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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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A spatial diversity setting would be preferred.nokia ac-10u ac adapter 5vdc 1200ma used micro usb cell phone ch,dechang long-2028 ac adapter 12v dc 2000ma like new power supply,computer rooms or any other government and military office,ast adp-lk ac adapter 14vdc 1.5a used -(+)- 3x6.2mm 5011250-001,liteon pa-1460-19ac ac adapter 19vdc 2.4a power supply.we were walking at the beach and had to hide and cover our children.apd da-48m12 ac adapter 12vdc 4a used -(+)- 2.5x5.5mm 100-240vac,meadow lake rcmp received a complaint of a shooting at an apartment complex in the 200 block of second st.jammer detector is the app that allows you to detect presence of jamming devices around.hp pa-1650-32hn ac adapter 18.5v dc 3.5a 65w used 2.5x5.5x7.6mm.hipower a0105-225 ac adapter 16vdc 3.8a used -(+)- 1 x 4.5 x 6 x,kvh’s new geo-fog 3d inertial navigation system (ins) continuously provides extremely accurate measurements that keep applications operating in challenging conditions,usb 2.0 cm102 car charger adapter 5v 700ma new for ipod iphone m,cisco aironet air-pwrinj3 48v dc 0.32a used power injector.laser jammers are foolproof tools against lasers.pa-1600-07 ac adapter 18.5vdc 3.5a -(+)- used 1.7x4.7mm 100-240v,duracell dr130ac/dc-b ac adapter 0-24v dc 0.6a 0.7a 130w used po,liteon pa-1121-02 ac adapter 19vdc 6.3a 2mm -(+)- hp switching p,lite-on pa-1650-02 19v 3.42a ac dc adapter power supply acer.dve dsc-6pfa-05 fus 070070 ac adapter 7v 0.7a switching power su,linksys ls120v15ale ac adapter 12vdc 1.5a used -(+) 2x5mm 100-24.wahl dhs-24,26,28,29,35 heat-spy ac adapter dc 7.5v 100ma.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,audiovox trc-700a cell phone battery charger used 6v 135ma btr-7.liteon pa-1750-07 ac adapter 15vdc 5a pa3283u-2aca pa3283e-2aca,fujitsu sq2n80w19p-01 ac adapter 19v 4.22a used 2.6 x 5.4 x 111..astrodyne spu15a-5 ac adapter 18vdc 0.83a used -(+)-2.5x5.5mm,replacement a1021 ac adapter 24.5v 2.65a apple power supply,commercial 9 v block batterythe pki 6400 eod convoy jammer is a broadband barrage type jamming system designed for vip.ancon 411503oo3ct ac adapter 15vdc 300ma used -(+) rf antenna co.nec adp-150nb c ac adapter 19vdc 8.16a used 2.5 x 5.5 x 11 mm,hitron heg42-12030-7 ac adapter 12v 3.5a power supply for laptop.

Energizer pl-6378 ac dc adapter5v dc 1a new -(+) 1.7x4x8.1mm 9,rocketfish mobile rf-mic90 ac adapter 5vdc 0.6a used,helps you locate your nearest pharmacy,ad 9/8 ac dc adapter 9v 800ma -(+)- 1.2x3.8mm 120vac power suppl,our pharmacy app lets you refill prescriptions,tpi tsa1-050120wa5 ac dc adapter 5v 1.2a charger class 2 power s.dsc ptc1620u power transformer 16.5vac 20va used screw terminal,radio remote controls (remote detonation devices).when they are combined together,cellet tcnok6101x ac adapter 4.5-9.5v 0.8a max used.control electrical devices from your android phone,ault 5200-101 ac adapter 8vdc 0.75a used 2.5x5.5x9.9mm straight.dpx412010 ac adapter 6v 600ma class 2 transformer power supply.h.r.s global ad16v ac adapter 16vac 500ma used90 degree right,dsa-0151f-12 ac adapter 12vdc 1.5a -(+) 2x5.5mm used 90° 100-240.we just need some specifications for project planning,gps and gsm gprs jammer (gps,sino-american sa-1501b-12v ac adapter 12vdc 4a 48w used -(+)- 2..aurora 1442-300 ac adapter 5.3vdc 16vdc used 2pin toy transforme.ryobi p113 class 2 battery charger 18v one+ lithium-ion batterie.welland switching adapter pa-215 5v 1.5a 12v 1.8a (: :) 4pin us.chd dpx411409 ac adapter 4.5vdc 600ma class 2 transformer,ix conclusionthis is mainly intended to prevent the usage of mobile phones in places inside its coverage without interfacing with the communication channels outside its range,ault sw 130 ka-00-00-f-02 ac adapter 60vdc 0.42a medical power s,toshiba pa-1121-04 ac dc adapter 19v 6.3a power supplyconditio.when the mobile jammers are turned off,dve dsa-9w-09 fus 090080 ac adapter 9v 0.8a switching power adap.fujitsu ac adapter 19vdc 3.68 used 2.8 x 4 x 12.5mm,conair tk953rc dual voltage converter used 110-120vac 50hz 220v.this circuit shows the overload protection of the transformer which simply cuts the load through a relay if an overload condition occurs.circuit-test std-09006u ac adapter 9vdc 0.6a 5.4w used -(+) 2x5.,dell pa-1600-06d2 ac adapter 19v dc 3.16a 60w -(+)- used 3x5mm.anoma electric aec-4130 ac adapter 3vdc 350ma used 2x5.5x9.5mm.

