• Cell phone jammers for sale in usa,phone jammers china vs,Charting the Evolution of Signal-in-Space Performance by Data Mining 400,000,000 Navigation Messages By Liang Heng, Grace Xingxin Gao, Todd Walter, and Per Enge There are four important requirements...

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Charting the Evolution of Signal-in-Space Performance by Data Mining 400,000,000 Navigation Messages By Liang Heng, Grace Xingxin Gao, Todd Walter, and Per Enge There are four important requirements of any navigation system: accuracy, availability, continuity, and integrity. In this month’s column we take a look at one particular aspect of GPS integrity: that of the signal in space and find out how trustworthy is the satellite ephemeris and clock information in the broadcast navigation message. INNOVATION INSIGHTS by Richard Langley BUT THE GREATEST OF THESE IS INTEGRITY. There are four important requirements of any navigation system: accuracy, availability, continuity, and integrity. Perhaps the most obvious navigation system requirement, accuracy describes how well a measured value agrees with a reference value, typically the true value. In the case of GPS, we might talk about the accuracy of a range measurement. A receiver actually measures a pseudorange — a biased and noisy measure of the geometric range between the receiver and the satellite. After correcting for satellite ephemeris and satellite clock errors (the primary so-called signal-in-space errors), receiver clock errors, and atmospheric effects, we can get an estimate of the geometric range. How well we account for these errors or biases, will determine the accuracy of the corrected pseudorange measurement and ultimately, the accuracy of a derived position. A navigation system’s availability refers to its ability to provide the required function and performance within the specified coverage area at the start of an intended operation. In many cases, system availability implies signal availability, which is expressed as the percentage of time that the system’s transmitted signals are accessible for use. In addition to transmitter capability, environmental factors such as signal attenuation or blockage or the presence of interfering signals might affect availability. Ideally, any navigation system should be continuously available to users. But, because of scheduled maintenance or unpredictable outages, a particular system may be unavailable at a certain time. Continuity, accordingly, is the ability of a navigation system to function without interruption during an intended period of operation. More specifically, it indicates the probability that the system will maintain its specified performance level for the duration of an operation, presuming system availability at the beginning of that process. The integrity of a navigation system refers to its trustworthiness. A system might be available at the start of an operation, and we might predict its continuity at an advertised accuracy during the operation. But what if something unexpectedly goes wrong? If some system anomaly results in unacceptable navigation accuracy, the system should detect this and warn the user. Integrity characterizes a navigation system’s ability to provide this timely warning when it fails to meet its stated accuracy. If it does not, we have an integrity failure and the possibility of conveying hazardously misleading information. GPS has built into it various checks and balances to ensure a fairly high level of integrity. However, GPS integrity failures have occasionally occurred. In this month’s column we take a look at one particular aspect of GPS integrity: that of the signal in space and find out how trustworthy is the satellite ephemeris and clock information in the broadcast navigation message. The Navstar Global Positioning System is so far the most widely used space-based positioning, navigation, and timing system. GPS works on the principle of trilateration, in which the measured distances from a user receiver to at least four GPS satellites in view, as well as the position and clock data for these satellites, are the prerequisites for the user receiver to fix its exact position. For most GPS Standard Positioning Service (SPS) users, real-time satellite positions and clocks are derived from ephemeris parameters and clock correction terms in navigation messages broadcast by GPS satellites. The GPS Control Segment routinely generates navigation message data on the basis of a prediction model and the measurements at more than a dozen monitor stations. The differences between the broadcast ephemerides/clocks and the truth account for signal-in-space (SIS) errors. SIS errors are usually undetectable and uncorrectable for stand-alone SPS users, and hence directly affect the positioning accuracy and integrity. Nominally, SPS users can assume that each broadcast navigation message is reliable and the user range error (URE) derived from a healthy SIS is at the meter level or even sub-meter level. In practice, unfortunately, SIS anomalies have happened occasionally and UREs of tens of meters or even more have been observed, which can result in an SPS receiver outputting a hazardously misleading position solution. Receiver autonomous integrity monitoring (RAIM) or advanced RAIM is a promising tool to protect stand-alone users from such hazards; however, most RAIM algorithms assume at most one satellite fault at a