Browsing by Author "Paine, Stephen"

Now showing 1 - 6 of 6
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    Open Access
    3D intrawall imaging using backprojection for synthetic aperture radar (SAR)
    (2024) Dass, Reevelen; Paine, Stephen
    The Council of Scientific and Industrial Research (CSIR) has evolving synthetic aperture radar (SAR) capabilities in the C-band and the L-band. Currently, these capabilities are used to generate aerial landscape images; however, to explore the feasibility of using this technology in different environments, an experimental SAR system has been developed. This is referred to as the wall scanner. The purpose of the wall scanner is to image the interior of a wall, revealing details of the substructures inside the wall such as conduits and piping. This is done by moving the antenna system across the wall surface to create SAR images using backprojection. The radar used two different types of antennas, a log periodic dipole array (LPDA) antenna and horn antenna. The horn antenna performed well in the experiments, producing images with minimal artefacts. On the contrary, the LPDA antenna did not perform as well in the experiments and as such the characteristics of the antenna were investigated. The investigation revealed that the antenna did not function throughout the frequency range specified by its manufacturer. This produced artefacts in the image; however, some of the effects of these artefacts were minimised by a series of preprocessing techniques. A variety of preprocessing techniques were used to improve image quality. In addition to compensating for the properties of the LPDA antenna, windowing and different methods of background subtraction were used. It was difficult to compensate for the antenna issues in preprocessing; however, windowing and background subtraction had a significant effect on the images that were produced. Two postprocessing techniques were used, gradient descent optimisation based on image contrast and polarimetry. The developed gradient descent optimiser was able to automatically adjust for the system group delay based on the contrast of the image. Polarimetry post-processing revealed that the horizontally transmitted horizontally received polarisation (HH) and vertically transmitted vertically received polarisation (VV) were effective in creating images in this environment; however, cross-polarisation in the form of horizontally transmitted vertically received polarisation (HV) was not effective. The wall scanning environment that was measured consisted of scanning both drywall and brick wall. This was split into three experiments. The experiments used different materials that were placed in front of a wall, behind the wall at a distance, and directly behind the wall. The wall scanner was able to successfully create images of the three different experiments for the drywall; however, the desired results for the brick wall were not achieved. For drywall, the substructures placed directly behind the wall were more difficult to see because they were masked by the wall and its sidelobes. The materials scanned were a copper pipe, a PVC pipe, a wooden beam, and a highly reflective calibration target. The calibration target and the copper target performed well in the three experiments. The wooden beam did not perform as well; especially when placed directly behind the wall; however, it was still visible in all experiments. The PVC performed the worst and was only faintly visible in the experiments and was not visible when placed directly behind the wall.
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    Design and Demonstration of a DAB Based RadCom System
    (2023) Norrie, Grant; Paine, Stephen
    The electromagnetic spectrum is becoming increasingly congested due to the growing demand for telecommunications and remote sensing applications. This poses the risk of spectrum bands being reallocated from radar to these applications with organisations such as telecommunication companies willing to pay billions of dollars to use particular bands. Traditionally, this limitation is overcome by the use of passive radar that leverages off of existing communication based transmitters for radar based applications. This passive radar approach to sharing the spectrum is a commensal approach with communications first and radar second. But these increasingly narrow bands allocated for radar and the complications of commensal systems provide the motivation to merge the traditionally separate communication and radar systems into a single radar first radar-communications or ‘RadCom' system. The goal of this system is to use a single hardware platform to transmit a standards based waveform, that can be used for both radar and communication applications simultaneously in a symbiotic nature. The development of the RadCom system was therefore divided into four sub-systems. This includes the development of the signal generation, communications, and radar processing chains while the final sub-system developed was the software-defined-hardware testbed. Development began with the adjustment of the Digital Audio Broadcasting signal. These DAB signals are described by the DAB mode structure, defining their time and frequency domain characteristics. This structure was generalised to describe the RadCom signal and used by the signal generation chain to facilitate the generation of Orthogonal Frequency Division Multiplexed signals. The same generation chain provided the ability to simultaneously encode bitstreams onto OFDM signals. The communication processing chain was developed to demodulate and decode the RadCom signal, thereby extracting the encoded bitstream. The radar processing chain was designed to implement clutter map removal, pulse cancellation and channel alignment procedures to complete range Doppler map processing. Finally, the testbed was developed using two Ettus USRP N210 SDR devices with SBX daughterboards as well as two 2.4 GHz antennas. This ensured that the system was able to simultaneously transmit and receive signals. Each subsystem was individually verified for correct operation prior to the completion of field tests. These verification procedures included bit error rate calculations, FERS simulations and controlled loopback tests. Field tests were conducted once these validation tests were completed. This involved the completion of a communications test, a static range test and moving target tests. Tests contained validation mechanisms such as reference bitstreams, GPS measurements and equivalent FERS simulations. These provided measurements to judge system performance against. Results included a bit error rate of 0 % for a close range direct link communications test, an expected 100 m static range measurement and GPS verified range doppler measurements. These results therefore demonstrated the correct operation of the system and therefore completed the design and demonstration of the RadCom system.
