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  • 1.
    Adjrad, M.
    et al.
    University of Leeds.
    Aguado, L.E.
    Advanced Digital Institute.
    Daly, M.
    University of Leeds.
    Kemp, A.
    University of Leeds.
    Junered, Marcus
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Lindström, J.
    Luleå tekniska universitet.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Mangin, F.
    France Developpement Conseil.
    Interference monitoring for GNSS bands in indoor and urban environments2007Ingår i: Proceedings of the 20th International Technical Meeting of the Satellite Division of the Institute of Navigation: ION GNSS 2007, Institute of Navigation, The , 2007, Vol. 4, s. 1211-1220Konferensbidrag (Refereegranskat)
    Abstract [en]

    A collaborative research project between the University of Leeds and Luleå University of Technology, Sweden, has taken place aiming to characterize the man-made noise in urban and indoor environments in the Galileo allocated frequency bands: E5 (1191.795 ± 25.575 MHz), E6 (1278.75 ± 20 MHz), and L1 (1575.42 ± 16 MHz), obviously, also covering the GPS L1 and L5 bands. This project has been co-funded by the European GNSS Supervisory Authority (EGSA), with funding from the 6th Framework Program of the European Community for research and technological development. The project includes the development of two receiver systems: the first instrument is based on the use of a spectrum analyzer (SA-based instrument), a wideband GNSS antenna, and a front-end capable of capturing each Galileo band separately using appropriate filtering and switches. The second instrument addresses the issues of cost and portability, providing interference detection and alarm triggering without the need for complex instrument. This is accomplished using low cost components in a small form factor where the instrument is based on a core GNSS front-end. This instrument will only cover the L1/E1 band. The interference measurement is obtained by combining the information from the automatic gain control (AGC) voltage that controls the AGC amplifier gain and the spectrum analysis of the analogue-to-digital converter (ADC) output raw data. The AGC information will be very important for detecting the presence of wideband interference signals where this will be difficult using spectrum analysis (in contrast to the case to narrowband interference signals). Control and data logging from both instruments are performed using a laptop computer where the spectrum analyzer traces and the FE-based instrument data are recorded for offline analysis via a suite of MATLAB® scripts. This paper describes the spectrum survey conducted at various indoor and urban locations, operationally significant to GNSS, in the North of the UK. The survey sites were selected to obtain geographically diverse measurement results and provide a general representation of the spectral environment. In addition, the temporal variation of man-made noise (MMN) is considered, this latter being correlated with the human activity at the measurement site, by performing the measurements day and night, weekdays and weekends.

  • 2.
    Akos, Dennis
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Ene, A.
    Stanford University.
    Thor, Jonas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    A prototyping platform for multi-frequency GNSS receivers2003Ingår i: ION GPS/GNSS Proceedings, Institute of Navigation, The , 2003Konferensbidrag (Refereegranskat)
    Abstract [en]

    The future satellite positioning/navigation systems (i.e. GPS and Galileo) will provide civil signals on multiple frequencies, similar to those currently available for military purposes only. This paper presents a direct RF sampling front end design well suited for multiple frequency satellite navigation receiver design. No frequency downconversion is necessary; rather the particular frequency bands of interest are intentionally aliased using a wide band analog-to-digital converter (ADC). The resulting samples are passed to the memory space of a host PC for storage, and are saved to disk for eventual processing of the multiple frequency transmissions. The present paper describes the design of the front-end, validates its concept with collected data, and discusses the variations on the design of a generic multiple frequency GPS front end. Methods for processing the data obtained by the front end design are also presented.

  • 3.
    Akos, Dennis
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    From, Markus
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Karlsson, Mattias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Larsson, Kjell
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Receiver measured time in the VDL mode 4 system2000Ingår i: IEEE 2000 Position Location and Navigation Symposium: San Diego, California, March 13 - 16, 2000, Piscataway, NJ: IEEE Communications Society, 2000, s. 309-316Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper details an investigation into the receiver measured time (RMT) concept of VDL Mode 4, basically the ability to derive estimates of time from the transmission of the VDL Mode 4 signals themselves. The RMT concept is based on determining the accurate time of transmission by measuring the time of arrival (TOA) of a received signal. The reverse aspect, or that of user position, can also be computed in the same manner and all computed simulations hold for errors in position. If synchronized time is available, or can be derived, then the user position can be computed based on signals from known transmitter locations. A complete, end-to-end RMT simulation model for the Gaussian filtered frequency shift keying (GFSK) and differential 8-phase shift keying (D8PSK) modulation techniques has been developed in which various transmitters, channels and receiver models as well as an RMT measurement system have been included. The timing results, which are included, are described in terms of two-sigma errors as a function of signal-to-noise ratios (SNRs). The performance varies for the different receiver structures over the typical operation region and for a 1-bit differential GFSK detector the two-sigma error is as low as 0.40 microseconds, corresponding to a ranging error of approximately 120 meters. When incorporating co-channel interference (CCI), multipath and Doppler frequency shifts the RMT performance has been shown to decrease in terms of higher two-sigma errors

