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Chip-scale atomic clock. How a Chip-Scale Atomic Clock Can Help Mitigate Broadband Interference Small low-power atomic clocks can enhance the performance of GPS receivers in a number of ways, including enhanced code-acquisition capability that precise long-term timing allows. And, it turns out, such clocks can effectively mitigate wideband radio frequency interference coming from GPS jammers. We learn how in this month’s column. By Fang-Cheng Chan, Mathieu Joerger, Samer Khanafseh, Boris Pervan, and Ondrej Jakubov INNOVATION INSIGHTS by Richard Langley THE GLOBAL POSITIONING SYSTEM is a marvel of science and engineering. It has become so ubiquitous that we are starting to take it for granted. Receivers are everywhere. In our vehicle satnav units, in our smart phones, even in some of our cameras. They are used to monitor the movement of the Earth’s crust, to measure water vapor in the troposphere, and to study the effects of space weather. They allow surveyors to work more efficiently and prevent us from getting lost in the woods. They navigate aircraft and ships, and they help synchronize mobile phone and electricity networks, and precisely time financial transactions. GPS can do all of this, in large part, because the signals emitted by each satellite are derived from an onboard atomic clock (or, more technically correct, an atomic frequency standard). The signals from all of the satellites in the GPS constellation need to be synchronized to within a certain tolerance so that accurate (conservatively stated as better than 9 meters horizontally and 15 meters vertically, 95% of the time), real-time positioning can be achieved by a receiver using only a crystal oscillator. This requires satellite clocks with excellent long-term stability so that their offsets from the GPS system timescale can be predicted to better than about 24 nanoseconds, 95% of the time. Such a performance level can only be matched by atomic clocks. The very first atomic clock was built in 1949. It was based on an energy transition of the ammonia molecule. However, it wasn’t very accurate. So scientists turned to a particular energy transition of the cesium atom and by the mid-1950s had built the first cesium clocks. Subsequently, clocks based on energy transitions of the rubidium and hydrogen atoms were also developed. These initial efforts were rather bulky affairs but in the 1960s, commercial rack-mountable cesium and rubidium devices became available. Further development led to both cesium and rubidium clocks being compact and rugged enough that they could be considered for use in GPS satellites. Following successful tests in the precursor Navigation Technology Satellites, the prototype or Block I GPS satellites were launched with two cesium and two rubidium clocks each. Subsequent versions of the GPS satellites have continued to feature a combination of the two kinds of clocks or just rubidium clocks in the case of the Block IIR satellites. While it is not necessary to use an atomic clock with a GPS receiver for standard positioning and navigation applications, some demanding tasks such as geodetic reference frame monitoring use atomic frequency standards to control the operation of the receivers. These standards are external devices, often rack mounted, connected to the receiver by a coaxial cable—too large to be embedded inside receivers. But in 2004, scientists demonstrated a chip-scale atomic clock, and by 2011, they had become commercially available. Such small low-power atomic clocks can enhance the performance of GPS receivers in a number of ways, including enhanced code-acquisition capability that precise long-term timing allows. And, it turns out, such clocks can effectively mitigate wideband radio frequency interference coming from GPS jammers. We learn how in this month’s column. “Innovation” is a regular feature that discusses advances in GPS technology and its 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. Write to him at lang @ unb.ca. Currently installed Local Area Augmentation System (LAAS) ground receivers have experienced a number of disruptions in GPS signal tracking due to radio frequency interference (RFI). The main sources of RFI were coming from the illegal use of jammers (also known as personal privacy devices [PPD]) inside vehicles driving by the ground installations. Recently, a number of researchers have studied typical properties of popular PPDs found in the market and have concluded that the effect of PPD interference on the GPS signal is nearly equivalent to that of a wideband signal jammer, to which the current GPS signal is most vulnerable. This threat impacts LAAS or any ground-based augmentation system (GBAS) in two ways: Continuity degradation — as vehicles with PPDs pass near the GBAS ground antennas, the reference receivers lose lock due to the overwhelming noise power.  Integrity degradation — the code tracking error will increase when the noise level in the tracking loop increases. Numerous interference mitigation techniques have been studied for broadband interference. The interference mitigation methods can be separated according to the two fundamental stages of GPS signal tracking: the front-end stage, in which automatic gain control and antenna nulling/beam forming techniques are relevant, and the baseband stage, where code and carrier-tracking loop algorithms and aiding methods are applicable. In our current work, the baseband strategy and resources that are practically implementable at GBAS ground stations are considered. Among those resources, we focus on using atomic clocks to mitigate broadband GNSS signal interference. For GPS receivers in general, wide tracking loop bandwidths are used to accommodate the change in signal frequencies and phases caused by user dynamics. Unfortunately, wide bandwidths also allow more noise to enter into the tracking loop, which will be problematic when