Browsing by Author "Broumandan, Ali"

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    A Ray-Tracing Technique to Characterize GPS Multipath in the Frequency Domain
    (2015-09-28) Gowdayyanadoddi, Naveen S.; Curran, James T.; Broumandan, Ali; Lachapelle, Gérard
    Multipath propagation is one of the major sources of error in GPS measurements. In this research, a ray-tracing technique is proposed to study the frequency domain characteristics of multipath propagation. The Doppler frequency difference, also known as multipath phase rate and fading frequency, between direct (line-of-sight, LOS) and reflected (non-line-of-sight, NLOS) signals is studied as a function of satellite elevation and azimuth, as well as distance between the reflector and the static receiver. The accuracy of the method is verified with measured Doppler differences from real data collected in a downtown environment. The use of ray-tracing derived predicted Doppler differences in a receiver, as a means of alleviating the multipath induced errors in the measurement, is presented and discussed.
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    Characterization of Signal Quality Monitoring Techniques for Multipath Detection in GNSS Applications
    (2017-07-05) Pirsiavash, Ali; Broumandan, Ali; Lachapelle, Gérard
    The performance of Signal Quality Monitoring (SQM) techniques under different multipath scenarios is analyzed. First, SQM variation profiles are investigated as critical requirements in evaluating the theoretical performance of SQM metrics. The sensitivity and effectiveness of SQM approaches for multipath detection and mitigation are then defined and analyzed by comparing SQM profiles and multipath error envelopes for different discriminators. Analytical discussions includes two discriminator strategies, namely narrow and high resolution correlator techniques for BPSK(1), and BOC(1,1) signaling schemes. Data analysis is also carried out for static and kinematic scenarios to validate the SQM profiles and examine SQM performance in actual multipath environments. Results show that although SQM is sensitive to medium and long-delay multipath, its effectiveness in mitigating these ranges of multipath errors varies based on tracking strategy and signaling scheme. For short-delay multipath scenarios, the multipath effect on pseudorange measurements remains mostly undetected due to the low sensitivity of SQM metrics.
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    Detection Performance of Polarization and Spatial Diversities for Indoor GNSS Applications
    (Hindawi Publishing Corporation, 2012-01-10) Zaheri, Mohammadreza; Broumandan, Ali; Dehghanian, Vahid; Lachapelle, Gérard
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    Detection Performance of Polarization and Spatial Diversities for Indoor GNSS Applications
    (2012-03-18) Zaheri, Mohammadreza; Broumandan, Ali; Dehghanian, Vahid; Lachapelle, Gérard
    Multipath fading in the form of signal power fluctuation poses a formidable challenge to GNSS signal detection in harsh multipath environments such as indoors. Antenna diversity techniques such as polarization and spatial diversities can be used to combat multipath fading in wireless propagation channels. This paper studies and compares GPS signal detection performance enhancements arising from the spatial and polarization diversity techniques. Performance enhancements are quantified from a theoretical perspective and later verified based on several test measurements in various indoor environments. Enhancement is quantified based on measuring the correlation coefficient values between diversity branches, SNR levels, and computing the level crossing rate and average fade duration. In addition, the processing gain is quantified and the performance of each individual diversity system is evaluated. Experimental results show that, for a given target detection performance in terms of the probability of false alarm and the probability of detection, the required input SNR level to meet the target detection performance can be significantly reduced utilizing the diversity system.
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    GNSS Code Multipath Mitigation by Cascading Measurement Monitoring Techniques
    (2018-06-19) Pirsiavash, Ali; Broumandan, Ali; Lachapelle, Gérard; O'Keefe, Kyle P. G.
