René Landry

Fuzzy corrections in a GPS/INS hybrid navigation system

A new concept regarding GPS/INS integration, based on artificial intelligence, i.e. adaptive neuro-fuzzy inference system (ANFIS) is presented. The GPS is used as reference during the time it is available. The data from GPS and inertial navigation system (INS) are used to build a structured knowledge base consisting of behavior of the INS in some special scenarios of vehicle motion. With the same data, the proposed fuzzy system is trained to obtain the corrected navigation data. In the absence of the GPS information, the system will perform its task only with the data from INS and with the fuzzy correction algorithm. This paper shows, using Matlab simulations, that as long as the GPS unavailability time is no longer than the previous training time and for the scenarios a priori defined, the accuracy of trained ANFIS, in absence of data from a reference navigation system, is better than the accuracy of stand-alone INS. The flexibility of model is also analyzed.

Low-cost MEMS sensor-based attitude determination system by integration of magnetometers and GPS: A real-data test and performance evaluation

Attitude determination systems utilizing low cost MEMS sensors are increasingly becoming important due to its advantages in terms of the quickly improved precision, robust, high dynamic response and more significantly inexpensive costs of development and usage. However the large noises inherent in low cost MEMS sensors degrade the derived attitude precision if utilized through the conventional methods, e.g. initial alignment, strapdown inertial navigation mechanization. Therefore the novel application approach suitable for MEMS needs to be investigated. This paper describes an attitude determination system that is based on low cost MEMS inertial sensor, a triad of magnetometers and a commercial GPS receiver. Two main issues are addressed in the paper; firstly determination of the attitude initials, the algorithm is based on a quaternion formulation, a representative of attitude, of Wahbapsilas problem, whereby the error quaternion becomes the estimated state and is corrected by two observations of the earth magnetic field and gravity respectively. After the estimates converge, the derived attitude parameters are employed to initialize the inertial navigation calculations. Due to the large noises in MEMS sensor, there is a demand for external velocity and/or position corrections in the MEMS navigation calculations when system experiences translational motions. Hence secondly, GPS solutions are integrated in a Kalman filter by providing external velocity and position observations. A Kalman dynamic model is designed appropriate for MEMS sensor noise characteristics. The bias and drift are estimated by the integrated Kalman filter, which enables the online calibrations of MEMS sensor. The proposed approach has been developed and its efficiency is demonstrated by various experimental scenarios with real MEMS data and they are compared with Novatel SPAN-IMU reference.

Acquisition of weak GNSS signals using a new block averaging pre-processing

In this paper, we introduce a new approach for the acquisition of weak GNSS signals. For the GPS L1 signal, we utilize the replication property of the C/A code within each data bit to introduce a block averaging pre-processing (BAP) approach for improving receiver robustness against undesired signals. A large number of weighted signal blocks is coherently accumulated and synchronously averaged to obtain a single block with improved signal power. We present several properties of the proposed GNSS signals enhancement technique and we analyze its robustness against noise and different classes of interferers. Thus, we develop a software defined acquisition procedure using the efficient FFT correlation approach. We propose two acquisition algorithms based on the BAP approach. The first scheme implements the parallel code phase search in finding the 2-D spectrum peak using circular cross-correlations. In the second scheme, we exploit the BAP for a fast acquisition performing the frequency estimation prior to the 1-D code-phase search.

Interference mitigation in spread spectrum systems by wavelet coefficients thresholding

This paper studies a potential EMI (Electro Magnetic Interference) rejection technique for the GPS Standard Positioning Service in an avionics environment. Its generalisation to any Direct Sequence Spread Spectrum (DSSS) Systems is also considered. The paper gives a brief overview of Wavelet Theory, which is well established for noise reduction but which is applied here to Continuous Wave Interference (CWI) and narrowband interference. The originality of this work lies in a method for signal rejection, taking into account features in both time and frequency domains to account for the non-stationary characteristics of the interference. Because the software-based receiver is more flexible, less expensive and more accurate compared with typical hardware receivers, a Generic GPS Receiver has been implemented in software [1] to validate the antijamming technique developed in this paper. The aim of the Monte Carlo simulations is to get a good idea of the Performances of the Wavelet Filter against a various types of Interferences and to compare the results with traditional processing.

An Adaptive Unscented Kalman Filtering Algorithm for MEMS/GPS Integrated Navigation Systems

MEMS/GPS integrated navigation system has been widely used for land-vehicle navigation. This system exhibits large errors because of its nonlinear model and uncertain noise statistic characteristics. Based on the principles of the adaptive Kalman filtering (AKF) and unscented Kalman filtering (AUKF) algorithms, an adaptive unscented Kalman filtering (AUKF) algorithm is proposed. By using noise statistic estimator, the uncertain noise characteristics could be online estimated to adaptively compensate the time-varying noise characteristics. Employing the adaptive filtering principle into UKF, the nonlinearity of system can be restrained. Simulations are conducted for MEMS/GPS integrated navigation system. The results show that the performance of estimation is improved by the AUKF approach compared with both conventional AKF and UKF.