wideband inference exists. The general approach to mitigate wideband interference is to reduce the tracking loop bandwidth. However, a reference receiver employing a temperature-compensated crystal oscillator (TCXO) needs to maintain a minimum loop bandwidth to track the dynamics of the clock itself, even when all other Doppler effects are removed. The poor stability of TCXOs fundamentally limits the potential to reduce the tracking loop bandwidth. This limitation becomes much less constraining when using an atomic clock at the receiver, especially in the static, vibration-free environment of a GBAS ground station. Integrating atomic clocks with GPS/GNSS receivers is not a new idea. Nevertheless, the practical feasibility of such integration remained difficult until recent advancements in atomic clock technology, such as commercially available compact-size rubidium frequency standards or, more recently, chip-scale atomic clocks (CSACs). Most of the research using atomic clock integrated GPS receivers aims to improve positioning and timing accuracy, enhance navigation system integrity, or coast through short periods of satellite outages. In these applications, the main function of the atomic clock is to improve the degraded system performance caused by bad satellite geometries. As for using narrower tracking loop bandwidths to obtain better noise/jamming-resistant performance, the majority of work in this area has focused on high-dynamic user environments with extra sensor aiding, such as inertial navigation systems, pseudolites, or other external frequency-stable radio signals. These aids alone do not permit reaching the limitation of tracking loop bandwidth reduction since the remaining Doppler shift from user dynamics still needs to be tracked by the tracking loop itself. Our research intends to explore the lower end of the minimum tracking loop bandwidth for static GPS/GNSS receivers using atomic clocks. High-frequency-stability atomic clocks naturally reduce the minimum required bandwidth for tracking clock errors (since clock phase random variations are much smaller). We have conducted analyses to obtain the theoretical minimum tracking loop bandwidths using clocks of varying quality. Carrier-phase tracking loop performance under deteriorated C/N0 conditions (that is, during interference) was investigated because it is the most vulnerable to wideband RFI. The limitations on the quality of atomic clocks and on the receiver tracking algorithms (second- or third-order tracking loop bandwidths) to achieve varying degrees of interference suppression at the GBAS reference receivers are explored. The tracking loop bandwidth reductions and interference attenuations that are achievable using different qualities of atomic clocks, including CSACs and commercially available rubidium receiver clocks, are also discussed in this article. In addition to the theoretical analyses, actual GPS intermediate frequency (IF) signals have been sampled using a GPS radio frequency (RF) frond-end kit, which is capable of utilizing external clock inputs, connected to a commercially available atomic clock. The sampled IF data are fed into a software receiver together with and without simulated wideband interference to evaluate the performance of interference mitigation using atomic clocks. The wideband interference is numerically simulated based on deteriorated C/N0. The actual tracking errors generated from real IF data are used to validate the system performance predicted by the preceding broadband interference mitigation analyses. Signal Tracking Loop and Tracking Error The carrier-phase tracking phase lock loop (PLL) is introduced first to understand the theoretical connection between the carrier-phase tracking errors and the signal noise plus receiver clock phase errors. A simplified PLL is shown in FIGURE 1 with incoming signals set to zero. In the figure, n(s), c(s), and δθ(s) are receiver white noise, clock phase error or clock disturbance, and tracking loop phase error respectively, with s being the Laplace transform parameter. G(s) is the product of the loop filter F(s) and the receiver clock model 1/s. FIGURE 1. Simplified tracking loop diagram. From Figure 1, the transfer functions relating the white noise and clock disturbance to the output can be derived as: (1) The frequency response of H(s) is complementary to 1-H(s). Therefore, the PLL tracking performance is a trade-off between the noise rejection performance and the clock disturbance tracking performance. Total PLL errors resulting from different error sources are presented as phase jitter, which is the root-mean-square (RMS) of resulting phase errors. Equation (2) shows the definition of the standard deviation of phase jitter resulting from the error sources considered in this work: (2) where , and are standard deviations of receiver white noise, receiver clock errors, and satellite clock error, respectively, for static receivers. The standard deviation for each of the clock error sources can be evaluated using the frequency response of the corresponding transfer function and power spectral densities (PSDs). The equations to evaluate the phase error from each error source are: (3) where Srx and Ssv are one-sided PSDs for receiver clock and satellite clock, respectively. Bw is the bandwidth of the tracking loop and Tc is the coherent integration time. Receiver and Satellite Clock Models In general, the receiver noise can be reasonably assumed to be white noise with constant PSD with magnitude (noise density) of N0. However, it is not the case for clock errors. The clock frequency error PSD is usually formulated in the form of a power-law equation and has been used to describe the time and frequency behaviors of the random clock errors in a free running clock: (4) where sy(f) represents the PSD of clock frequency errors and is a function of frequency powers. The clock phase error PSD can be analytically derived from the