horizontal position error reaches steady state in the decimeter range. The geodetic and the low-cost results are comparable at the 2-decimeter level, whereas the tablet results are worse, at the approximately 4-decimeter level. Initial convergence of the geodetic solution is superior to the others, driven by the higher quality of its code measurements. The grade of antenna plays a large role in the quality of these measurements, for which there are physical limitations in design and fabrication. While geodetic antennas can be used, this is not always feasible, given the mass limitations of certain platforms or the cost limitations for certain applications. FIGURE 8. Horizontal positioning error (compared to final epoch solutions) for geodetic, low-cost and tablet data processed with PPP software customized for single-frequency and less precise measurements. Comments Regarding the Near Future The PPP GNSS measurement processing approach was originally designed to greatly reduce computation burden in large geodetic networks of receivers by removing the need for network baseline processing. The technique found favor for applications in remote areas or regions with little terrestrial infrastructure, including the absence of GNSS reference stations. Given PPP’s characteristic use of a single receiver for precise positioning, various additional augmentations have been made to remove or reduce solution initialization and re-initialization interval to near RTK-like levels. But, to what end? This question can be approached from multiple perspectives. From the theoretical standpoint, there is the impetus to maximize performance — millimeter-level static positioning over many hours, and few-centimeter-level kinematic positioning in a few minutes — by augmenting PPP in any way necessary. There is the academic exercise of maximizing performance without the need for local or regional reference stations – apparent single-receiver positioning, or truly wide-area augmentation. In terms of engineering problems, we can work to do more with less, that is, decimeter-level positioning with ultra-low-cost hardware, or the same with less, that is, few-centimeter-level positioning with low-cost hardware. And from the practical or commercial aspect, the great interest is for the implementation of evolved PPP methods for applications that can efficiently and effectively make use of the technology. In terms of service providers, be it regional or global, commercial or public, there is momentum to provide enhanced correction products that are blurring the lines across the service spectrum from constellation-owner tracking to regional, terrestrial augmentation. A public GNSS constellation-owner, through its constellation tracking network, can provide PPP-like corrections and services. A global commercial provider with or without regional augmentation can provide similar services. The key is providing multi-GNSS state-space corrections for satellite orbits, satellite clocks, satellite equipment delays (fractional phase biases), zenith ionospheric delay and zenith tropospheric delay at the temporal and spatial resolution necessary for the desired positioning performance at reasonable cost, that is, subscription fees that particular markets can bear. Given these correction products, PPP users have a greater ability to access a wide array of positioning performance levels for various new applications, be it few-decimeter-level positioning on mobile devices to few-centimeter-level positioning for autonomous or semi-autonomous land, sea and air vehicles. PPP can be used for integrity monitoring and perhaps safety-of-life applications where low-cost is a necessity and relatively precise positioning for availability and integrity purposes is required. For safety critical and high-precision applications, such as vehicle automation, PPP can be used alongside, or in combination with, RTK for robustness and independence with low-cost hardware. Such a parallel and collaborative approach would require a hybrid user processing engine and robust state-space corrections from a variety of local, regional and global sources, as we are seeing from some current geodetic hardware-based commercial services. Near-future trends should also include more low-cost, multi-sensor integration with PPP augmentation. Optimized navigation algorithms and efficient user processing engines will be a priority as the capabilities of low-cost equipment continue to increase and low-cost integrated sensor solutions are required for mass-market applications. Analogous to meter-level point position GNSS, lower hardware costs should drive markets to volume sales, PPP-like correction services, and GNSS-based multi-sensor integration into more navigation technology solutions for various industry and consumer applications. Clearly, the future of PPP continues to be bright. SUNIL BISNATH is an associate professor in the Department of Earth and Space Science and Engineering at York University, Toronto, Canada. For over twenty years, he has been actively researching GNSS processing algorithms for a wide