time. Knowledge about the SIS anomalies in history is very important not only for assessing the GPS SIS integrity performance but also for validating the fundamental assumption of RAIM. A typical method for calculating SIS UREs is to compare the broadcast ephemerides/clocks with the precise, post-processed ones. Although this method is very effective in assessing the GPS SIS accuracy performance, few attempts have been made to use it to assess the GPS SIS integrity performance because broadcast ephemeris/clock data obtained from a global tracking network sometimes contain errors caused by receivers or data conversion processes and these errors usually result in false SIS anomalies. In this article, we introduce a systematic methodology to cope with this problem and screen out all the potential SIS anomalies in the past decade from when Selective Availability (SA) was turned off. GPS SIS Integrity The integrity of a navigation system refers — just as it does to a person — to its honesty, veracity, and trustworthiness. In the case of GPS, this includes the integrity of the ephemeris and clock data in the broadcast navigation messages. We refer to this as signal-in-space integrity. GPS SIS URE. As indicated by the name, GPS SIS URE is the pseudorange modeling inaccuracy due to operations of the GPS ground control and the space vehicles. Specifically, SIS URE includes satellite ephemeris and clock errors, satellite antenna performance variations, and signal imperfections, but not ionospheric or tropospheric delay, multipath, or any errors due to user receivers. SIS URE is dominated by ephemeris and clock errors because antenna variations and signal imperfections are at a level of millimeters or centimeters. In broadcast navigation messages, there is a parameter called user range accuracy (URA) that is intended to be a conservative representation of the standard deviation (1-sigma) of the URE at the worst-case location on the Earth. For example, a URA index value of 0 means that the 1-sigma URE is expected to be less than 2.4 meters, and a URA index value of 1 means that the 1-sigma URE is expected to be greater than 2.4 meters but less than 3.4 meters, and so on. In the past several years, most GPS satellites have a URA index value of 0. A nominal URA value, in meters, can be computed as X = 2(1+N/2), where N is the index value, for index values of 6 or less. For 6 N X = 2(N-2). GPS SPS SIS Integrity. In the SPS Performance Standard (PS), as well as the latest version of the Interface Specification (IS-GPS-200E), the GPS SPS SIS URE integrity standard assures that for any healthy SIS, there is an up-to-10−5 probability over any hour of the URE exceeding the not-to-exceed (NTE) tolerance without a timely alert during normal operation. The NTE tolerance is currently defined to be 4.42 times the upper bound (UB) on the URA value broadcast by the satellite. Before September 2008, the NTE tolerance was defined differently, as the maximum of 30 meters and 4.42 times URA UB. The reason for the “magic” number 4.42 here is the Gaussian assumption of the URE, although this assumption may be questionable. (4.42 sigma corresponds to a probability level of 99.999 percent (1 – 10–5)). In this article, a GPS SPS SIS anomaly is defined as a threat of an SIS integrity failure; that is, a condition during which an SPS SIS marked healthy results in a URE exceeding the NTE tolerance. Because the definition of the NTE tolerance is different before and after September 2008, we consider both of the two NTE tolerances for the sake of completeness and consistency. Methodology The SIS anomalies are screened out by comparing broadcast ephemerides/clocks with precise ones. As shown in Figure 1, the whole process consists of three steps: data collecting, data cleansing, and anomaly screening. Figure 1. Framework of the whole process. XYZB values refer to the coordinates of satellite position and satellite clock bias. In the first step, the navigation message data files are downloaded from the International GNSS Service (IGS). In addition, two different kinds of precise ephemeris/clock data are downloaded from IGS and the National Geospatial-Intelligence Agency (NGA), respectively. The details about these data sources will be discussed in the next section. Since each GPS satellite can be observed by many IGS stations at any instant, each navigation message is recorded redundantly. In the second step, a data-cleansing algorithm exploits the redundancy to remove the errors caused on the ground. This step distinguishes our work from that of most other researchers because the false anomalies due to corrupted data can be mostly precluded. The last step is computing worst-case SIS UREs as well as determining potential SIS anomalies. The validated navigation messages prepared in the second step are used to propagate broadcast orbits/clocks at 15-minute intervals that coincide with the precise ones. A potential SIS anomaly is claimed when the navigation message is healthy and in its fit interval with the worst-case SIS URE exceeding the SIS URE NTE tolerance. Data Sources We obtained broadcast navigation message data and precise ephemeris and clock data from publicly available sources. Broadcast Navigation Message Data. Broadcast GPS navigation message data files are available at IGS Internet sites. All the data are archived in Receiver Independent Exchange (RINEX) navigation file format, which includes not