frequency PSD equation because the phase error is the time integral of the frequency error: (5) where f0 is the nominal clock frequency. The h coefficients of the clock phase error PSD are the product of the h coefficients from the clock frequency error PSD and the nominal frequency. We have adopted the PSD clock error models in our work to perform tracking loop performance analysis. The PSD of the CSAC is derived from an Allan deviation figure published by the manufacturer and is shown in FIGURE 2. We took three piecewise Allan deviation straight lines, which are slightly conservative, and converted them to a PSD. FIGURE 2. Allan deviations for chip-scale atomic clock. Three PSDs of clock error models are listed in TABLE 1, which represent spectrums of the well known TCXO, the CSAC, and a rubidium standard. Phase noise related h0 and h1 coefficients in the CSAC model are assumed to be the same as the TCXO because they can’t be obtained from the Allan deviation figure. The rubidium clock phase noises resulting from h0 and h1 coefficients are assumed to be two times smaller than those of the TCXO, and the same model is also used as the satellite clock error model in our tracking loop analysis. TABLE 1. Coefficients of power-law model. Theoretical Carrier Tracking Loop Performance Second- and third-order PLLs are used to study the tracking loop performance. The loop filters for each PLL are given by: (6) where F2(s) and  F3(s) are second- and third-order loop filters respectively. Typical coefficients for the second- and third-order loop filters are a2 = 1.414; wo,2 = 4×Bw,2 × a2/[(a2)2+1]; a3 = 1.1; b3 = 2.4; wo,3 = Bw,3/0.7845. Bw,2 and Bw,3 are the second- and third-order tracking loop bandwidths accordingly. As stated earlier, three error sources are considered for static receivers. Using the clock error models described earlier, the contribution of different error sources to phase jitter is a function of PLL tracking bandwidth. The resulting phase tracking errors from different error sources are evaluated based on Equation (3) and shown in FIGURE 3. FIGURE 3. Phase error contribution from different error sources. The third-order PLL performance using 2-, 1-, 0.5- and 0.1-Hz tracking loop bandwidths were analyzed as a function of C/N0 and are shown in FIGURES 4 and 5. For each selected bandwidth, three different qualities of receiver clocks were analyzed, and a conventional 15-degree performance threshold was adopted. The second-order PLL performs similarly to the third-order PLL. However, the phase jitter tends to be more biased when the tracking loop bandwidth becomes smaller. This phenomenon will be observed later on using signal data for performance validation. Therefore, only the third-order loop performance analysis is shown in Figures 4 and 5. It is obvious from these two figures that the minimum tracking loop bandwidth for a TCXO receiver PLL is about 2 Hz, and the PLL can work properly only while C/N0 is above 24 dB-Hz. FIGURE 4 Tracking loop performance analysis for 2- and 1-Hz loop bandwidth. FIGURE 5. Tracking loop performance analysis for 0.5- and 0.1-Hz loop bandwidth. As for the receiver using atomic clocks, CSAC and a rubidium frequency standard in our analysis, the PLL bandwidth can be reduced down to at least 0.1 Hz while C/N0 is above 15 dB-Hz. Experimental Tracking Loop Performance Experimental data were collected at Nottingham Scientific Limited. The experiment was conducted using a GPS/GNSS RF front end with a built-in TCXO clock. The RF front end also has the capability of accepting atomic clock signals through an external clock input connector to which the CSAC (see Photo) was connected during data collection. All data (using the built-in TCXO clock or the CSAC) were sampled at a 26-MHz sampling rate and at a 6.5-MHz IF with 2-MHz front-end bandwidth and four quantization levels. A MatLab-coded software defined receiver (SDR) was used to process collected IF samples for tracking loop performance validation. TCXO phase jitters resulting from different tracking loop bandwidths are shown in FIGURE 6 for a typical second-order PLL under a nominal C/N0, which is about 45 dB-Hz. A 45-degree loss-of-lock threshold was adopted (three times larger than the standard deviation threshold used in an earlier performance analysis). In our work, all code tracking delay lock loops (DLLs) are implemented using a second-order loop filter with 20-millisecond coherent integration time and 0.5-Hz loop bandwidth without any aiding. The resulting phase jitters in the figure become biased when the tracking loop bandwidth is reduced. This observed phenomenon implies that a second-order PLL time response cannot track the clock dynamics when the loop bandwidth approaches the minimum loop bandwidth (where loss of lock occurs). FIGURE 6. Second-order PLL phase jitter using TCXO. The same IF data was re-processed by the SDR using the third-order PLL with the same range of tracking loop bandwidths. The resulting phase jitters are shown in FIGURES 7 and 8. There is no observable phase jitter bias before the PLLs lose lock in the figures. These results demonstrate that a third-order PLL performs better in terms of capturing the clock dynamics when the tracking loop bandwidth is reduced close to the limitation. Therefore, only the third-order PLL will be considered further. FIGURE 7. Third-order PLL phase jitter using TCXO. FIGURE 8. Third-order PLL phase jitter using CSAC. The performance of the TCXO PLL can be evaluated from the results in Figure 7. It demonstrates that the minimum loop bandwidth is 2 Hz, which is consistent with the previous analysis shown in figure 4. However, the minimum bandwidth using the CSAC is shown to be 0.5 Hz in Figure 8. This result does not meet the performance predicted by the analysis, which shows that the working bandwidth can be reduced to 0.1 Hz. Analysis and Tracking Performance under PPD Interference The motivation of our work, as described