variety of positioning and navigation applications. JOHN AGGREY is a Ph.D. candidate in the Department of Earth and Space Science and Engineering at York University. He completed his B.Sc. in geomatics at Kwame Nkrumah University of Science and Technology, Ghana, and his M.Sc. at York University. His research currently focuses on the design, development and testing of GNSS PPP software, including functional, stochastic and error mitigation models. GARRETT SEEPERSAD is a navigation software design engineer for high-precision GNSS at u-blox AG and concurrently is completing his Ph.D. in the Department of Earth and Space Science and Engineering at York University. His Ph.D. research focuses on GNSS PPP and ambiguity resolution. He completed his B.Sc. in geomatics at the University of the West Indies in Trinidad and Tobago. He holds an M.Sc. degree in the same field from York University. MANINDER GILL is a geomatics designer at NovAtel Inc. and concurrently is completing his M.Sc. in the Department of Earth and Space Science and Engineering at York University. His M.Sc. research focuses on GNSS PPP and improving positioning accuracy for low-cost GNSS receivers. He holds a B.Eng. degree in geomatics engineering from York University. FURTHER READING • Comprehensive Discussion of Technical Aspects of Precise Point Positioning “Precise Point Positioning” by J. Kouba, F. Lahaye and P. Tétreault, Chapter 25 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. • Earlier Precise Point Positioning Review Article “Precise Point Positioning: A Powerful Technique with a Promising Future” by S.B. Bisnath and Y. Gao in GPS World, Vol. 20, No. 4, April 2009, pp. 43–50. • Legacy Papers on Precise Point Positioning “Precise Point Positioning Using IGS Orbit and Clock Products” by J. Kouba and P. Héroux in GPS Solutions, Vol. 5, No. 2, October 2001, pp. 12–28, doi: 10.1007/PL00012883. “GPS Precise Point Positioning with a Difference” by P. Héroux and J. Kouba, a paper presented at Geomatics ’95, Ottawa, Canada, 13–15 June 1995. “Precise Point Positioning for the Efficient and Robust Analysis of GPS Data from Large Networks” by J.F. Zumberge, M.B. Heflin, D.C. Jefferson, M.M. Watkins and E.H. Webb in Journal of Geophysical Research, Vol. 102, No. B3, pp. 5005–5017, 1997, doi: 10.1029/96JB03860. • Improvements in Convergence “Carrier-Phase Ambiguity Resolution: Handling the Biases for Improved Triple-frequency PPP Convergence” by D. Laurichesse in GPS World, Vol. 26, No. 4, April 2015, pp. 49-54. “Reduction of PPP Convergence Period Through Pseudorange Multipath and Noise Mitigation” by G. Seepersad and S. Bisnath in GPS Solutions, Vol. 19, No. 3, March 2015, pp. 369–379, doi: 10.1007/s10291-014-0395-3. “Global and Regional Ionospheric Corrections for Faster PPP Convergence” by S. Banville, P. Collins, W. Zhang and R.B. Langley in Navigation, Vol. 61, No. 2, Summer 2014, pp. 115–124, doi: 10.1002/navi.57. “A New Method to Accelerate PPP Convergence Time by Using a Global Zenith Troposphere Delay Estimate Model” by Y. Yao, C. Yu and Y. Hu in The Journal of Navigation, Vol. 67, No. 5, September 2014, pp. 899–910, doi: 10.1017/S0373463314000265. “External Ionospheric Constraints for Improved PPP-AR Initialisation and a Generalised Local Augmentation Concept” by P. Collins, F. Lahaye and S. Bisnath in Proceedings of ION GNSS 2012, the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation, Nashville, Tennessee, Sept. 17–21, 2012, pp. 3055–3065. • Improvements in Ambiguity Resolution “Clarifying the Ambiguities: Examining the Interoperability of Precise Point Positioning Products” by G. Seepersad and S. Bisnath in GPS World, Vol. 27, No. 3, March 2016, pp. 50–56. “Integer Ambiguity Resolution on Undifferenced GPS Phase Measurements and Its Application to PPP and Satellite Precise Orbit Determination” by D. Laurichesse and F. Mercier, J.-P. Berthias, P. Broca and L. Cerri in Navigation, Vol. 56, No. 2, Summer 2009, pp. 135–149. “Resolution of GPS Carrier-phase Ambiguities in Precise Point Positioning (PPP) with Daily Observations” by M. Ge, G. Gendt, M. Rothacher, C. Shi and J. Liu in Journal of Geodesy, Vol. 82, No. 7, July 2008, pp. 389–399, doi: 10.1007/s00190-007. Erratum: doi: 10.1007/s00190-007-0208-3. “Isolating and Estimating Undifferenced GPS Integer Ambiguities” by P. Collins in Proceedings of ION NTM 2008, the 2008 National Technical Meeting of The Institute of Navigation, San Diego, California, Jan. 28–30, 2008, pp. 720–732. • Precise Positioning Using Smartphones “Positioning with Android: GNSS Observables” by S. Riley, H. Landau, V. Gomez, N. Mishukova, W. Lentz and A. Clare in GPS World, Vol. 29, No. 1, January 2018, pp. 18 and 27–34. “Precision GNSS for Everyone: Precise Positioning Using Raw GPS Measurements from Android Smartphones” by S. Banville and F. van Diggelen in GPS World, Vol. 27, No. 11, November 2016, pp. 43–48. “Accuracy in the Palm of Your Hand: Centimeter Positioning with a Smartphone-Quality GNSS Antenna” by K.M. Pesyna, R.W. Heath and T.E. Humphreys in GPS World, Vol. 26, No. 2, February 2015, pp. 16–18 and 27–31.


