International Journal of Navigation and Observation http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. Combination of the DVZ Method, Particle Filter, and Fuzzy Controller for Electric Wheelchair Navigation Tue, 18 Nov 2014 12:54:57 +0000 http://www.hindawi.com/journals/ijno/2014/137891/ Electric wheelchair is one of the many engines used for the movement of aged and disabled people. This paper introduces an obstacle avoidance using deformable virtual zone (DVZ), particle filter to improve localization and fuzzy controller to join desired target. This controller is developed to increase the independence of disabled and aged people, specifically those who suffer not only disability in the lower limbs but also visual disturbances. To overcome these problems, different perceptive abilities or sensors were introduced. In this context, we developed a control system composed by fuzzy controller to join a target, DVZ method for obstacle avoidance, and particle filter for localization. Also, we present the simulation results of the wheelchair navigation system. Malek Njah and Mohamed Jallouli Copyright © 2014 Malek Njah and Mohamed Jallouli. All rights reserved. P-RANSAC: An Integrity Monitoring Approach for GNSS Signal Degraded Scenario Tue, 23 Sep 2014 10:09:08 +0000 http://www.hindawi.com/journals/ijno/2014/173818/ Satellite navigation is critical in signal-degraded environments where signals are corrupted and GNSS systems do not guarantee an accurate and continuous positioning. In particular measurements in urban scenario are strongly affected by gross errors, degrading navigation solution; hence a quality check on the measurements, defined as RAIM, is important. Classical RAIM techniques work properly in case of single outlier but have to be modified to take into account the simultaneous presence of multiple outliers. This work is focused on the implementation of random sample consensus (RANSAC) algorithm, developed for computer vision tasks, in the GNSS context. This method is capable of detecting multiple satellite failures; it calculates position solutions based on subsets of four satellites and compares them with the pseudoranges of all the satellites not contributing to the solution. In this work, a modification to the original RANSAC method is proposed and an analysis of its performance is conducted, processing data collected in a static test. Gaetano Castaldo, Antonio Angrisano, Salvatore Gaglione, and Salvatore Troisi Copyright © 2014 Gaetano Castaldo et al. All rights reserved. The Use of Quick Response (QR) Codes in Landmark-Based Pedestrian Navigation Wed, 23 Apr 2014 13:31:31 +0000 http://www.hindawi.com/journals/ijno/2014/897103/ Vehicle navigation systems usually simply function by calculating the shortest fastest route over a road network. In contrast, pedestrian navigation can have more diverse concerns. Pedestrians are not constrained to road/path networks; their route may involve going into buildings (where accurate satellite locational signals are not available) and they have different priorities, for example, preferring routes that are quieter or more sheltered from the weather. In addition, there are differences in how people are best directed: pedestrians noticing landmarks such as buildings, doors, and steps rather than junctions and sign posts. Landmarks exist both indoors and outdoors. A system has been developed that uses quick response (QR) codes affixed to registered landmarks allowing users to localise themselves with respect to their route and with navigational instructions given in terms of these landmarks. In addition, the system includes images of each landmark helping users to navigate visually in addition to through textual instructions and route maps. The system runs on a mobile device; the users use the device’s camera to register each landmark’s QR code and so update their position (particularly indoors) and progress through the route itinerary. Anahid Basiri, Pouria Amirian, and Adam Winstanley Copyright © 2014 Anahid Basiri et al. All rights reserved. A Simple Three-Dimensional Matrix Method for Global Constellation Intrasatellite Link Topological Design Sun, 30 Mar 2014 07:43:25 +0000 http://www.hindawi.com/journals/ijno/2014/502158/ A three-dimensional matrix method is proposed in this paper for Global Navigation Satellite System (GNSS) constellation Intrasatellite Link (ISL) topological design. The rows and columns of proposed matrix contain the information of both constellation orbit planes and satellites in each orbit plane. The third dimension of proposed matrix represents the time sequences during constellation movement. The proposed method has virtues of better advantage of conceptual clarity and computational efficiency, meanwhile, some properties of ISLs in the constellation can be proved easily. At the second part of this paper, a link assignment