David J. Allerton

A review of multisensor fusion methodologies for aircraft navigation systems

This paper reviews currently existing fault-tolerant navigation system architectures and data fusion methods used in the design and development of integrated aircraft navigation systems and also compares their advantages and disadvantages. Four fault-tolerant navigation system architectures are reviewed and the associated Kalman filter architectures and algorithms are discussed. These techniques have been used in most integrated aircraft navigation systems. The aim of this review paper is to provide a guide for navigation system designers to develop future aircraft multisensor navigation systems.

From Model Specification to Simulation of Biologically Constrained Networks of Spiking Neurons

A declarative extensible markup language (SpineML) for describing the dynamics, network and experiments of large-scale spiking neural network simulations is described which builds upon the NineML standard. It utilises a level of abstraction which targets point neuron representation but addresses the limitations of existing tools by allowing arbitrary dynamics to be expressed. The use of XML promotes model sharing, is human readable and allows collaborative working. The syntax uses a high-level self explanatory format which allows straight forward code generation or translation of a model description to a native simulator format. This paper demonstrates the use of code generation in order to translate, simulate and reproduce the results of a benchmark model across a range of simulators. The flexibility of the SpineML syntax is highlighted by reproducing a pre-existing, biologically constrained model of a neural microcircuit (the striatum). The SpineML code is open source and is available at http://bimpa.group.shef.ac.uk/SpineML.

Flight simulation : past, present and future

This paper outlines the development of flight simulators used in civil training, military training and in engineering simulation. It describes the evolution of flight simulators and the typical architecture of a modern flight simulator. The technical innovations, which have occurred in modelling, motion systems and visual systems are reviewed. The paper also reviews the transfer of training in flight simulation, the application of simulation to engineering design and outlines problems which are encountered in flight simulation. The paper concludes by reviewing the current trends in flight simulation.

Wake Vortex Model for Real-Time Flight Simulation Based on Large Eddy Simulation

with asix-degree-of-freedom real-time flight simulator. The papercombines the use of largeeddy simulation dataas the basis of a wake vortex encounter model with methods to access the dataset in real time. The second half of this paper describes the data compression scheme implemented to reduce the size of the time-varying dataset. Additionally, rapid data access and issues regarding the real-time data management aspects are discussed. Analysis of the performance of the model is made and preliminary comparisons with a traditional analytical wake vortex model are discussed.

A graph-based silicon compiler for concurrent VLSI systems

A silicon compiler able to synthesize concurrent VLSI systems is described. This compiler differs from most existing silicon compilers as there is no target architecture, and yet results have shown that it performs reasonably well for a range of applications. It features a novel technique for control-step partitioning based on a precedence graph. Concurrency is detected and extracted from the input description in order to generate a fast implementation. The graph, which corresponds to a state diagram of the circuit, is further optimized using a simple rule-based approach. A controller able to control any number of concurrent processes, based on a synchronous token-passing mechanism, is generated. Control signals are submitted to two-level and multilevel logic minimization, and they can be implemented either as a programmable logic arrays (PLA) or with standard cells. The data path is generated as a netlist of technology-independent parameterized cells which are mapped into cells from a library by a module binder. The final layout is automatically generated by placement-and-routing programs.<<ETX>>

Redundant multi-mode filter for a navigation system

An approach is introduced to the design of a multi-mode navigation filter to combine a low-cost skewed redundant inertial measurement unit (SRTMU) with a multifunctional GPS (MF-GPS) receiver in order to implement a fault-tolerant aircraft navigation system, which can achieve the required navigation performance of conventional systems in terms of accuracy, integrity, continuity, and availability. The MF-GPS receiver provides raw GPS measurements for pseudo-range and range rate to compute the navigation solutions (position and velocity) and also multi-antenna carrier phase interferometric measurements to estimate the aircraft attitude solution, if the carrier phase data is reliable. A multi-mode navigation filter is designed which combines state and measurement fusion methods and processes the SRIMU and raw MF-GPS outputs to provide reliable position, velocity and attitude information, and also kinematic parameters required in control, guidance, and navigation applications. The feasibility and performance of this integrated design is assessed and evaluated by using simulation. The accuracy of inertial gyros used in the evaluation ranges from ldeg/h to 30deg/h, including low-cost inertial sensor technologies. The simulation studies presented here show that a multi-mode navigation filter can achieve sufficient reliability and accuracy and that SRIMU/MF-GPS integrated navigation systems may provide a cost-effective system for future regional aircraft, general aviation aircraft, and unmanned aerial vehicles

