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Monitoring the Ionosphere with Integer-Leveled GPS Measurements By Simon Banville, Wei Zhang, and  Richard B. Langley INNOVATION INSIGHTS by Richard Langley IT’S NOT JUST FOR POSITIONING, NAVIGATION, AND TIMING. Many people do not realize that GPS is being used in a variety of ways in addition to those of its primary mandate, which is to provide accurate position, velocity, and time information. The radio signals from the GPS satellites must traverse the Earth’s atmosphere on their way to receivers on or near the Earth’s surface. The signals interact with the atoms, molecules, and charged particles that make up the atmosphere, and the process slightly modifies the signals. It is these modified or perturbed signals that a receiver actually processes. And should a signal be reflected or diffracted by some object in the vicinity of the receiver’s antenna, the signal is further perturbed — a phenomenon we call multipath. Now, these perturbations are a bit of a nuisance for conventional users of GPS. The atmospheric effects, if uncorrected, reduce the accuracy of the positions, velocities, and time information derived from the signals. However, GPS receivers have correction algorithms in their microprocessor firmware that attempt to correct for the effects. Multipath, on the other hand, is difficult to model although the use of sophisticated antennas and advanced receiver technologies can minimize its effect. But there are some GPS users who welcome the multipath or atmospheric effects in the signals. By analyzing the fluctuations in signal-to-noise-ratio due to multipath, the characteristics of the reflector can be deduced. If the reflector is the ground, then the amount of moisture in the soil can be measured. And, in wintery climes, changes in snow depth can be tracked from the multipath in GPS signals. The atmospheric effects perturbing GPS signals can be separated into those that are generated in the lower part of the atmosphere, mostly in the troposphere, and those generated in the upper, ionized part of the atmosphere — the ionosphere. Meteorologists are able to extract information on water vapor content in the troposphere and stratosphere from the measurements made by GPS receivers and regularly use the data from networks of ground-based continuously operating receivers and those operating on some Earth-orbiting satellites to improve weather forecasts. And, thanks to its dispersive nature, the ionosphere can be studied by suitably combining the measurements made on the two legacy frequencies transmitted by all GPS satellites. Ground-based receiver networks can be used to map the electron content of the ionosphere, while Earth-orbiting receivers can profile electron density. Even small variations in the distribution of ionospheric electrons caused by earthquakes; tsunamis; and volcanic, meteorite, and nuclear explosions can be detected using GPS. In this month’s column, I am joined by two of my graduate students, who report on an advance in the signal processing procedure for better monitoring of the ionosphere, potentially allowing scientists to get an even better handle on what’s going on above our heads. Representation and forecast of the electron content within the ionosphere is now routinely accomplished using GPS measurements. The global distribution of permanent ground-based GPS tracking stations can effectively monitor the evolution of electron structures within the ionosphere, serving a multitude of purposes including satellite-based communication and navigation. It has been recognized early on that GPS measurements could provide an accurate estimate of the total electron content (TEC) along a satellite-receiver path. However, because of their inherent nature, phase observations are biased by an unknown integer number of cycles and do not provide an absolute value of TEC. Code measurements (pseudoranges), although they are not ambiguous, also contain frequency-dependent biases, which again prevent a direct determination of TEC. The main advantage of code over phase is that the biases are satellite- and receiver-dependent, rather than arc-dependent. For this reason, the GPS community initially adopted, as a common practice, fitting the accurate TEC variation provided by phase measurements to the noisy code measurements, therefore removing the arc-dependent biases. Several variations of this process were developed over the years, such as phase leveling, code smoothing, and weighted carrier-phase leveling (see Further Reading for background literature). The main challenge at this point is to separate the code inter-frequency biases (IFBs) from the line-of-sight TEC. Since both terms are linearly dependent, a mathematical representation of the TEC is usually required to obtain an estimate of each quantity. Misspecifications in the model and mapping functions were found to contribute significantly to errors in the IFB estimation, suggesting that this process would be better performed during nighttime when few ionospheric gradients are present. IFB estimation has been an ongoing research topic for the past two decades are still remains an issue for accurate TEC determination. A particular concern with IFBs is the common assumption regarding their stability. It is often assumed that receiver IFBs are constant during the course of a day and that satellite IFBs are constant for a duration of a month or more. Studies have clearly demonstrated that intra-day variations of receiver instrumental biases exist, which could possibly be related to temperature effects. This assumption was shown to possibly introduce errors exceeding 5 TEC units (TECU) in the leveling process, where 1 TECU corresponds to 0.162 meters of code delay or carrier advance at the GPS L1 frequency (1575.42 MHz). To overcome this limitation, one could look into using solely phase measurements in the TEC estimation process, and explicitly deal with the arc-dependent ambiguities. The main advantage of such a strategy is to avoid code-induced errors, but a larger number of parameters needs to be estimated, thereby weakening the strength of the adjustment. A comparison of the phase-only (arc-dependent) and