| 1. |
- Borowski, Holly, et al.
(författare)
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Detecting false signals with automatic gain control
- 2012
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Ingår i: GPS World. - 1048-5104. ; 23:4, s. 38-43
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Tidskriftsartikel (refereegranskat)abstract
- A component of most GPS receiver front-ends, the automatic gain control (AGC) can flag potential jamming and spoofing attacks. The detection method is simple to implement and accessible to most GPS receivers. It may be used alone or as a complement other anti-spoofing architectures. This article presents results from a baseline AGC characterization, develos a simple spoofing detection method, and demonstrate the results of that method on receiver data gathered in the presence of a live spoofing attack.
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| 2. |
- Isoz, Oscar, et al.
(författare)
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Assessment of GPS L1/Galileo E1 interference monitoring system for the airport environment
- 2011
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Ingår i: Proceedings of the 23rd international technical meeting of the Satellite Division of the Institute of Navigation, ION GNSS 2011. - Manassas, Va : Inst. of Navigation. - 9781618394750 ; , s. 1920-1930
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Konferensbidrag (refereegranskat)abstract
- How does the GPS Ll spectrum look like at a commercial airport? How frequently do radio frequency interference (RFI) incidents occur? To answer this, the GPS Ll/Galileo El band was monitored at two different airports for an extended period of time. The monitor stations continuously recorded the noise level using the automatic gain control (AGC) in the frontend. Also, the raw intermediate frequency (IF) signal was recorded at regular intervals as well as when the AGC level dropped below a certain threshold. In this paper the analysis of long-term measurements of the spectrum and AGC level at Luleå Airport outside Luleå, Sweden, and Kaohsiung International Airport in Kaohsiung City, Taiwan, is presented. The results shows that RFI incidents did occur at both airports, although more frequent at Kaohsiung International Airport. The measurements also show that the AGC level is useful in systems monitoring the RFI environment. Importantly, the measured data could be utilized for analyses toward the future introduction of GBAS for civil aviation authorities.
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| 3. |
- Isoz, Oscar, et al.
(författare)
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Development of a deployable low cost interference detection and localization system for the GNSS L1/E1 band
- 2010
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Ingår i: 5th ESA Workshop on Satellite Navigation Technologies and European Workshop on GNSS Signals and Signal Processing (NAVITEC). - Piscataway, NJ : IEEE Communications Society. - 9781424487400
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Konferensbidrag (refereegranskat)abstract
- There have already been a number of well documented cases where the GNSS signals have been interfered by different sources. A number of different methods has been developed to counteract this. One problem with doing experiments to validate the accuracy of interference detection system is that the GPS L1 band is protected, therefore it is difficult to get permission to deliberately broadcast on those frequencies. In this paper we present a novel way to test such a system. The proposed method will be validated by deploying a number of low cost nodes and then an attempt to localize the interference will be made.
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| 4. |
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| 5. |
- Isoz, Oscar, et al.
(författare)
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Intercalibration of microwave temperature sounders using radio occultation measurements
- 2015
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Ingår i: Journal of Geophysical Research - Atmospheres. - 2169-897X .- 2169-8996. ; 120:9, s. 3758-3773
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Tidskriftsartikel (refereegranskat)abstract
- This is a study of the usefulness of radio occultation (RO) data for intercomparing different microwave temperature (MWT) sounding instruments. The RO data used are from the Global Navigational Satellite System Receiver for Atmospheric Sounding on the Metop-A and B satellites. The MWT sounders investigated are the Advanced Microwave Sounding Unit-A instruments on the satellites NOAA 15, 16, and 18 and Metop-A. We collocate RO and MWT data and then use these collocations to study various aspects of the MWT instruments. In addition, two different versions of the MWT data are compared: standard operational data (OPR) and the NOAA Integrated Microwave Intercalibration Approach data (IMICA). The time series of monthly mean differences shows that there are robust patterns for each satellite and data version, which mostly drift only slowly over time. The intersatellite spread, measured by the standard deviation of the yearly mean values by all satellites, is between 0.1 and 0.4 K, depending on channel, with no significant differences between OPR and IMICA data. The only notable exception is Channel 8 of NOAA 16, which appears to have a time-varying offset of 0.5–1 K relative to the other instruments. At this point it is not clear whether this deviation is real or a sampling artifact, so further study is needed. Due to the large number of collocations used, it is possible to also investigate the scene brightness and scan angle dependence of the MWT bias (relative to RO). First results of such an analysis are presented and discussed. Particularly, the investigation of the scan angle dependence is novel, since this bias pattern is difficult to assess without RO data. Further work is needed on these angular dependences, before conclusions are robust enough to include in data recalibration efforts, but our overall conclusion is that RO collocations are a powerful tool for intercomparing MWT sounders.