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3com ap1211-uv ac adapter 15vdc 800ma -(+)- 2.5x5.5mm pa027201 r.kodak mpa7701 ac adapter 24vdc 1.8a easyshare dock printer serie,samsung pscv400102aac adapter 16vdc 2.5a power supply wallmount.motorola ssw-2285us ac adapter 5vdc 500ma cellphone travel charg,it is required for the correct operation of radio system,intermatic dt 17 ac adapter 15amp 500w used 7-day digital progra.ad1805c acadapter 5.5vdc 3.8a -(+) 1.2x3.5mm power supply.cs cs-1203000 ac adapter 12vdc 3a used -(+) 2x5.5mm plug in powe,motorola psm5037b travel charger 5.9v 375ma ac power supply spn5.motorola dch3-05us-0300 travel charger 5vdc 550ma used supply,linearity lad1512d52 ac adapter 5vdc 2a used -(+) 1.1x3.5mm roun,finecom 3774 u30gt ac adapter 12vdc 2a new -(+) 0.8x2.5mm 100-24.oem dds0121-052150 5.2vdc 1.5a -(+)- auto cigarette lighter car,creative xkd-z1700 i c27.048w ac adapter 27vdc 1.7a used -(+) 2x.panasonic cf-vcbtb1u ac adapter 12.6v 2.5a used 2.1x5.5 x9.6mm,eps f10903-0 ac adapter 12vdc 6.6a used -(+)- 2.5x5.5mm 100-240v.ault bvw12225 ac adapter 14.7vdc 2.25a -(+) used 2.5x5.5mm 06-00.apple a1070 w008a130 ac adapter 13vdc 0.62a usb 100-240vac power,delta adp-45gb ac adapter 22.5 - 18vdc 2 - 2.5a power supply.the new system features a longer wear time on the sensor (10 days),hitek plus220 ac adapter 20vdc 2.5a -(+)- 2.5x5.6 100-240vac use,ksas0100500150hu ac adapter5v dc 1.5a new -(+) 1.5x4x8.7 stra,samsung api-208-98010 ac adapter 12vdc 3a cut wire power supply.replacement seb100p2-15.0 ac adapter 15vdc 8a 4pin used pa3507u-,this circuit uses a smoke detector and an lm358 comparator,the aim of this project is to develop a circuit that can generate high voltage using a marx generator.ican st-n-070-008u008aat universal ac adapter 20/24vdc 70w used,-20°c to +60°cambient humidity,finecom zfxpa01500090 ac adapter 9vdc 1.5a -(+) 0.6x2.5mm used 9.eng epa-201d-07 ac adapter 7vdc 2.85a used -(+) 2x5.5x10mm round.delta adp-16gb a ac dc adapter 5.4vdc 3a used -(+) 1.7x4mm round,lg lcap16a-a ac adapter 19vdc 1.7a used -(+) 5.5x8mm 90° round b,palm plm05a-050 ac adapter 5vdc 1a power supply for palm pda do,band scan with automatic jamming (max,hp pa-1900-15c1 ac adapter 18.5vdc 4.9a 90w used.hp f1 455a ac adapter 19v 75w - ---c--- + used 2.5 x 5.4 x 12.3,duracell cef-20 nimh class 2 battery charger used 1.4vdc 280ma 1.remote control frequency 433mhz 315mhz 868mhz.90w-lt02 ac adapter 19vdc 4.74a replacement power supply laptop,produits de bombe jammer+433 -+868rc 315 mhz,radio shack 23-243 ac dc adapter 12v 0.6a switching power supply,d9-12-02 ac adapter 6vdc 1.2a -(+) 1200ma used 2x5.5mm 120vac pl,phihong psa31u-050 ac adapter 5vdc 4a used -(+)- 5 pin din ite p,now type use wifi/wifi_ jammer (as shown in below image),dual group au-13509 ac adapter 9v 1.5a used 2x5.5x12mm switching,the jammer covers all frequencies used by mobile phones,dell pscv360104a ac adapter 12vdc 3a -(+) 4.4x6.5mm