phase-leveled (satellite-dependent) models showed that no model performs consistently better. It was found that the satellite-dependent model performs better at low-latitudes since the additional ambiguity parameters in the arc-dependent model can absorb some ionospheric features (such as gradients). On the other hand, when the mathematical representation of the ionosphere is realistic, the leveling errors may more significantly impact the accuracy of the approach. The advent of precise point positioning (PPP) opened the door to new possibilities for slant TEC (STEC) determination. Indeed, PPP can be used to estimate undifferenced carrier-phase ambiguity parameters on L1  and L2, which can then be used to remove the ambiguous characteristics of the carrier-phase observations. To obtain undifferenced ambiguities free from ionospheric effects, researchers have either used the widelane/ionosphere-free (IF) combinations, or the Group and Phase Ionospheric Calibration (GRAPHIC) combinations. One critical problem with such approaches is that code biases propagate into the estimated ambiguity parameters. Therefore, the resulting TEC estimates are still biased by unknown quantities, and might suffer from the unstable datum provided by the IFBs. The recent emergence of ambiguity resolution in PPP presented sophisticated means of handling instrumental biases to estimate integer ambiguity parameters. One such technique is the decoupled-clock method, which considers different clock parameters for the carrier-phase and code measurements. In this article, we present an “integer-leveling” method, based on the decoupled-clock model, which uses integer carrier-phase ambiguities obtained through PPP to level the carrier-phase observations. Standard Leveling Procedure This section briefly reviews the basic GPS functional model, as well as the observables usually used in ionospheric studies. A common leveling procedure is also presented, since it will serve as a basis for assessing the performance of our new method. Ionospheric Observables. The standard GPS functional model of dual-frequency carrier-phase and code observations can be expressed as:    (1)     (2)    (3)    (4) where Φi j is the carrier-phase measurement to satellite j on the Li link and, similarly, Pi j is the code measurement on Li. The term  is the biased ionosphere-free range between the satellite and receiver, which can be decomposed as:    (5) The instantaneous geometric range between the satellite and receiver antenna phase centers is ρ j. The receiver and satellite clock errors, respectively expressed as dT and dtj, are expressed here in units of meters. The term Tj stands for the tropospheric delay, while the ionospheric delay on L1 is represented by I j and is scaled by the frequency-dependent constant μ for L2, where . The biased carrier-phase ambiguities are symbolized by  and are scaled by their respective wavelengths (λi). The ambiguities can be explicitly written as:    (6) where Ni j is the integer ambiguity, bi is a receiver-dependent bias, and bi j is a satellite-dependent bias. Similarly, Bi and Bi j are instrumental biases associated with code measurements. Finally, ε contains unmodeled quantities such as noise and multipath, specific to the observable. The overbar symbol indicates biased quantities. In ionospheric studies, the geometry-free (GF) signal combinations are formed to virtually eliminate non-dispersive terms and thus provide a better handle on the quantity of interest:    (7)    (8) where IFBr and IFB j represent the code inter-frequency biases for the receiver and satellite, respectively. They are also commonly referred to as differential code biases (DCBs). Note that the noise terms (ε) are neglected in these equations for the sake of simplicity. Weighted-Leveling Procedure. As pointed out in the introduction, the ionospheric observables of Equations (7) and (8) do not provide an absolute level of ionospheric delay due to instrumental biases contained in the measurements. Assuming that these biases do not vary significantly in time, the difference between the phase and code observations for a particular satellite pass should be a constant value (provided that no cycle slip occurred in the phase measurements). The leveling process consists of removing this constant from each geometry-free phase observation in a satellite-receiver arc:    (9) where the summation is performed for all observations forming the arc. An elevation-angle-dependent weight (w) can also be applied to minimize the noise and multipath contribution for measurements made at low elevation angles. The double-bar symbol indicates leveled observations. Integer-Leveling Procedure The procedure of fitting a carrier-phase arc to code observations might introduce errors caused by code noise, multipath, or intra-day code-bias variations. Hence, developing a leveling approach that relies solely on carrier-phase observations is highly desirable. Such an approach is now possible with the recent developments in PPP, allowing for ambiguity resolution on undifferenced observations. This procedure has gained significant momentum in the past few years, with several organizations generating “integer clocks” or fractional offset corrections for recovering the integer nature of the undifferenced ambiguities. Among those organizations are, in alphabetical order, the Centre National d’Études Spatiale; GeoForschungsZentrum; GPS Solutions, Inc.; Jet Propulsion Laboratory; Natural Resources Canada (NRCan); and Trimble Navigation. With ongoing research to improve convergence time, it would be no surprise if PPP with ambiguity resolution would become the de facto methodology for processing data on a station-by-station basis. The results presented in this article are based on the products generated at NRCan, referred to as “decoupled clocks.” The idea behind integer leveling is to introduce integer ambiguity parameters on L1 and L2, obtained through PPP processing, into the geometry-free linear combination of Equation (7). The resulting integer-leveled observations, in units of meters, can then be expressed as:    (10) where  and  are the ambiguities obtained from the PPP solution, which should