A Novel Optimal Configuration form Redundant MEMS Inertial Sensors Based on the Orthogonal Rotation Method

In order to improve the accuracy and reliability of micro-electro mechanical systems (MEMS) navigation systems, an orthogonal rotation method-based nine-gyro redundant MEMS configuration is presented. By analyzing the accuracy and reliability characteristics of an inertial navigation system (INS), criteria for redundant configuration design are introduced. Then the orthogonal rotation configuration is formed through a two-rotation of a set of orthogonal inertial sensors around a space vector. A feasible installation method is given for the real engineering realization of this proposed configuration. The performances of the novel configuration and another six configurations are comprehensively compared and analyzed. Simulation and experimentation are also conducted, and the results show that the orthogonal rotation configuration has the best reliability, accuracy and fault detection and isolation (FDI) performance when the number of gyros is nine.

Modification of an RBF ANN-Based Temperature Compensation Model of Interferometric Fiber Optical Gyroscopes

This paper presents modification of Radial Basis Function Artificial Neural Network (RBF ANN)-based temperature compensation models for Interferometric Fiber Optical Gyroscopes (IFOGs). Based on the mathematical expression of IFOG output, three temperature relevant terms are extracted, which include: (1) temperature of fiber loops; (2) temperature variation of fiber loops; (3) temperature product term of fiber loops. Then, the input-modified RBF ANN-based temperature compensation scheme is established, in which temperature relevant terms are transferred to train the RBF ANN. Experimental temperature tests are conducted and sufficient data are collected and post-processed to form the novel RBF ANN. Finally, we apply the modified RBF ANN based on temperature compensation model in two IFOGs with temperature compensation capabilities. The experimental results show the proposed temperature compensation model could efficiently reduce the influence of environment temperature on the output of IFOG, and exhibit a better temperature compensation performance than conventional scheme without proposed improvements.

Anti-jamming solution to narrowband CDMA interference problem

The main objective of this paper is to describe and simulate an adaptive interference cancelling technique named amplitude domain processing (ADP). The ADP filter will improve the GPS receivers robustness against all types of interference (coherent CW pulsed or continuous, chirp interference, etc). The ADP filter is designed in Matlab (Simulink) to show its performance and how it can be applied as an adaptive interference canceller to estimate and remove GPS jammers in a real time basis.

High speed IIR filter for XILINX FPGA

This paper makes a connection between digital signal representation, all potential twos complement multiplier for FPGA and one of the most original and powerful methods for multiplication: the Booth algorithm. The paper identifies the applications where constant coefficient multipliers cannot be used and states the advantages and drawbacks of all other techniques. At this point, the description of our anti-jamming IIR notch filter in XILINX FPGA becomes easier. This application note describes the functionality and integration of a real time IIR filter using 2 large multipliers at very high sampling rate in XC4020EPG223-2 device (up to 40 M samples/s). It also reveals the solution to an interesting design problem which emerges, and some additional enhancements since other papers, introducing a hybrid technique. Booth algorithm is shown to improve the CLB density and speed of FPGA circuit without any pipeline needed in IIR filtering.

Requirements for Communication Systems in Future Passenger Air Transportation

The Airports Council International (ACI) estimates that the number of global passengers will increase from over 5 billion passengers today to 12 billion by 2031. At the same time, major aircraft (A/C) manufacturers like Boeing and Airbus estimate that the worldwide commercial A/C fleet will increase 5% per year over the next 20 years, i.e. the commercial aviation market will be doubled. This growth will require not only new airports infrastructure but also investments in en-route and Air Traffic Management (ATM) systems. Part of such investments must be aimed to a growth in the capacity of the onboard communication systems. With increasing speed of Internet connections on land, passengers expect not only to be connected to the Internet but also to have good connectivity with high bandwidth to enable them the access and use of multitude applications during the flight. The need to be connected adds to the increased passenger traffic and even the implementation of new aviation standards such as: Controller-Pilot Data Link Communications (CPDLC), Future Air Navigation System (FANS), Automatic Dependent Surveillance-Broadcast (ADS-B), VHF Data Link mode 2/3/4 (VDL2/3/4), etc. Governmental initiatives such as NextGen in U.S.A. and Single European Sky ATM Research (SESAR) in Europe are forcing aviation companies to fulfill these needs to satisfy their customers while complying with regulations in different airspaces. As a result, the aviation industry faces a new paradigm in the communication system requirements, which is the subject of this paper. As a first requirement, the industry must be prepared for seamlessly adoption of future communication systems, standards, or regulation without this implying the continuous installation of new equipment, but rather the modification of the existing one. Today, any modernization of these systems represents a major change in airborne and on-land equipment, which means buying new equipment, installation of new antennas on the A/C, etc. The main repercussions of this lack of flexibility and scalability are that many of the systems currently used have become obsolete, their modernization, when possible, is highly constrained by previous limitations, and new deployments are painfully long. Therefore, the modernization of the onboard communication systems has to be flexible enough to address all these drawbacks. This paper also discusses several Requirements for Communication Systems in Future Passenger Air Transportation (RCSFPAT). Requirements like the bandwidth, which will depend on factors that cannot yet be predicted accurately (amount of increase in air traffic, capabilities of service providers, etc.). The two primary drivers for the RCSFPAT are: 1) to provide an appropriate communication infrastructure to support future air communication systems growth, and 2) to provide a consistent global solution to support the goal of fulfilling the communications requirements from passengers and communications between A/C Earth Stations (AESs) and Ground Earth Stations (GESs) thus to ensure flight safety. In order to provide worldwide coverage of the communication systems, the only current technology able to cover the oceanic regions is Satellite Communications (SatCom). Indeed, most of the airlines and A/C manufactures have signed