  • 4.
    Akos, Dennis
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Stockmaster, Michael
    Rockwell Collins, Cedar Wells.
    Tsui, James B.Y.
    Wright-Patterson Air Force Base, Dayton.
    Caschera, Joe
    Wright-Patterson Air Force Base, Dayton.
    Direct bandpass sampling of multiple distinct RF signals1999Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 47, nr 7, s. 983-988Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A goal in the software radio design philosophy is to place the analog-to-digital converter as near the antenna as possible. This objective has been demonstrated for the case of a single input signal. Bandpass sampling has been applied to downconvert, or intentionally alias, the information bandwidth of a radio frequency (RF) signal to a desired intermediate frequency. The design of the software radio becomes more interesting when two or more distinct signals are received. The traditional approach for multiple signals would be to bandpass sample a continuous span of spectrum containing all the desired signals. The disadvantage with this approach is that the sampling rate and associated discrete processing rate are based on the span of spectrum as opposed to the information bandwidths of the signals of interest. Proposed here is a technique to determine the absolute minimum sampling frequency for direct digitization of multiple, nonadjacent, frequency bands. The entire process is based on the calculation of a single parameter-the sampling frequency. The result is a simple, yet elegant, front-end design for the reception and bandpass sampling of multiple RF signals. Experimental results using RF transmissions from the US Global Positioning System-Standard Position Service (GPS-SPS) and the Russian Global Navigation Satellite System (GLONASS) are used to illustrate and verify the theory

  • 5.
    Axell, Erik
    et al.
    Swedish Defence Research Agency, Department of Robust Telecommunications.
    Eklöf, Fredrik M.
    Swedish Defence Research Agency, Department of Robust Telecommunications.
    Alexandersson, Mikael
    Swedish Defence Research Agency, Department of Robust Telecommunications.
    Johansson, Peter
    Swedish Defence Research Agency, Department of Robust Telecommunications.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Jamming detection in GNSS receivers: Performance evaluation of field trials2013Ingår i: Proceedings of the 26th international technical meeting of the Satellite Division of The Institute of Navigation, ION GNSS+ 2013, Sept. 16 - 20, 2013, Nashville Convention Cener, Nashville, Tennessee, Manassas, VA: Institute of Navigation, The , 2013, Vol. 3, s. 2542-2551Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this work, we evaluate the detection performance of a number of commercial interference detectors and, in addition, of a detector that uses the automatic gain control (AGC) levels as test statistic. The AGC detector has been implemented on a Novatel GPS receiver and on a Universal Software Radio Peripheral (USRP). The evaluations are based on actual measurements of GPS signals and different types of jamming signals, which have been performed at the Vidsel test range in northern Sweden. The AGC detector was shown to work well for all types of jamming signals, in particular the one implemented on the USRP. The Chronos CTL-3500 was also shown to perform quite well for all kinds of signals, although not as good as the USRP with an AGC detector. Quite surprisingly, the J-alert was only able to detect the wideband (20 MHz) signal but not the narrow band (<2MHz) signals. By contrast, the jamming indicator on the Ublox 6 receiver was only able to detect a slowly varying modulated CW (MCW) signal, but not the signals with larger bandwidth (2 and 20 MHz). We confirmed that C/N0-based detectors could work well in a static scenario, but are not suitable in a dynamic scenario, since they cannot distinguish between decreased GPS signal strength (e.g. indoors) and an increased interference level.

