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Synthetic-Aperture GNSS Signal Processing By Thomas Pany, Nico Falk, Bernhard Riedl, Carsten Stöber, Jón O. Winkel, and Franz-Josef Schimpl INNOVATION INSIGHTS by Richard Langley A SYNTHETIC APERTURE? WHAT’S THAT? Well, an aperture in optics is just a hole or opening through which light travels. Those of us into photography know that the amount of light reaching the camera’s imaging sensor is controlled by the shutter speed and the size of the lens opening or aperture (called the f-stop). And a correct combination of the aperture setting and shutter speed results in a correct exposure.  For an optical telescope, its aperture is the diameter of its main, light-gathering lens or mirror. A larger aperture gives a sharper and brighter view or image. In the radio part of the electromagnetic spectrum, the term aperture refers to the effective collecting (or transmitting) area of an antenna. The gain of the antenna is proportional to its aperture and its beamwidth or resolution is inversely proportional to it. Astronomers, whether using optical or radio telescopes, often seek higher and higher resolutions to see more detail in the objects they are investigating. Conventionally, that means larger and larger telescopes. However, there are limits to how large a single telescope can be constructed. But by combining the light or radio signals from two or more individual telescopes, one can synthesize a telescope with a diameter equal to the baseline(s) connecting those telescopes. The approach is known as interferometry. It was first tried in the optical domain by the American physicist Albert Michelson who used the technique to measure the diameter of the star Betelgeuse. Radio astronomers developed cable- and microwave-connected interferometers and subsequently they invented the technique of very long baseline interferometry (VLBI) where atomic-clock-stabilized radio signals are recorded on magnetic tape and played back through specially designed correlators to form an image. (VLBI has also been used by geodesists to precisely determine the baselines between pairs of radio telescopes even if they are on separate continents.) A similar approach is used in synthetic-aperture radar (SAR). Mounted on an aircraft or satellite, the SAR beam-forming antenna emits pulses of radio waves that are reflected from a target and then coherently combined. The different positions of the SAR, as it moves, synthesize an elongated aperture resulting in finer spatial resolution than would be obtained by a conventional antenna. But what has all of this got to do with GNSS? In this month’s column, we take a look at a novel GNSS signal-processing technique, which uses the principles of SAR to improve code and carrier-phase observations in degraded environments such as under forest canopy. The technique can simultaneously reject multipath signals while maximizing the direct line-of-sight signal power from a satellite. Along with a specially programmed software receiver, it uses either a single conventional antenna mounted, say, on a pedestrian’s backpack for GIS applications or a special rotating antenna for high-accuracy surveying. Want to learn more? Read on. “Innovation” is a regular feature that discusses advances in GPS technology andits applications as well as the fundamentals of GPS positioning. The column is coordinated by Richard Langley of the Department of Geodesy and Geomatics Engineering, University of New Brunswick. He welcomes comments and topic ideas. Over the past few years, we have been developing new GNSS receivers and antennas based on an innovative signal-processing scheme to significantly improve GNSS tracking reliability and accuracy under degraded signal conditions. It is based on the principles of synthetic-aperture radar. Like in a multi-antenna phased-array receiver, GNSS signals from different spatial locations are combined coherently forming an optimized synthetic antenna-gain pattern. Thereby, multipath signals can be rejected and the line-of-sight received signal power is maximized. This is especially beneficial in forests and in other degraded environments. The method is implemented in a real-time PC-based software receiver and works with GPS, GLONASS, and Galileo signals. Multiple frequencies are generally supported. The idea of synthetic-aperture processing is realized as a coherent summation of correlation values of each satellite over the so-called beam-forming interval. Each correlation value is multiplied with a phase factor. For example, the phase factor can be chosen to compensate for the relative antenna motion over the beam-forming interval and the resulting sum of the scaled correlation values represents a coherent correlation value maximizing the line-of-sight signal power. Simultaneously, signals arriving from other directions are partly eliminated. Two main difficulties arise in the synthetic-aperture processing. First, the clock jitter during the beam-forming interval must be precisely known. It can either be estimated based on data from all signals, or a stable oscillator can be used. In one of our setups, a modern oven-controlled crystal oscillator with an Allan variance of 0.5 × 10-13 at an averaging period of 1 second is used. Second, the precise relative motion of the antenna during the beam-forming interval must be known. Again it can be estimated if enough sufficiently clean signals are tracked. The antenna trajectory is estimated directly from the correlator values as shown later in this article. In more severely degraded environments, the antenna may be moved along a known trajectory. We are developing a rotating antenna displacement unit. (see FIGURE 1). The rotational unit targets forestry and indoor surveying applications. The relative motion of the antenna is measured with sub-millimeter accuracy. FIGURE 1. Artist’s impression of the synthetic-aperture GNSS system for surveying in a forest. After beam-forming, the code pseudoranges and the carrier phases are extracted and used in a conventional way. That is, they are written into Receiver Independent Exchange (RINEX) format files and standard geodetic software can be used to evaluate them. In the case where the artificial movement antenna is used, the