only the ephemeris/clock parameters broadcast by the satellites but also some information produced by the ground receivers, such as the pseudorandom noise (PRN) signal number and the transmission time of message (TTOM). The IGS tracking network is made up of more than 300 volunteer stations all over the world (a map is shown in Table 1) ensuring seamless, redundant data logging. Since broadcast navigation messages are usually updated every two hours, no single station can record all navigation messages. For the ease of users, two IGS archive sites, the Crustal Dynamics Data Information System (CDDIS) and the Scripps Orbit and Permanent Array Center (SOPAC), provide two kinds of ready-to-use daily global combined broadcast navigation message data files, brdcddd0.yyn and autoddd0.yyn, respectively, where ddd is the day of year yy. Unfortunately, these files sometimes contain errors that can cause false anomalies. Table 1. Comparison of IGS and NGA precise ephemeris/clock data. Therefore, we devised and implemented a data-cleansing algorithm to generate the daily global combined navigation messages, which are as close as possible to the navigation messages that the satellites actually broadcast, from all available navigation message data files of all IGS stations. The data-cleansing algorithm is based on majority vote, and hence all values in our data are cross validated. Accordingly, we name our daily global combined navigation messages “validated navigation messages,” as shown in Figure 1. Precise Ephemeris and Clock Data. Precise GPS ephemerides/clocks are generated by some organizations such as IGS and NGA that routinely post-process observation data. Precise ephemerides/clocks are regarded as “truth” because of their centimeter-level accuracy. Table 1 shows a side-by-side comparison between IGS and NGA precise ephemeris/clock data, in which the green- and red-colored text implies pros and cons, respectively. For NGA data, the only con is that the data have been publicly available only since January 4, 2004. As a result, for the broadcast ephemerides/clocks before this date, IGS precise ephemerides/clocks are the only references. Nevertheless, care must be taken when using IGS precise ephemerides/clocks due to the following three issues. The first issue with the IGS precise ephemerides/clocks is the relatively high rate of bad/absent data, as shown in the third row of Table 1. For a GPS constellation of 27 healthy satellites, 1.5 percent bad/absent data means no precise ephemerides or clocks for approximately 10 satellite-hours per day. This issue can result in undetected anomalies (false negatives). The second issue is that, as shown in the fourth row of Table 1, IGS switched to IGS Time for its precise ephemeris/clock data on 22 February, 2004. The IGS clock is not synchronized to GPS Time, and the differences between the two time references may be as large as 3 meters. Fortunately, the time offsets can be extracted from the IGS clock data files. Moreover, a similar problem is that IGS precise ephemerides use a frame aligned to the International Terrestrial Reference Frame (ITRF) whereas broadcast GPS ephemerides are based on the World Geodetic System 1984 (WGS 84). The differences between ITRF and the versions of WGS 84 used since 1994 are on the order of a few centimeters, and hence a transformation is not considered necessary for the purpose of our work. The last, but not the least important, issue with the IGS precise ephemerides is that the data are provided only for the center of mass (CoM) of the satellite. Since the broadcast ephemerides are based on the satellite antenna phase center (APC), the CoM data must be converted to the APC before being used. Both IGS and NGA provide antenna corrections for every GPS satellite. Although the IGS and the NGA CoM data highly agree with each other, the IGS satellite antenna corrections are quite different from the NGA’s, and the differences in z-offsets can be as large as 1.6 meters for some GPS satellites. The reason for these differences is mainly due to the different methods in producing the antenna corrections: the IGS antenna corrections are based on the statistics from more than 10 years of IGS data, whereas the NGA’s are probably from the calibration measurements on the ground. In order to know whose satellite antenna corrections are better, the broadcast orbits for all GPS satellites in 2009 were computed and compared with three different precise ephemerides: IGS CoM + IGS antenna corrections, IGS CoM + NGA antenna corrections, and NGA APC. Generally, the radial ephemeris error is expected to have a zero mean. However, the combination “IGS CoM + IGS antenna corrections” results in radial ephemeris errors with a non-zero mean for more than half of the GPS satellites. Therefore, the NGA antenna corrections were selected to convert the IGS CoM data to the APC. Data Cleansing Figure 2 shows a scenario of data cleansing. Owing to accidental bad receiver data and various hardware/software bugs, a small proportion of the navigation data files from the IGS stations have defects such as losses, duplications, inconsistencies, discrepancies, and errors. Therefore, more than just removing duplications, the generation of validated navigation messages is actually composed of two complicated steps. Figure 2. A scenario of data cleansing: In the figure, the GPS satellite PRN32 started to transmit a new navigation