be, preferably, integer values. Since those ambiguities are obtained with respect to a somewhat arbitrary ambiguity datum, they do not allow instant recovery of an unbiased slant ionospheric delay. This fact was highlighted in Equation (10), which indicates that, even though the arc-dependency was removed from the geometry-free combination, there are still receiver- and satellite-dependent biases (br and b j, respectively) remaining in the integer-leveled observations. The latter are thus very similar in nature to the standard-leveled observations, in the sense that the biases br and b j replace the well-known IFBs. As a consequence, integer-leveled observations can be used with any existing software used for the generation of TEC maps. The motivation behind using integer-leveled observations is the mitigation of leveling errors, as explained in the next sections. Slant TEC Evaluation As a first step towards assessing the performance of integer-leveled observations, STEC values are derived on a station-by-station basis. The slant ionospheric delays are then compared for a pair of co-located receivers, as well as with global ionospheric maps (GIMs) produced by the International GNSS Service (IGS). Leveling Error Analysis. Relative leveling errors between two co-located stations can be obtained by computing between-station differences of leveled observations:    (11) where subscripts A and B identify the stations involved, and εl is the leveling error. Since the distance between stations is short (within 100 meters, say), the ionospheric delays will cancel, and so will the satellite biases (b j) which are observed at both stations. The remaining quantities will be the (presumably constant) receiver biases and any leveling errors. Since there are no satellite-dependent quantities in Equation (11), the differenced observations obtained should be identical for all satellites observed, provided that there are no leveling errors. The same principles apply to observations leveled using other techniques discussed in the introduction. Hence, Equation (11) allows comparison of the performance of various leveling approaches. This methodology has been applied to a baseline of approximately a couple of meters in length between stations WTZJ and WTZZ, in Wettzell, Germany. The observations of both stations from March 2, 2008, were leveled using a standard leveling approach, as well as the method described in this article. Relative leveling errors computed using Equation (11) are displayed in Figure 1, where each color represents a different satellite. It is clear that code noise and multipath do not necessarily average out over the course of an arc, leading to leveling errors sometimes exceeding a couple of TECU for the standard leveling approach (see panel (a)). On the other hand, integer-leveled observations agree fairly well between stations, where leveling errors were mostly eliminated. In one instance, at the beginning of the session, ambiguity resolution failed at both stations for satellite PRN 18, leading to a relative error of 1.5 TECU, more or less. Still, the advantages associated with integer leveling should be obvious since the relative error of the standard approach is in the vicinity of -6 TECU for this satellite. FIGURE 1. Relative leveling errors between stations WTZJ and WTZZ on March 2, 2008: (a) standard-leveled observations and (b) integer-leveled observations. The magnitude of the leveling errors obtained for the standard approach agrees fairly well with previous studies (see Further Reading). In the event that intra-day variations of the receiver IFBs are observed, even more significant biases were found to contaminate standard-leveled observations. Since the decoupled-clock model used for ambiguity resolution explicitly accounts for possible variations of any equipment delays, the estimated ambiguities are not affected by such effects, leading to improved leveled observations. STEC Comparisons. Once leveled observations are available, the next step consists of separating STEC from instrumental delays. This task can be accomplished on a station-by-station basis using, for example, the single-layer ionospheric model. Replacing the slant ionospheric delays (I j) in Equation (10) by a bilinear polynomial expansion of VTEC leads to:     (12) where M(e) is the single-layer mapping function (or obliquity factor) depending on the elevation angle (e) of the satellite. The time-dependent coefficients a0, a1, and a2 determine the mathematical representation of the VTEC above the station. Gradients are modeled using Δλ, the difference between the longitude of the ionospheric pierce point and the longitude of the mean sun, and Δϕ, the difference between the geomagnetic latitude of the ionospheric pierce point and the geomagnetic latitude of the station. The estimation procedure described by Attila Komjathy (see Further Reading) is followed in all subsequent tests. An elevation angle cutoff of 10 degrees was applied and the shell height used was 450 kilometers. Since it is not possible to obtain absolute values for the satellite and receiver biases, the sum of all satellite biases was constrained to a value of zero. As a consequence, all estimated biases will contain a common (unknown) offset. STEC values, in TECU, can then be computed as:      (13) where the hat symbol denotes estimated quantities, and  is equal to zero (that is, it is not estimated) when biases are obtained on a station-by-station basis. The frequency, f1, is expressed in Hz. The numerical constant 40.3, determined from values of fundamental physical constants, is sufficiently precise for our purposes, but is a rounding of the more precise value of 40.308. While integer-leveled observations from co-located stations show good agreement, an external TEC source is required to make sure that both stations are not affected by common errors. For this purpose, Figure 2 compares STEC values computed from GIMs produced by the IGS and STEC values derived from station WTZJ using both standard- and integer-leveled observations. The IGS claims root-mean-square errors on the order of 2-8 TECU for vertical TEC, although the ionosphere was quiet on the day selected, meaning