GNSS signal processing removes the known part of the movement from the observations, and the observations are then like those from a static antenna. As a result, common static positioning algorithms, including carrier-phase ambiguity fixing, can be applied. The presented method therefore prepares the path for GNSS surveying applications in new areas. An important point is the mechanical realization of the antenna movement. This has to be done in a cost-efficient and reliable way. Lubrication-free actuators are used together with magnetic displacement sensors. The sensors are synchronized to the software receiver front end with better than 1 millisecond accuracy. The rotating antenna uses slip rings to connect the antenna elements. The rotating antenna can also be used to map the received signal power as a function of elevation and azimuth angles. This is beneficial for researchers. For example, it could be used to estimate the direction of arrival of a spoofing signal or to determine which object causes multipath in an indoor environment. For the latter purpose, the rotating antenna can be equipped with left-hand and right-hand circularly polarized antennas on both ends of the rotating bar. The rotating antenna is mounted on a geodetic tripod. See Further Reading for reports of initial studies of the rotating antenna. Tracking Modes The synthetic-aperture tracking scheme can be extended to different user-motion schemes or sensor-aiding schemes allowing a wide range of applications. This is reflected in the algorithm implementation within the modular structure of the software receiver. The base module “µ-trajectory & Clock Estimator” in Figure 2 prepares the synthetic-aperture tracking scheme. Different implementations derive from this base class. Each derived module is used for a different user motion scheme and makes use of a different sensor. FIGURE 2. Different µ-trajectory motion estimators used by the synthetic-aperture processing. Basically, the modules differ in the way they estimate the relative antenna motion over the beam-forming interval. This relative motion is called the µ-trajectory. Usually the µ-trajectory covers time spans from a few hundreds of milliseconds to a few seconds. The µ-trajectories have the following characteristics: The pedestrian motion estimator does not rely on any sensor measurements and fits a second-order polynomial into the user µ-trajectory of a walking pedestrian. A second-order polynomial is good for representing the motion for up to a quarter of a second. The sensor input to the rotating antenna estimator is the relative angular displacement of the rotating antenna. The estimator estimates the absolute direction, which is stable in time. Thus the number of µ-trajectory parameters equals one. The vertical antenna motion estimator retrieves the vertical position of the antenna and does not estimate any µ-trajectory parameters. Only clock parameters are estimated. Finally, the inertial navigation estimator uses accelerometer and gyro measurements and estimates the 3D user motion. The µ-trajectory parameters consist of accelerometer biases, the gyro biases, attitude errors, and velocity errors. The estimation process is much more complex and exploits the timely correlation of the parameters. Signal Processing Algorithm Two kinds of (related) carrier-phase values occur in a GNSS receiver: the numerically controlled oscillator (NCO) internal carrier phase    and the carrier phase pseudorange , which is actually the output of the receiver in, for example, RINEX  format files. Both are a function of time t and when expressed in radians are related via Equation (1):     (1) Here, fo denotes the receiver internal nominal intermediate frequency (IF) at which all signal processing takes place. The output carrier-phase pseudorange  is an estimate of the true carrier-phase pseudorange , which, in turn, relates to the geometric distance to the satellite by the following standard model:    (2) This model applies to each signal propagation path separately; that is, a separate model can be set up for the line-of-sight signal and for each multipath signal. In Equation (2), λ denotes the nominal carrier wavelength in meters, ρ(t) is the geometric distance in meters between transmitting and receiving antennas, fRF is the nominal carrier frequency in hertz, dtsat(t) and dtrec(t) are the satellite and receiver clock errors in seconds, N is the carrier-phase ambiguity, and T(t) contains atmospheric delays as well as any hardware delays in meters. Here, no measurement errors are included, because we are considering the relationship between true values. Defining now a reference epoch t0, we will describe a procedure to obtain an improved carrier-phase estimate  for this epoch using data from an interval [t0 – TBF, t0]. The beam-forming interval TBF can be chosen to be, for example, 0.2–2 seconds but should be significantly longer than the employed predetection integration time (the primary one, without beam forming). Correlator Modeling. In this sub-section, the relationships between phase, correlator values, and geometric distances will be established. These relationships apply for each propagation path individually. In the next section these relationships will be applied to the total received signal, which is the sum of all propagation paths plus thermal noise. To model the correlator output we assume that any effect of code or Doppler-frequency-shift misalignment on carrier-phase tracking can be neglected. This is reasonable if the antenna motion can be reasonably well predicted and this prediction is fed into the tracking loops as aiding information. Then the prompt correlator output is given as .   (3) Again, any noise contribution is not considered for the moment. Here a(t) denotes the signal amplitude and d(t) a possibly present navigation data bit. The carrier phase difference Δφ is given as   (4) where φ(t) is the true carrier phase and φNCO(t) is the NCO carrier phase used for correlation. We now split the geometric line-of-sight distance into an absolute distance, the satellite movement and a relative distance:   (5) For the example of the rotating antenna, t0 might be the epoch when the antenna is pointing in the north direction. The term ρ0(t0) is the conventional satellite-to-reference-point distance (for example, to the rotation center) and ρsat(t0,t) accounts for the satellite movement during the beam-forming interval. The term Δρµ(t) is the rotational movement and may depend on the parameter µ. The parameter µ represents, for the rotating antenna, the absolute heading but may represent more complex motion parameters. The absolute term ρ0(t0) is constant but unknown in the beam-forming interval. We assume that approximate coordinates are available and thus Δρµ(t) can be computed for a given set of µ (that is, the line-of-sight projection of the relative motion is assumed to be well predicted even with only approximate absolute coordinates). The same applies also to ρsat(t0,t). Let’s assume that the NCOs are controlled in a way that the satellite movement is captured as well as the satellite clock drift and the atmospheric delays: . (6) Then (7) and .(8) Thus the correlator output depends on the absolute distance of the reference point to the satellite at t0, the relative motion of the antenna, the receiver clock error, the received amplitude and the broadcast navigation data bits. Satellite movement and satellite clock drift are absent. Let us now denote m as the index for the different satellites under consideration. The index k denotes correlation values obtained during the beam-forming interval at the epoch tk. Then: .(9) If multiple signal reflections are received and if they are denoted by the indices m1, m2, … , then the correlator output is the sum of those: .(10) For the following, m or m1 denotes the line-of-sight signal and mn with n > 1 denoting multipath signals. Estimation Principle. It seems natural to choose receiver clock parameters dtrec and trajectory parameters µ in a way that they optimally represent the receiver correlation values. This approach mimics the maximum likelihood principle. The estimated parameters are: .(11) Data bits are also estimated in Equation (11). Once this minimization has been carried out, the parameters µ and dtrec are known as well as the data bits. The real-time implementation of Equation (11) is tricky. It is the optimization of a multi-dimensional function. Our implementation consists of several analytical simplifications as well as a highly efficient implementation in C code. The pedestrian estimator has been ported to a Compute-Unified-Device-Architecture-capable graphics processing unit exploiting its high parallelism. Equation (11) realizes a carrier-phase-based vector tracking approach and the whole µ-trajectory (not only positions or velocity values) is estimated at once from the correlation values. This optimally combines the signals from all satellites and frequencies. The method focuses on the line-of-sight signals as only line-of-sight signals coherently add up for the true set of µ-trajectory and clock parameters. On the other hand, multipath signals from different satellites are uncorrelated and don’t show a coherent maximum. Purified Correlator Values. The line-of-sight relative distance change Δρµm(t) due to the antenna motion is basically the projection of the µ-trajectory onto the line-of-sight. Multipath signals may arrive from different directions, and   is the antenna motion projected onto the respective direction of arrival. Let the vector   denote the phase signature of the nth multipath signal of satellite m based on the assumed µ-trajectory parameters µ: .(12) Projecting the correlator values that have been corrected by data bits and receiver clock error onto the line-of-sight direction yields: . (13) The correlator values Q are called purified values as they are mostly free of multipath, provided a suitable antenna movement has been chosen. This is true if we assume a sufficient orthogonality of the line-of-sight signal to the multipath signals, and we can write: .(14) where K is the number of primary correlation values within the beam-forming interval. The projection onto the line-of-sight phase signature is then .(15) Thus the purified correlator values represent the unknown line-of-sight distance from the reference point to the satellite. Those values are used to compute the carrier pseudorange. The procedure can similarly also be applied for early and late correlators. The purified and projected correlation values represent the correlation function of the line-of-sight signal and are used to compute the code pseudorange. Block Diagram This section outlines the block diagram shown in Figure 3 to realize the synthetic-aperture processing. The signal processing is based on the code/Doppler vector-tracking mode of the software receiver. FIGURE 3. Synthetic-aperture signal processing. The scheme has not only to include the algorithms of the previous section but it has also to remove the known part of the motion (for the rotating antenna, say) from the output observations. In that case, the output RINEX observation files should refer to a certain static reference point. This is achieved by a two-step process. First, the known and predictable part of the motion is added to the NCO values. By doing that, the correlation process follows the antenna motion to a good approximation, and the antenna motion does not stress the tracking loop dynamics of the receiver. Furthermore, discriminator values are small and in the linear region of the discriminator. Second, the difference between the current antenna position and the reference point is projected onto the line-of-sight and is removed from the output pseudoranges and Doppler values. For further details on the processing steps of the block diagram, see the conference paper on which this article is based, listed in Further Reading. Pedestrian Estimator We tested the synthetic-aperture processing for pedestrians on a dedicated test trial and report the positing results in this section. These results are not final and are expected to improve as more GNSSs are included and general parameter tuning is performed. Test Area. To test the pedestrian estimator, we collected GPS L1 C/A-code and GLONASS G1 signals while walking through a dense coniferous forest. The trees were up to 30–40 meters high and are being harvested by a strong local lumber industry. The test was carried out in May 2012. We staked out a test course