  • 6.
    Axell, Erik
    et al.
    Swedish Defence Research Agency, Department of Robust Telecommunications.
    Eklöf, Fredrik M.
    Swedish Defence Research Agency, Department of Robust Telecommunications.
    Alexandersson, Mikael
    Swedish Defence Research Agency, Department of Robust Telecommunications.
    Johansson, Peter
    Swedish Defence Research Agency, Department of Robust Telecommunications.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Jamming detection in GNSS receivers: Performance evaluation of field trials2015Ingår i: Navigation, ISSN 0028-1522, E-ISSN 2161-4296, Vol. 62, nr 1, s. 73-82Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We evaluate the detection performance of several commercial interference detectors and of a detector that uses the automatic gain control (AGC) level as a test statistic. The evaluations are based on actual measurements of GPS signals and different types of jamming signals, and were performed at the Vidsel test range in northern Sweden.The AGC detector and the Chronos CTL-3500 were shown to work well for all types of jamming signals. The J-alert was able to detect a wideband (20 MHz) signal but not the narrow band (<2 MHz) signals. By contrast, the jamming indicator on a Ublox 6H receiver was only able to detect a slowly varying modulated CW signal, but not signals with larger bandwidth (>2 MHz). We confirmed that C/N0-based Android application detectors could work well in static scenarios but are not suitable in dynamic scenarios, since they cannot distinguish between decreased GPS signal strength and increased interference

  • 7.
    Backén, Staffan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Antenna array calibration using live GNSS signals2006Ingår i: Proceedings of the third ESA Workshop on Satellite Navigation User Equipment Technologies: NAVITEC 2006, 2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    An anechoic chamber free approach to GNSS antenna array gain and phase calibration is proposed and evaluated for a stationary array. The constellation change of the satellites was used to measure the variations in gain and phase over two twelve hour periods. The results was compared to an array calibrated using traditional methods in an anechoic chamber. It is shown that the method agrees well with the traditional method. Care was taken to make sure interference and multipath levels were low.The processing is performed using acquisition and tracking loop software implemented in Matlab. The IF data is recorded with a multi front end recording system.

  • 8.
    Backén, Staffan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Akos, Dennis
    GNSS antenna arrays: hardware requirements for algorithm implementation2006Konferensbidrag (Refereegranskat)
  • 9.
    Backén, Staffan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Akos, Dennis
    GNSS antenna arrays: hardware requirements for algorithm implementation2006Rapport (Övrigt vetenskapligt)
    Abstract [en]

    GNSS antenna arrays and beam forming/nulling have long been studied from an algorithm perspective. However, the hardware and implementation design issues are not as well understood. A low cost data collection platform for continuous recording of eight simultaneous IF streams are presented with an analysis of its performance. Also, the requirements on front end components are examined, specifically their impact on array processing versus single antenna processing. Focus is exclusively on digital beam forming as that is the only feasible approach for advanced algorithm implementation, and differences between traditional receiver architectures and a software defined radio approach will be emphasized. It is found that simultaneous recording of multiple IF streams allows for great flexibility in the field of antenna array processing for GNSS. Also, commercial off the shelf components shows sufficient performance, although care must be taken regarding issues such as phase consistency and cross talk between front ends.

  • 10.
    Backén, Staffan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Nordenvaad, Magnus Lundberg
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Post-processing dynamic GNSS antenna array calibration and deterministic beamforming2008Ingår i: Proceedings of the 21th International Technical Meeting of the Satellite Division of the Institute of Navigation: ION GNSS 2008, 2008, Vol. 3, s. 1311-1319Konferensbidrag (Refereegranskat)
    Abstract [en]

    An array processing GNSS (Global Navigation Satellite System) receiver may provide increased accuracy, reliability and integrity by forming beams towards satellites and nulls towards interference or reflective surfaces. Also, software defined receivers have proven themselves versatile and provide a convenient environment to implement novel algorithms.This paper first describes the gain/phase calibration of a seven element custom array antenna and proceeds to compare the single antenna performance to that of the performance attained by forming beams towards the satellites. IF (Intermediate Frequency) data, high rate samples representing the received signal in a narrow band around the GPS L1 frequency, from an array antenna have been recorded both in an environment with open sky conditions and also in more challenging areas (central Boulder, Colorado). Simultaneously, data from a high quality GPS based INS was recorded in order to obtain accurate estimates of position/ orientation. Calibration of the system (including antennas and front-ends) was performed using data from the benign environment, and based on this information, deterministic beams were formed towards the satellites using data from the semi-urban dataset. The single antenna accuracy was then compared to the position obtained by processing after forming beams.