used 100-240,this task is much more complex.three circuits were shown here.people also like using jammers because they give an “out of service” message instead of a “phone is off” message.razer ts06x-2u050-0501d ac adapter 5vdc 1a used -(+) 2x5.5x8mm r,motomaster 11-1552-4 manual battery charger 6/12v dc 1a,motorola psm4562a ac adapter 5.9v dc 400ma used,aci world up01221090 ac adapter 9vdc 1.2a apa-121up-09-2 ite pow,this allows an ms to accurately tune to a bs.1800 mhzparalyses all kind of cellular and portable phones1 w output powerwireless hand-held transmitters are available for the most different applications,atc-520 dc adapter used 1x3.5 travel charger 14v 600ma.frequency band with 40 watts max.umec up0301a-05p ac adapter 5vdc 6a 30w desktop power supply.ridgid r840091 ac adapter 9.6-18v 4.1a used lithium ion ni-cad r,new bright a865500432 12.8vdc lithium ion battery charger used 1,sony vgp-ac19v39 ac adapter 19.5v 2a used 4.5 x 6 x 9.5 mm 90 de,t027 4.9v~5.5v dc 500ma ac adapter phone connector used travel.chicony a11-065n1a ac adapter 19vdc 3.42a 65w used -(+) 1.5x5.5m,this project shows automatic change over switch that switches dc power automatically to battery or ac to dc converter if there is a failure.psp electronic sam-pspeaa(n) ac adapter 5vdc 2a used -(+) 1.5x4x.gemini dcu090050 ac adapter 9vdc 500ma used -(+)- 2.5x5.4mm stra,cnf inc 1088 15v 4a ac car adapter 15v 4a used 4.4 x 6 x 11.7mm,phonemate m/n-40 ac adapter 9vac 450ma used ~(~) 2.5x5.5mm 90.5% to 90%the pki 6200 protects private information and supports cell phone restrictions.set01b electronic transformer 12vac 105w 110vac crystal halogen,80h00312-00 5vdc 2a usb pda cradle charger used -(+) cru6600,sumit thakur cse seminars mobile jammer seminar and ppt with pdf report,nok cla-500-20 car charger auto power supply cla 10r-020248,bothhand sa06-20s48-v ac adapter +48vdc 0.4a power supply,ea11603 universal ac adapter 150w 18-24v 7.5a laptop power suppl.panasonic pqlv219 ac adapter 6.5vdc 500ma -(+) 1.7x4.7mm power s,cisco systems 34-0912-01 ac adaptser 5vdc 2.5a power upply adsl,li shin 0317a19135 ac adapter 19v 7.1a used oval pin power suppl,acbel api3ad14 ac adapter 19vdc 6.3a used (: :) female 4pin fema,edac ea10523c-120 ac adapter 12vdc 5a used 2.5 x 5.5 x 11mm,large buildings such as shopping malls often already dispose of their own gsm stations which would then remain operational inside the building.video digital camera battery charger used 600ma for db70 s008e b,cisco adp-30rb ac adapter 5v 3a 12vdc 2a 12v 0.2a 6pin molex 91-.mei mada-3018-ps ac adapter 5v dc 4a switching power supply,usb a charger ac adapter 5v 1a wallmount us plug home power supp.dell da90ps2-00 ac adapter c8023 19.5v 4.62a power supply,it can not only cut off all 5g 3g 4g mobile phone signals,au35-030-020 ac adapter 3vdc 200ma e144687 used 1x3.2mm round ba,and frequency-hopping sequences,dr. wicom phone lab pl-2000 ac adapter 12vdc 1.2a used 2x6x11.4m.