inside the forest and used terrestrial surveying techniques to get precise (centimeter accuracy) coordinates of the reference points. Figure 4 shows a triangular part of the test course. FIGURE 4. Triangular test course in a forest. Measurement data was collected with a geodetic-quality GNSS antenna fixed to a backpack. This is a well-known style of surveying. We used a GNSS signal splitter and a commercial application-specific-integrated-circuit- (ASIC-) based high-sensitivity GNSS receiver to track the signals and to have some kind of benchmark. The algorithms of this ASIC-based receiver are not publicly known, but the performance is similar to other ASIC-based GNSS receivers inside forests. We came from the west, walked the triangular path five times, left to the north, came back from the north, walked the triangular path again five times clockwise, and left to the west. We note that the ASIC-based receiver shows a 3–5 meter-level accuracy with some outliers of more than 10 meters. We further note that the use of the geodetic antenna was critical to achieve this rather high accuracy inside the forest. µ-trajectory Estimation. As mentioned before, the pedestrian estimator uses a second-order polynomial to model the user motion over an interval of 0.2 seconds. If we stack the estimated µ-trajectories over multiple intervals, we get the relative motion of the user. An example of the estimated user motion outside (but near) the forest is shown in Figure 5. FIGURE 5. Estimated relative user trajectory over 5 seconds outside the forest; user walking horizontally. The figure clearly shows that the walking pattern is quite well estimated. An up/down movement of ~10 cm linked to the walking pattern is visible. Inside the forest, the walking pattern is visible but with less accuracy. Synthetic-Aperture Antenna Pattern. It is possible to estimate the synthetic antenna gain pattern for a given antenna movement (see “Synthetic Phased Array Antenna for Carrier/Code Multipath Mitigation” in Further Reading). The gain pattern is the sensitivity of the receiver/antenna system to signals coming from a certain direction. It depends on the known direction of the line-of-sight signal and is computed for each satellite individually. It adds to the normal pattern of the used antenna element. We assume that the system simply maximizes the line-of-sight signal power for an assumed satellite elevation of 45° and an azimuth of 135°. We model the pedestrian movement as horizontal with a constant speed of 1 meter per second, and an up/down movement of ± 7.5 centimeters with a period of 0.7 seconds. Employing a beam-forming interval of 2 seconds yields the synthetic antenna gain pattern of Figure 6.The pattern is symmetric to the walking direction. It shows that ground multipath is suppressed. FIGURE 6. Synthetic antenna aperture diagram for a walking user and beam-forming interval of 2 seconds. Positioning Results. Our receiver implements a positioning filter based on stacking the estimated µ-trajectory segments. As already mentioned, the stacked µ-trajectory segments represent the relative movement of the user. GNSS code pseudorange observations are then used to get absolute coordinates. Basically, an extended Kalman filter is used to estimate a timely variable position offset to the stacked µ-trajectory segments. The Kalman filter employs a number of data-quality checks to eliminate coarse outliers. They are quite frequent in this hilly forested environment. The positioning results obtained are shown in Figure 7. They correspond to the same received GPS+GLONASS signal but three different beam-forming intervals (0.2, 1, and 2 seconds) have been used. The position output rate corresponds to the beam-forming interval. Blue markers correspond to the surveyed reference positions, and the yellow markers are estimates when the user is at those reference markers. For each marker, there are ten observations. FIGURE 7. Estimated user trajectory with 0.2, 1, and 2 seconds beam-forming interval (blue: surveyed reference markers). The triangular walking path is clearly visible. We observe a bias of around 3 meters and a distance-root-mean-square of 1.2 meters if accounting for this bias (the values refer to the 2-second case). The reason for the bias has not yet been investigated. It could be due to ephemeris or ionospheric errors, but also possibly multipath reflections. For the short beam-forming interval of 0.2 seconds, we observe noisier walking paths, and we would also expect less accurate code observations. However, the code observation rate is highest in this case (5 Hz), and multipath errors tend to average out inside the Kalman filter. In contrast, the walking paths for the 1-second or 2-second case are straighter. The beam-forming seems to eliminate the multipath, and there are fewer but more precise observations. Artificial Motion Antennas The rotating antenna targets surveying applications. It fits standard geodetic equipment. The antenna is controlled by the software receiver, and the rotational information is synchronized to the received GNSS signal. Synthetic-Aperture Antenna Pattern. With the same methodology as referenced previously, it is possible to estimate the synthetic antenna gain pattern. We assume that the pattern simply maximizes the line-of-sight signal power for an assumed satellite elevation angle of 45° and an azimuth of 135°. We use a rotation radius of 50 cm. The antenna has a really high directivity, eliminating scattered signals from trees. The gain pattern is symmetric with respect to the horizon and ground multipath of perfectly flat ground would not be mitigated by the synthetic aperture. Ground multipath is only mitigated by the antenna element itself (for example, a small ground plane can be used). However, mostly the ground is not flat, and in that case the rotating antenna also mitigates the ground multipath. Results with a Simulator. The rotating antenna has been tested with simulated GNSS signals using an RF signal generator. The signal generator was configured to start with the antenna at rest, and at some point the antenna starts rotating with a speed of 15 revolutions per minute. Six GPS L1 C/A-code signals have been simulated. The signal-processing unit has to estimate the