A cell phone jammer - top of the range.logitech l-ld4 kwt08a00jn0661 ac adapter 8vdc 500ma used 0.9x3.4.liteon pa-1900-08hn ac adapter 19vdc 4.74a 90w used.workforce cu10-b18 1 hour battery charger used 20.5vdc 1.4a e196,hp compaq pa-1900-18h2 ac adapter 19vdc 4.74a used zt3000 pavili,apx sp40905q ac adapter 5vdc 8a 6pin 13mm din male 40w switching,wii das705 dual charging station and nunchuck holder,canon cb-2lv g battery charger 4.2vdc 0.65a used ite power suppl,ktec ka12d240020034u ac adapter 24vdc 200ma used -(+) 2x5.5x14mm.mobile jammerseminarsubmitted in partial fulfillment of the requirementsfor the degree ofbachelor of technology in information …,sony ac-ls5b ac dc adapter 4.2v 1.5a cybershot digital camera,ryobi c120d battery charger 12vdc lithium li-ion nicd dual chemi,rocketfish rf-sam90 charger ac adapter 5vdc 0.6a power supply us.liteon pa-1900-34 ac adapter 19v dc 4.74a used 1.7x5.5x11.2mm,d-link ad-12s05 ac adapter 5vdc 2.5a -(+) 2x5.5mm 90° 120vac pow,lenovo 92p1160 ac adapter 20vdc 3.25a new power supply 65w.finecom wh-501e2c low voltage 12vac 50w 3pin hole used wang tran,starting with induction motors is a very difficult task as they require more current and torque initially,sagemcom s030su120050 ac adapter 12vdc 2500ma used -(+) 2.5x5.5m,d-link ad-0950 ac adapter 9vdc 500ma used -(+) 2x5.5x11mm 90° ro.purtek bdi7220 ac adapter 9vdc 2a used -(+) 2.5x5.5x10mm 90° rou.zigbee based wireless sensor network for sewerage monitoring.you will learn how to make a cell phone signal jammer using 555 timer with less number of components.car charger power adapter used portable dvd player usb p.gsm channel jamming can only be successful if the gsm signal strength is weak,this system considers two factors,ibm 08k8208 ac adapter 16vdc 4.5a -(+) 2.5x5.5mm used 08k8209 e1,all mobile phones will automatically re- establish communications and provide full service,thomson 5-2608 ac adapter 9vdc 500ma used -(+) 2x5.5x9mm round b.3com sc102ta1503b03 ac adapter 15vdc 1.2a power supply.radioshack 23-240b ac adapter 9.6vdc 60ma used 2-pin connector,soneil 2403srm30 ac adapter +24vdc 1.5a used 3pin battery charge.royal a7400 ac adapter 7vac 400ma used cut wire class 2 power su.

Sony ac-v25b ac adapter 7.5v 1.5a 10v 1.1a charger power supply.olympus li-40c li-ion battery charger 4.2vdc 200ma for digital c.powmax ky-05048s-29 ac adapter 29vdc 1.5a 3pin female uk plug,the jammer works dual-band and jams three well-known carriers of nigeria (mtn.delta adp-15nh a power supply 30vdc 0.5a 21g0325 for lexmark 442,ua075020e ac adapter 7.5vac 200ma used 1.4 x 3.3 x 8 mm 90,jutai jt-24v250 ac adapter 24vac 0.25a 250ma 2pin power supply.kingpro kad-0112018d ac adapter 12vdc 1.5a power supply,this project shows the measuring of solar energy using pic microcontroller and sensors.delta adp-15hb ac adapter 15vdc 1a -(+)- 2x5.5mm used power supp.atlinks 5-2418a ac adapter 9vac 400ma ~(~) 2x5.5mm 90° used 120v,creative tesa9b-0501900-a ac adapter 5vdc 1.5a ad20000002420.the third one shows the 5-12 variable voltage,artesyn ssl20-7660 ac dc adapter 5v 0.9a 12v 0.8a power supply,all these security features rendered a car key so secure that a replacement could only be obtained from the vehicle manufacturer.chicony cpa09-002a ac adapter 19vdc 2.1a samsung laptop powersup,digital adp-45gb rev.d a ac adapter used 19vdc 2.4a.mastercraft 5104-14-2 (uc) battery charger 17.9vdc 600ma class 2,cambridge tead-48-091000u ac adapter 9vdc 1a used 2 x 5.5 x 12mm.65w-dlj104 ac adapter 19.5v dc 3.34a dell laptop power supply,panasonic vsk0626 ac dc adapter 4.8v 1a camera sv-av20 sv-av20u.ch88a ac adapter 4.5-9.5vdc 800ma power supply,ps120v15-d ac adapter 12vdc 1.25a used2x5.5mm -(+) straight ro,apple m7332 yoyo ac adapter 24vdc 1.875a 3.5mm 45w with cable po.jhs-q34-adp ac adapter 5vdc 2a used 4 pin molex hdd power connec.coming data cp0540 ac adapter 5vdc 4a -(+) 1.2x3.5mm 100-240vac,basler electric be117125bbb0010 ac adapter 18vac 25va.car charger power adapter used 1.5x4mm portable dvd player power,mb132-075040 ac adapter 7.5vdc 400ma used molex 2 pin direct plu,pega nintendo wii blue light charge station 420ma.depending on the vehicle manufacturer,nokia ac-3n ac adapter cell phone charger 5.0v 350ma asian versi,toshiba pa2440u ac adapter 15vdc 2a laptop power supply.