  • 11.
    Backén, Staffan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Akos, Dennis
    Wilson, Steve G.
    University of Boulder at Colorado.
    RF replay system for narrowband GNSS if signals2011Ingår i: IEEE Transactions on Aerospace and Electronic Systems, ISSN 0018-9251, E-ISSN 1557-9603, Vol. 47, nr 1, s. 586-595Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Although GNSS RF signal simulators have long possessed the capability to generate scenarios they are, for example, not yet able to model a realistic scenario with complex multipath. Software defined receivers bridge the gap between simulated and real data to the extent that they may offer a replay capability, where a data set is first recorded to disk and later can be processed several times. Unfortunately, the recorded data generally can not be used by other GNSS receivers, making receiver to receiver comparisons difficult and time consuming.This paper describes a system capable of replaying recorded IF data into any narrow bandwidth L1 GNSS receiver, including an evaluation of the difference (position, timing and SNR) between live and replayed data using a high sensitivity, consumer grade receiver. The performance of the replayed data set was found to match that of the live data.

  • 12.
    Backén, Staffan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Nordenvaad, Magnus Lundberg
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Akos, Dennis
    A novel software defined research receiver architecture2009Ingår i: Proceedings of the 13th IAIN World Congress: Stockholm, 27-30 October 2009, Nordic Institute of Navigation , 2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    Software defined receivers (SDR) are an increasingly important tool within the GNSS research community as the high level of flexibility offer a significant advantage over traditional hardware implementations. Over the last decade, software receivers have been used to investigate techniques as diverse as bi-static radar (additional correlators), multipath mitigation techniques, GPS/INS integration and array processing.Mentioned above are only a few examples of features that could be required of an SDR, other include support for new signals (Galileo, GPS L5), multiple data file formats, high sensitivity and support for very long data sets. The large number of available features should ideally be coupled with program simplicity (such that other people can understand the program) and efficiency. This paper discusses these issues and proposes several solutions such asgeneralized data buffers (that is trivial to extend for new data formats) and a unified tracking structure (regardless of signal modulation). Examples are given using a Matlab implementation based on the Borre/Akos book Ä Software-Defined GPS and Galileo Receiver", however with significant modifications. Where critical, Java is used to increase performance while maintaining cross platform compatibility. Near real-time operation is available under optimal circumstances and the receiver currently supports GPS C/A- and GPS P-code signals.

  • 13.
    Borowski, Holly
    et al.
    University of Colorado, Boulder.
    Isoz, Oscar
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Lo, Sherman
    Stanford GPS Laboratory.
    Eklöf, Fredrik
    FOI.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Detecting false signals with automatic gain control2012Ingår i: GPS World, ISSN 1048-5104, Vol. 23, nr 4, s. 38-43Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 14.
    Chu, Tianxing
    et al.
    University of Colorado, Boulder.
    Vinande, Eric
    University of Colorado, Boulder.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Weinstein, Brian
    University of Colorado, Boulder.
    GNSS receiver evaluation: record-and-playback test methods2010Ingår i: GPS World, ISSN 1048-5104, Vol. 21, nr 1, s. 28-34Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Researchers at the university of Colorado have successfully used radio frequency record-and-playback systems (RPS) have gathered importance commercially because it offers the best way to test hardware receivers. RPS constitutes a stark contrast to more traditional signal simulators that use pre-defined trajectories and mathematical models to determine appropriate RF output. Positioning performance of a satellite navigation receiver under test (RUT) is coupled with its RF front-end system and local oscillator quality. The required equipment and connections are minimal when performing RPS drive testing, as no RUTs are included. It overcomes the fidelity limits of simulator-based testing, especially when considering the difficult-to-model urban environment. During receiver development, it requires only a single drive test for each location, as sampled RF data can be replayed from disk

  • 15.
    Do, J.
    et al.
    Stanford University.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Enge, P.K.
    Department of Aeronautics, Stanford University.
    L and S bands spectrum survey in the San Francisco Bay area2004Ingår i: PLANS 2004: Position Location and Navigation Symposium ; Monterey, California, April 26 - 29, 2004, Piscataway, NJ: IEEE Communications Society, 2004, s. 566-572Konferensbidrag (Refereegranskat)
    Abstract [en]

    The Global Positioning System (GPS) is a radio frequency (RF) communication system that consists of transmitters on the satellites and receivers on the ground. Because of substantial path loss, the received signal power from satellites is extremely weak and even below the thermal noise floor and as such is very sensitive to changes in the underlying noise floor. The goal of this work is to investigate the radio spectrum environment in the GPS band along with two additional bands, the Unified-S band and 2.4 GHz Industrial Scientific and Medical (ISM) band. The spectrum survey was conducted at various locations in the San Francisco Bay area including various urban, rural areas and airports and harbors which are operational significant to GPS. The measurement data collected in this study will provide a more accurate representation of the current status and the characteristics of the spectrum environment. Geographical variation within the sites will reveal correlation between the spectrum environment and the level of urbanization and also a comparative study on the frequency bands under different level of regulations can be used to investigate the effectiveness of the current spectrum policy