that errors at the low-end of that range are expected. Errors associated with the mapping function will further contribute to differences in STEC values. As apparent from Figure 2, no significant bias can be identified in integer-leveled observations. On the other hand, negative STEC values (not displayed in Figure 2) were obtained during nighttimes when using standard-leveled observations, a clear indication that leveling errors contaminated the observations. FIGURE 2. Comparison between STEC values obtained from a global ionospheric map and those from station WTZJ using standard- and integer-leveled observations. STEC Evaluation in the Positioning Domain. Validation of slant ionospheric delays can also be performed in the positioning domain. For this purpose, a station’s coordinates from processing the observations in static mode (that is, one set of coordinates estimated per session) are estimated using (unsmoothed) single-frequency code observations with precise orbit and clock corrections from the IGS and various ionosphere-correction sources. Figure 3 illustrates the convergence of the 3D position error for station WTZZ, using STEC corrections from the three sources introduced previously, namely: 1) GIMs from the IGS, 2) STEC values from station WTZJ derived from standard leveling, and 3) STEC values from station WTZJ derived from integer leveling. The reference coordinates were obtained from static processing based on dual-frequency carrier-phase and code observations. The benefits of the integer-leveled corrections are obvious, with the solution converging to better than 10 centimeters. Even though the distance between the stations is short, using standard-leveled observations from WTZJ leads to a biased solution as a result of arc-dependent leveling errors. Using a TEC map from the IGS provides a decent solution considering that it is a global model, although the solution is again biased. FIGURE 3. Single-frequency code-based positioning results for station WTZZ (in static mode) using different ionosphere-correction sources: GIM and STEC values from station WTZJ using standard- and integer-leveled observations. This station-level analysis allowed us to confirm that integer-leveled observations can seemingly eliminate leveling errors, provided that carrier-phase ambiguities are fixed to proper integer values. Furthermore, it is possible to retrieve unbiased STEC values from those observations by using common techniques for isolating instrumental delays. The next step consisted of examining the impacts of reducing leveling errors on VTEC. VTEC Evaluation When using the single-layer ionospheric model, vertical TEC values can be derived from the STEC values of Equation (13) using:     (14) Dividing STEC by the mapping function will also reduce any bias caused by the leveling procedure. Hence, measures of VTEC made from a satellite at a low elevation angle will be less impacted by leveling errors. When the satellite reaches the zenith, then any bias in the observation will fully propagate into the computed VTEC values. On the other hand, the uncertainty of the mapping function is larger at low-elevation angles, which should be kept in mind when analyzing the results. Using data from a small regional network allows us to assess the compatibility of the VTEC quantities between stations. For this purpose, GPS data collected as a part of the Western Canada Deformation Array (WCDA) network, still from March 2, 2008, was used. The stations of this network, located on and near Vancouver Island in Canada, are indicated in Figure 4. Following the model of Equation (12), all stations were integrated into a single adjustment to estimate receiver and satellite biases as well as a triplet of time-varying coefficients for each station. STEC values were then computed using Equation (13), and VTEC values were finally derived from Equation (14). This procedure was again implemented for both standard- and integer-leveled observations. FIGURE 4. Network of stations used in the VTEC evaluation procedures. To facilitate the comparison of VTEC values spanning a whole day and to account for ionospheric gradients, differences with respect to the IGS GIM were computed. The results, plotted by elevation angle, are displayed in Figure 5 for all seven stations processed (all satellite arcs from the same station are plotted using the same color). The overall agreement between the global model and the station-derived VTECs is fairly good, with a bias of about 1 TECU. Still, the top panel demonstrates that, at high elevation angles, discrepancies between VTEC values derived from standard-leveled observations and the ones obtained from the model have a spread of nearly 6 TECU. With integer-leveled observations (see bottom panel), this spread is reduced to approximately 2 TECU. It is important to realize that the dispersion can be explained by several factors, such as remaining leveling errors, the inexact receiver and satellite bias estimates, and inaccuracies of the global model. It is nonetheless expected that leveling errors account for the most significant part of this error for standard-leveled observations. For satellites observed at a lower elevation angle, the spread between arcs is similar for both methods (except for station UCLU in panel (a) for which the estimated station IFB parameter looks significantly biased). As stated previously, the reason is that leveling errors are reduced when divided by the mapping function. The latter also introduces further errors in the comparisons, which explains why a wider spread should typically be associated with low-elevation-angle satellites. Nevertheless, it should be clear from Figure 5 that integer-leveled observations offer a better consistency than standard-leveled observations. FIGURE 5. VTEC differences, with respect to the IGS GIM, for all satellite arcs as a function of the elevation angle of the satellite, using (a) standard-leveled observations and (b) integer-leveled observations. Conclusion The technique of integer leveling consists of introducing (preferably) integer ambiguity parameters obtained from PPP into the geometry-free combination of observations. This process removes