and optimal routing problem is proposed using three-dimensional topology matrixes, which aimed to minimize the relay hops during the process of data uploading to whole constellation network. Moreover, some practical constrains as antenna beam coverage and relative velocity are considered and analyzed in detail. Finally, some numerical simulations are provided, and the results demonstrated the promising performance of proposed topological method in reduction of computation burden, clear ISL conception, and so forth; the efficiency of provided optimal ISL routing problem is also proved. Xiaoliang Wang, Yansong Meng, Zhe Su, Gang Wang, Lixin Zhang, and Deren Gong Copyright © 2014 Xiaoliang Wang et al. All rights reserved. Use of the Wavelet Transform for Interference Detection and Mitigation in Global Navigation Satellite Systems Wed, 26 Feb 2014 12:28:47 +0000 http://www.hindawi.com/journals/ijno/2014/262186/ Radio frequency interference detection and mitigation are becoming of paramount importance due to the increasing number of services and applications based on the position obtained by means of Global Navigation Satellite Systems. A way to cope with such threats is the implementation in the receiver of advanced signal processing algorithm able to raise proper warning or improve the receiver performance. In this paper, we propose a method based on the Wavelet Transform able to split the useful signal from the interfering component in a transformed domain. The wavelet packet decomposition and proper statistical thresholds allow the algorithm to show very good performance in case of multiple pulse interference as well as in the case of narrowband interference, two scenarios in which traditional countermeasures might not be effective. Luciano Musumeci and Fabio Dovis Copyright © 2014 Luciano Musumeci and Fabio Dovis. All rights reserved. Benefit of the NeQuick Galileo Version in GNSS Single-Point Positioning Wed, 27 Nov 2013 08:27:56 +0000 http://www.hindawi.com/journals/ijno/2013/302947/ The GNSS measurements are strongly affected by ionospheric effects, due to the signal propagation through ionosphere; these effects could severely degrade the position; hence, a model to limit or remove the ionospheric error is necessary. The use of several techniques (DGPS, SBAS, and GBAS) reduces the ionospheric effect, but implies the use of expensive devices and/or complex architectures necessary to meet strong requirements in terms of accuracy and reliability for safety critical application. The cheapest and most widespread GNSS devices are single frequency stand-alone receivers able to partially correct this kind of error using suitable models. These algorithms compute the ionospheric delay starting from ionospheric model, which uses parameters broadcast within the navigation messages. NeQuick is a three-dimensional and time-dependent ionospheric model adopted by Galileo, the European GNSS, and developed by International Centre for Theoretical Physics (ICTP) together with Institute for Geophysics, Astrophysics, and Meteorology of the University of Graz. The aim of this paper is the performance assessment in single point positioning of the NeQuick Galileo version provided by ESA and the comparison with respect to the Klobuchar model used for GPS; the analysis is performed in position domain and the errors are examined in terms of RMS and maximum error for the horizontal and vertical components. A deep analysis is also provided for the application of the exanimated model in the first possible Galileo only position fix. Antonio Angrisano, Salvatore Gaglione, Ciro Gioia, Marco Massaro, and Salvatore Troisi Copyright © 2013 Antonio Angrisano et al. All rights reserved. Kalman Filter-Based Hybrid Indoor Position Estimation Technique in Bluetooth Networks Sun, 22 Sep 2013 16:48:25 +0000 http://www.hindawi.com/journals/ijno/2013/570964/ This paper presents an extended Kalman filter-based hybrid indoor position estimation technique which is based on integration of fingerprinting and trilateration approach. In this paper, Euclidian distance formula is used for the first time instead of radio propagation model to convert the received signal to distance estimates. This technique combines the features of fingerprinting and trilateration approach in a more simple and robust way. The proposed hybrid technique works in two stages. In the first stage, it uses an online phase of fingerprinting and calculates nearest neighbors (NN) of the target node, while in the second stage it uses trilateration approach to estimate the coordinate without the use of radio propagation model. The distance between calculated NN and detective access points (AP) is estimated using Euclidian distance formula. Thus, distance between NN and APs provides radii for trilateration approach. Therefore, the position estimation accuracy compared to the