  • 16.
    Gao, Grace Xingxin
    et al.
    Stanford University.
    Lorenzo, David S. De
    Stanford University.
    Chen, Alan
    Stanford University.
    Lo, Sherman C.
    Stanford University.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Walter, Todd
    Stanford University.
    Enge, Per
    Stanford University.
    Galileo GIOVE: A Broadcast E5 Codes and their Application to Acquisition and Tracking2007Ingår i: National technical meeting: Institute of Navigation : NTM 2007 ; January 22 - 24, 2007, San Diego, California, USA, Fairfax, Va: Institute of Navigation, The , 2007, Vol. 2, s. 936-946Konferensbidrag (Refereegranskat)
  • 17.
    Isoz, Oscar
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Akos, Dennis
    Development of a deployable low cost interference detection and localization system for the GNSS L1/E1 band2010Ingår i: 5th ESA Workshop on Satellite Navigation Technologies and European Workshop on GNSS Signals and Signal Processing (NAVITEC), Piscataway, NJ: IEEE Communications Society, 2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 18.
    Isoz, Oscar
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Akos, Dennis
    Balaei, Asghar
    University of New South Wales, Sydney.
    Interference detection and localization in GPS L1 band2010Ingår i: Proceedings of the 2010 International Technical Meeting of The Institute of Navigation, Manassas, VA: Institute of Navigation, The , 2010, s. 925-929Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 19.
    Isoz, Oscar
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Lindgren, Tore
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Sun, Chih-Cheng
    National Cheng Kung University.
    Jan, Shau-Shiun
    National Cheng Kung University.
    Assessment of GPS L1/Galileo E1 interference monitoring system for the airport environment2011Ingår i: Proceedings of the 23rd international technical meeting of the Satellite Division of the Institute of Navigation, ION GNSS 2011: Sept. 19 - 23, 2011, Oregon Convention Cener, Portland, Oregon, Manassas, Va: Inst. of Navigation , 2011, Vol. 3, s. 1920-1930Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 20.
    Isoz, Oscar
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Kinch, Kjartan
    Niels Bohr Institute, Copenhagen University.
    Bonnedal, Magnus
    RUAG Space, Gothenburg.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Interference from terrestrial sources and its impact on the GRAS GPS radio occultation receiver2014Ingår i: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 49, nr 1, s. 1-6Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 21.
    Junered, Marcus
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Adjrad, Mounir
    University of Leeds.
    Aguado, Enrique
    University of Leeds.
    Daly, Michael
    University of Leeds.
    Kemp, Andrew
    University of Leeds.
    Instrumentation development for the measurement and characterisation of indoor and urban canyon ambient noise floor in the Galileo frequency bands2006Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The Galileo satellite navigation system will offer new frequency bands as well as share existing spectrum with parallel systems. The development of the Galileo system will significantly improve the already high level of accuracy, availability, reliability and integrity provided by current satellite navigation systems. However, in urban canyon and indoor locations there is a significant performance loss due to high levels of attenuation, signal masking and multipath. Receiver design for positioning in challenging areas like this is dependent on accurate characterization of the signal andnoise environments. Effects of signal propagation into urban canyons and indoors is relatively well known. However, the noise characteristics are largely unknown, especially the effect on the noise floor in the sensitive Galileo bands from the proliferation of electronic devices. This paper describes the design and development of a measurement instrument to characterise the underlying thermal interference noise floor in the various frequency bands in which Galileo will operate. The design trade-offs and designs are presented along with initial instrument testing. The instrument will be used in a joint measurements campaign between Luleå Technical University and the University of Leeds.