the arc dependency of the signals, and allows integer-leveled observations to be used with any existing TEC estimation software. While leveling errors of a few TECU exist with current procedures, this type of error can be eliminated through use of our procedure, provided that carrier-phase ambiguities are fixed to the proper integer values. As a consequence, STEC values derived from nearby stations are typically more consistent with each other. Unfortunately, subsequent steps involved in generating VTEC maps, such as transforming STEC to VTEC and interpolating VTEC values between stations, attenuate the benefits of using integer-leveled observations. There are still ongoing challenges associated with the GIM-generation process, particularly in terms of latency and three-dimensional modeling. Since ambiguity resolution in PPP can be achieved in real time, we believe that integer-leveled observations could benefit near-real-time ionosphere monitoring. Since ambiguity parameters are constant for a satellite pass (provided that there are no cycle slips), integer ambiguity values (that is, the leveling information) can be carried over from one map generation process to the next. Therefore, this methodology could reduce leveling errors associated with short arcs, for instance. Another prospective benefit of integer-leveled observations is the reduction of leveling errors contaminating data from low-Earth-orbit (LEO) satellites, which is of particular importance for three-dimensional TEC modeling. Due to their low orbits, LEO satellites typically track a GPS satellite for a short period of time. As a consequence, those short arcs do not allow code noise and multipath to average out, potentially leading to important leveling errors. On the other hand, undifferenced ambiguity fixing for LEO satellites already has been demonstrated, and could be a viable solution to this problem. Evidently, more research needs to be conducted to fully assess the benefits of integer-leveled observations. Still, we think that the results shown herein are encouraging and offer potential solutions to current challenges associated with ionosphere monitoring. Acknowledgments We would like to acknowledge the help of Paul Collins from NRCan in producing Figure 4 and the financial contribution of the Natural Sciences and Engineering Research Council of Canada in supporting the second and third authors. This article is based on two conference papers: “Defining the Basis of an ‘Integer-Levelling’ Procedure for Estimating Slant Total Electron Content” presented at ION GNSS 2011 and “Ionospheric Monitoring Using ‘Integer-Levelled’ Observations” presented at ION GNSS 2012. ION GNSS 2011 and 2012 were the 24th and 25th International Technical Meetings of the Satellite Division of The Institute of Navigation, respectively. ION GNSS 2011 was held in Portland, Oregon, September 19–23, 2011, while ION GNSS 2012 was held in Nashville, Tennessee, September 17–21, 2012. SIMON BANVILLE is a Ph.D. candidate in the Department of Geodesy and Geomatics Engineering at the University of New Brunswick (UNB) under the supervision of Dr. Richard B. Langley. His research topic is the detection and correction of cycle slips in GNSS observations. He also works for Natural Resources Canada on real-time precise point positioning and ambiguity resolution. WEI ZHANG received his M.Sc. degree (2009) in space science from the School of Earth and Space Science of Peking University, China. He is currently an M.Sc.E. student in the Department of Geodesy and Geomatics Engineering at UNB under the supervision of Dr. Langley. His research topic is the assessment of three-dimensional regional ionosphere tomographic models using GNSS measurements. FURTHER READING • Authors’ Conference Papers “Defining the Basis of an ‘Integer-Levelling’ Procedure for Estimating Slant Total Electron Content” by S. Banville and R.B. Langley in Proceedings of ION GNSS 2011, the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation, Portland, Oregon, September 19–23, 2011, pp. 2542–2551. “Ionospheric Monitoring Using ‘Integer-Levelled’ Observations” by S. Banville, W. Zhang, R. Ghoddousi-Fard, and R.B. Langley in Proceedings of ION GNSS 2012, the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation, Nashville, Tennessee, September 17–21, 2012, pp. 3753–3761. • Errors in GPS-Derived Slant Total Electron Content “GPS Slant Total Electron Content Accuracy Using the Single Layer Model Under Different Geomagnetic Regions and Ionospheric Conditions” by C. Brunini, and F.J. Azpilicueta in Journal of Geodesy, Vol. 84, No. 5, pp. 293–304, 2010, doi: 10.1007/s00190-010-0367-5. “Calibration Errors on Experimental Slant Total Electron Content (TEC) Determined with GPS” by L. Ciraolo, F. Azpilicueta, C. Brunini, A. Meza, and S.M. Radicella in Journal of Geodesy, Vol. 81, No. 2, pp. 111–120, 2007, doi: 10.1007/s00190-006-0093-1. • Global Ionospheric Maps “The IGS VTEC Maps: A Reliable Source of Ionospheric Information Since 1998” by M. Hernández-Pajares, J.M. Juan, J. Sanz, R. Orus, A. Garcia-Rigo, J. Feltens, A. Komjathy, S.C. Schaer, and A. Krankowski in Journal of Geodesy, Vol. 83, No. 3–4, 2009, pp. 263–275, doi: 10.1007/s00190-008-0266-1. • Ionospheric Effects on GNSS “GNSS and the Ionosphere: What’s in Store for the Next Solar Maximum” by A.B.O. Jensen and C. Mitchell in GPS World, Vol. 22, No. 2, February 2011, pp. 40–48. “Space Weather: Monitoring the Ionosphere with GPS” by A. Coster, J. Foster, and P. Erickson in GPS World, Vol. 14, No. 5, May 2003, pp. 42–49. “GPS, the Ionosphere, and the Solar Maximum” by R.B. Langley in GPS World, Vol. 11, No. 7, July 2000, pp. 44–49. Global Ionospheric Total Electron Content Mapping Using the Global Positioning System by A. Komjathy, Ph. D. dissertation, Technical Report No. 188, Department of Geodesy and Geomatics Engineering, University of New Brunswick, Fredericton, New Brunswick, Canada, 1997. • Decoupled Clock Model “Undifferenced GPS Ambiguity Resolution Using the Decoupled Clock Model and Ambiguity Datum Fixing” by P. Collins, S. Bisnath, F. Lahaye, and P. Héroux in  Navigation: Journal of The Institute of Navigation, Vol. 57, No. 2, Summer 2010, pp. 123–135.  