lateration approach is better. Kalman filter is used to further enhance the accuracy of the estimated position. Simulation and experimental results validate the performance of proposed hybrid technique and improve the accuracy up to 53.64% and 25.58% compared to lateration and fingerprinting approaches, respectively. Fazli Subhan, Halabi Hasbullah, and Khalid Ashraf Copyright © 2013 Fazli Subhan et al. All rights reserved. Time Synchronization and Performance of BeiDou Satellite Clocks in Orbit Thu, 05 Sep 2013 13:34:32 +0000 http://www.hindawi.com/journals/ijno/2013/371450/ The time model of Beidou satellite clocks is analyzed. The general relations of satellite clocks with the system time are studied. The error sources of two-way radio time transfer between satellites and uplink stations are analyzed. The uncertainty of type A is about 0.3 ns in Beidou system. All the satellite clocks in orbit of Beidou satellite navigation system are evaluated by the clock offsets observed by the two-way radio time transfer. The frequency stabilities at a sample time of 10000 s and 1 day for all the satellite clocks are better than . It means that the performance of Beidou satellite clocks in orbit is consistent with the ground test, and the results in orbit are a little better than those in ground vacuum. Han Chunhao, Cai Zhiwu, Lin Yuting, Liu Li, Xiao Shenghong, Zhu Lingfeng, and Wang Xianglei Copyright © 2013 Han Chunhao et al. All rights reserved. Navigation Facility for High Accuracy Offline Trajectory and Attitude Estimation in Airborne Applications Thu, 05 Sep 2013 08:30:47 +0000 http://www.hindawi.com/journals/ijno/2013/397686/ The paper focuses on a navigation facility, relying on commercial-off-the-shelf (COTS) technology, developed to generate high-accuracy attitude and trajectory measurements in postprocessing. Target performance is cm-level positioning with tenth of degree attitude accuracy. The facility is based on the concept of GPS-aided inertial navigation but comprises carrier-phase differential GPS (CDGPS) processing and attitude estimation based on multiantenna GPS configurations. Expected applications of the system include: (a) performance assessment of integrated navigation systems, developed for general aviation aircraft and medium size unmanned aircraft systems (UAS); (b) generation of reference measurements to evaluate the flight performance of airborne sensors (e.g., radar or laser); and (c) generation of reference trajectory and attitude for improving imaging quality of airborne remote sensing data. The paper describes system architecture, selected algorithms for data processing and integration, and theoretical performance evaluation. Experimental results are also presented confirming the effectiveness of the implemented approach. A. Renga, G. Fasano, D. Accardo, M. Grassi, U. Tancredi, G. Rufino, and A. Simonetti Copyright © 2013 A. Renga et al. All rights reserved. An Intuitive Approach to Inertial Sensor Bias Estimation Tue, 02 Jul 2013 11:13:45 +0000 http://www.hindawi.com/journals/ijno/2013/762758/ A simple approach to gyro and accelerometer bias estimation is proposed. It does not involve Kalman filtering or similar formal techniques. Instead, it is based on physical intuition and exploits a duality between gimbaled and strapdown inertial systems. The estimation problem is decoupled into two separate stages. At the first stage, inertial system attitude errors are corrected by means of a feedback from an external aid. In the presence of uncompensated biases, the steady-state feedback rebalances those biases and can be used to estimate them. At the second stage, the desired bias estimates are expressed in a closed form in terms of the feedback signal. The estimator has only three tunable parameters and is easy to implement and use. The tests proved the feasibility of the proposed approach for the estimation of low-cost MEMS inertial sensor biases on a moving land vehicle. Vasiliy M. Tereshkov Copyright © 2013 Vasiliy M. Tereshkov. All rights reserved. GNSS Reliability Testing in Signal-Degraded Scenario Tue, 26 Mar 2013 14:47:43 +0000 http://www.hindawi.com/journals/ijno/2013/870365/ Multiconstellation satellite navigation is critical in signal-degraded environments where signals are strongly corrupted. In this case, the use of a single GNSS system does not guarantee an accurate and continuous positioning. A possible approach to solve this problem is the use of multiconstellation receivers that provide additional measurements and allows robust reliability testing; in this work, a GPS/GLONASS combination is considered. In urban scenario, a modification of the classical RAIM technique is necessary taking into account frequent multiple blunders. The FDE schemes analysed are the “Observation Subset Testing,” “Forward-Backward Method,” and “Danish Method”; they are obtained by combining