Sensor fusion methods for synthetic vision systems

A millimetric radar imaging sensor can project a forward-looking view in a head-up display (HUD) to provide enhanced vision in the final stages of an approach, particularly in conditions of very low visibility. Although this increases situational awareness for the flight crew, the image quality is poor and there is no direct measure of system integrity. This paper describes a synthetic vision system using real-time image feature extraction to detect the runway in the image. This information is combined with knowledge of the aircraft position and attitude to provide flight guidance cues and to monitor the aircraft flight path. In the initial phase of the approach, GPS measurements are used to align the inertial reference system. During the final stages of an approach, inertial reference measurements are combined with imaging data to locate the vertices of the runway. Sensor fusion methods are used to provide flight guidance cues in the HUD and to determine system integrity measurements of the imaging system. A synthetic vision system overlays the computed runway position on the cluttered radar image and displays essential flight data. The paper outlines a radar model of the sensor, which runs on a PC-based visual system. This model has been used to provide a realistic real-time radar image during development of the tracking algorithms. The inertial reference system and the tracking system are also modeled and combined in an extended Kalman filter to provide flight guidance and to give timely warning of system failures to the flight crew. The paper describes the sensor fusion method developed for failure detection and provides examples of low visibility approaches flown in a flight simulator, to demonstrate the effectiveness of these techniques.

The design of a real-time engineering flight simulator for the rapid prototyping of avionics systems and flight control systems

This paper describes the design of a real-time flight simulator, which is based on a modular architecture of PCs coupled by Ethernet. The simulator is required to provide a rapid prototyping environment to support the design and evaluation of avionics systems and flight control systems. Methods are described to ensure real-time implementation of the equations of motions using a standard PC and the provision of real-time graphics to simulate aircraft displays using SVGA. The paper includes analysis of the performance of the flight modelling methods and the simulation of aircraft displays. The paper concludes that high fidelity flight models and aircraft displays can be implemented using standard PC platforms and Ethernet cards, if attention is given to the design of the simulator architecture. The resultant simulator provides a rapid prototyping environment, standardising on the packet format and low-level packet protocols of Ethernet,

The architecture of RIG: A RISC for image generation in a multi-microprocessor environment

Abstract RIG is a fast Reduced Instruction Set Processor suitable for Real-Time Image Generation (RTIG) Geometric Computations. It is designed to be used in a parallel processing architecture, so that high polygon throughput can be achieved. RIG is a 16 MIPS processor that can execute the geometric computations required in RTIG at least ten times faster than a MC68000-12Mhz microprocessor due to the following innovations and characteristics: • • A novel “Data Ready” technique, in which data is available without waiting for external memory. Data is transferred in burst mode (via DMA) directly into processor internal registers in parallel with processing. • • “Indices” to the General-Purpose Registers instead of “Register Windows” schemes, as a fast and efficient parameter passing mechanism in procedure calls. • • Fast multiplication and division instructions together with a three-staged pipeline architecture with “data forwarding”. • • Extremely fast interaction with a parallel processing system with minimum overhead.

Real-time modeling of a radar sensor for enhanced vision

Millimetric radar imaging systems have been used to improve situational awareness for flight crew in low visibility approaches. The image from the sensor is projected in a Head-Up Display (HUD) and, for aircraft without Cat-III auto-land facilities, can provide sufficient cues to continue a manual approach past the normal decision height. However, these images may be cluttered, features are often difficult to detect and there is no direct indication of system integrity. Guidance cues can be displayed in the HUD by tracking runway features in the radar image and the use of sensor fusion methods to detect variation in the size and shape of the runway can provide integrity monitoring, for timely warning of system malfunction. In order to develop real-time tracking algorithms, it is necessary to generate synthetic radar images, which exhibit the properties of actual millimetric radar sensors. This paper outlines the model of a radar sensor used to generate real-time radar images incorporating appropriate attenuation and clutter properties. These images are derived from standard 3D visual databases and have been integrated in a flight simulator using a commercial image generation system. The radar model incorporates the effects of material properties of objects, the sensor range and grazing angles and includes atmospheric attenuation. Examples of the radar images are presented in the paper together with a summary of the real-time performance of the radar model to simulate millimeter wave radar images using a proprietary workstation.