    Various measurement monitoring techniques are investigated to mitigate the effect of global navigation satellite systems (GNSS) code multipath through error correction, stochastic weighting of measurements and detection and exclusion (or de-weighting) of affected measurements. Following a comprehensive review of each approach, the paper focuses on detection/exclusion and detection/de-weighting techniques where several single and dual-frequency monitoring metrics are employed in a combination with time-averaging and the M of N detection strategy. A new Geometry-Free (GF) detection metric is proposed given its capability to be combined with a preceding Code-Minus-Carrier (CMC)-based error correction to reduce the number of excluded or de-weighted measurements and thus preserve the measurement geometry. Three geometry-based algorithms, namely measurement subset testing, consecutive exclusion and iterative change of measurement weights are investigated to address multipath scenarios with multiple simultaneously affected measurements. Experimental results are provided using GPS L1, L2C and L5 data collected in multipath environments for static and kinematic scenarios. For GPS L1, the proposed combined method shows more than 38% improvement over a conventional Carrier-to-Noise-density ratio (C/N₀)-based Least-Squares (LS) solution in all but deep urban canyons. Lower performance was observed for L2C and L5 frequencies with a limited number of satellites in view.
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    GNSS Interference Mitigation Using Antenna Array Processing
    (2013-04-19) Daneshmand, Saeed; Lachapelle, Gérard; Broumandan, Ali
    Although hundreds of millions receivers are used worldwide, the performance of location-based services provided by GNSS is still compromised by interference which can range from unintentional distortion due to multipath propagation to intentionally menacing spoofing signals. Hence, the requirement for proper mitigation techniques becomes a must in GNSS receivers for robust, accurate and reliable positioning. Recently, interference mitigation techniques utilizing antenna arrays have gained significant attention in GNSS communities. Although at the time of this thesis, employing antenna array in GNSS applications is mostly limited to academic research and possibly sophisticated military applications, it is expected that in the near future, antenna array-based receivers will become widespread in civilian markets as well. Rapid advances in electronic systems and antenna design technology make previously hardware and software challenging problems easier to solve. Furthermore, due to the significant effort devoted to miniaturization of RF front-ends and antennas, the size of antenna array-based receivers will no longer be an issue. Given the above, this thesis investigates the use of antenna arrays in GNSS interference mitigation applications. It starts by proposing a new spatial processing technique capable of mitigating both high power interference and coherent and correlated GNSS multipath signals. It then follows by introducing three new methods that take advantage of spatial and temporal processing in three different GNSS applications. In the first method, the use of spatial-temporal processing for multipath mitigation in the form of a synthetic array is studied. A new method utilizing a moving antenna array is proposed to deal with highly correlated multipath components and also to increase the degree of freedom of the beamformer by synthesizing a larger antenna array. Thus, the array’s degree of freedom is not limited to the number of physical antenna elements. This method can be employed to mitigate multipath signals in vehicular navigation applications. The second method investigates benefits of spatial-temporal processing algorithms for improving narrowband interference mitigation performance. The limitations of previous space-time filters are analyzed and a new approach that employs the inherent periodic feature of GNSS signals in conjunction with the spatial-temporal processing to improve the performance of existing space-time filters is proposed. It is shown that in some interference scenarios, a space-time filter subject to the distortionless constraint may cause a significant degradation to the signal-to-noise ratio (SINR), which can be alleviated by employing the periodicity in the structure of the filter. In the third method the advantage of spatial-temporal processing for the purpose of GNSS spoofing mitigation is studied. A new mitigation approach, which removes the spoofing signal LOS component as well as its multipath reflections before the despreading process of GNSS signals, is introduced. This in turn decreases the computational complexity and processing time. Therefore, this method can be either employed as an inline standalone pre-processing unit for conventional GNSS receivers or it could easily be integrated in the next generation of receivers. Several simulations and real data analyses are used to evaluate and show the effectiveness of the proposed methods.