different basic statistical tests. The considered FDE methods are modified to optimize their behaviour in urban scenario. Specifically a preliminary check is implemented to screen out bad geometries. Moreover, a large blunder could cause multiple test failures; hence, a separability index is implemented to avoid the incorrect exclusion of blunder-free measurements. Testing the RAIM algorithms of GPS/GLONASS combination to verify the benefits relative to GPS only case is a main target of this work too. The performance of these methods is compared in terms of RMS and maximum error for the horizontal and vertical components of position and velocity. A. Angrisano, C. Gioia, S. Gaglione, and G. del Core Copyright © 2013 A. Angrisano et al. All rights reserved. Assessment of Different Sensor Configurations for Collaborative Driving in Urban Environments Sun, 10 Mar 2013 10:52:09 +0000 http://www.hindawi.com/journals/ijno/2013/767313/ Vehicle-to-vehicle relative navigation of a network of vehicles travelling in an urban canyon is assessed using least-squares and Kalman filtering covariance simulation techniques. Between-vehicle differential GPS is compared with differential GPS augmented with between-vehicle ultrawideband range and bearing measurements. The three measurement types are combined using both least-squares and Kalman filtering to estimate the horizontal positions of a network of vehicles travelling in the same direction on a road in a simulated urban canyon. The number of vehicles participating in the network is varied between two and nine while the severity of the urban canyon was varied from 15-to 65-degree elevation mask angles. The effect of each vehicle’s azimuth being known a priori, or unknown is assessed. The resulting relative positions in the network of vehicles are then analysed in terms of horizontal accuracy and statistical reliability of the solution. The addition of both range and bearing measurements provides protection levels on the order of 2 m at almost all times where DGPS alone only rarely has observation redundancy and often exhibits estimated accuracies worse than 200 m. Reliability is further improved when the vehicle azimuth is assumed to be known a priori. Mark G. Petovello, Kyle O'Keefe, Phil Wei, and Chaminda Basnayake Copyright © 2013 Mark G. Petovello et al. All rights reserved. INS Assisted Fuzzy Tracking Loop for GPS-Guided Missiles and Vehicular Applications Wed, 27 Feb 2013 15:32:37 +0000 http://www.hindawi.com/journals/ijno/2013/750385/ Autonomous Navigation Systems used in missiles and other high dynamic platforms are mostly dependent on the Global Positioning System (GPS). GPS users face limitations in terms of missile high dynamics and signal interference. Receiver’s tracking loops bandwidth requirements to avoid these problems are conflicting. The paper presents a novel signal frequency and phase tracking algorithm for very high dynamic conditions, which mitigates the conflicting choice of bandwidths and reduces tracking loop measurement noise. It exploits the flexibility of fuzzy control systems for directly generating the required Numerically Controlled Oscillator (NCO) tuning frequency using phase and frequency discriminators information and is labeled Fuzzy Frequency Phase Lock Loop (FFPLL). Because Fuzzy Systems can be computationally demanding and an Inertial Navigation System (INS) is often onboard the vehicle, an assisted INS Doppler version has been designed and is also proposed. Assessment of the new GPS tracking method is performed with both simulated and experimental data under jamming conditions. The main enhancements of the proposed system consist in reduced processing time, improved tracking continuity and faster reacquisition time. Ahmed M. Kamel, Valerie Renaudin, John Nielsen, and Gérard Lachapelle Copyright © 2013 Ahmed M. Kamel et al. All rights reserved. Human-Induced Effects on RSS Ranging Measurements for Cooperative Positioning Mon, 19 Nov 2012 14:37:44 +0000 http://www.hindawi.com/journals/ijno/2012/959140/ We present experimental evaluations of human-induced perturbations on received-signal-strength-(RSS-) based ranging measurements for cooperative mobile positioning. To the best of our knowledge, this work is the first attempt to gain insight and understand the impact of both body loss and hand grip on the RSS for enhancing proximity measurements among neighbouring devices in cooperative scenarios. Our main contribution is represented by experimental investigations. Analysis of the errors introduced in the distance estimation using path-loss-based methods has been carried out. Moreover, the exploitation of human-induced perturbations for enhancing the final positioning accuracy through cooperative schemes has been assessed. It has been proved that the effect of cooperation is very limited if human factors are not taken into account