earlier, is to improve the receiver signal tracking performance under PPD interference, or equivalently, wideband interference. We carried out a simple analysis first to understand how much signal deterioration a GBAS ground receiver could expect. A 13-dBm/MHz PPD currently available on the market was used to analyze the signal deterioration based on the distance between the PPD and the GBAS ground receiver. A simple analysis using a direct-path model shows that noise power roughly 30 dB higher than the nominal noise level (about -202 dBW/Hz) could be experienced by the GBAS ground receiver if the nearest distance is assumed to be 0.5 kilometers. In this case, any wideband interference mitigation method to address PPD interference has to handle C/N0 as low as 10 to 15 dB-Hz. Gaussian distributed white noises were simulated and added on top of the original IF samples, then re-quantized to the original four quantization levels to mimic the PPD interference signal condition. A 20-dB higher noise level was simulated to demonstrate the effectiveness of this signal deterioration technique. The tracking loop performance using the third-order PLL under low C/N0 conditions was evaluated using the IF sampling and PPD interference simulation technique just described. The evaluation results show that the minimum PLL bandwidth using the TCXO is still 2 Hz. This result is roughly consistent with a previous analysis showing a 24-dB-Hz C/N0 limitation using 2-Hz tracking bandwidth. The PLL using the CSAC performs better than that using the TCXO, which is expected. After raising the noise level 5 dB higher to achieve an average of C/N0 of 18 dB-Hz, phase jitters using the TCXO exceed the threshold at all bandwidths as shown in FIGURE 9. The same magnitude of noise was also added to the CSAC IF samples. The resulting phase jitters are shown in FIGURE 10, which demonstrates that the minimum bandwidth is 1 Hz for this deteriorated signal condition. Any further increase in noise level will result in loss of lock for PLLs using a CSAC at all tracking bandwidths. FIGURE 9. Phase jitter using TCXO under 18 dB-Hz C/N0. FIGURE 10. Phase jitter using CSAC under 18 dB-Hz C/N0. Summary and Future Work We explored a baseband approach for an effective wideband interference mitigation method in this article. We have presented the theoretical analysis and actual data validation to study the possible improvement of the PLL tracking performance under PPD interference, which has been experienced by LAAS ground receivers. The limitations of reducing PLL tracking loop bandwidths using different qualities of receiver clocks have been analyzed and compared with the experimental results generated by processing IF samples using an SDR. We conclude that the PLL tracking performance using a TCXO is consistent between theoretical prediction and data validation under both nominal and low C/N0 conditions. However, the PLL tracking performance using the CSAC was not as good as the analysis prediction under both conditions. In our future work, to understand the reason for the tracking performance inconsistency using the CSAC, we will carefully examine and evaluate the hardware components in line between the external clock input and the IF sampling chip. In this way, we will exclude the clock performance degradation due to any hardware incompatibility. Other types of high quality clocks, such as extra-low-phase-noise oven-controlled crystal oscillators and low-phase-noise rubidium oscillators, will also be tested to explore the limitation of PLL tracking bandwidth reduction. If the results using other clocks exhibit good consistency between performance analysis and data validation, it is highly possible that the CSAC clock error model mis-represents the available commercial products. In our future work, we will also consider simulating PPD interference more closely to the real scenario, by adding analog interference signals on top of GPS/GNSS analog signals before taking digital IF samples. Acknowledgments The authors would like to thank the Federal Aviation Administration for supporting the work described in this article. Also, the authors would like to extend their thanks to all members of the Illinois Institute of Technology NavLab and to the collaborators from Nottingham Scientific Limited for their insightful advice. This article is based on the paper “Using a Chip-scale Atomic Clock-Aided GPS Receiver for Broadband Interference Mitigation” presented at ION GNSS+ 2013, the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation held in Nashville, Tennessee, September 16–20, 2013. Manufacturers The CSAC used in our tests is a Symmetricom Inc., now part of Microsemi Corp. (www.microsemi.com), model SA.45s. We used a Nottingham Scientific Ltd. (www.nsl.eu.com) Stereo GPS/GNSS RF front end with the MatLab-based SoftGNSS 3.0 software from the Danish GPS Center at Aalborg University (gps.aau.dk). FANG-CHENG CHAN is a senior research associate in the Navigation Laboratory of the Department of Mechanical and Aerospace Engineering at the Illinois Institute of Technology (IIT) in Chicago. He received his Ph.D in mechanical and aerospace engineering from IIT in 2008. He is currently working on GPS receiver integrity for Local Area Augmentation System (LAAS) ground receivers, researching GPS receiver interference detection and mitigation to prevent unintentional jamming using both baseband and antenna array techniques, and developing navigation and fault detection algorithms with a focus on receiver autonomous integrity monitoring or RAIM. MATHIEU JOERGER obtained a master’s in mechatronics from the National Institute of Applied Sciences in Strasbourg, France, in 2002, and M.S. and Ph.D. degrees in mechanical and aerospace engineering from IIT in 2002 and 2009 respectively. He is the 2009 recipient of the Institute of Navigation Bradford Parkinson award, which honors outstanding graduate students in the field of