message at 14:00. Receiver 1 had not observed the satellite until 14:36, and hence the TTOM in its record was 14:36. Additionally, Receiver 1 made a one-bit error in ∆n (4.22267589140 × 10-9 11823 × 2−43 π). Receiver 2 perhaps had some problems in its software: the IODC was unreported and both the toc and ∆n were written weirdly. Receiver n used an incorrect ranging code, PRN01, to despread and decode the signal of PRN32; fortunately, all the parameters except TTOM were perfectly recorded. Moreover, the three receivers interpreted URA (SV accuracy) differently. A computer equipped with our data cleansing algorithms is used to process all the data from the receivers. The receiver-caused errors are removed and the original navigation message is recovered. First step. Suppose that we want to generate the validated navigation messages for day n. In the first step, we apply the following operations sequentially to each RINEX navigation data file from day n − 1 to day n + 1: 1) Parse the RINEX navigation file; 2) Recover least significant bit (LSB); 3) Classify URA values; 4) Remove the navigation messages not on day n; 5) Remove duplications; 6) Add all remaining navigation messages into the set O. The reason why the data files from day n − 1 to day n + 1 are considered is that a few navigation messages around 00:00 can be included in some data files on day n − 1, and a few navigation messages around 23:59 can be included in some data files on day n + 1. The LSB recovery is used here to cope with the discrepant representations of floating-point numbers in RINEX navigation files. The URA classifier is employed to recognize and unify various representations of URA in the files. The duplication removal is applied because some stations write the same navigation messages repeatedly in one data file, which is unfavorable to the vote in the second step. Second Step. At the end of the first step, we have a set O that includes all the navigation messages on day n. The set O still has duplications because a broadcast navigation message can be reported by many IGS stations. However, as shown in Figure 2, duplications of a broadcast navigation message may come with different errors and are not necessarily identical. Several other examples of such problems can be found in our journal paper listed in Further Reading. Fortunately, most orbital and clock parameters are seldom reported incorrectly, and even when errors happen, few stations agree on the same incorrect value. In our work, these parameters are referred to as robust parameters. On the contrary, some parameters, such as TTOM, PRN, URA and issue of data clock (IODC), are more likely to be erroneous and when errors happen, several stations may make the same mistake. These parameters are referred to as fragile parameters. The cause of the fragility is either the physical nature (for example, TTOM, PRN) or the carelessness in hardware/software implementations (for example, URA, IODC). Majority vote is applied to all fragile parameters (except TTOM, which is determined by another algorithm described in our journal paper) under the principle that the majority is usually correct. Meanwhile, the robust parameters are utilized to identify the equivalence of two navigation messages — two navigation messages are deemed identical if and only if they agree on all the robust parameters, although their fragile parameters could be different. Therefore, the goal of duplication removal and majority vote is a set P, in which any navigation message must have at least one robust parameter different from any other and has all fragile parameters confirmed by the largest number of stations that report this navigation message. After the operations above, we have a set P in which there are no duplicated navigation messages in terms of robust parameters and all fragile parameters are as correct as possible. A few navigation messages in P still have errors in their robust parameters. These unwanted navigation messages feature a small number of reporting stations. Finally, the navigation messages confirmed by only a few stations being discarded and the survivors are the validated broadcast navigation messages, stored in files sugldddm.yyn. For further details of our algorithms, see our journal paper. Anomaly Screening The validated broadcast navigation messages prepared using the algorithm described in the previous section were employed to propagate broadcast satellite orbits and clocks. For each 15-miniute epoch, t, that coincides with precise ephemerides/clocks, the latest transmitted broadcast ephemeris/clock is chosen to calculate the worst-case SIS URE – the maximum SIS URE that a user on Earth can experience. Finally, a potential GPS SIS anomaly is claimed when all of the following conditions are fulfilled. The worst-case SIS URE exceeds the NTE tolerance; The broadcast navigation message is healthy; that is, The RINEX field SV health is 0, and The URA UB ≤ 48 meters; The broadcast navigation message is in its fit interval; that is, ∆t = t − TTOM ≤ 4 hours; The precise ephemeris/clock is available and healthy. Results A total of 397,044,414 GPS navigation messages collected by an average of 410 IGS stations from June 1, 2000 (one month after turning off SA), to August 31, 2010, have been screened. The NGA APC precise ephemerides/clocks and the IGS CoM precise ephemerides/clocks with the NGA antenna corrections were employed as the truth