when performing experimental activities. Francescantonio Della Rosa, Mauro Pelosi, and Jari Nurmi Copyright © 2012 Francescantonio Della Rosa et al. All rights reserved. Performance Analysis of Alignment Process of MEMS IMU Mon, 12 Nov 2012 15:10:07 +0000 http://www.hindawi.com/journals/ijno/2012/731530/ The procedure of determining the initial values of the attitude angles (pitch, roll, and heading) is known as the alignment. Also, it is essential to align an inertial system before the start of navigation. Unless the inertial system is not aligned with the vehicle, the information provided by MEMS (microelectromechanical system) sensors is not useful for navigating the vehicle. At the moment MEMS gyroscopes have poor characteristics and it’s necessary to develop specific algorithms in order to obtain the attitude information of the object. Most of the standard algorithms for the attitude estimation are not suitable when using MEMS inertial sensors. The wavelet technique, the Kalman filter, and the quaternion are not new in navigation data processing. But the joint use of those techniques for MEMS sensor data processing can give some new results. In this paper the performance of a developed algorithm for the attitude estimation using MEMS IMU (inertial measurement unit) is tested. The obtained results are compared with the attitude output of another commercial GPS/IMU device by Xsens. The impact of MEMS sensor measurement noises on an alignment process is analysed. Some recommendations for the Kalman filter algorithm tuning to decrease standard deviation of the attitude estimation are given. Vadim Bistrov Copyright © 2012 Vadim Bistrov. All rights reserved. GNSS Spoofing Detection Based on Signal Power Measurements: Statistical Analysis Tue, 06 Nov 2012 13:54:26 +0000 http://www.hindawi.com/journals/ijno/2012/313527/ A threat to GNSS receivers is posed by a spoofing transmitter that emulates authentic signals but with randomized code phase and Doppler values over a small range. Such spoofing signals can result in large navigational solution errors that are passed onto the unsuspecting user with potentially dire consequences. An effective spoofing detection technique is developed in this paper, based on signal power measurements and that can be readily applied to present consumer grade GNSS receivers with minimal firmware changes. An extensive statistical analysis is carried out based on formulating a multihypothesis detection problem. Expressions are developed to devise a set of thresholds required for signal detection and identification. The detection processing methods developed are further manipulated to exploit incidental antenna motion arising from user interaction with a GNSS handheld receiver to further enhance the detection performance of the proposed algorithm. The statistical analysis supports the effectiveness of the proposed spoofing detection technique under various multipath conditions. V. Dehghanian, J. Nielsen, and G. Lachapelle Copyright © 2012 V. Dehghanian et al. All rights reserved. Advances in Signal Tracking for GNSS Receivers: Theory and Implementation Sun, 21 Oct 2012 07:39:41 +0000 http://www.hindawi.com/journals/ijno/2012/821516/ Carles Fernández-Prades, Heidi Kuusniemi, Pau Closas, and Marteen Uijt de Haag Copyright © 2012 Carles Fernández-Prades et al. All rights reserved. Nonlinear Bayesian Tracking Loops for Multipath Mitigation Wed, 17 Oct 2012 14:10:37 +0000 http://www.hindawi.com/journals/ijno/2012/359128/ This paper studies Bayesian filtering techniques applied to the design of advanced delay tracking loops in GNSS receivers with multipath mitigation capabilities. The analysis includes tradeoff among realistic propagation channel models and the use of a realistic simulation framework. After establishing the mathematical framework for the design and analysis of tracking loops in the context of GNSS receivers, we propose a filtering technique that implements Rao-Blackwellization of linear states and a particle filter for the nonlinear partition and compare it to traditional delay lock loop/phase lock loop-based schemes. Pau Closas, Carles Fernández-Prades, José Diez, and David de Castro Copyright © 2012 Pau Closas et al. All rights reserved. Accurate GLONASS Time Transfer for the Generation of the Coordinated Universal Time Tue, 25 Sep 2012 08:48:34 +0000 http://www.hindawi.com/journals/ijno/2012/353961/ The spatial techniques currently used in accurate time transfer are based on GPS, TWSTFT, and GLONASS. The International Bureau of Weights and Measures (BIPM) is mandated for the generation of Coordinated Universal Time (UTC) which is published monthly in the BIPM Circular T. In 2009, the international Consultative Committee for Time and Frequency (CCTF) recommended the use of multitechniques in time transfer to ensure precision, accuracy, and robustness in UTC. To