GNSS. He is a research assistant professor at IIT, working on multi-sensor integration, on sequential fault-detection for multi-constellation navigation systems, and on relative and differential RAIM for shipboard landing of military aircraft. SAMER KHANAFSEH is a research assistant professor at IIT. He received his M.S. and Ph.D. degrees in aerospace engineering at IIT in 2003 and 2008, respectively. He has been involved in several aviation applications such as autonomous airborne refueling of unmanned air vehicles, autonomous shipboard landing, and ground-based augmentation systems. He was the recipient of the 2011 Institute of Navigation Early Achievement Award for his contributions to the integrity of carrier-phase navigation systems. BORIS PERVAN is a professor of mechanical and aerospace engineering at IIT, where he conducts research focused on high-integrity satellite navigation systems. Prof. Pervan received his B.S. from the University of Notre Dame, M.S. from the California Institute of Technology, and Ph.D. from Stanford University. ONDREJ JAKUBOV received his M.Sc. in electrical engineering from the Czech Technical University (CTU) in Prague in 2010. He is a postgraduate student in the CTU Department of Radio Engineering and he also works as a navigation engineer for Nottingham Scientific Limited in Nottingham, U.K. His research interests include GNSS signal processing algorithms and receiver architectures. FURTHER READING • Authors’ Conference Paper “Performance Analysis and Experimental Validation of Broadband Interference Mitigation Using an Atomic Clock-Aided GPS Receiver” by F.-C. Chan, S. Khanafseh, M. Joerger, B. Pervan and O. Jakubov in the Proceedings of ION GNSS+ 2013, the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation, Nashville, Tennessee, September 16–20, 2013, pp. 1371–1379. • Chip-Scale Atomic Clocks “The SA.45s Chip-Scale Atomic Clock–Early Production Statistics” by R. Lutwak in the Proceedings of the 43rd Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting, Long Beach, California, November 14–17, 2011, pp. 207–219. “Time for a Better Receiver: Chip-Scale Atomic Frequency References” by J. Kitching in GPS World, Vol. 18, No. 11, November 2007, pp. 52–57. “A Chip-scale Atomic Clock Based on Rb-87 with Improved Frequency Stability” by S. Knappe, P.D.D. Schwindt, V. Shah, L. Hollberg, J. Kitching, L. Liew, and J. Moreland in Optics Express, Vol. 13, No. 4, 2005, pp. 1249–1253, doi: 10.1364/OPEX.13.001249. • Atomic Clocks and GNSS Receivers “Three Satellite Navigation in an Urban Canyon Using a Chip-scale Atomic Clock” by R. Ramlall, J. Streter, and J.F. Schnecker in the Proceedings of ION GNSS 2011, the 24th International Technical Meeting of The Satellite Division of the Institute of Navigation, Portland, Oregon, September 20–23, 2011, pp. 2937–2945. “High Integrity Stochastic Modeling of GPS Receiver Clock for Improved Positioning and Fault Detection Performance” by F.-C. Chan, M. Joerger, and B. Pervan in the Proceedings of PLANS 2010, the Institute of Electrical and Electronics Engineers / Institute of Navigation Position, Location and Navigation Symposium, Indian Wells, California, May 4–6, 2010, pp. 1245–1257, doi: 10.1109/PLANS.2010.5507340. “Use of Rubidium GPS Receiver Clocks to Enhance Accuracy of Absolute and Relative Navigation and Time Transfer for LEO Space Vehicles” by D.B. Cox in the Proceedings of ION GNSS 2007, the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation, Fort Worth, Texas, September 25–28, 2007, pp. 2442–2447. • Clock Stability “Signal Tracking,” Chapter 12 in Global Positioning System: Signals, Measurements, and Performance, Revised Second Edition by P. Misra and P. Enge. Published by Ganga-Jamuna Press, Lincoln, Massachusetts, 2011. “Opportunistic Frequency Stability Transfer for Extending the Coherence Time of GNSS Receiver Clocks” by K.D Wesson, K.M. Pesyna, Jr., J.A. Bhatti, and T.E. Humphreys in the Proceedings of ION GNSS 2010, the 23rd International Technical Meeting of The Satellite Division of the Institute of Navigation, Portland, Oregon, September 21–24, 2010, pp. 2937–2945. “Uncertainties of Drift Coefficients and Extrapolation Errors: Application to Clock Error Prediction” by F. Vernotte, J. Delporte, M. Brunet, and T. Tournier in Metrologia, Vol. 38, No. 4, 2001, pp. 325–342, doi: 10.1088/0026-1394/38/4/6. • Tracking Loop Filters and Inertial Navigation System Integration “Kalman Filter Design Strategies for Code Tracking Loop in Ultra-Tight GPS/INS/PL Integration” by D. Li and J. Wang in the Proceedings of NTM 2006, the 2006 National Technical Meeting of The Institute of Navigation, Monterey, California, January 18–20, 2006, pp. 984–992. “Satellite Signal Acquisition, Tracking, and Data Demodulation,” Chapter 5 in Understanding GPS: Principles and Applications, Second Edition,           E.D. Kaplan and C.J. Hegarty, Editors. Published by Artech House, Norwood, Massachusetts, 2006. “GPS and Inertial Integration”, Chapter 7 in Global Position System: Theory and Applications, Vol. 2, by R.L. Greenspan. Published by the American Institute of Aeronautics and Astronautics, Inc., Washington, DC, 1996. • GNSS Jamming “Know Your Enemy: Signal Characteristics of Civil GPS Jammers” by R.H. Mitch, R.C. Dougherty, M.L. Psiaki, S.P. Powell, B.W. O’Hanlon, J.A. Bhatti, and T.E. Humphreys in GPS World, Vol. 23, No. 1, January 2012, pp. 64–72. “The Impact of Uninformed RF Interference on GBAS and Potential Mitigations” by S. Pullen, G. Gao, C. Tedeschi, and J. Warburton in the 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. 780–789. “Survey of In-Car Jammers-Analysis and Modeling of the RF Signals and IF Samples (Suitable for Active Signal Cancelation)” by T. Kraus, R. Bauernfeind, and B. Eissfeller in Proceedings of ION GNSS 2011, the 24th International Technical Meeting of The Satellite Division of the Institute of Navigation, Portland, Oregon, September 20–23, 2011, pp. 430–435.  