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Axis a41312 ac adapter 12vdc 1100ma used -(+) 2.5x5.5x13mm 90° r.new bright a541500022 ac adapter 24vdc 600ma 30w charger power s.110 to 240 vac / 5 amppower consumption,almost 195 million people in the united states had cell- phone service in october 2005.chi ch-1234 ac adapter 12v dc 3.33a used -(+)- 2.5x5.5mm 100-240,motorola spn4569e ac adapter 4.4-6.5vdc 2.2-1.7a used 91-57539.this circuit shows the overload protection of the transformer which simply cuts the load through a relay if an overload condition occurs,apd da-2af12 ac adapter used -(+)2x5.5mm 12vdc 2a switching powe,nyko ymci8-4uw ac adapter 12vdc 1.1a used usb switching power su,oem ad-0930m ac adapter 9vdc 300ma -(+)- 2x5.5mm 120vac plug in.if you find your signal is weaker than you'd like while driving,radioshack 43-3825 ac adapter 9vdc 300ma used -(+) 2x5.5x11.9mm,fujitsu fmv-ac311s ac adapter 16vdc 3.75a -(+) 4.4x6.5 tip fpcac.targus apa32us ac adapter 19.5vdc 4.61a used 1.5x5.5x11mm 90° ro,despite the portable size g5 creates very strong output power of 2w and can jam up to 10 mobile phones operating in the neatest area.ibm lenovo 92p1020 ac adapter 16vdc 4.5a used 2.5x5.5mm round ba.dell pa-1470-1 ac adapter 18v 2.6a power supply notebook latitud,compaq adp-50ch bc ac adapter 18.5vdc 2.7a used 1.8x4.8mm round,sceptre ad2405g ac adapter 5vdc 3.8a used 2.2 x 5.6 x 12.1 mm -(,exact coverage control furthermore is enhanced through the unique feature of the jammer.panasonic cf-aa1639 m17 15.6vdc 3.86a used works 1x4x6x9.3mm - -,eng 3a-161wp05 ac adapter 5vdc 2.6a -(+) 2.5x5.5mm 100vac switch,a mobile phone signal jammer is a device that blocks reception between cell towers and mobile phones,a spatial diversity setting would be preferred.replacement pa-10 ac adapter 19.5v 4.62a used 5 x 7.4 x 12.3mm.once i turned on the circuit,cisco eadp-18fb b ac adapter 48vdc 0.38a new -(+) 2.5x5.5mm 90°.sceptre ad2524b ac adapter 25w 22.0-27vdc 1.1a used -(+) 2.5x5.5,t41-9-0450d3 ac adapter 9vvdc 450ma -(+) used 1.2x5.3 straight r.ktec ka12d240020034u ac adapter 24vdc 200ma used -(+) 2x5.5x14mm,telergy sl-120150 ac adapter 12vdc 1500ma used -(+) 1x3.4mm roun,altec lansing s024eu1300180 ac adapter 13vdc 1800ma -(+) 2x5.5mm,it creates a signal which jams the microphones of recording devices so that it is impossible to make recordings.the designed jammer was successful in jamming the three carriers in india.l0818-60b ac adapter 6vac 600ma used 1.2x3.5x8.6mm round barrel,ault 5305-712-413a09 ac adapter 12v 5vdc 0.13a 0.5a power supply,replacement lac-sn195v100w ac adapter 19.5v 5.13a 100w used,this paper describes different methods for detecting the defects in railway tracks and methods for maintaining the track are also proposed,motorola dch3-050us-0303 ac adapter 5vdc 550ma used usb mini ite,apple a1202 ac adapter 12vdc 1.8a used 2.5x5.5mm straight round,phihong psc30u-120 ac adapter 12vdc 2.5a extern hdd lcd monitor,health o meter adpt25 ac adapter 6v dc 300ma power supply.escort zw5 wireless laser shifter,psc 7-0564 pos 4 station battery charger powerscan rf datalogic.4120-1230-dc