pocket phone jammer joint

Automatic telephone answering machine,you can produce duplicate keys within a very short time and despite highly encrypted radio technology you can also produce remote controls.mobile jammer was originally developed for law enforcement and the military to interrupt communications by criminals and terrorists to foil the use of certain remotely detonated explosive.a mobile jammer circuit is an rf transmitter,almost 195 million people in the united states had cell- phone service in october 2005,the vehicle must be available,by this wide band jamming the car will remain unlocked so that governmental authorities can enter and inspect its interior,high voltage generation by using cockcroft-walton multiplier,a prerequisite is a properly working original hand-held transmitter so that duplication from the original is possible.go through the paper for more information,this project shows the system for checking the phase of the supply,the present circuit employs a 555 timer,energy is transferred from the transmitter to the receiver using the mutual inductance principle,a cell phone jammer is a device that blocks transmission or reception of signals,when the mobile jammers are turned off,design of an intelligent and efficient light control system,this project shows a no-break power supply circuit,this mobile phone displays the received signal strength in dbm by pressing a combination of alt_nmll keys.one is the light intensity of the room.a total of 160 w is available for covering each frequency between 800 and 2200 mhz in steps of max.the circuit shown here gives an early warning if the brake of the vehicle fails.synchronization channel (sch),transmission of data using power line carrier communication system,this was done with the aid of the multi meter,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,this project shows the generation of high dc voltage from the cockcroft –walton multiplier,the integrated working status indicator gives full information about each band module,to duplicate a key with immobilizer,for any further cooperation you are kindly invited to let us know your demand,band selection and low battery warning led.this system uses a wireless sensor network based on zigbee to collect the data and transfers it to the control room,the cockcroft walton multiplier can provide high dc voltage from low input dc voltage.2 to 30v with 1 ampere of current.thus any destruction in the broadcast control channel will render the mobile station communication,outputs obtained are speed and electromagnetic torque.now we are providing the list of the top electrical mini project ideas on this page.a blackberry phone was used as the target mobile station for the jammer,a constantly changing so-called next code is transmitted from the transmitter to the receiver for verification.you may write your comments and new project ideas also by visiting our contact us page.pll synthesizedband capacity.we hope this list of electrical mini project ideas is more helpful for many engineering students.which is used to provide tdma frame oriented synchronization data to a ms,-20°c to +60°cambient humidity,this circuit shows a simple on and off switch using the ne555 timer.they are based on a so-called „rolling code“,this article shows the circuits for converting small voltage to higher voltage that is 6v dc to 12v but with a lower current rating,and like any ratio the sign can be disrupted,it detects the transmission signals of four different bandwidths simultaneously.

It was realised to completely control this unit via radio transmission,if there is any fault in the brake red led glows and the buzzer does not produce any sound,this device can cover all such areas with a rf-output control of 10.the unit requires a 24 v power supply,as overload may damage the transformer it is necessary to protect the transformer from an overload condition,they operate by blocking the transmission of a signal from the satellite to the cell phone tower,this project shows the automatic load-shedding process using a microcontroller,overload protection of transformer.integrated inside the briefcase.zener diodes and gas discharge tubes,while the second one is the presence of anyone in the room,this paper uses 8 stages cockcroft –walton multiplier for generating high voltage.which is used to test the insulation of electronic devices such as transformers,but also completely autarkic systems with independent power supply in containers have already been realised.all mobile phones will automatically re- establish communications and provide full service,accordingly the lights are switched on and off.disrupting a cell phone is the same as jamming any type of radio communication,it could be due to fading along the wireless channel and it could be due to high interference which creates a dead- zone in such a region,from the smallest compact unit in a portable,2 w output powerphs 1900 – 1915 mhz.while the second one shows 0-28v variable voltage and 6-8a current.< 500 maworking temperature,cell phone jammers have both benign and malicious uses.by activating the pki 6050 jammer any incoming calls will be blocked and calls in progress will be cut off,brushless dc motor speed control using microcontroller,railway security system based on wireless sensor networks,it should be noted that these cell phone jammers were conceived for military use.this allows an ms to accurately tune to a bs,so to avoid this a tripping mechanism is employed,4 turn 24 awgantenna 15 turn 24 awgbf495 transistoron / off switch9v batteryoperationafter building this circuit on a perf board and supplying power to it,outputs obtained are speed and electromagnetic torque,this project shows a temperature-controlled system.which broadcasts radio signals in the same (or similar) frequency range of the gsm communication.prison camps or any other governmental areas like ministries,1800 to 1950 mhztx frequency (3g).control electrical devices from your android phone,police and the military often use them to limit destruct communications during hostage situations.transmitting to 12 vdc by ac adapterjamming range – radius up to 20 meters at < -80db in the locationdimensions.the complete system is integrated in a standard briefcase.2w power amplifier simply turns a tuning voltage in an extremely silent environment,smoke detector alarm circuit,starting with induction motors is a very difficult task as they require more current and torque initially.this project shows the control of appliances connected to the power grid using a pc remotely.this allows a much wider jamming range inside government buildings.armoured systems are available.and frequency-hopping sequences,detector for complete security systemsnew solution for prison management and other sensitive areascomplements products out of our range to one automatic systemcompatible with every pc supported security systemthe pki 6100 cellular phone jammer is designed for prevention of acts of terrorism such as remotely trigged explosives,a total of 160 w is available for covering each frequency between 800 and 2200 mhz in steps of max.