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| 6. |
- Isoz, Oscar, et al.
(författare)
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Interference detection and localization in GPS L1 band
- 2010
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Ingår i: Proceedings of the 2010 International Technical Meeting of The Institute of Navigation. - Manassas, VA : Institute of Navigation, The. - 9781617381157 ; , s. 925-929
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Konferensbidrag (refereegranskat)abstract
- The GNSS signals are very weak and therefore sensitive to interference. Since the usage of GNSS based services continues to increase, there is a need to develop a cost effective method to detect and localize interference sources. In this paper one such system will be presented. The system uses independent front ends that collects raw IF data. After the collection is done, the files are synchronized in time and frequency so that they can be cross correlated and the time difference of arrival of the interference signal is estimated. This paper will present the initial results from a test in May 2009 where the four stations were deployed and exposed to interference. It will be shown that the system is capable of both detection and localization of wide band interference.
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| 7. |
- Isoz, Oscar
(författare)
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Interference detection and localization in the GPS L1 frequency band
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The usage of Global Navigation Satellite Systems (GNSS) in general and the American GPS in particular increases everyday and so does the number of applications where it is used. The GNSS receivers relies on receiving signals from satellites orbiting the earth at an altitude of about 20 000 km and the signals received by the receiver are signicantly weaker then the background noise. Due to the weak signals it is fairly easy to intentionally or accidentally make it very hard or even impossible for a receiver to detect and track the satellites.With this in mind there is a need to develop cost eective methods to detect and localize interference so that appropriate counter measures can be taken. A number of methods have been proposed to detect and localize these sources. The complexity of these methods ranges from requiring future cellphones to contain software to monitor the GNSS environment to dedicated systems with multiple antennas and complicated hardware. In this thesis, two complementary methods will be presented which can detect and also localize interference in the GNSS bands using minimum amount of equipment. The equipment is based around a type of GNSS "receiver" that only samples the GNSS frequency so that it can be processed using a software dened GNSS eceiver. It will be shown that it is capable of detecting and localizing interference sources while also be cost eective and easily deployable. The rst technique is based on measuring the received power level. Since the GNSS signals are below the noise oor, the number of visible satellites will not aect the received power level. Instead the received power level will be aected by changes in the spectrum and changes in the receiver hardware. The GNSS signal is fairly robust against interference so an interferer usually has to have a signicantly higher signal power than the received power from the satellites in order to cause problems for the receiver. By monitoring the received signal power using multiple receivers it is possible to both detect interference and estimate the position of the transmitter. This method requires very little bandwidth but since the signal is measured in the analog domain it is sensitive to process variations between dierent receivers. Also, the nonlinear behaviour of the analog components in the receiver limits the accuracy of the position estimations. To improve the accuracy of the interference localization, a second method has been evaluated. In this method the GNSS samples recorded by dierent receivers at different locations is compared. When a GNSS receiver calculates a position it is actually calculating the time it takes for the signals to travel from the satellite to the receiver. This made it possible to synchronize data from multiple independent receivers both in time and frequency and then estimate the time dierence of arrival of the interfering signal between the dierent receivers. Both localization methods were evaluated during experiments done with assistance from the Swedish armed forces research agency (FOI). It will be shown that the signal power measurement can be used as a detector for interference and that the GPS signal can be used to synchronize data from independent stations so that the dierence in distance to a wideband transmitter can be estimated. To determine the amount of interference in the GPS L1 band two measurement campaigns were made. The rst campaign, measured where interference might be present in an urban area using a car mounted receiver. The other campaign took place at two airports in the summer and fall of 2011 and measured the interference level from xed antennas over an extended period of time.All research was done using the GPS L1 signal but the methods can easily be applied to other GNSS signals as well.
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| 8. |
- Isoz, Oscar, et al.
(författare)
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Interference from terrestrial sources and its impact on the GRAS GPS radio occultation receiver
- 2014
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Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 49:1, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that terrestrial GPS/Global Navigation Satellite Systems (GNSS) receivers are vulnerable and have suffered from intentional and unintentional interference sources. Unfortunately, space-based GPS/GNSS receivers are not exempt from radio frequency interference originating from the Earth. This paper explores data recorded by the GNSS Receiver for Atmospheric Sounding (GRAS) instrument onboard MetOp-A in September 2007, which is assumed to be representative of the typical environment for GPS/GNSS instrumentation in LEO orbit. Within these data it is possible to detect both pulsed interference and variations in the background noise. One plausible source of the pulsed interference is identified. We also show that neither the pulsed interference nor the variations in the background noise degrades the performance of the higher level products from GRAS.