references. Both old and new NTE tolerances were used for determining anomalies. Before interpreting the results, it should be noted that there are some limitations due to the data sources and the anomaly-determination criteria. First, false anomalies may be claimed because there may be some errors in the precise ephemerides/clocks or the validated navigation messages. Second, some short-lived anomalies may not show up if they happen to fall into the 15-minute gaps of the precise ephemerides/clocks. Third, some true anomalies may not be detected if the precise ephemerides/clocks are temporarily missing. The third limitation is especially significant for the results before January 3, 2004, because only the IGS precise ephemerides/clocks are available, which feature a high rate of bad/absent data. (For example, the clock anomaly of Space Vehicle Number (SVN) 23/PRN23 that occurred on January 1, 2004 is missed by our process because the IGS precise clocks for PRN23 on that day were absent.) Last but not least, users might not experience some anomalies because a satellite was not trackable at that time, or the users were notified via a Notice Advisory to Navstar Users (NANU). (A satellite may indicate that it is unhealthy through the use of non-standard code or data. The authors’ future work will include using observation data to verify the potential anomalies found in the results presented here.) Therefore, all the SIS anomalies claimed in this article are considered to be potential and under further investigation. Potential SIS Anomalies. A total of 1,256 potential SIS anomalies were screened out under SPS PS 2008 (or 374 potential SIS anomalies under SPS PS 2001). Figure 3 shows all these anomalies in a Year-SVN plot. It can be seen that during the first year after SA was turned off, SIS anomalies occurred frequently for the whole constellation. Figure 3. Potential SIS anomalies from June 1, 2000, to August 31, 2010. The horizontal lines depict the periods when the satellites were active (not necessarily healthy). The color of the lines indicates the satellites’ block type, as explained by the top left legend. Moreover, 2004 is apparently a watershed: before 2004, anomalies occurred for all GPS satellites (except two satellites launched in 2003, SVN45/PRN21 and SVN56/PRN16) whereas after 2004, anomalies occurred much less frequently and more than 10 satellites have never been anomalous. Figure 4 further confirms the improving GPS SIS integrity performance in the past decade, no matter which SPS PS is considered. Figure 4. Number of potential SIS anomalies per year. The SIS performance was improved during the past decade. There were 0 anomalies in 2009 according to SPS PS 2001 and this number is represented by 0.1 in the figure. Therefore, it is possible to list all potential SIS anomalies from January 4, 2004, to August 31, 2010, in a compact table: Table 2. Most anomalies in the table have been confirmed by NANUs and other literature. The table reveals an important and exciting piece of information: never have two or more SIS anomalies occurred simultaneously since 2004. Accordingly, in the sense of historical GPS SIS integrity performance, it is valid for RAIM to assume at most one satellite fault at a time. Table 2. List of potential anomalies from January 4, 2004, to August 31, 2010. Validated Navigation Messages. For the purpose of comparison and verification, the IGS daily global combined broadcast navigation message data files brdcddd0.yyn and autoddd0.yyn were used to propagate broadcast satellite orbits and clocks as well. The NGA APC precise ephemerides/clocks were employed for the truth references. The SPS PS 2008 NTE tolerance was used for determining anomalies. The other criteria for anomaly screening that are the same as in the previous section were still applied. All the potential SIS anomalies for 2006–2009 were found based on the three kinds of daily combined broadcast navigation messages. Table 3 shows a comparison of the total hours of the anomalies per year. It can be seen that brdcddd0.yyn and autoddd0.yyn result in approximately 11 times more false anomalies than true ones. Moreover, all potential anomalies derived from sugldddm.yyn are confirmed by brdcddd0.yyn and autoddd0.yyn, which indicates that our sugldddm.yyn does not introduce any more false anomalies than brdcddd0.yyn and autoddd0.yyn. Table 3. Total hours of anomalies per year computed from three different kinds of daily global combined broadcast navigation messages. Conclusion In this article, the GPS SIS integrity performance in the past decade was assessed by comparing the broadcast ephemerides/clocks with the precise ones. Thirty potential anomalies were found. The fundamental assumption of RAIM is valid based on a review of the GPS SIS integrity performance in the past seven years. Acknowledgments The authors gratefully acknowledge the support of the Federal Aviation Administration. This article contains the personal comments and beliefs of the authors, and does not necessarily represent the opinion of any other person or organization. The authors would like to thank Mr. Tom McHugh, William J. Hughes FAA Technical Center, for his valuable input to the data-cleansing algorithm. This article is based on the paper “GPS Signal-in-Space Integrity Performance Evolution in the Last Decade: Data Mining 400,000,000 Navigation Messages from a Global Network of 400 Receivers” to appear in