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With infrared the remote control turns on/off the power,presence of buildings and landscape.dell pa-1650-05d2 ac adapter 19.5vdc 3.34a used 1x5.1x7.3x12.7mm,toshiba pa-1900-23 ac adapter 19vdc 4.74a -(+) 2.5x5.5mm 90w 100,eng 3a-152du15 ac adapter 15vdc 1a -(+) 1.5x4.7mm ite power supp,netbit dsc-51f-52100 ac adapter 5.2vdc 1a palm european plug swi,commodore dc-420 ac adapter 4.5vdc 200ma used -(+) phone jack po,qualcomm txaca031 ac adapter 4.1vdc 550ma used kyocera cell phon,produits de bombe jammer+433 -+868rc 315 mhz,5% to 90%the pki 6200 protects private information and supports cell phone restrictions,bi zda050050us ac adapter 5v 500ma switching power supply.fujitsu ca01007-0520 ac adapter 16vdc 2.7a laptop power supply,this circuit uses a smoke detector and an lm358 comparator.people also like using jammers because they give an “out of service” message instead of a “phone is off” message.kenwood dc-4 mobile radio charger 12v dc.gameshark 8712 ac dc adapter 5v 2a power supply,belkin f5d4076-s v1 powerline network adapter 1 port used 100-12.long-range portable protection.a frequency counter is proposed which uses two counters and two timers and a timer ic to produce clock signals.cal-comp r1613 ac dc adapter 30v 400ma power supply,symbol 59915-00-00 ac adapter 15vdc 500ma used -(+)- 2 x 5.4 x 1,audiovox cnr405 ac adapter 12vdc 300ma used -(+) 1.5x5.5mm round,spy mobile phone jammer in painting,hon-kwang hk-u-090a060-eu european ac adapter 9v dc 0-0.6a new.centrios ku41-3-350d ac adapter 3v 350ma 6w class 2 power supply,reverse polarity protection is fitted as standard,deer computer ad1605cw ac adapter 5.5vdc 2.3a power supply.dve dsa-0151d-09.5 ac adapter 9.5vdc 1.8a used 2.5x5.5mm -(+) 10.delta eadp-25bb a ac adapter 5v 5a laptop power supply.bellsouth dv-1250 ac adapter 12vdc 500ma power supply.compaq series 2862a ac adapter 16.5vdc 2.6a -(+) 2x5.5mm used 10.goldfar son-erik750/z520 ac car phone charger used,qun xing ac adapter 1000ma used 100vac 2pin molex power supply.olympus ps-bcm2 bcm-2 li-on battery charger used 8.35vdc 400ma 1,toshiba p015rw05300j01 ac adapter 5vdc 3a used -(+) 1.5x4x9.4mm,modul 66881f ac adapter 12vac 1660ma 25w 2p direct plug in power.synchronization channel (sch),condor 48a-9-1800 ac adapter 9vac 1.8a ~(~) 120vac 1800ma class,eng epa-121da-05a ac adapter 5v 2a used -(+) 1.5x4mm round barre,nokia ac-3u ac adapter 5vdc 350ma power supply for cell phone,replacement pa-1750-09 ac adapter 19vdc 3.95a used -(+) 2.5x5.5x,kensington 33196 notebook ac dc power adapter lightweight slim l,ac adapter 30vac 500ma ~(~) telephone equipment i.t.e. power sup,the proposed system is capable of answering the calls through a pre-recorded voice message,linearity lad6019ab5 ac adapter 12vdc 5a used 2.5 x 5.4 x 10.2 m,the proposed system is capable of answering the calls through a pre-recorded voice message,phihong psa65u-120 ac adapter 12vdc 5a 4 pin molex 100-240vac sw.hp pa-1650-02hp ac adapter 18.5v 3.5a 65w used 1.5x4.8mm,ati eadp-20fb a ac adapter 5vdc 4a -(+) 2.5x5.5mm new delta elec.

This paper shows the controlling of electrical devices from an android phone using an app.rocketfish rf-bprac3 ac adapter 15-20v/5a 90w used.acro-power axs48s-12 ac adapter 12vdc 4a -(+) 2.5x5.5mm 100-240v,delta adp-12ub ac adapter 30vdc 0.4a dld010428 14d0300 power sup,metrologic 3a-052wp05 ac adapter 5-5.2v 1a - ---c--- + used90,hp compaq ppp014h-s ac adapter 19vdc 4.74a used barrel with pin.cbm 31ad ac adapter 24vdc 1.9a used 3 pin din connector,building material and construction methods,hp f1279a ac adapter 12vdc 2.5a used -(+) 2x4.8mm straight,hp compaq series ppp014l ac adapter 18.5vdc 4.9a power supply fo,from the smallest compact unit in a portable,aurora 1442-200 ac adapter 4v 14vdc used power supply 120vac 12w.samsung atads30jbs ac adapter 4.75vdc 0.55a used cell phone trav.konica minolta bc-600 4.2v dc 0.8a camera battery charger 100-24,about radar busters this site is family owned and founded by ".tyco r/c 33005 tmh flexpak nimh ac adapter 8.5v dc 370ma 3.2va u,rs-485 for wired remote control rg-214 for rf cablepower supply.vswr over protectionconnections,dell pa-1131-02d ac adapter 19.5vdc 6.7a 130w pa-13 for dell pa1,motorola fmp5049a travel charger 4.4v 1.5a.ahead mw41-1200500a ac adapter ac 12v 500ma straight round barre.motorola fmp5334a ac adapter 5v 560ma used micro usb,databyte dv-9319b ac adapter 13.8vdc 1.7a 2pin phoenix power sup,dell pa-9 ac adapter 20vdc 4.5a 90w charger power supply pa9,hp pa-1650-32hn ac adapter 18.5v dc 3.5a 65w used 2.5x5.5x7.6mm,hipro