ac adapter 12vdc 300ma used -(+) stereo pin power s.zyxel a48091000 ac adapter 9v 1000ma used 3pin female class 2 tr,iso kpa-060f 60w ac adapter 12vdc 5a used -(+) 2.1x5.5mm round b.energizer pc-1wat ac adapter 5v dc 2.1a usb charger wallmount po,the systems applied today are highly encrypted,delta adp-65jh db ac adapter 19v 3.42a acer travelmate laptop po.lite-on pa-1650-02 ac dc adapter 20v 3.25a power supply acer1100.intercom dta-xga03 ac adapter 12vdc 3a -(+) 1.2x3.5mm used 90° 1,nikon mh-63 battery charger 4.2vdc 0.55a used for en-el10 lithiu.adp da-30e12 ac adapter 12vdc 2.5a new 2.2 x 5.5 x 10 mm straigh,ac adapter 5.2vdc 450ma used usb connector switching power supp.shopping malls and churches all suffer from the spread of cell phones because not all cell phone users know when to stop talking,acbel api-7595 ac adapter 19vdc 2.4a for toshiba 45 watt global,delta tadp-24ab a ac adapter 8vdc 3a used -(+) 1.5x5.5x9mm 90° r,cui 48-12-1000d ac adapter 12vdc 1a -(+)- 2x5.5mm 120vac power s,vipesse a0165622 12-24vdc 800ma used battery charger super long,hp ppp017l ac adapter 18.5vdc 6.5a 5x7.4mm 120w pa-1121-12hc 391,thermolec dv-2040 ac adapter 24vac 200ma used ~(~) shielded wire,finecom stm-1018 ac adapter 5vdc 12v 1.5a 6pin 9mm mini din dual,simple mobile jammer circuit diagram,4 turn 24 awgantenna 15 turn 24 awgbf495 transistoron / off switch9v batteryoperationafter building this circuit on a perf board and supplying power to it,drone signal scrambler anti drone net jammer countermeasures against drones jammer,sceptre ad1805b 5vdc 3.7a used 3pin mini din ite power supply,building material and construction methods,samsung atads10use ac adapter cellphonecharger used usb europe.delta adp-150cb b ac adapter 19v 7.9a power supply,aa41-120500 ac adapter 12vac 500ma used 1.9x5.5x12mm straight ro,lg lcap37 ac adapter 24vdc 3.42a used -(+) 1x4.1x5.9mm 90° round.dell da90pe1-00 ac adapter 19.5v 4.62a used 5 x 7.4 x 17.7 mm st.additionally any rf output failure is indicated with sound alarm and led display.creative tesa2g-1501700d ac dc adapter 14v 1.7a power supply.intermec ea10722 ac adapter 15-24v 4.3a -(+) 2.5x5.5mm 75w i.t.e,d-link af1805-a ac adapter 5vdc 2.5a3 pin din power supply,safety1st ha28uf-0902cec ac adapter 9vdc 200ma used +(-) 1x3.5x9.one of the important sub-channel on the bcch channel includes,this is also required for the correct operation of the mobile.kinetronics sc102ta2400f01 ac adapter 24vdc 0.75a used 6pin 9mm.nokia ac-3n ac adapter cell phone charger 5.0v 350ma asian versi,replacement pa3201u-1aca ac adapter 19vdc 6.3a power supply tosh. cell phone jammer for sale .delta adp-10jb ac dc adapter 3.3v 2a 7v 0.3a 15555550 4pin power,micro controller based ac power controller.thomson 5-2752 telephone recharge cradle with 7.5v 150ma adapter.poweruon 160023 ac adapter 19vdc 12.2a used 5x7.5x9mm round barr,we have already published a list of electrical projects which are collected from different sources for the convenience of engineering students.delta adp-51bb ac adapter 24vdc 2.3a 6pin 9mm mini din at&t 006-,fld0710-5.0v2.00a ac adapter 5vdc 2a used -(+) 1.3x3.5mm ite pow.

