Interference detection and localization in the GPS L1 frequency band

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.Godkänd; 2012; 20120120 (osciso); LICENTIATSEMINARIUM Ämnesområde: Industriell elektronik/Industrial Electronics Examinator: Adj professor Dennis Akos, Institutionen för system- och rymdteknik, Luleå tekniska universitet Diskutant: Universitetslektor Magnus Lundberg-Nordenvaad, Institutionen för informationsteknologi, Uppsala universitet Tid: Fredag den 24 februari 2012 kl 13.00 Plats: A109, Luleå tekniska universite

Estimation of the Impact on GNSS Receivers From Hall Thruster Engines

Godkänd; 2014; Bibliografisk uppgift: Slutrapport för ett delprojekt inom NRFP2 med titeln "Predikterbar prestanda för GNSS-applikationer"; 20141006 (osciso

Interference in Global Positioning System Signals and its Effect on Positioning and Remote Sensing

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.Godkänd; 2015; 20150508 (vith); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Oscar Isoz Ämne: Rymdteknik/Space Technology Avhandling: Interference in Global Positioning Systems Signals and its Effect on Positioning and Remote Sensing Opponent: Docent Oliver Julien, Head of the SIGnal processing and NAVigation (SIGNAV) Research Group, Ecole Nationale de l’Aviation Civile (ENAC), Toulouse, Frankrike Ordförande: Gäst professor Stefan Buehler, Avd för rymdteknik, Institutionen för system- och rymdteknik, Luleå tekniska universitet Tid: Tisdag 16 juni kl 10.00 Plats: Aulan IRF – Kiruna Campus, Luleå tekniska universite

Detection and localization of wide band interference in the global positioning system L1 band using cross correlation techniques

Society is getting more and more dependent on the usage of global navigational satellite systems (GNSS). The signals recieved from the satellites are very weak and therefore sensitive to interference. If the GNSS signal gets interfered in an area, there is a potential risk for economic damages or even loss of life. When something is interfering with the signal, then the interference needs to be detected and the source localized in order to ensure the functionality of GNSS in the area. There is a number of ways that the source of interference can be located. This report focuses on a method that uses time difference of arrival (TDOA) for estimation of the position. Collection of data is made by a number of independent front ends with unsynchronized clocks that sample the GNSS signal and sends it to a central server.The server processes the collected data with a software based GNSS receiver and calculates the doppler frequency for each satellite as well as extracting the navigational data from the data. The navigational data is then used to syncronize the different datastreams in time. Correlation is made between the datasets in order to detect interference. When interference is detected, the difference in time is calculated between the correlation peak of the satellite signal and the peak from the interference. This gives the TDOA between the front ends. After TDOA has been calculated between a number of different front ends, localization of the interference source is performed by estimation of the intersection between of the hyperbolic lines that is created from the TDOA. The main focus has been investigating the characteristics of the cross-correlation function (CCF) for determining its behaviour for a GPS signal with and without interference. In comparison with other methods such as measurement of the AGC and calculation of the C/No, the CCF based method has been proven to be more sensitive but also much more computationally expensive.Validerat; 20101217 (root

Interference detection and localization in GPS L1 band

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.Godkänd; 2010; 20100511 (osciso

GNSS interference detection and localization using a network of low cost front-end modules

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.Godkänd; 2007; 20071019 (staffan

Assessment of GPS L1/Galileo E1 interference monitoring system for the airport environment

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.How does the GPS L1 spectrum look like at a commercial airport? How frequently do radio frequency interference (RFI) incidents occur? To answer this, the GPS L1/Galileo E1 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 Lueå 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.Godkänd; 2011; Bibliografisk uppgift: 1 CD-ROM; 20111021 (osciso

Mobile optical measurements of emissions and fenceline concentrations from oil and gas production

The mobile measurement platform and optical methods used in the SQAMD project1 allowed for mapping concentrations and measuring fluxes from a large number of sources and source types, and provided very useful information on the relative contribution of small stationary sources to alkane and BTEX emissions in the SCAB. Sources ranged from single oil wells to large tank farms, refineries, and off shore installations. Note that these sources are not subjected to the same regulatory requirements as larger industrial facilities. Future studies aimed at improving the emission estimates in SCAB should include a larger subset of units from all major source categories, and a better characterization of their spatial and temporal variability

Measurements of fugitive emissions of vocs from stationary sources using the SOF method - Standardization efforts and results from recent studies in California

The Solar Occultation Flux (SOF) method is used to screen and quantify VOC emissions from industrial conglomerates down to sub-areas in individual plants, such as a few tank process area or water treatment areas. The SOF method has been applied in several larger campaigns in both Europe and in the US (Mexico City 2006, Texas 2006/2009/2011/2012; Le Havre 2008, Rotterdam 2008/2010 and Antwerp 2010/2016, California 2013/20T5, Tianjin China 2016) and in more than 100 individual plant surveys over the world. The technique has been validated by comparison to other methods and tracer gas releases and it typically has an uncertainty of 30%, mostly due to uncertainties in the wind field. In the various campaign studies it has been found that the measured emissions obtained with SOF are 3–10 times higher than the reported emission obtained by calculations. The SOF method is Best Available Technology in Europe for quantitative measurements of diffuse emissions from refineries and the chemical sector. The technique is presently being standardized by the European CEN