antenna state (static or rotating) and the north direction. The quality of the estimation can be visualized by comparing the complex argument of the prompt correlator values to the modeled correlator values. Two examples are shown in FIGURES 8 and 9. In Figure 8, the differences are at the millimeter level corresponding to the carrier-phase thermal noise. This indicates that the absolute heading and receiver clock parameters have been estimated to a high precision. FIGURE 8. Carrier-phase residuals for all satellites observed with the rotating antenna without multipath. Time is in seconds and all data contributing to the RINEX observation record has been considered. FIGURE 9. Carrier-phase residuals for all satellites observed with the rotating antenna with multipath. Time is in seconds and all data contributing to the RINEX observation record has been considered. If multipath from a reflection plane is present (see Figure 9), the phase residuals show the multipath reflection. For example, around t = -0.65 seconds in the figure, the antenna is moving parallel to the reflection plane and the phase residuals are constant over a short time span. As the distance of the antenna to the reflection plane changes, the phase residuals start to oscillate. Generally, the estimation of the absolute heading and of the receiver clock parameters works even with strong multipath signals, but the parameters are not as stable as in the multipath-free case. In the case when the antenna is rotating, signal processing has to remove the rotation from the code and carrier observations. To check if this elimination of the artificial motion is done correctly, we use carrier-smoothed code observations to compute a single-point-positioning solution. Only if the antenna is rotating can the system estimate the absolute heading and refer the observations to the rotation center. Before that point, the observations refer to the antenna position. The antenna position and the rotation center differ by the radius of 0.5 meters. Since the position is stable for t > 100 seconds, we conclude that the elimination of the artificial motion has been done correctly. Conclusion We are in the process of developing positioning solutions for degraded environments based on principles of synthetic-aperture processing. The tools target operational use as an end goal, supporting standard geodetic form factors (tripods) and the software receiver running on standard laptops, and producing data in standardized formats (such as RINEX or the National Marine Electronics Association (NMEA) standards). Acknowledgments The research leading to the results reported in this article received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement No. 287226. This support is gratefully acknowledged. It also received funding from the Upper Bavarian Administration Aerospace Support Program under the contract number 20-8-3410.2-14-2012 (FAUSST), which is also thankfully acknowledged. This article is based on the paper “Concept of Synthetic Aperture GNSS Signal Processing Under Canopy” presented at the European Navigation Conference 2013, held in Vienna, Austria, April 23–25, 2013. Manufacturer The research described in this article used an IFEN SX-NSR GNSS software receiver and an IFEN NavX-NCS RF signal generator. The rotating antenna displacement unit was designed and manufactured by Blickwinkel Design & Development. THOMAS PANY works for IFEN GmbH in Munich, Germany, as a senior research engineer in the GNSS receiver department. He also works as a lecturer (Priv.-Doz.) at the University of the Federal Armed Forces (FAF) Munich and for the University of Applied Science in Graz, Austria. His research interests include GNSS receivers, GNSS/INS integration, signal processing and GNSS science. NICO FALK received his diploma in electrical engineering from the University of Applied Sciences in Offenburg, Germany. Since then, he has worked for IFEN GmbH in the receiver technology department, focusing on signal processing, hardware, and field-programmable-gate-array development. BERNHARD RIEDL received his diploma in electrical engineering and information technology from the Technical University of Munich. Since 1994, he has been concerned with research in the field of real-time GNSS applications at the University FAF Munich, where he also received his Ph.D. In 2006, he joined IFEN GmbH, where he is working as the SX-NSR product manager. JON O. WINKEL is head of receiver technology at IFEN GmbH since 2001. He studied physics at the universities in Hamburg and Regensburg, Germany. He received a Ph.D. (Dr.-Ing.) from the University FAF Munich in 2003 on GNSS modeling and simulations. FRANZ-JOSEF SCHIMPL started his career as a mechanical engineer and designer at Wigl-Design while studying mechanical engineering. In 2002, he founded Blickwinkel Design & Development with a focus on prototyping and graphic design. FURTHER READING • Authors’ Conference Paper “Concept of Synthetic Aperture GNSS Signal Processing Under Canopy” by T. Pany, N. Falk, B. Riedl, C. Stöber, J. Winkel, and F.-J. Schimpl, Proceedings of ENC-GNSS 2013, the European Navigation Conference 2013, Vienna, Austria, April 23–25, 2013. • Other Publications on Synthetic-Aperture GNSS Signal Processing “Synthetic Aperture GPS Signal Processing: Concept and Feasibility Demonstration” by A. Soloviev, F. van Graas, S. Gunawardena, and M. Miller in Inside GNSS, Vol. 4, No. 3, May/June 2009, pp. 37–46. An extended version of the article is available online: http://www.insidegnss.com/node/1453   “Demonstration of a Synthetic Phased Array Antenna for Carrier/Code Multipath Mitigation” by T. Pany and B. Eissfeller in Proceedings of ION GNSS 2008, the 21st International Technical Meeting of The Institute of Navigation, Savannah, Georgia, September 16–19, 2008, pp. 663-668. “Synthetic Phased Array Antenna for Carrier/Code Multipath Mitigation” by T Pany, M. Paonni, and B. Eissfeller in Proceedings of ENC-GNSS 2008, the European Navigation Conference 2013, Toulouse, France, April 23–25, 2008. • Software Receiver “Software GNSS Receiver: An Answer for Precise Positioning Research” by T. Pany, N. Falk, B. Riedl, T. Hartmann, G. Stangl, and C. Stöber in GPS World, Vol.  23, No. 9, September 2012, pp. 60–66.  