complement the existing GPS and TWSTFT time links, in November 2009 the first two GLONASS time links were introduced into the UTC worldwide time link network. By November 2011, 6 GLONASS time links are used in the UTC computation. In the frame of the application in the UTC computation, we establish the technical features of GLONASS time transfer: the short- and long-term stabilities, the calibration process, and in particular the impact of the multiple GLONASS frequency biases. We then outline various considerations for future developments, including the uses of P-codes and carrier-phase information. Z. Jiang and W. Lewandowski Copyright © 2012 Z. Jiang and W. Lewandowski. All rights reserved. A Comparison of Parametric and Sample-Based Message Representation in Cooperative Localization Wed, 12 Sep 2012 15:31:21 +0000 http://www.hindawi.com/journals/ijno/2012/281592/ Location awareness is a key enabling feature and fundamental challenge in present and future wireless networks. Most existing localization methods rely on existing infrastructure and thus lack the flexibility and robustness necessary for large ad hoc networks. In this paper, we build upon SPAWN (sum-product algorithm over a wireless network), which determines node locations through iterative message passing, but does so at a high computational cost. We compare different message representations for SPAWN in terms of performance and complexity and investigate several types of cooperation based on censoring. Our results, based on experimental data with ultra-wideband (UWB) nodes, indicate that parametric message representation combined with simple censoring can give excellent performance at relatively low complexity. Jaime Lien, Ulric J. Ferner, Warakorn Srichavengsup, Henk Wymeersch, and Moe Z. Win Copyright © 2012 Jaime Lien et al. All rights reserved. Receiver Design for Time-Based Ranging with IEEE 802.11b Signals Wed, 08 Aug 2012 13:21:33 +0000 http://www.hindawi.com/journals/ijno/2012/743625/ This paper presents a ranging receiver architecture able to timestamp IEEE 802.11b Wireless LAN signals with sub-100 picosecond precision enabling time-based range measurements. Starting from the signal model, the performance of the proposed architecture is assessed in terms of statistical bounds when perturbed by zero-mean additive white Gaussian noise (AWGN) as well as in case of multipath propagation. Results of the proposed architecture, implemented in a Field Programmable Gate Array-(FPGA-) based prototype, are presented for different environments. For AWGN channels, the prototype system is able to attain an accuracy of 1.2 cm while the ranging accuracy degrades in dynamic multipath scenarios to about 0.6 m for 80% of the measurements due to the limited bandwidth of the signal. Reinhard Exel Copyright © 2012 Reinhard Exel. All rights reserved. Pedestrian Tracking Solution Combining an Impulse Radio Handset Transmitter with an Ankle-Mounted Inertial Measurement Unit Tue, 31 Jul 2012 10:02:43 +0000 http://www.hindawi.com/journals/ijno/2012/603254/ We address the indoor tracking problem by combining an Impulse Radio-Ultra-Wideband handset with an ankle-mounted Inertial Measurement Unit embedding an accelerometer and a gyroscope. The latter unit makes possible the detection of the stance phases to overcome velocity drifts. Regarding radiolocation, a time-of-arrival estimator adapted to energy-based receivers is applied to mitigate the effects of dense multipath profiles. A novel quality factor associated with this estimator is also provided as a function of the received signal-to-noise ratio, enabling us to identify outliers corresponding to obstructed radio links and to scale the covariance matrix of radiolocation measurements. Finally, both radio and inertial subsystems are loosely-coupled into one single navigation solution relying on a specific extended Kalman filter. In the proposed fusion strategy, processed inertial data control the filter state prediction whereas Combined Time Differences Of Arrival are formed as input observations. These combinations offer low computational complexity as well as a unique filter structure over time, even after removing outliers. Experimental results obtained in a representatively harsh indoor environment emphasize the complementarity of the two technologies and the relevance of the chosen fusion method while operating with low-cost, noncollocated, asynchronous, and heterogeneous sensors. Joe Youssef, Benoît Denis, Christelle Godin, and Suzanne Lesecq Copyright © 2012 Joe Youssef et al. All rights reserved. GPS Vulnerability to Spoofing Threats and a Review of Antispoofing Techniques Wed, 18 Jul 2012 15:51:42 +0000 http://www.hindawi.com/journals/ijno/2012/127072/ 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. Ali Jafarnia-Jahromi, Ali Broumandan, John Nielsen, and Gérard Lachapelle Copyright © 