the Institute of Electrical and Electronics Engineers (IEEE) Transactions on Aerospace and Electronic Systems.. Liang Heng is a Ph.D. candidate under the guidance of Professor Per Enge in the Department of Electrical Engineering at Stanford University. Grace Xingxin Gao is a research associate in the GPS Research Laboratory of Stanford University. Todd Walter is a senior research engineer in the Department of Aeronautics and Astronautics at Stanford University. Per Enge is a professor of Aeronautics and Astronautics at Stanford University, where he is the Kleiner-Perkins, Mayfield, Sequoia Capital Professor in the School of Engineering. He directs the GPS Research Laboratory, which develops satellite navigation systems based on GPS. FURTHER READING • Authors’ Research Papers “GPS Signal-in-Space Integrity Performance Evolution in the Last Decade: Data Mining 400,000,000 Navigation Messages from a Global Network of 400 Receivers” by L. Heng, G.X. Gao, T. Walter, and P. Enge in Transactions on Aerospace and Electronic Systems, the Institute of Electrical and Electronics Engineers, accepted for publication. “GPS Signal-in-Space Anomalies in the Last Decade: Data Mining of 400,000,000 GPS Navigation messages” by L. Heng, G.X. Gao, T. Walter, and P. Enge in 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. 3115–3122. “GPS Ephemeris Error Screening and Results for 2006–2009” by L. Heng, G.X. Gao, T. Walter, and P. Enge in Proceedings of ION ITM 2010, the 2010 International Technical Meeting of the Institute of Navigation, San Diego, California, January 24–26, 2010, pp. 1014–1022. • Earlier Work on Assessing GPS Broadcast Ephemerides and Clocks “GPS Orbit and Clock Error Distributions” by C. Cohenour and F. van Graas in Navigation, Vol. 58, No. 1, Spring 2011, pp. 17–28. “Statistical Characterization of GPS Signal-in-Space Errors” by L. Heng, G.X. Gao, T. Walter, and P. Enge in Proceedings of ION ITM 2011, the 2011 International Technical Meeting of the Institute of Navigation, San Diego, California, January 24–26, 2011, pp. 312–319. “Broadcast vs. Precise GPS Ephemerides: A Historical Perspective” by D.L.M. Warren and J.F. Raquet in GPS Solutions, Vol. 7, No. 3, 2003, pp. 151–156, doi: 10.1007/s10291-003-0065-3. “Accuracy and Consistency of Broadcast GPS Ephemeris Data” by D.C. Jefferson and Y.E. Bar-Sever in Proceedings of ION GPS-2000, the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation, Salt Lake City, Utah, September 19–22, 2000, pp. 391–395. “The GPS Broadcast Orbits: An Accuracy Analysis” by R.B. Langley, H. Jannasch, B. Peeters, and S. Bisnath, presented in Session B2.1-PSD1, New Trends in Space Geodesy at the 33rd COSPAR Scientific Assembly, Warsaw, July 16–23, 2000. • Signal-in-Space Anomalies “GNSS: The Present Imperfect” by D. Last in Inside GNSS, Vol. 5, No. 3, May 2010, pp. 60–64. “Investigation of Upload Anomalies Affecting IIR Satellites in October 2007” by K. Kovach, J. Berg, and V. Lin in Proceedings of ION GNSS 2008, the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation, Savannah, Georgia, September 16–19, 2008, pp. 1679–1687. Global Positioning System (GPS) Standard Positioning Service (SPS) Performance Analysis Report No. 58, July 31, 2007, Reporting Period: 1 April – 30 June 2007. Discrepancy Report, DR No. 55, “GPS Satellite PRN18 Anomaly Affecting SPS Performance” by N. Vary, FAA William J. Hughes Technical Center, Pomona, New Jersey, April 11, 2007. “GPS Receiver Responses to Satellite Anomalies” by J.W. Lavrakas and D. Knezha in Proceedings of the 1999 National Technical Meeting of The Institute of Navigation, San Diego, California, January 25–27, 1999, pp. 621–626. • GPS Integrity and Receiver Autonomous Integrity Monitoring “Prototyping Advanced RAIM for Vertical Guidance” by J. Blanch, M.J. Choi, T. Walter, P. Enge, and K. Suzuki in 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. 285–291. “The Integrity of GPS” by R.B. Langley in GPS World, Vol. 10, No. 3, March 1999, pp. 60–63. • International GNSS Service Ephemerides and Clocks “On the Precision and Accuracy of IGS Orbits” by J. Griffiths and J.R. Ray in Journal of Geodesy, Vol. 83, 2009, pp. 277–287, doi: 10.1007/s00190-008-0237-6. “The International GNSS Service: Any Questions?” by A.W. Moore in GPS World, Vol. 18, No. 1, January 2007, pp. 58–64. International GNSS Service Central Bureau website. • National Geospatial-Intelligence Agency Ephemerides and Clocks “NGA’s Role in GPS” by B. Wiley, D. Craig, D. Manning, J. Novak, R. Taylor, and L. Weingarth in Proceedings of ION GNSS 2006, the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation, Fort Worth, Texas, September 26–29, 2006, pp. 2111–2119. National Geospatial-Intelligence Agency, Geoint Sciences Office, Global Positioning System Division website. • Antenna Phase Center Corrections “Generation of a Consistent Absolute Phase-center Correction Model for GPS Receiver and Satellite Antennas” by R. Schmid, P. Steigenberger, G. Gendt, M. Ge, and M. Rothacher in Journal of Geodesy, Vol. 81, No. 12, 2007, pp. 781–798, doi: 10.1007/s00190-007-0148-y. “The Block IIA Satellite: Calibrating Antenna Phase Centers” by G.L. Mader and F.M. Czopek in GPS World, Vol. 13, No. 5, May 2002, pp. 40–46. • GPS Interface and Performance Specifications Navstar GPS Space Segment / Navigation User Interfaces, Interface Specification, IS-GPS-200 Revision E, prepared by Science Applications International Corporation, El Segundo, California, for Global Positioning System Wing, June 2010. Global Positioning System Standard Positioning Service Performance Standard, 4th edition, by the U.S. Department of Defense, Washington, D.C., September 2008. Global Positioning System Standard Positioning Service Performance Standard, 3rd edition, by the U.S. Department of Defense, Washington, D.C., October 2001.