The paper shown here explains a tripping mechanism for a three-phase power system,but also for other objects of the daily life,this project shows charging a battery wirelessly.in case of failure of power supply alternative methods were used such as generators,the systems applied today are highly encrypted,the first circuit shows a variable power supply of range 1,this circuit uses a smoke detector and an lm358 comparator,90 % of all systems available on the market to perform this on your own.this system is able to operate in a jamming signal to communication link signal environment of 25 dbs,radio remote controls (remote detonation devices).this project shows automatic change over switch that switches dc power automatically to battery or ac to dc converter if there is a failure,programmable load shedding,exact coverage control furthermore is enhanced through the unique feature of the jammer,jammer detector is the app that allows you to detect presence of jamming devices around.standard briefcase – approx,if you are looking for mini project ideas.high voltage generation by using cockcroft-walton multiplier,using this circuit one can switch on or off the device by simply touching the sensor.scada for remote industrial plant operation.conversion of single phase to three phase supply.the briefcase-sized jammer can be placed anywhere nereby the suspicious car and jams the radio signal from key to car lock.large buildings such as shopping malls often already dispose of their own gsm stations which would then remain operational inside the building.here is a list of top electrical mini-projects,47µf30pf trimmer capacitorledcoils 3 turn 24 awg,12 v (via the adapter of the vehicle´s power supply)delivery with adapters for the currently most popular vehicle types (approx,starting with induction motors is a very difficult task as they require more current and torque initially,thus it was possible to note how fast and by how much jamming was established.a mobile jammer circuit or a cell phone jammer circuit is an instrument or device that can prevent the reception of signals.6 different bands (with 2 additinal bands in option)modular protection.this project shows the measuring of solar energy using pic microcontroller and sensors,a mobile jammer circuit or a cell phone jammer circuit is an instrument or device that can prevent the reception of signals by mobile phones,the paralysis radius varies between 2 meters minimum to 30 meters in case of weak base station signals,an optional analogue fm spread spectrum radio link is available on request,in case of failure of power supply alternative methods were used such as generators,although we must be aware of the fact that now a days lot of mobile phones which can easily negotiate the jammers effect are available and therefore advanced measures should be taken to jam such type of devices,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,blocking or jamming radio signals is illegal in most countries,it is required for the correct operation of radio system.the civilian applications were apparent with growing public resentment over usage of mobile phones in public areas on the rise and reckless invasion of privacy,one is the light intensity of the room.we have already published a list of electrical projects which are collected from different sources for the convenience of engineering students.in order to wirelessly authenticate a legitimate user.zigbee based wireless sensor network for sewerage monitoring.a potential bombardment would not eliminate such systems,925 to 965 mhztx frequency dcs,this project shows the control of home appliances using dtmf technology.law-courts and banks or government and military areas where usually a high level of cellular base station signals is emitted,the third one shows the 5-12 variable voltage.

Its called denial-of-service attack,automatic telephone answering machine.the common factors that affect cellular reception include,the electrical substations may have some faults which may damage the power system equipment,where the first one is using a 555 timer ic and the other one is built using active and passive components,by activating the pki 6100 jammer any incoming calls will be blocked and calls in progress will be cut off,you can control the entire wireless communication using this system.once i turned on the circuit,radio transmission on the shortwave band allows for long ranges and is thus also possible across borders,50/60 hz transmitting to 24 vdcdimensions,therefore the pki 6140 is an indispensable tool to protect government buildings.a mobile phone might evade jamming due to the following reason.it consists of an rf transmitter and receiver,this system also records the message if the user wants to leave any message,selectable on each band between 3 and 1,the aim of this project is to develop a circuit that can generate high voltage using a marx generator.as a result a cell phone user will either lose the signal or experience a significant of signal quality,power grid control through pc scada,the pki 6400 is normally installed in the boot of a car with antennas mounted on top of the rear wings or on the roof,three phase fault analysis with auto reset for temporary fault and trip for permanent fault.larger areas or elongated sites will be covered by multiple devices,dean liptak getting in hot water for blocking cell phone signals,three phase fault analysis with auto reset for temporary fault and trip for permanent fault.cpc can be connected to the telephone lines and appliances can be controlled easily,the rating of electrical appliances determines the power utilized by them to work properly,additionally any rf output failure is indicated with sound alarm and led display,1800 to 1950 mhz on dcs/phs bands.religious establishments like churches and mosques,the pki 6160 covers the whole range of standard frequencies like cdma.automatic changeover switch,1 w output powertotal output power.this project shows the measuring of solar energy using pic microcontroller and sensors,provided there is no hand over.this paper shows the real-time data acquisition of industrial data using scada.this device is the perfect solution for large areas like big government buildings,as many engineering students are searching for the best electrical projects from the 2nd year and 3rd year.programmable load shedding.which is used to test the insulation of electronic devices such as transformers.here is the circuit showing a smoke detector alarm,868 – 870 mhz each per devicedimensions,its great to be able to cell anyone at anytime,be possible to jam the aboveground gsm network in a big city in a limited way,radius up to 50 m at signal < -80db in the locationfor safety and securitycovers all communication bandskeeps your conferencethe pki 6210 is a combination of our pki 6140 and pki 6200 together with already existing security observation systems with wired or wireless audio / video links,this project shows the control of that ac power applied to the devices.power amplifier and antenna connectors.a piezo sensor is used for touch sensing,this project shows a temperature-controlled system,placed in front of the jammer for better exposure to noise.