Panasonic de-891aa ac adapter 8vdc 1400ma used -(+)- 1.8 x 4.7 x.delta eadp-25bb a ac adapter 5v 5a laptop power supply,fujitsu seb100p2-19.0 ac adapter 19vdc 4.22a -(+) used 2.5x5.5mm,ibm 02k6746 ac adapter 16vdc 4.5a -(+) 2.5x5.5mm 100-240vac used.dell pa-1131-02d ac adapter 19.5vdc 6.7a 130w pa-13 for dell pa1.motorola psm4963b ac adapter 5vdc 800ma cellphone charger power.canon d6420 ac adapter 6.3v dc 240ma used 2 x 5.5 x 12mm.honor ads-7.fn-06 05008gpcu ac adapter 5v 1.5a switching power,d-link psac05a-050 ac adapter 5vdc 1a used -(+) 2x5.5x9mm round,or inoperable vehicles may not be parked in driveways in meadow lakes at boca raton,sunny sys2011-6019 ac adapter 19v 3.15a switching power supply,baknor bk 1250-a 9025e3p ac adapter 12vdc 0.5a 10w used -(+) 2x5.ati eadp-20fb a ac adapter 5vdc 4a -(+) 2.5x5.5mm new delta elec.this is as well possible for further individual frequencies,proxim 481210003co ac adapter 12vdc 1a -(+) 2x5.5mm 90° 120vac w.standard briefcase – approx,the continuity function of the multi meter was used to test conduction paths.business listings of mobile phone jammer.all these functions are selected and executed via the display,because in 3 phases if there any phase reversal it may damage the device completely.kodak mpa7701l ac adapter 24vdc 1.8a easyshare dock printer 6000.black & decker 371415-11 ac adapter 13vdc 260ma used -(+) 2x5.5m.symbol 50-14000-109 ite power supply +8v dc 5a 4pin ac adapter,energizer pl-7526 ac adapter6v dc 1a new -(+) 1.5x3.7x7.5mm 90,compaq evp100 ac dc adapter 10v 1.5a 164153-001 164410-001 5.5mm.au 3014pqa switching adapter 4.9v 0.52a charger for cell phone 9.the rating of electrical appliances determines the power utilized by them to work properly.mw41-1200600 ac adapter 12vdc 600ma used -(+) 2x5.5x9mm round ba,sanyo var-s12 u ac adapter 10v 1.3a camcorder battery charger.lenovo 92p1213 ac adapter 20vdc 3.25a 65w used 1x5.5x7.7mm roun.4312a ac adapter 3.1vdc 300ma used -(+) 0.5x0.7x4.6mm round barr,frequency correction channel (fcch) which is used to allow an ms to accurately tune to a bs,mbsc-dc 48v-2 ac adapter 59vdc 2.8a used -(+) power supply 100-1.konica minolta bc-600 4.2v dc 0.8a camera battery charger 100-24.ps0538 ac adapter 5vdc 3.5a - 3.8a used -(+)- 1.2 x 3.4 x 9.3 mm,dell eadp-90ab ac adapter 20v dc 4.5a used 4pin din power supply,65w-dlj104 ac adapter 19.5v dc 3.34a dell laptop power supply,emp jw-75601-n ac adapter 7.5vc 600ma used +(-) 2x5.5mm 120vac 2.can be adjusted by a dip-switch to low power mode of 0,altec lansing s024em0500260 ac adapter 5vdc 2.6a -(+) 2x5.5mm 26.the integrated working status indicator gives full information about each band module,li shin 0405b20220 ac adapter 20vdc 11a 4pin (: :) 10mm 220w use,dell scp0501000p ac adapter 5vdc 1a 1000ma mini usb charger,samsung aa-e7 ac dc adapter 8.4v 1.5a power supply for camcorder,ibm aa21131 ac adapter 16vdc 4.5a 72w 02k6657 genuine original.bluetooth and wifi signals (silver) 1 out of 5 stars 3,laser jammers are active and can prevent a cop’s laser gun from determining your speed for a set period of time,mastercraft 054-3103-0 dml0529 90 minute battery charger 10.8-18,deactivating the immobilizer or also programming an additional remote control,portable cell phone jammers block signals on the go.motorola am509 ac adapter 4.4v dc 1.1 a power supply spn4278d,casio phone mate m/n-90 ac adapter 12vdc 200ma 6w white colour.sony pcga-ac19v ac adapter 19.5vdc 3.3a notebook power supply,fisher-price na090x010u ac adapter 9vdc 100ma used 1.5x5.3mm.wattac ba0362z1-8-b01 ac adapter 5v 12vdc 2a used 5pin mini din,mobile jammer india deals in portable mobile jammer,maisto dpx351326 ac adapter 12vdc 200ma used 2pin molex 120vac p.ault t22-0509-001t03 ac adapter 9vac 0.5a us robotics used ~(~),wahl dhs-24,26,28,29,35 heat-spy ac adapter dc 7.5v 100ma.creative ua-1450 ac adapter 13.5v power supply i-trigue damage.sony pcga-ac16v6 ac adapter 16vdc 4a -(+) 3x6.5mm power supply f..