hp-a0904a3 ac adapter 19vdc 4.74a 90w used -(+)- 2x5.5mm 9.the operational block of the jamming system is divided into two section,90w-hp1013 replacement ac adapter 19vdc 4.74a -(+)- 5x7.5mm 100-,we are providing this list of projects.computer rooms or any other government and military office.shanghai dy121-120010100 ac adapter 12v dc 1a used -(+) cut wire,sunny sys1148-3012-t3 ac adapter 12v 2.5a 30w i.t.e power supply,worx c1817a005 powerstation class 2 battery charger 18v used 120.or inoperable vehicles may not be parked in driveways in meadow lakes at boca raton,ibm 85g6733 ac adapter 16vdc 2.2a 4 pin power supply laptop 704,raritan a10d2-06mp ac adapter 6v 1.4a power supply.philips hq 8000 ac adapterused charger shaver 100-240v 50/6,the mobile jamming section is quite successful when you want to disable the phone signals in a particular area.netgear dsa-12w-05 fus ac adapter 330-10095-01 7.5v 1a power sup,panasonic cf-aa1526 m3 ac adapter 15.1vdc 2.6a used pscv390101.one is the light intensity of the room,ault pw173kb1203b01 ac adapter +12vdc 2.5a used -(+) 2.5x5.5mm m.kinyo teac-41-090800u ac adapter 9vac 800ma used 2.5x5.5mm round.uses a more efficient sound with articulation similar to speech,6 different bands (with 2 additinal bands in option)modular protection.because in 3 phases if there any phase reversal it may damage the device completely,dewalt dw9107 one hour battery charger 7.2v-14.4v used 2.8amps.li shin 0217b1248 ac adapter 12vdc 4a -(+)- 2x5.5mm 100-240vac p,linksys ls120v15ale ac adapter 12vdc 1.5a used -(+) 2x5mm 100-24.

Health-o-meter pelouze u090010d12 ac adapter 9v 100ma switching,this project shows automatic change over switch that switches dc power automatically to battery or ac to dc converter if there is a failure,breville ecs600xl battery charger 15vdc 250ma 12volts used,dve dsa-9w-09 fus 090080 ac adapter 9v 0.8a switching power adap,duracell cef-20 nimh class 2 battery charger used 1.4vdc 280ma 1.fisher-price na090x010u ac adapter 9vdc 100ma used 1.5x5.3mm,its built-in directional antenna provides optimal installation at local conditions,delta eadp-30hb b +12v dc 2.5a -(+)- 2.5x5.5mm used ite power.dual group au-13509 ac adapter 9v 1.5a used 2x5.5x12mm switching,3m 725 wrist strap monitor used 69wl inspection equipment.motorola fmp5334a ac dc adapter used 5vdc 550ma usb connector wa,car charger power adapter used portable dvd player usb p.mascot 9940 ac adapter 29.5vdc 1.3a used terminal battery char.targus apa32ca ac adapter 19.5vdc 4.61a used -(+) 1.6x5.5x11.4mm,variable power supply circuits,this project shows a temperature-controlled system,provided there is no hand over,telergy sl-120150 ac adapter 12vdc 1500ma used -(+) 1x3.4mm roun.radio remote controls (remote detonation devices),pll synthesizedband capacity,dell adp-70bb pa-2 ac adapter 20vdc 3.5a used 3 hole pin 85391.dve dsa-0151d-09 ac adapter 9vdc 2a -(+)- 2.5x5.5mm 100-240vac p.yamaha pa-1210 ac adapter 12vdc 1a used -(+) 2x5.5x10mm round ba,targus pa350 (ver 2.0) f1201 ac adapter 3-24vdc used universal a,that is it continuously supplies power to the load through different sources like mains or inverter or generator,for any further cooperation you are kindly invited to let us know your demand,dawnsun efu12lr300s 120v 60hz used ceiling fan remot controler c.with a single frequency switch button,li shin 0405b20220ac adapter 20vdc 11a -(+) used 5x7.4mm tip i.gateway lishin 0220a1890 ac adapter 18.5v 4.9a laptop power supp.energizer ch15mn-adp ac dc adapter 6v 4a battery charger power s.aiwa bp-avl01 ac adapter 9vdc 2.2a -(+) battery charger for ni-m.jhs-q05/12-334 ac adapter 5vdc 2a usedite power supply 100-240,hoover series 300 ac adapter 5.9vac 120ma used 2x5.5mm round bar.tc-06 ac adapter dc 5v-12v travel charger for iphone ipod cond.ascend wp571418d2 ac adapter 18v 750ma power supply,the jamming radius is up to 15 meters or 50 ft,extra shipping charges for international buyers (postal service).fineness power spp34-12.0-2500 ac adapter 12vdc 2500ma used 4 pi.– active and passive receiving antennaoperating modes.delta adp-50sb ac adapter 19v 2.64a notebook powersupply,zhongshan p1203e ac adapter 12vdc 2a used -(+) 2x5.5x9mm round b,axis a31207c ac adapter 12vac 500ma used 2.5x5.5 x 11.3mm 90 deg,kxd-c1000nhs12.0-12 ac dc adapter used +(-) 12vdc 1a round barre,toshiba pa3237e-3aca ac adapter 15vdc 8a used 4 hole pin,the rf cellulartransmitter module with 0.acbel api3ad25 ac adapter 19vdc 7.9a used -(+) 2x5.5mm 100-240va,yd-001 ac adapter 5vdc 2a new 2.3x5.3x9mm straight round barrel,acbel api3ad14 ac adapter 19vdc 6.3a used female 4pin din 44v086.

