Automotive radar target detection using ambiguity function

The risk of collision increases, as the number of cars on the road increases. Automotive radar is an important way to improve road traffic safety and provide driver assistance. Adaptive cruise control, parking aid, pre-crash warning etc. are some of the applications of automotive radar which are already in use in many luxury cars today. In automotive radar a commonly used modulation waveform is the linear frequency modulated continuous waveform (FMCW); the return signal contains the range and velocity information about the target related through the beat frequency equation. Existing techniques retrieve target information by applying a threshold to the Fourier power spectrum of the returned signal, to eliminate weak responses. This method has a risk of missing a target in a multi-target situation if its response falls below the threshold. It is also common to use multiple wide angle radar sensors to cover a wider angle of observation. This results in detecting a large number of targets. The ranges and velocities of targets in automotive applications create ambiguity which is heightened by the large number of responses received from wide angle set of sensors. This thesis reports a novel strategy to resolve the range-velocity ambiguity in the interpretation of FMCW radar returns that is suitable for use in automotive radar. The radar ambiguity function is used in a novel way with the beat frequency equation relating range and velocity to interpret radar responses. This strategy avoids applying a threshold to the amplitude of the Fourier spectrum of the radar return. This novel radar interpretation strategy is assessed by a simulation which demonstrates that targets can be detected and their range and velocity estimated without ambiguity using the combined information from the radar returns and existing radar ambiguity function

Development of a Full-Field Time-of-Flight Range Imaging System

A full-field, time-of-flight, image ranging system or 3D camera has been developed from a proof-of-principle to a working prototype stage, capable of determining the intensity and range for every pixel in a scene. The system can be adapted to the requirements of various applications, producing high precision range measurements with sub-millimetre resolution, or high speed measurements at video frame rates. Parallel data acquisition at each pixel provides high spatial resolution independent of the operating speed. The range imaging system uses a heterodyne technique to indirectly measure time of flight. Laser diodes with highly diverging beams are intensity modulated at radio frequencies and used to illuminate the scene. Reflected light is focused on to an image intensifier used as a high speed optical shutter, which is modulated at a slightly different frequency to that of the laser source. The output from the shutter is a low frequency beat signal, which is sampled by a digital video camera. Optical propagation delay is encoded into the phase of the beat signal, hence from a captured time variant intensity sequence, the beat signal phase can be measured to determine range for every pixel in the scene. A direct digital synthesiser (DDS) is designed and constructed, capable of generating up to three outputs at frequencies beyond 100 MHz with the relative frequency stability in excess of nine orders of magnitude required to control the laser and shutter modulation. Driver circuits were also designed to modulate the image intensifier photocathode at 50 Vpp, and four laser diodes with a combined power output of 320 mW, both over a frequency range of 10-100 MHz. The DDS, laser, and image intensifier response are characterised. A unique method of measuring the image intensifier optical modulation response is developed, requiring the construction of a pico-second pulsed laser source. This characterisation revealed deficiencies in the measured responses, which were mitigated through hardware modifications where possible. The effects of remaining imperfections, such as modulation waveform harmonics and image intensifier irising, can be calibrated and removed from the range measurements during software processing using the characterisation data. Finally, a digital method of generating the high frequency modulation signals using a FPGA to replace the analogue DDS is developed, providing a highly integrated solution, reducing the complexity, and enhancing flexibility. In addition, a novel modulation coding technique is developed to remove the undesirable influence of waveform harmonics from the range measurement without extending the acquisition time. When combined with a proposed modification to the laser illumination source, the digital system can enhance range measurement precision and linearity. From this work, a flexible full-field image ranging system is successfully realised. The system is demonstrated operating in a high precision mode with sub-millimetre depth resolution, and also in a high speed mode operating at video update rates (25 fps), in both cases providing high (512 512) spatial resolution over distances of several metres

Integrated perception, modeling, and control paradigm for bistatic sonar tracking by autonomous underwater vehicles

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 357-364).In this thesis, a fully autonomous and persistent bistatic anti-submarine warfare (ASW) surveillance solution is developed using the autonomous underwater vehicles (AUVs). The passive receivers are carried by these AUVs, and are physically separated from the cooperative active sources. These sources are assumed to be transmitting both the frequency-modulated (FM) and continuous wave (CW) sonar pulse signals. The thesis then focuses on providing novel methods for the AUVs/receivers to enhance the bistatic sonar tracking performance. Firstly, the surveillance procedure, called the Automated Perception, is developed to automatically abstract the sensed acoustical data from the passive receiver to the track report that represents the situation awareness. The procedure is executed sequentially by two algorithms: (i) the Sonar Signal Processing algorithm - built with a new dual-waveform fusion of the FM and CW signals to achieve reliable stream of contacts for improved tracking; and (ii) the Target Tracking algorithm - implemented by exploiting information and environmental adaptations to optimize tracking performance. Next, a vehicular control strategy, called the Perception-Driven Control, is devised to move the AUV in reaction to the track report provided by the Automated Perception. The thesis develops a new non-myopic and adaptive control for the vehicle. This is achieved by exploiting the predictive information and environmental rewards to optimize the future tracking performance. The formulation eventually leads to a new information-theoretic and environmental-based control. The main challenge of the surveillance solution then rests upon formulating a model that allows tracking performance to be enhanced via adaptive processing in the Automated Perception, and adaptive mobility by the Perception-Driven Control. A Unified Model is formulated in this thesis that amalgamates two models: (i) the Information-Theoretic Model - developed to define the manner at which the FM and CW acoustical, the navigational, and the environmental measurement uncertainties are propagated to the bistatic measurement uncertainties in the contacts; and (ii) the Environmental-Acoustic Model - built to predict the signal-to-noise power ratios (SNRs) of the FM and CW contacts. Explicit relationships are derived in this thesis using information theory to amalgamate these two models. Finally, an Integrated System is developed onboard each AUV that brings together all the above technologies to enhance the bistatic sonar tracking performance. The system is formulated as a closed-loop control system. This formulation provides a new Integrated Perception, Modeling, and Control Paradigm for an autonomous bistatic ASW surveillance solution using AUVs. The system is validated using the simulated data, and the real data collected from the Generic Littoral Interoperable Network Technology (GLINT) 2009 and 2010 experiments. The experiments were conducted jointly with the NATO Undersea Research Centre (NURC).by Raymond Hon Kit Lum.Sc.D

