11 research outputs found
Development and performance evaluation of a multistatic radar system
Multistatic radar systems are of emerging interest as they can exploit spatial diversity, enabling improved
performance and new applications. Their development is being fuelled by advances in enabling technologies
in such fields as communications and Digital Signal Processing (DSP). Such systems differ from
typical modern active radar systems through consisting of multiple spatially diverse transmitter and receiver
sites. Due to this spatial diversity, these systems present challenges in managing their operation as
well as in usefully combining the multiple sources of information to give an output to the radar operator.
In this work, a novel digital Commercial Off-The-Shelf (COTS) based coherent multistatic radar
system designed at University College London, named âNetRadâ, has been developed to produce some
of the first published experimental results, investigating the challenges of operating such a system, and
determining what level of performance might be achievable. Full detail of the various stages involved
in the combination of data from the component transmitter-receiver pairs within a multistatic system is
investigated, and many of the practical issues inherent are discussed.
Simulation and subsequent experimental verification of several centralised and decentralised detection
algorithms in terms of localisation (resolution and parameter estimation) of targets was undertaken.
The computational cost of the DSP involved in multistatic data fusion is also considered. This gave a
clear demonstration of several of the benefits of multistatic radar. Resolution of multiple targets that
would have been unresolvable in a conventional monostatic system was shown. Targets were also shown
to be plotted as two-dimensional vector position and velocities from use of time delay and Doppler shift
information only. A range of targets were used including some such as walking people which were
particularly challenging due to the variability of Radar Cross Section (RCS).
Performance improvements were found to be dependant on the type of multistatic radar, method of
data fusion and target characteristics in question. It is likely that future work will look to further explore
the optimisation of multistatic radar for the various measures of performance identified and discussed in
this work
Radar-Based Multi-Target Classification Using Deep Learning
Real-time, radar-based human activity and target recognition has several applications in various fields. Examples include hand gesture recognition, border and home surveillance, pedestrian recognition for automotive safety and fall detection for assisted living. This dissertation sought to improve the speed and accuracy of a previously developed model classifying human activity and targets using radar data for outdoor surveillance purposes. An improvement in accuracy and speed of classification helps surveillance systems to provide reliable results on time. For example, the results can be used to intercept trespassers, poachers or smugglers. To achieve these objectives, radar data was collected using a C-band pulse-Doppler radar and converted to spectrograms using the Short-time Fourier transform (STFT) algorithm. Spectrograms of the following classes were utilised in classification: one human walking, two humans walking, one human running, moving vehicles, a swinging sphere and clutter/noise. A seven-layer residual network was proposed, which utilised batch normalisation (BN), global average pooling (GAP), and residual connections to achieve a classification accuracy of 92.90% and 87.72% on the validation and test data, respectively. Compared to the previously proposed model, this represented a 10% improvement in accuracy on the validation data and a 3% improvement on the test data. Applying model quantisation provided up to 3.8 times speedup in inference, with a less than 0.4% accuracy drop on both the validation and test data. The quantised model could support a range of up to 89.91 kilometres in real-time, allowing it to be used in radars that operate within this range
Robust distributed resource allocation for cellular vehicle-to-vehicle communication
Mit Release 14 des LTE Standards unterstĂŒtzt dieser die direkte Fahrzeug-zu-Fahrzeug-Kommunikation ĂŒber den Sidelink. Diese Dissertation beschĂ€ftigt sich mit dem Scheduling Modus 4, einem verteilten MAC-Protokoll ohne Involvierung der Basisstation, das auf periodischer Wiederverwendung von Funkressourcen aufbaut. Der Stand der Technik und eine eigene Analyse des Protokolls decken verschiedene Probleme auf. So wiederholen sich Kollisionen von Paketen, wodurch manche Fahrzeuge fĂŒr lĂ€ngere Zeit keine sicherheitskritischen Informationen verbreiten können. Kollisionen entstehen vermehrt auch dadurch, dass Hidden-Terminal-Probleme in Kauf genommen werden oder verĂ€nderliche PaketgröĂen und -raten schlecht unterstĂŒtzt werden. Deshalb wird ein Ansatz namens "Scheduling based on Acknowledgement Feedback Exchange" vorgeschlagen. ZunĂ€chst wird eine Funkreservierung in mehrere ineinander verschachtelte Unter-Reservierungen mit verschiedenen Funkressourcen unterteilt, was die Robustheit gegenĂŒber wiederholenden Kollisionen erhöht. Dies ist