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    GPS Vulnerability to Spoofing Threats and a Review of Antispoofing Techniques
    (Hindawi Publishing Corporation, 2012-05-29) Jafarnia-Jahromi, Ali; Broumandan, Ali; Nielsen, John; Lachapelle, Gérard
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    GPS Vulnerability to Spoofing Threats and a Review of Antispoofing Techniques
    (2012-07-18) Jafarnia-Jahromi, Ali; Broumandan, Ali; Nielsen, John; Lachapelle, Gérard
    GPS-dependent positioning, navigation, and timing synchronization procedures have a significant impact on everyday life. Therefore, such a widely used system increasingly becomes an attractive target for illicit exploitation by terrorists and hackers for various motives. As such, spoofing and antispoofing algorithms have become an important research topic within the GPS discipline. This paper will provide a review of recent research in the field of GPS spoofing/anti-spoofing. The vulnerability of GPS to a spoofing attack will be investigated and then different spoofing generation techniques will be discussed. After introducing spoofing signal model, a brief review of recently proposed anti-spoofing techniques and their performance in terms of spoofing detection and spoofing mitigation will be provided. Limitations of anti-spoofing algorithms will be discussed and some methods will be introduced to ameliorate these limitations. In addition, testing the spoofing/anti-spoofing methods is a challenging topic that encounters some limitations due to stringent emission regulations. This paper will also provide a review of different test scenarios that have been adopted for testing anti-spoofing techniques.
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    Improved Navigation Solution Utilizing Antenna Diversity Systems in Multipath Fading Environments
    (2012-12-18) Sadrieh, Seyed Nima; Lachapelle, Gérard; Broumandan, Ali
    There is an intense effort on increasing the signal detection and tracking capabilities of Global Navigation Satellite System (GNSS) receivers in shaded areas where receivers suffer significant degradation due to attenuation and multipath. In order to overcome signal attenuation and multipath fading, more processing gain is required. Increasing the coherent integration time is traditionally known as the main source of processing gain. However, the mobile user is typically in motion while using the receiver, which limits the coherent integration gain. Diversity schemes constitute another source of processing gain that can be utilized to enhance signal detection and parameter estimation performance by providing additional processing gain. Given the coherent integration time limit and spatial/temporal characters of indoor GNSS channels, a diversity system composed of spatially separated antennas is developed and tested in this thesis. The performance of this diversity system is assessed at three different levels namely signal detection, parameter estimation and navigation solution. The performance of different combining methods at different levels is assessed theoretically and practically using real GPS L1 data collected in different indoor environments. An analysis of different metrics such as deflection coefficients, ROC curves and satellite availability, shows that the detection performance is considerably enhanced when utilizing the above diversity scheme. Proposing an analytical model based on sphere of scatterers model and considering the antenna gain pattern, Doppler measurements error sources in multipath environment are characterized. It is shown that Doppler measurements are of limited value for positioning purpose in harsh multipath environments. Combining pseudoranges of diversity branches based on their instantaneous qualities, represented by their epoch-by-epoch SNR, the pseudorange precision is enhanced significantly. Finally, improved satellite availability, along with enhanced pseudorange, makes a remarkable improvement in positioning accuracy.
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    Performance of Narrowband Signal Detection under Correlated Rayleigh Fading Based on Synthetic Array
    (2009-10-15) Broumandan, Ali; Nielsen, John; Lachapelle, Gérard
    The performance of a single moving antenna receiver in detecting a narrowband signal under correlatedRayleigh fading is considered. The spatial motion of the antenna during signal capture provides a realization of a synthetic antenna array. As shown, there is a net processing gain obtained by using a synthetic antenna array compared to the equivalent static antenna in Rayleigh fading environments subject to constant processing time. The performance analysis is based on average Signal-to-Noise Ratio (SNR) metrics fordesign parameters of probability of detection and probability of false alarm. An optimum detector based on Estimator-Correlator (EC) is developed, and its performance is compared with that of suboptimal Equal-Gain (EG) combiner in different channel correlation scenarios. It is shown that in moderate channel correlation scenarios the detection performance of EC and EG is identical. The sensitivity of the proposed method to knowledge of motion parameters is also investigated. An extensive set of measurements based on CDMA-2000 pilot signals using the static antenna and synthetic array are used to experimentally verify these theoretical findings.