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    Fractional-N PLL-Based Waveform Synthesis for FMCW SAR
    (2024) Gwasira, Thomas; Paine, Stephen
    Achieving high-quality transmitted and local oscillator signals is a core objective in the design and implementation of high-resolution radar imaging systems, as the reconstructed images depict the interaction of the signals with elements in the scene. This dissertation concerns optimisation of the imaging capabilities of a frequency modulated continuous wave (FMCW) synthetic aperture radar (SAR) system, named the miloSAR, by improving the frequency synthesis aspects of the system. This is done by considering the phase-locked loop (PLL) synthesiser employed and waveforms, thereof, in terms of dynamic response characteristics and frequency response characteristics. The dynamic response component entails studying parameters which include the modulation period, modulation bandwidth, sweep rate, pulse repetition frequency (PRF) and slew rate among others and their influence on SAR image quality of the system in question. It was discovered that to better the performance of the system as it relates to these parameters, the radar system and the synthesiser had to be modelled and characterised in order to realise more optimal waveforms such as the sawtooth waveform which previously was not possible owing to limited information on the PLL's dynamics. Furthermore, the signal acquisition system was redesigned to increase the data rate of the system from 11 MB/s to 43.231 MB/s, thus, allowing support for higher PRFs and sample rates. Frequency response characteristics involve stability of both the synthesiser and the generated waveforms. The main issues related to this were identified to be ramp non-linearity, spurs and phase noise. Phase noise was the primary concern for this work since sufficient ramp linearity was achieved by the synthesiser and spurs have been addressed in another author's work on the miloSAR. Two independent synthesisers were, in fact, used to realise the heterodyne architecture required for the miloSAR and they were observed to exhibit significant phase instability. Due to the range correlation filtering effect achieved by using the same clock as the reference inputs of the PLLs and the ADC clock, phase noise caused by strong targets was considered to be less of a concern. However, the phase noise skirt of antenna leakage was identified as a major cause of performance degradation since the leakage is high in power and its phase noise skirt, in regions where range correlation filtering does not occur, swamps weaker radar returns. This becomes an even bigger problem when the PLL bandwidth is increased to improve the PLL's dynamics. The insights from both perspectives of the waveform synthesis problem were combined to give an instructive conclusion on how waveform synthesis must be carried out for the miloSAR and recommendations for a more performant system were proposed.
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    Generalized Passive Radar Processing Chain For Use With Different Signals of Opportunity
    (2024) Benz, Heinrich; Paine, Stephen
    A Passive Radar (PR) is a multi-static RAdio Detection and Ranging (radar) that makes use of signals transmitted by Illuminators of Opportunity (IoO)'s to detect targets in a scene. An IoO is any preexisting transmitter that is used as the illuminator for the PR such as Frequency Modulation (FM) radio. The exact performance of a PR depends on both the physical geometry of the transmitter and receiver combination as well as the signal properties of the IoO. By using multiple different IoO's concurrently, transmitter diversity can be increased, improving overall system performance and reliability as well as improving resilience against jamming. Typically this would require separate processing pipelines specific to each signal type. This is cumbersome, requiring separate maintenance, deployment and streamlining for each one. In this project a generalised PR processing pipeline capable of efficiently processing any signal to create an appropriate range-Doppler output is proposed and demonstrated. A typical PR processing pipeline consists of primarily four stages; pre-processing, DSI-cancellation, range-Doppler map generation and finally detection and tracking. The pre-processing stage is signal dependant and therefore cannot be generalized. DSI-cancellation is the most resource intensive of the stages and along with range-Doppler map generation, detection and tracking can be generalised. Digital signals such as Orthogonal Frequency Division and Multiplexing (OFDM) signals have high bandwidths and are required to be processed in the Frequency-Domain (FD). Therefore, an appropriate FD Direct Signal Interference (DSI) cancellation algorithm that works for both analogue and digital signals was necessary for the generalised processing pipeline. For this, an investigation into the use of Extensive Cancellation Algorithm by Carrier/Doppler (ECA-CD), a FD approach, applied to FM signals for generalisation was carried out. By generating Amplitude Range-Doppler (ARD) maps and comparing the results to ARD maps generated when using Conjugate Gradient Least Square (CGLS), a Time Domain (TD) approach, for cancellation, it was found that ECA-CD is an effective and efficient cancellation algorithm for FM signals. It was, therefore, selected as the DSI-cancellation algorithm for the processing chain. To demonstrate the feasability of the suggested chain, three signals were used; FM, DVB-T2 and Long Term Evolution (LTE) as these represent some of the most commonly used IoO's. The results demonstrate that an efficient generalised processing chain can be realised using an FD approach with ECA-CD for DSI-cancellation and Batches for ARD processing.