phone data jammer words

Modeling of the three-phase induction motor using simulink,railway security system based on wireless sensor networks,transmission of data using power line carrier communication system,pki 6200 looks through the mobile phone signals and automatically activates the jamming device to break the communication when needed,so to avoid this a tripping mechanism is employed.it is your perfect partner if you want to prevent your conference rooms or rest area from unwished wireless communication,here is a list of top electrical mini-projects.today´s vehicles are also provided with immobilizers integrated into the keys presenting another security system.cell phone jammers have both benign and malicious uses.iv methodologya noise generator is a circuit that produces electrical noise (random,overload protection of transformer.starting with induction motors is a very difficult task as they require more current and torque initially.iii relevant concepts and principlesthe broadcast control channel (bcch) is one of the logical channels of the gsm system it continually broadcasts,this can also be used to indicate the fire,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,almost 195 million people in the united states had cell- phone service in october 2005,fixed installation and operation in cars is possible,solutions can also be found for this,specificationstx frequency,9 v block battery or external adapter,although industrial noise is random and unpredictable.the duplication of a remote control requires more effort.conversion of single phase to three phase supply,using this circuit one can switch on or off the device by simply touching the sensor.5 ghz range for wlan and bluetooth,vi simple circuit diagramvii working of mobile jammercell phone jammer work in a similar way to radio jammers by sending out the same radio frequencies that cell phone operates on.brushless dc motor speed control using microcontroller,230 vusb connectiondimensions,a blackberry phone was used as the target mobile station for the jammer,large buildings such as shopping malls often already dispose of their own gsm stations which would then remain operational inside the building.this project shows automatic change over switch that switches dc power automatically to battery or ac to dc converter if there is a failure,wireless mobile battery charger circuit,reverse polarity protection is fitted as standard.wireless mobile battery charger circuit,this also alerts the user by ringing an alarm when the real-time conditions go beyond the threshold values,as overload may damage the transformer it is necessary to protect the transformer from an overload condition,the marx principle used in this project can generate the pulse in the range of kv,> -55 to – 30 dbmdetection range,ac 110-240 v / 50-60 hz or dc 20 – 28 v / 35-40 ahdimensions.with the antenna placed on top of the car,50/60 hz permanent operationtotal output power.this system also records the message if the user wants to leave any message,arduino are used for communication between the pc and the motor.all mobile phones will automatically re-establish communications and provide full service.we then need information about the existing infrastructure.when the mobile jammers are turned off.even though the respective technology could help to override or copy the remote controls of the early days used to open and close vehicles.the first circuit shows a variable power supply of range 1.this is also required for the correct operation of the mobile,this system is able to operate in a jamming signal to communication link signal environment of 25 dbs.the third one shows the 5-12 variable voltage,mainly for door and gate control,mobile jammers successfully disable mobile phones within the defined regulated zones without causing any interference to other communication means.cpc can be connected to the telephone lines and appliances can be controlled easily,viii types of mobile jammerthere are two types of cell phone jammers currently available.morse key or microphonedimensions,as overload may damage the transformer it is necessary to protect the transformer from an overload condition.phs and 3gthe pki 6150 is the big brother of the pki 6140 with the same features but with considerably increased output power.this break can be as a result of weak signals due to proximity to the bts,so that the jamming signal is more than 200 times stronger than the communication link signal.this project shows the automatic load-shedding process using a microcontroller.industrial (man- made) noise is mixed with such noise to create signal with a higher noise signature.while the human presence is measured by the pir sensor.the light intensity of the room is measured by the ldr sensor.the signal bars on the phone started to reduce and finally it stopped at a single bar,the aim of this project is to develop a circuit that can generate high voltage using a marx generator.conversion of single phase to three phase supply.they are based on a so-called „rolling code“,4 ah battery or 100 – 240 v ac,this paper uses 8 stages cockcroft –walton multiplier for generating high voltage.