2012 Ali Jafarnia-Jahromi et al. All rights reserved. Effectiveness of GNSS Spoofing Countermeasure Based on Receiver CNR Measurements Tue, 17 Jul 2012 09:06:20 +0000 http://www.hindawi.com/journals/ijno/2012/501679/ A perceived emerging threat to GNSS receivers is posed by a spoofing transmitter that emulates authentic signals but with randomized code phase and Doppler over a small range. Such spoofing signals can result in large navigational solution errors that are passed onto the unsuspecting user with potentially dire consequences. In this paper, a simple and readily implementable processing rule based on CNR estimates of the correlation peaks of the despread GNSS signals is developed expressly for reducing the effectiveness of such a spoofer threat. Consequently, a comprehensive statistical analysis is given to evaluate the effectiveness of the proposed technique in various LOS and NLOS environments. It is demonstrated that the proposed receiver processing is highly effective in both line-of-sight and multipath propagation conditions. J. Nielsen, V. Dehghanian, and G. Lachapelle Copyright © 2012 J. Nielsen et al. All rights reserved. Two-Step Galileo E1 CBOC Tracking Algorithm: When Reliability and Robustness Are Keys! Wed, 11 Jul 2012 14:09:48 +0000 http://www.hindawi.com/journals/ijno/2012/135401/ The majority of 3G mobile phones have an integrated GPS chip enabling them to calculate a navigation solution. But to deliver continuous and accurate location information, the satellite tracking process has to be stable and reliable. This is still challenging, for example, in heavy multipath and non-line of sight (NLOS) environments. New families of Galileo and GPS navigation signals, such as Alternate Binary Offset Carrier (AltBOC), Composite Binary Offset Carrier (CBOC), and Time-Multiplex Binary Offset Carrier (TMBOC), will bring potential improvements in the pseudorange calculation, including more signal power, better multipath mitigation capabilities, and overall more robust navigation. However, GNSS signal tracking strategies have to be more advanced in order to profit from the enhanced properties of the new signals.In this paper, a tracking algorithm designed for Galileo E1 CBOC signal that consists of two steps, coarse and fine, with different tracking parameters in each step, is presented and analyzed with respect to tracking accuracy, sensitivity and robustness. The aim of this paper is therefore to provide a full theoretical analysis of the proposed two-step tracking algorithm for Galileo E1 CBOC signals, as well as to confirm the results through simulations as well as using real Galileo satellite data. Aleksandar Jovanovic, Cécile Mongrédien, Youssef Tawk, Cyril Botteron, and Pierre-André Farine Copyright © 2012 Aleksandar Jovanovic et al. All rights reserved. On the Impact of Channel Cross-Correlations in High-Sensitivity Receivers for Galileo E1 OS and GPS L1C Signals Thu, 28 Jun 2012 13:53:48 +0000 http://www.hindawi.com/journals/ijno/2012/132078/ One of the most promising features of the modernized global navigation satellite systems signals is the presence of pilot channels that, being data-transition free, allow for increasing the coherent integration time of the receivers. Generally speaking, the increased integration time allows to better average the thermal noise component, thus improving the postcorrelation SNR of the receiver in the acquisition phase. On the other hand, for a standalone receiver which is not aided or assisted, the acquisition architecture requires that only the pilot channel is processed, at least during the first steps of the procedure. The aim of this paper is to present a detailed investigation on the impact of the code cross-correlation properties in the reception of Galileo E1 Open Service and GPS L1C civil signals. Analytical and simulation results demonstrate that the S-curve of the code synchronization loop can be affected by a bias around the lock point. This effect depends on the code cross-correlation properties and on the receiver setup. Furthermore, in these cases, the sensitivity of the receiver to other error sources might increase, and the paper shows how in presence of an interfering signal the pseudorange bias can be magnified and lead to relevant performance degradation. Davide Margaria, Beatrice Motella, and Fabio Dovis Copyright © 2012 Davide Margaria et al. All rights reserved. Particle-Filter-Based WiFi-Aided Reduced Inertial Sensors Navigation System for Indoor and GPS-Denied Environments Mon, 25 Jun 2012 13:36:08 +0000 http://www.hindawi.com/journals/ijno/2012/753206/ Indoor navigation is challenging due to unavailability of satellites-based signals indoors. Inertial Navigation Systems (INSs) may be used as standalone navigation indoors. However, INS suffers from growing drifts without bounds due to error accumulation. On the other