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    Performance of Narrowband Signal Detection under Correlated Rayleigh Fading Based on Synthetic Array
    (Hindawi Publishing Corporation, 2009-07-27) Broumandan, Ali; Nielsen, John; Lachapelle, Gérard
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    Receiver-level Signal and Measurement Quality Monitoring for Reliable GNSS-based Navigation
    (2019-01-09) Pirsiavash, Ali; Lachapelle, Gerard Jules; O'Keefe, Kyle P. G.; Broumandan, Ali; Lichti, Derek D.; Gao, Yang; Lohan, Elena-Simona
    Global Navigation Satellite Systems (GNSS) are widely used in everyday and safety of life services as the main system for positioning and timing solutions. Reliability and service integrity are of utmost importance given a variety of error sources and threats. In the case of aviation and maritime applications, system integrity includes ground and space-based augmentation systems. These externally-aided monitoring systems do not provide a satisfactory solution for land users due to the multiplicity of error sources in the user's local environment, such as multipath. This research investigates receiver level stand-alone integrity monitoring solutions for such users. The methodology is based on Signal and Measurement Quality Monitoring (SQM and MQM) to detect and exclude or de-weight faulty measurements, with multipath and spoofing being the major concerns. Different monitoring metrics are defined and investigated for multipath detection and new geometry-based exclusion and de-weighting techniques are developed. Following an analytical discussion of metric sensitivity and effectiveness, simulated and field data analysis are provided to verify practical performance. Results obtained for the designed SQM and MQM-based detection metrics show reliable performance of 3 to 5 m Minimum Detectable Multipath Error (MDME). Although limited by multipath characteristics and measurement geometry, when detected faulty measurements are excluded or de-weighted, positioning performance improves for various multipath scenarios. In order to effectively classify multipath and spoofing, a spoofing simulator is designed, implemented and tested for selected time and position spoofing scenarios. A new spoofing strategy is described to investigate the minimum number of satellite signals required for an effective spoofing attack. Results show that in an overlapped spoofing scenario, at least 60% of signals are spoofed and thus distorted. This rate of signal distortion is not the case in all but harsh multipath scenarios and is used to distinguish spoofing attacks from multipath. More importantly, it is shown that distortion of more than half of the signals makes position solutions unreliable regardless of the error source. For selected scenarios, two-dimensional time/frequency widely-spaced SQM metrics are also developed to detect spoofing signals with about 3% false alarm probability imposed by multipath and other sources of signal distortion.
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    Spatial Characterization of GNSS Multipath Channels
    (Hindawi Publishing Corporation, 2012-02-07) Keshvadi, Hatef; Broumandan, Ali; Lachapelle, Gérard
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    Spatial Characterization of GNSS Multipath Channels
    (2012-05-16) Keshvadi, Hatef; Broumandan, Ali; Lachapelle, Gérard
    There is a growing interest in detecting and processing Global Navigation Satellite System (GNSS) signals in indoors and urban canyons by handheld devices. To overcome the signal attenuation problem in such adverse fading environments, long coherent integration is normally used. Moving the antenna arbitrarily while collecting signals is generally avoided as it temporally decorrelates the signals and limits the coherent integration gain. This decorrelation is a function of the antenna displacement and geometry of reflectors and angle of arrival of the received signal. Hence, to have an optimum receiver processing strategy it is crucial to characterize the multipath fading channel parameters. Herein, Angle of Arrival (AoA) and Angle Spread (AS) along with signal spatial correlation coefficient and fading intensity in GNSS multipath indoor channels are defined and quantified theoretically and practically. A synthetic uniform circular array utilizing a right-hand circular polarized (RHCP) antenna has been used to measure the spatial characteristics of indoor GNSS fading channels. Furthermore, rotating effect of a circular polarized antenna on the synthetic array processing and AoA estimation has been characterized. The performance of the beamforming technique via array gain is also assessed to explore the advantages and limitations of beamforming in fading conditions.