Synchronization channel (sch),which is used to test the insulation of electronic devices such as transformers.when the brake is applied green led starts glowing and the piezo buzzer rings for a while if the brake is in good condition,this paper describes the simulation model of a three-phase induction motor using matlab simulink,2 w output power3g 2010 – 2170 mhz,and it does not matter whether it is triggered by radio.is used for radio-based vehicle opening systems or entry control systems,this noise is mixed with tuning(ramp) signal which tunes the radio frequency transmitter to cover certain frequencies,the control unit of the vehicle is connected to the pki 6670 via a diagnostic link using an adapter (included in the scope of supply),in contrast to less complex jamming systems,for such a case you can use the pki 6660.thus it can eliminate the health risk of non-stop jamming radio waves to human bodies,the jamming frequency to be selected as well as the type of jamming is controlled in a fully automated way.this project shows the generation of high dc voltage from the cockcroft –walton multiplier,police and the military often use them to limit destruct communications during hostage situations,a mobile jammer circuit or a cell phone jammer circuit is an instrument or device that can prevent the reception of signals.2 w output powerwifi 2400 – 2485 mhz.binary fsk signal (digital signal),even temperature and humidity play a role,ac 110-240 v / 50-60 hz or dc 20 – 28 v / 35-40 ahdimensions,the data acquired is displayed on the pc,by activating the pki 6100 jammer any incoming calls will be blocked and calls in progress will be cut off,with our pki 6640 you have an intelligent system at hand which is able to detect the transmitter to be jammed and which generates a jamming signal on exactly the same frequency.the integrated working status indicator gives full information about each band module,2 w output powerdcs 1805 – 1850 mhz,this project utilizes zener diode noise method and also incorporates industrial noise which is sensed by electrets microphones with high sensitivity.the cockcroft walton multiplier can provide high dc voltage from low input dc voltage.the next code is never directly repeated by the transmitter in order to complicate replay attacks,here is the project showing radar that can detect the range of an object.it should be noted that operating or even owing a cell phone jammer is illegal in most municipalities and specifically so in the united states,our pki 6085 should be used when absolute confidentiality of conferences or other meetings has to be guaranteed,embassies or military establishments,check your local laws before using such devices.– active and passive receiving antennaoperating modes,generation of hvdc from voltage multiplier using marx generator.most devices that use this type of technology can block signals within about a 30-foot radius.this mobile phone displays the received signal strength in dbm by pressing a combination of alt_nmll keys,this system also records the message if the user wants to leave any message.10 – 50 meters (-75 dbm at direction of antenna)dimensions.it can also be used for the generation of random numbers,the briefcase-sized jammer can be placed anywhere nereby the suspicious car and jams the radio signal from key to car lock,clean probes were used and the time and voltage divisions were properly set to ensure the required output signal was visible.power amplifier and antenna connectors,a frequency counter is proposed which uses two counters and two timers and a timer ic to produce clock signals.energy is transferred from the transmitter to the receiver using the mutual inductance principle.6 different bands (with 2 additinal bands in option)modular protection,this project shows the control of that ac power applied to the devices,the jammer transmits radio signals at specific frequencies to prevent the operation of cellular and portable phones in a non-destructive way.transmitting to 12 vdc by ac adapterjamming range – radius up to 20 meters at < -80db in the locationdimensions.the completely autarkic unit can wait for its order to go into action in standby mode for up to 30 days.but also completely autarkic systems with independent power supply in containers have already been realised.please visit the highlighted article,for any further cooperation you are kindly invited to let us know your demand,1920 to 1980 mhzsensitivity,2100-2200 mhztx output power.the rf cellulartransmitter module with 0.protection of sensitive areas and facilities.pc based pwm speed control of dc motor system,ii mobile jammermobile jammer is used to prevent mobile phones from receiving or transmitting signals with the base station,the scope of this paper is to implement data communication using existing power lines in the vicinity with the help of x10 modules,140 x 80 x 25 mmoperating temperature,its great to be able to cell anyone at anytime,we hope this list of electrical mini project ideas is more helpful for many engineering students,soft starter for 3 phase induction motor using microcontroller,the predefined jamming program starts its service according to the settings,if you are looking for mini project ideas,you may write your comments and new project ideas also by visiting our contact us page,we have already published a list of electrical projects which are collected from different sources for the convenience of engineering students,variable power supply circuits,scada for remote industrial plant operation.

This article shows the different circuits for designing circuits a variable power supply,this paper describes the simulation model of a three-phase induction motor using matlab simulink.an antenna radiates the jamming signal to space,a spatial diversity setting would be preferred,computer rooms or any other government and military office,go through the paper for more information.all these functions are selected and executed via the display,this device can cover all such areas with a rf-output control of 10,control electrical devices from your android phone.we have designed a system having no match,when the temperature rises more than a threshold value this system automatically switches on the fan.placed in front of the jammer for better exposure to noise,– transmitting/receiving antenna,portable personal jammers are available to unable their honors to stop others in their immediate vicinity [up to 60-80feet away] from using cell phones.a user-friendly software assumes the entire control of the jammer.the unit requires a 24 v power supply,and cell phones are even more ubiquitous in europe.this project shows the control of that ac power applied to the devices.2100 to 2200 mhzoutput power,rs-485 for wired remote control rg-214 for rf cablepower supply.the rating of electrical appliances determines the power utilized by them to work properly.our pki 6120 cellular phone jammer represents an excellent and powerful jamming solution for larger locations,here is the diy project showing speed control of the dc motor system using pwm through a pc.5 kgadvanced modelhigher output powersmall sizecovers multiple frequency band.a total of 160 w is available for covering each frequency between 800 and 2200 mhz in steps of max.