  • 22.
    Junered, Marcus
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Esterhuizen, Stephan
    University of Colorado, Boulder.
    Akos, Dennis
    University of Colorado, Boulder.
    Axelrad, Penina
    University of Colorado, Boulder.
    A Modular GPS Remote Sensing Receiver for Small Platforms2006Ingår i: Proceedings of the ION GNSS 2006, Institute of Navigation, The , 2006, s. 634-642Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper focuses on the processing of experimental data collected with a small modular GPS bistatic radar software receiver on a balloon flight. The receiver is designed for remote sensing purposes and the design process will be covered in some detail. GPS bistatic radar focuses on the surfacereflected signal, which can be used to determine properties of the reflection surface, including roughness, ocean wave height and also ranging to the surface. In the past, a mixture of both ASIC-based and software receivers have been used, but these require desktop or laptop computers to operate them. Previous receiver configurations have been prohibitively large and could not be mounted on smaller platforms. This design features two analog front-ends with a common clock, a FPGA and USB bridge to move the digital samples to a Linux-based Single Board Computer. The system features a modular design and allows for easy integration with other analog frontends.Airborne data collected with this instrument near Boulder, Colorado during a balloon flight will be presented. The data from the balloon flight has been processed to extract the height above ground using GPS bistatic radar as an altimeter and the GPS position as a reference. GTOPO30 Digital Elevation Models have been used to estimate the surface elevation used for height estimates in the altimeter. This project opens up new opportunities to perform remote sensing with cheaper and smaller platforms.

  • 23.
    Lindgren, Tore
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    A multistatic GNSS synthetic aperture radar for surface characterization2008Ingår i: IEEE Transactions on Geoscience and Remote Sensing, ISSN 0196-2892, E-ISSN 1558-0644, Vol. 46, nr 8, s. 2249-2253Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bistatic global navigation satellite system (GNSS) radar has received increased attention in recent years within both the radar and GNSS communities. In this paper, the traditional bistatic GNSS radar and bistatic synthetic aperture radar (SAR) concepts are fused into a more generic multistatic GNSS SAR system for surface characterization. This is done by using the range and Doppler processing techniques on signals transmitted by multiple satellites to determine the angular dependence of the surface reflectivity. The method has also been tested experimentally, and the results are presented.

  • 24.
    Lindgren, Tore
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Akos, Dennis
    Non-specular point reflections in GNSS bistatic radar2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper the impact of using different measurement platforms with different qualities is discussed. Data collected during three different measurement campaigns were used in this study. The data collected over Iowa, USA, in July, 2005, which were from a low flying airplane (low altitude and high dynamics), a data set collected from a stratospheric balloon outside Boulder, USA, in April, 2006 (high altitude, low dynamics), and a data set collected at the Boulder Atmospheric Observatory (BAO) outside Boulder, USA, in April, 2006 (low altitude, stationary).

  • 25.
    Lindgren, Tore
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Backén, Staffan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Estimation of the complex far-field of an antenna array using live GNSS signals and the equivalent electric current method2009Ingår i: Proceedings of the 13th IAIN World Congress, Stockholm, 27-30 October 2009, Nordic Institute of Navigation , 2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    When using antenna arrays with GNSS receivers both the gain and the phase of the far-field radiation pattern may be distorted due to coupling effects. This problem can often be characterized in the design process of the antenna or by measurements in a measurement range. This is, however, not always possible and it is then necessary to characterize the antenna using live measurements. In this paper the equivalent electric current method is used to estimate the gain and phase of the far-field of an antenna array for a GPS receiver. In the method, the complex far-field pattern of an antenna is estimated using the distribution of the electric current, which is described using suitable basis functions. The method was evaluated using data collected by a 7-element GPS antenna array. The results show agreement between the model and measured results.

  • 26.
    Lindgren, Tore
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Vinande, Eric
    University of Colorado, Boulder.
    Akos, Dennis
    Masters, Dallas
    University of Colorado, Boulder.
    Axelrad, Penina
    University of Colorado, Boulder.
    Measurement of backscattered GPS signals2006Ingår i: Position, Location, and Navigation Symposium, IEEE Communications Society, 2006, s. 664-669Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper describes a technique utilizing GPS ground reflections (GPS bistatic radar) to detect objects with a significant radar cross section located on the surface of the earth. GPS bistatic radar has been shown to be effective as a radar altimeter and for characterization of the reflection surface but has thus far not been shown to be effective for object detection. The technique uses ground reflections with longer path delay than the shortest path specular reflection. Data was collected using a COTS software receiver and post-processed using an in-house tool. Regions with ground reflections were overlayed on aerial imagery to identify possible sources.

  • 27.
    Lindström, Jonas
    et al.
    Luleå tekniska universitet.
    Akos, Dennis
    Isoz, Oscar
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Junered, Marcus
    GNSS interference detection and localization using a network of low cost front-end modules2007Ingår i: Proceedings of the 20th International Technical Meeting of the Satellite Division of the Institute of Navigation: Sept. 25 - 28, 2007, Fort Worth Convention Center, Fort Worth, Texas, Institute of Navigation, The , 2007, s. 1165-1172Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 28.
    Norton, Amanda
    et al.
    University of Colorado, Boulder.
    Lindgren, Tore
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Akos, Dennis
    A study of bistatic GNSS radar2006Ingår i: GIS development: Asia Pacific edition, Vol. 10, nr 6Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    One of the more recent areas of GNSS research of increasing popularity is the study of reflected GNSS signals. This will enable the use of GNSS as a passive radar system that can be used as an alternative to radar altimetry and for ground feature characterization. Of interest is also the possibility to use GNSS signals for object detection. The advantage of using GNSS signals as a passive radar system is that it has complete earth coverage. The signals are, however, weak and the computational load associated with the analysis is heavy.