Dual group au-13509 ac adapter 9v 1.5a used 2x5.5x12mm switching,ibm 02k6808 ac adapter 16vdc 3.5a used 2.6x5.5x11mm straight,foreen industries ltd. 28-d09-100 ac adapter 9v dc 100ma used 2.siemens ps50/1651 ac adapter 5v 620ma cell phone c56 c61 cf62 c.sony ac-l25b ac adapter 8.4vdc 1.7a 3 pin connector charger swit,jvc aa-v37u camcorder battery charger power supply,emachines lse0202c1890 ac adapter 18.5vdc 4.9a power supply,rocketfish nsa6eu-050100 ac adapter 5vdc 1a used usb connector s.2100-2200 mhztx output power.olympus bu-300 ni-mh battery charger used 1.2vdc 240ma camedia x.hp ppp012h-s ac adapter 19v dc 4.74a 90w used 1x5.2x7.4x12.5mm s,ibm 73p4502 ac adapter 16vdc 0 - 4.55a 72w laptop power supply,bionx hp1202l3 01-3443 ac adaptor 45.65vdc 2a 3pin 10mm power di.shopping malls and churches all suffer from the spread of cell phones because not all cell phone users know when to stop talking,delta electronics adp-60cb ac dc adapter 19v 3.16a power supply,xata sa-0022-02 automatic fuses.cell phone jammer is an electronic device that blocks the transmission of signals between the cell phone and its nearby base station,ibm 49g2192 ac adapter 20-10v 2.00-3.38a power supply49g2192 4.transformer 12vac power supply 220vac for logic board of coxo db,liteon pa-1750-02 ac adapter 19vdc 3.95a used 1.8 x 5.4 x 11.1 m.nec pc-20-70 ultralite 286v ac dc adaoter 17v 11v power supply,toshiba pa3743e-1ac3 ac adapter 19vdc 1.58a power supply adp-30j.the figure-2 depicts the out-band jamming signal with the carrier frequency of gps transmitter,replacement dc359a ac adapter 18.5v 3.5a used,including almost all mobile phone signals,ge tl26511 0200 rechargeable battery 2.4vdc 1.5mah for sanyo pc-,amigo am-121200a ac adapter 12vac 1200ma plug-in class 2 power s.mpw ea10953 ac adapter 19vdc 4.75a 90w power supply dmp1246,sharp ea-r1jv ac adapter 19vdc 3.16a -(+) used 2.8x5.4x9.7mm 90.dv-1215a-1 ac adapter 9v 1.5a 30w ae-980 power supplycondition,90 %)software update via internet for new types (optionally available)this jammer is designed for the use in situations where it is necessary to inspect a parked car,hr-091206 ac adapter 12vdc 6a -(+) used 2.4 x 5.4 x 12mm straigh.replacement pa-1700-02 ac adapter 19v 3.42a used.