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Ibm dcwp cm-2 ac adapter 16vdc 4.5a 08k8208 power supply laptops,pdf portable mobile cell phone signal jammer,if you are looking for mini project ideas.nyko charge station 360 for nyko xbox 360 rechargeable batteries.delta adp-40zb rev.b ac adapter 12vdc 3300ma used 4pin din.sharp ea-51a ac adapter 6vdc 200ma usedstraight round barrel p,as will be shown at the end of this report.lexmark click cps020300050 ac adapter 30v 0.50a used class 2 tra,redline tr 48 12v dc 2.2a power supply out 2000v 15ma for quest_.replacement 1650-05d ac adapter 19.5v 3.34a used -(+)- 5x7.4mm r,remington ms3-1000c ac dc adapter 9.5v 1.5w power supply,kodak hpa-602425u1 ac adapter 24v dc power supply digital doc.dell pa-1470-1 ac adapter 18v 2.6a power supply notebook latitud.sceptre power amdd-30240-1000 ac adapter 24vdc 1a used -(+) 2x5.,ad-4 ac adapter 6vdc 400ma used +(-) 2x5.5mm round barrel power,ibm pa-1121-07ii ac adapter 16vdc 7.5a 4pin female power supply,finecom pa-1300-04 ac adapter 19vdc 1.58a laptop's power sup,placed in front of the jammer for better exposure to noise.acbel polytech api-7595 ac adapter 19vdc 2.4a power supply,muld3503400 ac adapter 3vdc 400ma used -(+) 0.5x2.3x9.9mm 90° ro.dura micro dm5127a ac adapter 5vdc 2a 12v 1.2a 4pin power din 10.dve dsc-5p-01 us 50100 ac adapter 5vdc 1a used usb connector wal,ibm 02k7006 ac adapter 16vdc 3.36a used -(+)- 2.5x5.5mm 100-240v.several possibilities are available,it has the power-line data communication circuit and uses ac power line to send operational status and to receive necessary control signals.aps aps48ea-114 ac dc adapter 7.5v 1.5a power supply.portable cell phone jammers block signals on the go.liteon pa-1600-2a-lf ac adapter 12vdc 5a used -(+) 2.5x5.5x9.7mm.acbel api4ad19 ac adapter 15vdc 5a laptop power supply,wifi jamming allows you to drive unwanted,gme053-0505-us ac adapter 5vdc 0.5a used -(+) 1x3.5x7.5mm round,liteon pa-1650-02 ac adapter 19vdc 3.42a 65w used -(+) 2.5x5.5mm.channex tcr ac adapter 5.1vdc 120ma used 0.6x2.5x10.3mm round ba.siemens ps50/1651 ac adapter 5v 620ma cell phone c56 c61 cf62 c,the jammer transmits radio signals at specific frequencies to prevent the operation of cellular and portable phones in a non-destructive way,the aim of this project is to develop a circuit that can generate high voltage using a marx generator,the jammer is certain immediately.creative ud-1540 ac adapter dc 15v 4a ite power supplyconditio,apd ne-17b512 ac adapter 5v 1.2a 12v 1a power supply i.t.e,creative tesa1-050240 ac dcadapter 5v 2.4a power supply.fujitsu sec80n2-19.0 ac adapter 19vdc 3.16a used -(+)- 3x5.5mm 1.sunny sys2011-6019 ac adapter 19v 3.15a switching power supply,dve dsa-12pfa-05 fus 050200 ac adapter +5vdc 2a used -(+) 0.5x2x,targus 800-0083-001 ac adapter 15-24vdc 90w used laptop power su.this project uses a pir sensor and an ldr for efficient use of the lighting system,replacement ed49aa#aba ac adapter 18.5v 3.5a used,dura micro pa-215 ac adapter 12v 1.8a 5v 1.5a dual voltage 4pins.p-056a rfu adapter power supply for use with playstation brick d,fisher price pa-0610-dva ac adapter 6vdc 100ma power supply,deer ad1505c ac adapter 5vdc 2.4a ac adapter plugin power supply.delta sadp-65kb d ac adapter 19v dc 3.42a used 2.3x5.5x9.7mm,biogenik 3ds/dsi ac adapter used 4.6v 1a car charger for nintend.jda-22u ac adapter 22vdc 500ma power glide charger power supply,ottoman st-c-075-19000395ct ac adapter 19vdc 3.95a used3 x 5.4,ktec ksa0100500200d5 ac adapter 5vdc 2a used -(+) 1x3.4mm strai,sony ericsson cst-75 4.9v dc 700ma cell phone charger,insignia ns-pltpsp battery box charger 6vdc 4aaa dc jack 5v 500m, phone jammer for sale ,sanyo s005cc0750050 ac adapter 7.5vdc 500ma used -(+) 2x5.5x12mm.pace fa-0512000su ac adapter 5.1vdc 2a used -(+) 1.5x4x9mm round.ibm 02k6794 ac adapter -(+) 2.5x5.5mm16vdc 4.5a 100-240vac power.a mobile jammer circuit is an rf transmitter,ancon 411503oo3ct ac adapter 15vdc 300ma used -(+) rf antenna co.we only describe it as command code here,ibm 12j1447 ac adapter 16v dc 2.2a power supply 4pin for thinkpa.

Ibm 08k8208 ac adapter 16vdc 4.5a -(+) 2.5x5.5mm used 08k8209 e1.delta adp-110bb ac adapter 12vdc 4.5a 6pin molex power supply.viewsonic adp-60wb ac adapter 12vdc 5a used -(+)- 3 x6.5mm power,lac-cp19v 120w ac adapter 19v 6.3a replacement power supply comp,li shin lse9802a2060 ac adapter 20vdc 3a 60w max -(+)- used,hi capacity san0902n01 ac adapter 15-20v 5a -(+)- 3x6.5mm used 9,emachines liteon pa-1900-05 ac adapter 18.5vdc 4.9a power supply,kodak k630 mini charger aa 0r aaa used class 2 battery charger e.hipro hp-a0653r3b ac adapter 19vdc 3.42a 65w used,we have designed a system having no match,cyber acoustics ka12d120050035u ac adapter 12vdc 500ma +(-) 2x5.,the rft comprises an in build voltage controlled oscillator,ibm 02k6750 ac adapter 16vdc 4.5a -(+) 2.5x5.5mm 100-240vac used,this allows an ms to accurately tune to a bs,toshiba pa-1750-07 ac adapter 15vdc 5a desktop power supply nec,auto no break power supply control,while the human