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| 9. |
- Isoz, Oscar
(författare)
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Interference in Global Positioning System Signals and its Effect on Positioning and Remote Sensing
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- GPS and the other GNSS systems (GLONASS, Galileo and Beidou-2/COMPASS) is used to position billions of devices and is saving lives, the environment and money on a daily basis. GNSS enables anyone to determine their own unique global location. But the system can be fragile, it can easily be disabled or manipulated so that the calculated position from the receivers becomes incorrect. This can be done either intenionally or unintentionally. Further, many GNSS signals are located in shared frequency bands where other transmitters are allowed to broadcast as well. These transmitters can forexample be long range radars or distance montitoring equipment for aviation.In this thesis, it is demonstrated how one such radar can be detected and localized using data collected by the GNSS receiver for atmospheric sounding (GRAS). It is shown that the detected radar did not cause any measurable degradation of the temperature profiles generated from the collected data. Measurements from the GRAS sensor is also used as a reference to compare temperature soundings from the passive Advanced MicrowaveSounding Unit-A (AMSU-A) sensors that measures emission from Oxygen around 56 GHz.Further, work focusing on the detection of ground based interference is presented. It is shown how low cost independent units can be used for long term montitoring of the interference environment at key locations. Using collected data from the measurements at an area closed to the public, it is further shown how these units can be used to localize sources of broadband interference. Interference can also be generated from certain types of engines. One of the included contributions presents a theoretical analysis of the impact on GPS from an electrical engine intended for satellite propulsion. Even if the engine generates powerful broadband emission, since it is pulsed, the impact on the GPS receiver will most likely be minimal.
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| 10. |
- Lindström, Jonas, et al.
(författare)
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GNSS interference detection and localization using a network of low cost front-end modules
- 2007
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Ingår i: Proceedings of the 20th International Technical Meeting of the Satellite Division of the Institute of Navigation. - : Institute of Navigation, The. ; , s. 1165-1172
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Konferensbidrag (refereegranskat)abstract
- The expanding fields of usage for global satellite navigation systems (GNSS) have been made possible thanks to the general technological progress. The forthcoming advent of the European Galileo system increases the availability to the user of possible GNSS ranging sources, which even further will increase the dynamic interest in satellite navigation applications. Even so, fundamental problems about satellite navigation persist. One primary issue is that the signals are weak and thus subject to interference, intentional as well as unintentional, especially under delicate conditions. Indoors navigation cannot be said being an original design criteria of the GPS system, however has become actualized by technological achievements making this possible. In metropolitan areas the availability increment from Galileo is welcome; however the main advantage from this second system, for single L1 frequency users, will come in the urban canyon environment where a major issue for GPS users is low availability. Within this urban environment interference pose threats to availability and the ability to achieve accurate position solutions. This paper will discuss different kinds of interference within the GNSS L1 band, their characteristics, and ways of detecting their presence and location. The primary tool that will be utilized for this task is an L1 band front-end ASIC module with a USB interface to a computer. With this low cost sensor module it is possible to deploy a larger number of these over a selected area to monitor for interference. The key idea is to synchronize measurements and post-process collected data at a central server in order to detect, classify and locate the source of interference. Since multi-bit front-ends use an automatic gain control (AGC) to optimize usage of dynamic range with respect to the incoming signal sampling this control level is the primary metric for the measure of the absolute incoming power level (thermal noise or thermal noise plus interference). The ability to read out this AGC metric in parallel with the sampled IF data gives the possibility to make absolute measurements regarding power levels. Since the front-end based module is built up from low-cost integrated circuit components, calibration is useful to obtain individual characteristics. At a first stage, calibration is made against a noise generator providing a Gaussian noise over a wide band and a signal generator providing a continuous wave at different frequencies within the L1 band. This is to examine bandwidth limitations of the instrument. A second stage calibration using a spectrum analyzer as a reference will ultimately provide a reference to absolute measurements. This paper will provide the following: (1) the design of a low cost GNSS L1-band ASIC front end with USB computer interface capable of provide both AGC and raw IF samples; (2) calibration process for this module to obtain absolute input levels; (3) data and testing results from the utilization of an individual module as an interference detection resource; (4) data and testing results from a network-based approach utilizing multiple sensors with a common server to provide detection and localization of interference sources. The final result, the network based sensor grid, will demonstrate how such low cost modules can be deployed over a wide geographic area and be used to quickly detect and isolates sources of interference which GNSS operation would be considered critical.
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