Geometric and frequency scalable transistor behavioural model for MMIC design

This thesis presents research in developing and validating scaling in terms of geometry and frequency for Behavioural models in order to extend their functionality. Geometric and frequency scalability, once thought to be limited only to Physical and Compact models, greatly reduces the number of measurements for model generation. Besides saving precious time and effort, measurements do not need to be collected at high frequency or power levels, reducing the cost of purchasing measurement hardware. Scaling in terms of geometry is achieved by combining accurate measurement based non-linear look-up table models of a reference (smaller) transistor with the appropriate passive embedding networks. Experimental results show that the scalable model is successful in predicting the performance of devices up to 5 times larger in gate periphery on two separate Gallium Nitride wafers, one measured at 5 GHz and another at 9 GHz. This approach provides a robust utilization of Behavioural models by providing performance predictions at power levels beyond the limitations of high frequency measurement systems. The geometric scalable Behavioural model was also used in a CAD environment to help create a prototype single cell MMIC amplifier for operation at 5 GHz. Although the targeted performance was not achieved due to mismatch, the non-linear Behavioural model is still able to predict the performance of the actual fabricated circuit. The work in this thesis also introduces the first formulation and approach that enables Behavioural models to be frequency scalable. The experimental results T MINGHAO KOH ABSTRACT IV on HFETs from 2 different Gallium Nitride wafers measured from 2 GHz to 8 GHz (2 octaves), support theoretical analysis that frequency domain Behavioural models defined in the admittance domain have frequency scalable coefficients. Load-pull results show that the model can accurately predict nonlinear behaviour at frequencies that were not used during the model extraction process

Automatic Multilevel Feature Abstraction in Adaptable Machine Vision Systems

Vision is a complex task which can be accomplished with apparent ease by biological systems, but for which the design of artificial systems is difficult. Although machine vision systems can be successfully designed for a specific task, under certain conditions, they are likely to fail if circumstances change. This was the motivation for the research into ways in which systems can be self-designing and adaptable to new visual tasks. The research was conducted in three vital areas of concern for machine vision systems. The first area is finding a suitable architecture for forming an appropriate representation for the current task. The research investigated the application of Hypernetworks theory to building a multilevel, generally-applicable representation, through repeated application of a fundamental 'self-similarity' principle, that parts of objects assembled under a particular relation at one level, form whole objects at the next. Results show that this is potentially a powerful approach for autonomously generating an adaptable system-architecture suitable for multiple visual tasks. The second area is the autonomous extraction of suitable low-level features, which the research investigated through random generation of minimally-constrained pixel-configurations and algorithmic generation of homogeneous and heterogeneous polygons. The results suggest that, despite the simplicity of the features making them vulnerable to image transformations, these are promising approaches worth developing further. The third area is automatic feature selection. The research explored management of 'dimensionality' and of 'combinatorial explosion', as well as how to locate relevant features at multiple representation levels, in the context of 'emergence' of structure. Results indicate that this approach can find useful 'intermediate-level' constructs through analysis of the connectivity of the simplices representing objects at higher levels. The research concludes that the proposed novel approaches to tackling the above issues, in particular the application of hypernetworks to the formation of multilevel representations and the resulting emergence of higher-level structure, is fruitful

A frequency modulated envelope delay FSCW radar for multiple-target applications

A frequency modulated (FM) FSCW radar technique that uses the envelope delay to determine range information is described. The analysis shows that the measured delay produced by the FM FSCW system consists of a term proportional to the delay of the strongest reflection and a superimposed oscillation with a period equal to the difference in the target delays. A practical system able to measure target distance by determining the delay experienced by a tone modulated FM test signal reflected from the two targets is described, A feature of this design is the use of a digital phase detector based upon an IQ correlation algorithm to accurately measure the modulation phase delay and, hence, distance. While the system is being developed to measure the bagasse-water interface at the diffuser in a sugar milling process, the technique is quite general and could be applied to other close-range radar problem