die Grundlage fĂŒr eine verteilte Staukontrolle, die die PeriodizitĂ€tseigenschaft nicht verletzt. AuĂerdem können so verĂ€nderliche PaketgröĂen oder -raten besser abgebildet werden. Durch die periodische Wiederverwendung können Acknowledgements fĂŒr Funkressourcen statt fĂŒr Pakete ausgesendet werden. Diese können in einer Bitmap in den Padding-Bits ĂŒbertragen werden. Mittels der Einbeziehung dieser Informationen bei der Auswahl von Funkressourcen können Hidden-Terminal-Probleme effizient vermieden werden, da die Acknowledgements auch eine Verwendung dieser Funkressource ankĂŒndigen. Kollisionen können nun entdeckt und eine Wiederholung vermieden werden. Die Evaluierung des neuen MAC-Protokolls wurde zum groĂen Teil mittels diskreter-Event-Simulationen durchgefĂŒhrt, wobei die Bewegung jedes einzelnen Fahrzeuges simuliert wurde. Der vorgeschlagene Ansatz fĂŒhrt zu einer deutlich erhöhten Paketzustellrate. Die Verwendung einer anwendungsbezogenen Awareness-Metrik zeigt, dass die ZuverlĂ€ssigkeit der Kommunikation durch den Ansatz deutlich verbessert werden kann. Somit zeigt sich der prĂ€sentierte Ansatz als vielversprechende Lösung fĂŒr die erheblichen Probleme, die der LTE Modus 4 mit sich bringt.The LTE Standard added support for a direct vehicle-to-vehicle communication via the Sidelink with Release 14. This dissertation focuses on the scheduling Mode 4, a distributed MAC protocol without involvement of the base station, which requires the periodic reuse of radio resources. The state of the art and a own analysis of this protocol unveil multiple problems. For example, packet collisions repeat in time, so that some vehicles are unable to distribute safety-critical information for extended periods of time. Collisions also arise due to the hidden-terminal problem, which is simply put up with in Mode 4. Additionally, varying packet sizes or rates can hardly be supported. Consequently, an approach called "Scheduling based on Acknowledgement Feedback Exchange" is proposed. Firstly, a reservation of radio resources is split into multiple, interleaved sub-reservations that use different radio resources. This increases the robustness against repeating collisions. It is also the basis for a distributed congestion control that does not violate the periodicity. Moreover, different packet rates or sizes can be supported. The periodic reuse of radio resources enables the transmission of acknowledgements for radio resources instead of packets. These can be transmitted in a bitmap inside the padding bits. Hidden-terminal problems can be mitigated by considering the acknowledgements when selecting radio resources as they announce the use of these radio resources. Collisions can also be detected and prevented from re-occurring. The evaluation of the MAC protocol is mostly performed using discrete-event simulations, which model the movement of every single vehicle. The presented approach leads to a clear improvement of the packet delivery rate. The use of an application-oriented metric shows that the communication robustness can be improved distinctly. The proposed approach hence presents itself as a promising solution for the considerable problems of LTE Mode 4
Measurement and modelling of bistatic sea clutter
There is a growing interest in bistatic radars; however, such systems cannot reach their full potential
unless the designer has a proper understanding of the environment in which they operate. Rather little
information has been published on bistatic clutter and out-of-plane bistatic sea clutter in particular. This
is due to a number of factors including the inherent complexity of conducting bistatic radar trials and the
resulting lack of high quality bistatic data.
In this thesis the collection and analysis of a unique set of bistatic sea clutter data is described.
To achieve this objective a novel multistatic radar system was developed. The nodes do not need to be
physically connected. This system has a peak transmitted power of more than 500 W. Synchronisation in
time and frequency was achieved using GPS disciplined oscillators built and designed at the University
of Cape Town.
Using the above system simultaneous bistatic and monostatic sea clutter and target signatures were
recorded in the UK and South Africa at various geometries and weather conditions. Parts of this unique
data set related to out-of-plane bistatic sea clutter was analysed in this thesis. The data covered both
co- and cross-polarised sea clutter data at low grazing angles with bistatic angles between 30° and 120°.
Data sets covering a range of conditions with sea states from 2 â 5.
Using the recorded data it was shown that the ratio of the bistatic normalised radar cross section
to the monostatic normalised radar cross section dropped as the scattering angle was increased until
the scattering angle was around 90°. Furthermore, the cross-polarised bistatic normalised radar cross
section was found to be larger than the cross-polarised monostatic normalised radar cross section when
the scattering angle was around 90°.
A new empirical model for predicting bistatic normalised radar cross section has been developed.
The model is applicable to both in-plane and out-of-plane geometries. The model was able to provide a
good fit to both UCL and external data.