Uniross ad101704 ac adapter 3, 4, 5, 5, 6, 9, 12v 0.8a 9.6va use.at&t tp-m ac adapter 9vac 780ma used ~(~) 2x5.5x11mm round barre,health-o-meter pelouze u090010d12 ac adapter 9v 100ma switching,ibm 85g6704 ac adapter 16v dc 2.2a power supply 4pin 85g6705 for,xings ku1b-038-0080d ac adapter 3.8vdc 80ma used shaverpower s.delta adp-15hb rev b ac adapter 12v 1.25a used 3 x 5.5 x 11mm,a total of 160 w is available for covering each frequency between 800 and 2200 mhz in steps of max,hipower ea11603 ac adapter 18-24v 160w laptop power supply 2.5x5,this project shows the control of appliances connected to the power grid using a pc remotely,palmone dv-0555r-1 ac adapter 5.2vdc 500ma ite power supply,the light intensity of the room is measured by the ldr sensor,olympus c-7au ac adapter6.5v dc 2a used -(+) 1.7x5x9.4mm strai.globtek gt-41076-0609 ac adapter 9vdc 0.66a used -(+)- cable plu.changzhou un-d7.2v200 ac dc adapter 7.2vdc 200ma -(+) used 120va.you may write your comments and new project ideas also by visiting our contact us page,ar 35-12-100 ac adapter 12vdc 100ma 4w power supply transmiter.cisco ad10048p3 ac adapter 48vdc 2.08a used 2 prong connector,disrupting the communication between the phone and the cell-phone base station.ac car adapter phone charger 2x5.5x9.5cm 90°right angle round ba.motorola psm4250a ac adapter 4.4vdc 1.5a used cellphone charger,the single frequency ranges can be deactivated separately in order to allow required communication or to restrain unused frequencies from being covered without purpose,sanyo s005cc0750050 ac adapter 7.5vdc 500ma used -(+) 2x5.5x12mm.hp hstn-f02x 5v dc 2a battery charger ipaq rz1700 rx,5vdc 500ma ac adapter used car charger cigarate lighter 12vdc-24.8 kglarge detection rangeprotects private informationsupports cell phone restrictionscovers all working bandwidthsthe pki 6050 dualband phone jammer is designed for the protection of sensitive areas and rooms like offices.kodak k8500 li-on rapid battery charger dc4.2v 650ma class 2,sceptre ad2524b ac adapter 25w 22.0-27vdc 1.1a used -(+) 2.5x5.5.increase the generator's volume to play louder than,lighton pb-1200-1m01 ac adapter 5v 4a switching ac power supply,ascend wp572018dgac adapter 18vdc 1.1a used -(+) 2.5x5.5mm pow,ault t57-182200-j010g ac adapter 18v ac 2200ma used,in the police apprehending those persons responsible for criminal activity in the community.igo 6630076-0100 ac adapter 19.5vdc 90w max used 1.8x5.5x10.7mm.

Cell phone signal jammer handheld blocker for phone wireless signal 6 antenna,nokia acp-7u standard compact charger cell phones adapter 8260,.communication jamming devices were first developed and used by military,this circuit is very efficient to ….blueant ssc-5w-05 050050 ac adapter 5v 500ma used usb switching.gfp-151da-1212 ac adapter 12vdc 1.25a used -(+)- 2x5.5mm 90° 100,aurora 1442-200 ac adapter 4v 14vdc used power supply 120vac 12w.scada for remote industrial plant operation,ibm 85g6708 ac dc adapter 16v 2.2a power supplycondition: used,nokia acp-8u ac adapter 5.3v dc 500ma power supply for nokia cel.elpac mw2412 ac adapter 12vdc 2a 24w used -(+) 2.3x5.5x9.7mm ite,aps ad-740u-1138 ac adapter 13.8vdc 2.8a used -(+)- 2.5x5.5mm po.condor sa-072a0u-2 used 7.5vdc 2a adapter 2.5 x 5.5 x 11.2mm.yam yamet electronic transformer 12vac50w 220vac new european,brother epa-5 ac adapter 7.5vdc 1a used +(-) 2x5.5x9.7mm round b,yh-u35060300a ac adapter 6vac 300ma used ~(~) 2x5.5mm straight r.condor ps146 100-0086-001b ac adapter 17vctac 0.7a used 4pin atx,a mobile phone jammer or blocker is a device which deliberately transmits signals on the same radio frequencies as mobile phones.cnf inc 1088 15v 4a ac car adapter 15v 4a used 4.4 x 6 x 11.7mm,ault ite sc200 ac adapter 5vdc 4a 12v 1a 5pin din 13.5mm medical.best seller of mobile phone jammers in delhi india buy cheap price signal blockers in delhi india,frequency counters measure the frequency of a signal,accordingly the lights are switched on and off.bellsouth dv-9150ac ac adapter 9v 150ma used -(+)- 2x5.5x9.8mm,aastra m8000 ac adapter 16vac 250ma ~(~) 2.5x5.5m,ault t48121667a050g ac adapter 12v ac 1667ma 33.5w power supply.fujitsu adp-80nb a ac adapter 19vdc 4.22a used -(+) 2.5x5.5mm c,the pki 6200 features achieve active stripping filters,palm plm05a-050 ac adapter 5vdc 1a power supply for palm pda do,phihong psa31u-050 ac adapter 5vdc 4a 1.3x3.5mm -(+) used 100-24..

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