  • 29.
    Powell, Sara J.
    et al.
    Department of Aerospace, Engineering Sciences, University of Colorado.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Backén, Staffan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Altimetry using gnss reflectrometry for L52012Ingår i: 2012 6th ESA Workshop on Satellite Navigation Technologies (Navitec 2012) & European Workshop on GNSS Signals and Signal Processing: Noordwijk, 5 - 7 December 2012, Piscaaway, NJ: IEEE Communications Society, 2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    GNSS reflectrometry offers a low cost alternative for Earth remote sensing and is used to measure, for example, ocean altimetry, wind speed, wind direction and modeling of the ocean surface state. A bistatic configuration, using one right-handed circular polarized and one left-handed circular polarized antenna, was built for this experiment in order to measure direct and reflected L1 and L5 signals. The direct and reflected signals were compared and the path difference between them calculated, leading to altitude measurements with both L1 and L5 signals. Compared to publicly available signals on L1, the higher code rate of L5 will provide higher measurement sensitivity

  • 30.
    Psiaki, M.L
    et al.
    Cornell University, Ithaca.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Thor, Jonas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    A comparison of direct radio frequency sampling and conventional GNSS receiver architectures2005Ingår i: Navigation, ISSN 0028-1522, E-ISSN 2161-4296, Vol. 52, nr 2, s. 71-81Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The novel concept of a direct radio frequency (RF) sampling receiver front end was analyzed, experimentally tested, and compared with a traditional superheterodyne front end that uses mixing to downconvert the signal before sampling. This study's goal was to demonstrate that signal power and phase are not adversely influenced by the use of direct RF sampling. The direct RF sampling strategy examined in this work uses sampling rates that are much lower than the carrier frequency but more than twice the signal bandwidth. Such a system employs a bandpass filter in front of the analog-to-digital converter (ADC) to avoid sensitivity loss via aliasing of out-of-band noise and interfering signals. This design approach was evaluated analytically to determine the effects of sample clock jitter, and experimental results using GPS signals were used to confirm the analytical results. The results indicate that direct RF sampling yields performance equivalent to that of superheterodyne mixing

  • 31.
    Psiaki, M.L.
    et al.
    Cornell University, Ithaca.
    Thor, Jonas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    A comparison of "direct RF sampling" and "downconvert & sampling" GNSS receiver architectures2003Ingår i: ION GPS/GNSS Proceedings, Institute of Navigation, The , 2003Konferensbidrag (Refereegranskat)
    Abstract [en]

    The new direct RF sampling GNSS receiver front concept has been analyzed, experimentally tested, simulated, and compared to a traditional superheterodyne front end that uses mixing to down-convert the signal before sampling. The goal of this study has been to demonstrate that signal power and carrier tracking are not adversely influenced by the use of direct RF sampling. The direct RF sampling strategy that has been examined uses sampling rates that are much lower than the carrier frequency but that are more than twice the information bandwidth. Such a system employs a bandpass filter in front of the analog-todigital converter to avoid sensitivity loss via aliasing of out-of-band noise and interfering signals. This design approach has been evaluated analytically to determine the effects of sample clock jitter, and experimental and simulation results have been used to confirm the analytical results. The experiments have used computer data acquisition systems to record the outputs of direct RF sampling front ends that were connected to roof-top patch antennas. The results indicate that direct RF sampling yields equivalent performance to superheterodyne mixing if sample timing jitter is kept below well defined limits.

  • 32.
    Thor, Jonas
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    A direct RF sampling multifrequency GPS receiver2002Ingår i: IEEE Position Location and Navigation Symposium, Piscataway, NJ: IEEE Communications Society, 2002, s. 44-51Konferensbidrag (Refereegranskat)
    Abstract [en]

    The future satellite positioning/navigation systems (both GPS and Galileo) will provide civil signals on multiple frequencies, similar to that currently available only for military use. The multiple distinct frequencies will provide many advantages to users of the navigation systems. This paper presents a direct RF sampling front end design well suited for multiple frequency satellite navigation receiver design. No frequency down conversion is necessary, rather the particular frequency bands of interest are intentionally aliased using a wide band ADC. The resulting samples are passed, via a doubling buffering FPGA design, to the memory space of a host PC for storage as well as eventually processing of the multiple frequency transmissions. This paper describes the design of the front-end, validates its concept with collected data, and discusses the variations on the design of a generic multiple frequency GPS front end.