The temporal correlation properties of both monostatic and bistatic data were studied. It was found
that the speckle component of both bistatic and monostatic clutter decorrelated in tens of milliseconds,
with the decorrelation time longer for bistatic clutter. The texture of both bistatic and monostatic clutter
had similar autocorrelation functions and had similar decorrelation times. By comparing the texture and intensity autocorrelation functions it was concluded that the compound model still holds.
It was also found that bistatic clutter was less âspikyâ than monostatic clutter particularly at horizontal
polarisation. This was due to the reduction in the intensity of the spikes due to specular reflections.
By combing the effects of the reduction in reflectivity and spikiness it was shown that a bistatic radar
would require a smaller signal to interference ratio than a monostatic radar for the same probability of
detection and probability of false alarm. This was more evident at angles close to 90° and for horizontal
polarisation.
In summary this thesis reports the collection and analysis of novel simultaneous monostatic and
bistatic sea clutter and target data. This was achieved by the development of a unique multistatic radar
system. This work has resulted in significant advances in both netted radar technology and understanding
of bistatic sea clutter
The application of digital techniques to an automatic radar track extraction system
'Modern' radar systems have come in for much criticism in recent years, particularly in the aftermath of the Falklands campaign. There have also been notable failures in commercial designs, including the well-publicised 'Nimrod' project which was abandoned due to persistent inability to meet signal processing requirements. There is clearly a need for improvement in radar signal processing techniques as many designs rely on technology dating from the late 1970's, much of which is obsolete by todayâs standards. The Durham Radar Automatic Track Extraction System (RATES) is a practical implementation of current microprocessor technology, applied to plot extraction of surveillance radar data. In addition to suggestions for the design of such a system, results are quoted for the predicted performance when compared with a similar product using 1970's design methodology. Suggestions are given for the use of other VLSI techniques in plot extraction, including logic arrays and digital signal processors. In conclusion, there is an illustrated discussion concerning the use of systolic arrays in RATES and a prediction that this will represent the optimum architecture for future high-speed radar signal processors
Cooperative Radio Communications for Green Smart Environments
The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: âą Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environmentsâą Measurements, characterization, and modelling of radio channels beyond 4G networksâą Key issues in Vehicle (V2X) communicationâą Wireless Body Area Networks, including specific Radio Channel Models for WBANsâą Energy efficiency and resource management enhancements in Radio Access Networksâą Definitions and models for the virtualised and cloud RAN architecturesâą Advances on feasible indoor localization and tracking techniquesâą Recent findings and innovations in antenna systems for communicationsâą Physical Layer Network Coding for next generation wireless systemsâą Methods and techniques for MIMO Over the Air (OTA) testin
Cooperative Radio Communications for Green Smart Environments
The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: âą Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environmentsâą Measurements, characterization, and modelling of radio channels beyond 4G networksâą Key issues in Vehicle (V2X) communicationâą Wireless Body Area Networks, including specific Radio Channel Models for WBANsâą Energy efficiency and resource management enhancements in Radio Access Networksâą Definitions and models for the virtualised and cloud RAN architecturesâą Advances on feasible indoor localization and tracking techniquesâą Recent findings and innovations in antenna systems for communicationsâą Physical Layer Network Coding for next generation wireless systemsâą Methods and techniques for MIMO Over the Air (OTA) testin
Combined optimisation of waveform and quantisation thresholds for multistatic radar systems
The problem of designing waveform and quantisation thresholds is studied in a multistatic radar setting, where distributed receivers are connected to a fusion centre via capacity constraints. Different from the previous cloud radio-multistatic radar system which utilises an additive quantisation Gaussian noise model, a real quantisation system is designed. The authors first optimise the waveform without quantisation. Then they compress the received signal at receivers into a scalar without any performance degradation. Furthermore, the scalar quantiser is adopted and quantisation thresholds are designed. Numerical simulations are performed and the effectiveness of combined waveform and thresholds optimisation strategy is demonstrated
Combined optimisation of waveform and quantisation thresholds for multistatic radar systems
The problem of designing waveform and quantisation thresholds is studied in a multistatic radar setting, where distributed receivers are connected to a fusion centre via capacity constraints. Different from the previous cloud radio-multistatic radar system which utilises an additive quantisation Gaussian noise model, a real quantisation system is designed. The authors first optimise the waveform without quantisation. Then they compress the received signal at receivers into a scalar without any performance degradation. Furthermore, the scalar quantiser is adopted and quantisation thresholds are designed. Numerical simulations are performed and the effectiveness of combined waveform and thresholds optimisation strategy is demonstrated.</p