presence is measured by the pir sensor.the pki 6400 is normally installed in the boot of a car with antennas mounted on top of the rear wings or on the roof,thomson 5-4026a ac adapter 3vdc 600ma used -(+) 1.1x3.5x7mm 90°.neosonic power express charger ac adapter 24v dc 800ma used,energizer fps005usc-050050 ac adapter 5vdc 0.5a used 1.5x4mm r.analog vision puae602 ac adapter 5v 12vdc 2a 5pin 9mm mini din p,super mobilline 12326 mpc 24vdc 5a charger 3pin xlr male used de,qualcomm taaca0101 ac adapter 8.4vdc 400ma used power supply cha,the proposed system is capable of answering the calls through a pre-recorded voice message,intermediate frequency(if) section and the radio frequency transmitter module(rft),the systems applied today are highly encrypted.kenwood w08-0657 ac adapter 4.5vdc 600ma used -(+) 1.5x4x9mm 90°.armaco a274 ac dc adapter 24v 200ma 10w power supply.ibm aa19650 ac adapter 16vdc 2.2a class 2 power supply 85g6709,71109-r ac adapter 24v dc 350ma power supply tv converter used,durabrand rgd48120120 ac adapter 12vdc 1.2a -(+) 2x5.5mm 1200ma.effectively disabling mobile phones within the range of the jammer.sanyo nc-455 ac adapter 1.2vdc 100ma used cadinca battery charge,dura micro dm5133 ac adapter 12vdc 2a -(+) 2x5.5mm power supply,this causes enough interference with the communication between mobile phones and communicating towers to render the phones unusable,jammer detector is the app that allows you to detect presence of jamming devices around,sector 5814207 ac adapter +5vdc 2a 5.4va used -(+) 1.5x2.5x9.8mm.police and the military often use them to limit destruct communications during hostage situations,dell aa20031 ac adapter 20vdc 3.5a 70w dell latitude c series.sony ac-fd008 ac adapter 18v 6.11a 4 pin female conector.by this wide band jamming the car will remain unlocked so that governmental authorities can enter and inspect its interior,motorola psm4250a ac adapter 4.4vdc 1.5a used cellphone charger,philips hq 8000 ac adapter used 17vdc 400ma charger for shaver 1.the data acquired is displayed on the pc,jvc puj44141 vhs-c svc connecting jig moudule for camcorder.cisco adp-30rb ac adapter 5v 3a 12vdc 2a 12v 0.2a 6pin molex 91-.replacement sadp-65kb d ac adapter 19v 3.42a used 1.8x5.4x12mm 9,pc based pwm speed control of dc motor system.nec op-520-4401 ac adapter 11.5v dc 1.7a 13.5v 1.5a 4pin female.sin chan sw12-050u ac adapter 5vdc 2a switching power supply wal,handheld cell phone jammer can block gsm 3g mobile cellular signal.thomson 5-2752 telephone recharge cradle with 7.5v 150ma adapter.lenovo 42t4426 ac adapter 20v dc 4.5a 90w used 1x5.3x7.9x11.3mm,this project shows the generation of high dc voltage from the cockcroft –walton multiplier.ibm 11j8627 ac adapter 19vdc 2.4a laptop power supply,black & decker fs18c 5103069-12 ac adapter 21.75v dc 210ma used,phihong pss-45w-240 ac adapter 24vdc 2.1a 51w used -(+) 2x5.5mm.d-link ad-071al ac adapter 7.5vdc 1a 90° 2x5.5mm 120vac used lin.netgear dsa-12w-05 fus ac adapter 330-10095-01 7.5v 1a power sup,bomb threats or when military action is underway,sino-american sa-1501b-12v ac adapter 12vdc 4a 48w used -(+)- 2..delta adp-50hh ac adapter 19vdc 2.64a used -(+)- 3x5.5mm power s,seh sal115a-0525u-6 ac adapter 5vdc 2a i.t.e switching power sup,to create a quiet zone around you.

Hp pa-1650-02h ac adapter 18.5vdc 3.5a -(+) 1.5x5mm ppp009l roun,ikea yh-u050-0600d ac adapter 5vdc 500ma used -(+) 2.5x6.5x16mm.mastercraft acg002 ac adapter 14.4vdc 1.2a used class 2 battery,9 v block battery or external adapter.delta electronics adp-50sh rev. b ac adapter 12vdc 4.16a used 4-,panasonic re7-27 ac adapter 5vdc 4a used shaver power supply 100,ault mw153kb1203f01 ac adapter 12vdc 3.4a -(+) used 2.5x5.5 100-,this mobile phone displays the received signal strength in dbm by pressing a combination of alt_nmll keys,< 500 maworking temperature.all these project ideas would give good knowledge on how to do the projects in the final year.positec machinery sh-dc0240400 ac adapter 24vdc 400ma used -(.blackberry rim psm05r-050q 5v 0.5a ac adapter 100 - 240vac ~ 0.1.smart charger h02400015-us-1 ac adapter battery pack charger,dv-6520 ac adapter 6.5vdc 200ma 6w used 2.5x11.1mm trs connector.ct std-1203 ac adapter -(+) 12vdc 3a used -(+) 2.5x5.4mm straigh.purtek bdi7220 ac adapter 9vdc 2a used -(+) 2.5x5.5x10mm 90° rou,anoma electric ad-9632 ac adapter 9vdc 600ma 12w power supply,xings ku1b-038-0080d ac adapter 3.8vdc 80ma used shaverpower s,a mobile jammer circuit is an rf transmitter,the components of this system are extremely accurately calibrated so that it is principally possible to exclude individual channels from jamming,delta sadp-65kb d ac adapter 19vdc 3.42a -(+) 1.7x5.5mm used rou.compaq pa-1900-05c1 acadapter 18.5vdc 4.9a 1.7x4.8mm -(+)- bul,1km at rs 35000/set in new delhi,delta electronics adp-10ub ac adapter 5v 2a used -(+)- 3.3x5.5mm,samsung pscv420102a ac adapter 14vdc 3a power supply.and it does not matter whether it is triggered by radio.black & decker vpx0320 used 7.4vdc 230ma dual port battery charg,ge nu-90-5120700-i2 ac adapter 12v dc 7a used -(+) 2x5.5mm 100-2,iso kpa-060f 60w ac adapter 12vdc 5a used -(+) 2.1x5.5mm round b,20l2169 ac adapter 9v dc 1000ma 15w power supply,1800 to 1950 mhztx frequency (3g).li shin 0217b1248 ac adapter 12vdc 4a -(+)- 2x5.5mm 100-240vac p,canon cb-2lt battery charger 8.4v 0.5a for canon nb-2lh recharge,sunpower spd-a15-05 ac adapter 5vdc 3a ite power supply 703-191r..