side, the IEEE 802.11 WLAN (WiFi) is widely adopted which prompted many researchers to use it to provide positioning indoors using fingerprinting. However, due to WiFi signal noise and multipath errors indoors, WiFi positioning is scattered and noisy. To benefit from both WiFi and inertial systems, in this paper, two major techniques are applied. First, a low-cost Reduced Inertial Sensors System (RISS) is integrated with WiFi to smooth the noisy scattered WiFi positioning and reduce RISS drifts. Second, a fast feature reduction technique is applied to fingerprinting to identify the WiFi access points with highest discrepancy power to be used for positioning. The RISS/WiFi system is implemented using a fast version of Mixture Particle Filter for state estimation as nonlinear non-Gaussian filtering algorithm. Real experiments showed that drifts of RISS are greatly reduced and the scattered noisy WiFi positioning is significantly smoothed. The proposed system provides smooth indoor positioning of 1 m accuracy 70% of the time outperforming each system individually. M. M. Atia, M. J. Korenberg, and A. Noureldin Copyright © 2012 M. M. Atia et al. All rights reserved. Optimized Carrier Tracking Loop Design for Real-Time High-Dynamics GNSS Receivers Sun, 03 Jun 2012 15:23:05 +0000 http://www.hindawi.com/journals/ijno/2012/651039/ Carrier phase estimation in real-time Global Navigation Satellite System (GNSS) receivers is usually performed by tracking loops due to their very low computational complexity. We show that a careful design of these loops allows them to operate properly in high-dynamics environments, that is, accelerations up to 40 g or more. Their phase and frequency discriminators and loop filter are derived considering the digital nature of the loop inputs. Based on these ideas, we propose a new loop structure named Unambiguous Frequency-Aided Phase-Locked Loop (UFA-PLL). In terms of tracking capacity and noise resistance UFA-PLL has the same advantages of frequently used coupled-loop schemes, but it is simpler to design and to implement. Moreover, it can keep phase lock in situations where other loops cannot. The loop design is completed selecting the correlation time and loop bandwidth that minimize the pull-out probability, without relying on typical rules of thumb. Optimal and efficient ways to smooth the phase estimates are also presented. Hence, high-quality phase measurements—usually exploited in offline and quasistatic applications—become practical for real-time and high-dynamics receivers. Experiments with fixed-point implementations of the proposed loops and actual radio signals are also shown. Pedro A. Roncagliolo, Javier G. García, and Carlos H. Muravchik Copyright © 2012 Pedro A. Roncagliolo et al. All rights reserved. A Novel Quasi-Open Loop Architecture for GNSS Carrier Recovery Systems Sun, 03 Jun 2012 10:09:21 +0000 http://www.hindawi.com/journals/ijno/2012/324858/ The problem of designing robust systems to track global navigation satellite system (GNSS) signals in harsh environments has gained high attention. The classical closed loop architectures, such as phase locked loops, have been used for many years for tracking, but in challenging applications their design procedure becomes intricate. This paper proposes and demonstrates the use of a quasi-open loop architecture to estimate the time varying carrier frequency of GNSS signals. Simulation results show that this scheme provides an additional degree of freedom to the design of the whole architecture. In particular, this additional degree of freedom eases the design of the loop filter in harsh environments. Muhammad Tahir, Letizia Lo Presti, and Maurizio Fantino Copyright © 2012 Muhammad Tahir et al. All rights reserved. A New Multipath Mitigation Method for GNSS Receivers Based on an Antenna Array Thu, 31 May 2012 11:58:52 +0000 http://www.hindawi.com/journals/ijno/2012/804732/ The well-known Space-Alternating Generalized Expectation Maximisation (SAGE) algorithm has been recently considered for multipath mitigation in Global Navigation Satellite System (GNSS) receivers. However, the implementation of SAGE in a GNSS receiver is a challenging issue due to the numerous number or parameters to be estimated and the important size of the data to be processed. A new implementation of the SAGE algorithm is proposed in this paper in order to reach the same efficiency with a reduced complexity. This paper focuses on the trade-off between complexity and performance thanks to the Cramer Rao bound derivation. Moreover, this paper shows how the proposed algorithm can be integrated with a classical GNSS tracking loop. This solution is thus a very promising approach for multipath mitigation. Sébastien Rougerie, Guillaume Carrié, François Vincent, Lionel Ries, and Michel Monnerat Copyright © 2012 Sébastien Rougerie et al. All rights reserved.