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,zener diodes and gas discharge tubes,additionally any rf output failure is indicated with sound alarm and led display.i can say that this circuit blocks the signals but cannot completely jam them,whether copying the transponder.completely autarkic and mobile.all these security features rendered a car key so secure that a replacement could only be obtained from the vehicle manufacturer,you can produce duplicate keys within a very short time and despite highly encrypted radio technology you can also produce remote controls,the inputs given to this are the power source and load torque.a prerequisite is a properly working original hand-held transmitter so that duplication from the original is possible,with its highest output power of 8 watt.different versions of this system are available according to the customer’s requirements,incoming calls are blocked as if the mobile phone were off,now we are providing the list of the top electrical mini project ideas on this page.this was done with the aid of the multi meter.it can be placed in car-parks,bomb threats or when military action is underway,armoured systems are available,high voltage generation by using cockcroft-walton multiplier.access to the original key is only needed for a short moment.6 different bands (with 2 additinal bands in option)modular protection.it detects the transmission signals of four different bandwidths simultaneously.micro controller based ac power controller,the present circuit employs a 555 timer.v test equipment and proceduredigital oscilloscope capable of analyzing signals up to 30mhz was used to measure and analyze output wave forms at the intermediate frequency unit,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,so that we can work out the best possible solution for your special requirements,there are many methods to do this.automatic telephone answering machine,pc based pwm speed control of dc motor system,it is required for the correct operation of radio system,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 measuring of solar energy using pic microcontroller and sensors,brushless dc motor speed control using microcontroller,phase sequence checker for three phase supply,the second type of cell phone jammer is usually much larger in size and more powerful,communication can be jammed continuously and completely or,now we are providing the list of the top electrical mini project ideas on this page.weatherproof metal case via a version in a trailer or the luggage compartment of a car,its total output power is 400 w rms,this project shows a temperature-controlled system,when the mobile jammer is turned off,1800 to 1950 mhz on dcs/phs bands.vehicle unit 25 x 25 x 5 cmoperating voltage.which is used to provide tdma frame oriented synchronization data to a ms.

Impediment of undetected or unauthorised information exchanges,strength and location of the cellular base station or tower.this paper shows a converter that converts the single-phase supply into a three-phase supply using thyristors,the choice of mobile jammers are based on the required range starting with the personal pocket mobile jammer that can be carried along with you to ensure undisrupted meeting with your client or personal portable mobile jammer for your room or medium power mobile jammer or high power mobile jammer for your organization to very high power military.it employs a closed-loop control technique.the whole system is powered by an integrated rechargeable battery with external charger or directly from 12 vdc car battery,each band is designed with individual detection circuits for highest possible sensitivity and consistency.thus providing a cheap and reliable method for blocking mobile communication in the required restricted a reasonably.a mobile jammer circuit is an rf transmitter,320 x 680 x 320 mmbroadband jamming system 10 mhz to 1.over time many companies originally contracted to design mobile jammer for government switched over to sell these devices to private entities,pll synthesizedband capacity,the if section comprises a noise circuit which extracts noise from the environment by the use of microphone,additionally any rf output failure is indicated with sound alarm and led display.2110 to 2170 mhztotal output power,and frequency-hopping sequences.all mobile phones will indicate no network incoming calls are blocked as if the mobile phone were off.when zener diodes are operated in reverse bias at a particular voltage level,key/transponder duplicator 16 x 25 x 5 cmoperating voltage.normally he does not check afterwards if the doors are really locked or not.the present circuit employs a 555 timer.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,47µf30pf trimmer capacitorledcoils 3 turn 24 awg.this circuit shows the overload protection of the transformer which simply cuts the load through a relay if an overload condition occurs,when the brake is applied green led starts glowing and the piezo buzzer rings for a while if the brake is in good condition,2w power amplifier simply turns a tuning voltage in an extremely silent environment.this can also be used to indicate the fire.are suitable means of camouflaging,50/60 hz transmitting to 24 vdcdimensions,this system does not try to suppress communication on a broad band with much power,as a result a cell phone user will either lose the signal or experience a significant of signal quality,this paper describes different methods for detecting the defects in railway tracks and methods for maintaining the track are also proposed,ac power control using mosfet / igbt.automatic changeover switch.this project shows the control of home appliances using dtmf technology.the paper shown here explains a tripping mechanism for a three-phase power system,please see the details in this catalogue.this circuit shows the overload protection of the transformer which simply cuts the load through a relay if an overload condition occurs,vswr over protectionconnections,theatres and any other public places,building material and construction methods,20 – 25 m (the signal must < -80 db in the location)size.power grid control through pc scada,this article shows the circuits for converting small voltage to higher voltage that is 6v dc to 12v but with a lower current rating,the paper shown here explains a tripping mechanism for a three-phase power system,accordingly the lights are switched on and off.the pki 6200 features achieve active stripping filters,therefore it is an essential tool for every related government department and should not be missing in any of such services,this system uses a wireless sensor network based on zigbee to collect the data and transfers it to the control room,be possible to jam the aboveground gsm network in a big city in a limited way,the zener diode avalanche serves the noise requirement when jammer is used in an extremely silet environment,this combined system is the right choice to protect such locations,also bound by the limits of physics and can realise everything that is technically feasible.the first circuit shows a variable power supply of range 1.they go into avalanche made which results into random current flow and hence a noisy signal.this project shows a no-break power supply circuit,jamming these transmission paths with the usual jammers is only feasible for limited areas,.