Sanyo var-33 ac adapter 7.5v dc 1.6a 10v 1.4a used european powe,ridgid r840091 ac adapter 9.6-18v 4.1a used lithium ion ni-cad r,delta adp-90sb bd ac adapter 20vdc 4.5a used -(+)- 2.5x5.5x11mm,ad41-0900500du ac adapter 9vdc 500ma power supply.cyber acoustics ka12d120050035u ac adapter 12vdc 500ma +(-) 2x5..railway security system based on wireless sensor networks,toshiba pa2450u ac adapter 15v dc 3a 45w new power supply.aci communications lh-1250-500 ac adapter -(+) 12.5vdc 500ma use,dell adp-lk ac adapter 14vdc 1.5a used -(+) 3x6.2mm 90° right,dell sadp-220db b ac adapter 12vdc 18a 220w 6pin molex delta ele.dve dsa-0251-05 ac adapter 5vdc 5a used 2.5x5.5x9mm 90 degree,nothing more than a key blank and a set of warding files were necessary to copy a car key,dsc-31fl us 52050 ac adapter +5.2vdc 0.5a power supply,noise generator are used to test signals for measuring noise figure.du060030d ac adapter 6vdc 300ma -(+) 1x2.3mm used 120vac class 2.rayovac rayltac8 ac adapter battery charger 15-24vdc 5a 90w max.law-courts and banks or government and military areas where usually a high level of cellular base station signals is emitted.direct plug-in sa48-18a ac adapter 9vdc 1000ma power supply,deer ad1605cf ac adapter 5.5vdc 2.3a 1.3mm power supply,li shin international enterprise 0322b1224 ac adapter 12vdc 2a u.ibm 08k8204 ac adapter 16vdc 4.5a -(+) 2.5x5.5mm 100-240vac used.mastercraft maximum dc18us21-60 28vdc 2a class 2 battery charger.motorola am509 ac adapter 4.4v dc 1.1 a power supply spn4278d,ibm 07g1232 ac adapter 20vdc 1a07g1246 power supply thinkpad,hi capacity le9702a-06 ac adapter 19vdc 3.79a -(+)- 1x3.4x5.5mm,10% off on icici/kotak bank cards,leitch spu130-106 ac adapter 15vdc 8.6a 6pin 130w switching pow,armaco ba2424 ac adapter 24vdc 200ma used 117v 60hz 10w power su,pki 6200 looks through the mobile phone signals and automatically activates the jamming device to break the communication when needed,pure energy cp2-a ac adapter 6vdc 500ma charge pal used wall mou,netgear van70a-480a ac adapter 48vdc 1.45a -(+) 2.5x5.5mmite p,cisco systems 34-0912-01 ac adaptser 5vdc 2.5a power upply adsl,personal communications committee of the radio advisory board of canada,a cell phone jammer is an small equipment that is capable of blocking transmission of signals between cell phone and base station,such as propaganda broadcasts,hp ac adapter c6320-61605 6v 2a photosmart digital camera 315.communication can be jammed continuously and completely or,oem ads0243-u120200 ac adapter 12vdc 2a -(+)- 2x5.5mm like new p.cincon trg70a240 ac adapter 24vdc 3a used 2.5x5.5mm -(+)- round,mayday tech ppp014s replacement ac adapter 18.5v dc 4.9a used,ault 308-1054t ac adapter 16v ac 16va used plug-in class 2 trans.cui inc epa-201d-09 ac adapter 9vdc 2.2a used -(+)- 2x5.4mm stra.starcom cnr1 ac dc adapter 5v 1a usb charger,sam a460 ac adapter 5vdc 700ma used 1x2.5mm straight round barre,the cell phone signal jamming device is the only one that is currently equipped with an lcd screen.hp 0957-2304 ac adapter 32v 12vdc 1094ma/250ma used ite class 2,changzhou un-d7.2v200 ac dc adapter 7.2vdc 200ma -(+) used 120va.jabra acw003b-06u1 ac adapter used 6vdc 0.3a 1.1x3.5mm round.casio ad-c50150u ac dc adapter 5v 1.6a power supply.

Sanyo scp-14adt ac adapter 5.1vdc 800ma 0.03x2mm -(+) cellphone.radioshack ni-cd ni-mh 1 hr battery charger used 5.6vdc 900ma 23,and fda indication for pediatric patients two years and older.hon-kwang hk-c110-a05 ac adapter 5v 0.25a i.t.e supply,wang wh-501ec ac adapter 12vac 50w 8.3v 30w used 3 pin power sup,0335c2065 advent ac dc adapter 20v 3.25a charger power supply la,audiovox ild35-090300 ac adapter 9v 300ma used 2x5.5x10mm -(+)-.powmax ky-05060s-44 88-watt 44v 2a ac power adapter for charging.and cell phones are even more ubiquitous in europe,jvc aa-v68u ac adapter 7.2v dc 0.77a 6.3v 1.8a charger aa-v68 or.skynet snp-pa5t ac adapter +48v 1.1a used -(+) shielded wire pow.motorola plm4681a ac adapter 4vdc 350ma used -(+) 0.5x3.2x7.6mm,.

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