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    Micro-doppler classification of humans and animals using FMCW radar
    (2025) Manga, Amisha; Paine, Stephen; Taylor, John-Philip
    This research attempts to address the issue of animal poaching by exploring human and animal target classification by making use of micro-Doppler data generated by a Frequency-Modulated Continuous Wave (FMCW) radar. Raw Analogue to Digital Converter (ADC) data was collected of human and animal species including dogs, horses and cows. Signal processing techniques such as creating range-Doppler and Constant False Alarm Rate (CFAR) maps for detection and using Short-Time Fourier Transform (STFT) for spectrogram generation were applied. Principal Component Analysis (PCA) was employed as the method for data reduction. The dataset was subsequently classified and evaluated across various target class configurations, comparing both the full dataset and its PCA-reduced versions, using Convolutional Neural Networks (CNN), k-Nearest Neighbors (kNN), Random Forest (RF) and Support Vector Machine (SVM) models. Following this, a two-stage classification process was implemented to further refine the analysis. In the first stage, the 4 above-mentioned classifiers were used to distinguish between humans and animals. In the second stage, these classifiers differentiated among the specific animal species. The study experimented with all 16 permutations of classifier combinations, such as SVM-CNN and kNN-RF. Notably, the SVM-SVM combination achieved the highest accuracy at 97.66%, closely matching the 97.5% accuracy outcome obtained in the multi-class classification of humans versus dogs, horses and cows. The PCA-reduced set yielded results closely comparable to those from the full dataset evaluation, confirming its effectiveness. This study highlights the challenges of data collection in natural settings and the need for publicly accessible micro-Doppler data of animal targets to further this research area. Recommendations for future work include developing tracking algorithms tailored to various animal movement patterns. The findings indicate that low-cost radar surveillance systems with micro-Doppler classification technology hold promising application in animal conservation-oriented efforts.
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    Platform and Pipeline Development for a FMCW Radar System for Vital Sign Detection
    (2025) Bowden, Nicholas; Paine, Stephen; Patel Amir
    Frequency Modulated Continuous Wave (FMCW) Radar has become a frequently examined technology for the purposes of ubiquitous vital sign monitoring applications. Vital sign monitoring of heart rate and respiration rate is important because it gives key physiological insights into the health of individual people. Having vital sign technology that allows for constant and ubiquitous monitoring would be of great benefit to people and physicians around the world. Most vital sign research outputs focus on singular parts of the vital sign monitoring problem, often heavily relying on machine learning and enormous datasets of pre-processed data to detect vital signs and compensate for artefacts introduced by breathing and other motion. This dissertation details the design of a system from the ground up to collect raw and unprocessed data and then goes further to explain the design a processing pipeline to validate the data from the system. This provided maximum versatility and flexibility for future research outputs. To validate the system and pipeline for vital sign detection, several sets of experiments were done with increasing complexity to identify points of failure within the pipeline. Complexity was added by adding layers of motion. First, the participant was in seated position and recordings were taken while the participant held his breath. Second, again in a seated position, recordings were taken while the participant was asked to inhale and exhale to visual cues. For these sets of experiments the pipeline performed well with accuracy ranging from 80% to over 90%. For the third set of experiments, the participant was asked to walk backwards and forwards during the recording session. Even after compensating for the movement, the accuracy of the system dropped significantly to below 60%. Compensation for large scale motion was achieved using a simple test rig by subtracting the known motion from the signal. However, the human walking motion was too complex to remove with just a simple subtraction. This complexity comes from the fact that walking requires multiple moving parts and these are all measured by the radar whereas with the rig, there is only one part that is moving. After exhausting traditional filtering and other standard Digital Signal Processing (DSP) techniques, this dissertation concludes that future work should probably adopt a Machine Learning (ML) approach to compensate for complex motions such as walking.