  • 33.
    Vinande, E.
    et al.
    University of Colorado.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Masters, D.
    University of Colorado.
    Axelrad, P.
    University of Colorado.
    Esterhuizen, S.
    University of Colorado.
    GPS bistatic radar measurements of aircraft altitude and ground objects with a software receiver2005Ingår i: Proceedings of the 61st Annual meeting of the Institute of Navigation, Institute of Navigation, The , 2005, s. 528-534Konferensbidrag (Refereegranskat)
    Abstract [en]

    The GPS bistatic radar concept exploits the differences between direct and ground reflected signals received from one or more GPS satellites to aid in navigation or for remote sensing of the surface or transmission medium. This paper provides an overview of an implementation of the technique using a MATLAB-based software receiver and presents example results from an overland flight test. The sample data set was collected during a twenty minute segment of a flight test performed with a NASA Gulfstream V on 20-August-2004. Raw GPS data samples were recorded at 16 MHz from zenith- and nadir-pointing GPS antennas through a custom RF front end and data logger. These samples were post-processed using C/A code software GPS receiver techniques. The bistatic radar measurements are converted to a height above ground level and reflected signal-to-noise ratio. The height measurements are found to follow the trends computed based on receiver solved for height and digital elevations. Signal power is highly correlated with ground type with water returns producing the highest power reflections followed by large man made objects.

  • 34.
    Vinande, E.
    et al.
    University of Colorado, Boulder.
    Almqvist, J.
    University of Colorado, Boulder.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Full-state software GNSS and reduced MEMS IMU measurement processing for urban navigation2009Ingår i: Proceedings fo the 22nd international technical meeting of the Satellite Division of the Institute of Navigation, ION GNSS 2009: Sept. 22 - 25, 2009, Savanna Convention Center, Savannah, Georgia, Manassas, Va: Institute of Navigation, The , 2009, s. 2901-2909Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents an integration of partial-IMU measurements into the codebase of an existing software GNSS receiver for land vehicle navigation. Full-state filtering was implemented in contrast to the traditional error-state filtering approach. The Kalman filter time update was performed with IMU acceleration and rotation measurements while the measurement update was performed with GNSS pseudorange and Doppler measurements. Inertial component biases were estimated while the vehicle velocity was below 1.2 m/s for at least 5 seconds. A truth reference system composed of a hardware GPS receiver and tactical-grade IMU provided a truth trajectory for experimental comparison. The results from a drive test in downtown Denver, CO showed a solution availability increase from 95% to 100% with the addition of partial-IMU to the software receiver. Horizontal positioning and heading angle 50th percentile errors also showed a corresponding decrease (8.4 m to 4.2 m and 5.3° to 1.7°, respectively).

  • 35.
    Vinande, E.
    et al.
    University of Colorado, Boulder.
    Almqvist, J.
    Luleå tekniska universitet.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Improvements to software GNSS and reduced MEMS IMU measurement processing for urban navigation2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper extends work previously performed in the area of integrating reduced-cluster MEMS IMU and GNSS measurements in urban navigation conditions. These reduced-cluster IMU configurations are implemented since the typical dynamic conditions of land vehicles are well known. Specifically, this work utilizes a single-axis gyro for heading, a tri-axis accelerometer for velocity updates, and a commercially available software GPS receiver. The reduced inertial cluster is mounted in-line with the vehicle forward-right-down axes. Previous work by the authors has addressed the estimation of IMU mounting angles relative to the vehicle frame [1]. The vehicle frame is assumed parallel to the road surface. Therefore, any vehicle pitch and roll angles are due to local terrain variations.is work utilizes a single-axis gyro for heading, a tri-axis accelerometer for velocity updates, and a commercially available software GPS receiver. The reduced inertial cluster is mounted in-line with the vehicle forward-right-down axes. Previous work by the authors has addressed the estimation of IMU mounting angles relative to the vehicle frame [1]. The vehicle frame is assumed parallel to the road surface. Therefore, any vehicle pitch and roll angles are due to local terrain variations....

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