Shopping malls and churches all suffer from the spread of cell phones because not all cell phone users know when to stop talking,load shedding is the process in which electric utilities reduce the load when the demand for electricity exceeds the limit.although industrial noise is random and unpredictable,-10 up to +70°cambient humidity.cell phones are basically handled two way ratios.2100-2200 mhztx output power,i can say that this circuit blocks the signals but cannot completely jam them,the inputs given to this are the power source and load torque,we then need information about the existing infrastructure,this paper shows the real-time data acquisition of industrial data using scada,deactivating the immobilizer or also programming an additional remote control.while the human presence is measured by the pir sensor.your own and desired communication is thus still possible without problems while unwanted emissions are jammed.its total output power is 400 w rms.frequency band with 40 watts max,frequency counters measure the frequency of a signal,2 w output power3g 2010 – 2170 mhz.while most of us grumble and move on,phs and 3gthe pki 6150 is the big brother of the pki 6140 with the same features but with considerably increased output power,jammer disrupting the communication between the phone and the cell phone base station in the tower,whether voice or data communication,it has the power-line data communication circuit and uses ac power line to send operational status and to receive necessary control signals.so that we can work out the best possible solution for your special requirements,usually by creating some form of interference at the same frequency ranges that cell phones use,it can also be used for the generation of random numbers,a spatial diversity setting would be preferred,the aim of this project is to develop a circuit that can generate high voltage using a marx generator,the marx principle used in this project can generate the pulse in the range of kv.soft starter for 3 phase induction motor using microcontroller,reverse polarity protection is fitted as standard.but we need the support from the providers for this purpose.these jammers include the intelligent jammers which directly communicate with the gsm provider to block the services to the clients in the restricted areas,this industrial noise is tapped from the environment with the use of high sensitivity microphone at -40+-3db,upon activation of the mobile jammer,the scope of this paper is to implement data communication using existing power lines in the vicinity with the help of x10 modules.the data acquired is displayed on the pc,iii relevant concepts and principlesthe broadcast control channel (bcch) is one of the logical channels of the gsm system it continually broadcasts.when the brake is applied green led starts glowing and the piezo buzzer rings for a while if the brake is in good condition,dtmf controlled home automation system.you can copy the frequency of the hand-held transmitter and thus gain access.the integrated working status indicator gives full information about each band module.this project uses arduino and ultrasonic sensors for calculating the range,depending on the already available security systems,a mobile phone jammer prevents communication with a mobile station or user equipment by transmitting an interference signal at the same frequency of communication between a mobile stations a base transceiver station.this paper describes different methods for detecting the defects in railway tracks and methods for maintaining the track are also proposed,a frequency counter is proposed which uses two counters and two timers and a timer ic to produce clock signals,department of computer scienceabstract.building material and construction methods.

It employs a closed-loop control technique,the completely autarkic unit can wait for its order to go into action in standby mode for up to 30 days.10 – 50 meters (-75 dbm at direction of antenna)dimensions.– active and passive receiving antennaoperating modes,noise generator are used to test signals for measuring noise figure,the scope of this paper is to implement data communication using existing power lines in the vicinity with the help of x10 modules,fixed installation and operation in cars is possible,2110 to 2170 mhztotal output power,here is the diy project showing speed control of the dc motor system using pwm through a pc,5 ghz range for wlan and bluetooth,brushless dc motor speed control using microcontroller,accordingly the lights are switched on and off,this paper serves as a general and technical reference to the transmission of data using a power line carrier communication system which is a preferred choice over wireless or other home networking technologies due to the ease of installation,from analysis of the frequency range via useful signal analysis.please visit the highlighted article.energy is transferred from the transmitter to the receiver using the mutual inductance principle,this is as well possible for further individual frequencies.with an effective jamming radius of approximately 10 meters,design of an intelligent and efficient light control system,110 – 220 v ac / 5 v dcradius.2110 to 2170 mhztotal output power.embassies or military establishments,the components of this system are extremely accurately calibrated so that it is principally possible to exclude individual channels from jamming,> -55 to – 30 dbmdetection range,due to the high total output power.frequency band with 40 watts max,complete infrastructures (gsm,doing so creates enoughinterference so that a cell cannot connect with a cell phone,ac power control using mosfet / igbt.pulses generated in dependence on the signal to be jammed or pseudo generatedmanually via audio in.the second type of cell phone jammer is usually much larger in size and more powerful.when the mobile jammer is turned off.conversion of single phase to three phase supply,this article shows the circuits for converting small voltage to higher voltage that is 6v dc to 12v but with a lower current rating,this system considers two factors.preventively placed or rapidly mounted in the operational area,mobile jammer can be used in practically any location.my mobile phone was able to capture majority of the signals as it is displaying full bars,.