2003 IEEE International Conference on Acoustics, Speech, and Signal Processing, 2003. Proceedings. (ICASSP '03).
A coarray-based synthetic aperture beamformer using stepped-frequency signal synthesis and post-d... more A coarray-based synthetic aperture beamformer using stepped-frequency signal synthesis and post-data acquisition processing is presented for wideband imaging of near-field scenes. The proposed beamformer formulation and implementation finds key applications in through-the-wall microwave imaging and landmine detection problems. While coarray techniques offer significant reduction in array elements for a given angular resolution, stepped-frequency realization of wideband systems simplifies implementation and offers flexibility in beamforming. Proof of concept is provided using real data collected in an anechoic chamber. Comments Comments
2017 XXXIInd General Assembly and Scientific Symposium of the International Union of Radio Science (URSI GASS), 2017
Models of radar systems are required for a variety of reasons. The sophistication of these models... more Models of radar systems are required for a variety of reasons. The sophistication of these models is highly dependant on their purpose; for instance microwave radar models which are designed to be integrated into existing wargaming simulation frameworks will often be low-fidelity models. The development of similar models of over-the-horizon radar is particulary challenging. This is due to the highly variable propagation environment in which such systems are required to operate: even the lowest fidelity model of an OTH radar must model the environmental conditions appropriately. The “base level” environmental modelling required to accurately characterise OTH radar performance is the climatology, i.e. diurnal, seasonal and solar cycle variations. In this paper we detail a climatological model of OTH radar (CMOR) developed using high frequency (HF) radio wave raytracing techniques. We discuss how this model may be integrated into low-fidelity wargaming simulations, used to provide init...
Transmission of spatially diverse orthogonal waveforms in radar to support enhanced illumination ... more Transmission of spatially diverse orthogonal waveforms in radar to support enhanced illumination control and surveillance timeline management has been recently discussed in the radar literature. Such use of orthogonal waveforms in radar (sometimes referred to as MIMO radar) is potentially attractive in modern HF over-the-horizon (skywave) radar systems. However, HF radar implementation of orthogonal waveforms present some special challenges to waveform design. HF radars operate over several octaves of RF frequency, have array inter-element spacing which deviates significantly from one half-wavelength, use nonlinear power amplifiers, and have stringent spectral occupancy requirements. Implementation of specific orthogonal waveform types present their own particular design requirements, but some issues are generic and span a wide range of waveform classes. In particular, operation with over-sampled arrays can give rise to excessive reactive power. This can be mitigated by the use of a...
[1991] Conference Record of the Twenty-Fifth Asilomar Conference on Signals, Systems & Computers
Abstract The authors demonstrate the application of the Wigner-Ville time-frequency distribution,... more Abstract The authors demonstrate the application of the Wigner-Ville time-frequency distribution, the bispectrum, the time-varying bispectrum, and Gerr's third-order Wigner distribution to some underwater acoustic data. They also demonstrate the merit of including higher-order spectral information when signaturing underwater acoustic sources. It is pointed out that conventional signal analysis procedures do not utilize all the information available in many practical signal analysis problems. It is shown that the use of higher- ...
A challenging task in over-the-horizon radar (OTHR) is the tracking of target altitude. It has be... more A challenging task in over-the-horizon radar (OTHR) is the tracking of target altitude. It has been shown that the micro-multipaths due to ocean/ground reflections may reveal important information about the elevation maneuvering of a target. The Doppler signature of such micro-multipath signals is typically composed of three components having close nonlinear time-frequency behaviors. In this paper, we develop novel timefrequency analysis techniques for the characterization of Doppler effect of micro-multipath signals. The proposed method is based on the local analysis of the signal phase, followed by a stationarization operator. In the warped representation domain, the multi-component nonlinear Doppler signatures become stationary, thus allowing the application of spectral analysis tools. The results presented are based on real data and illustrate the potential of the proposed methods.
We present a numerical modelling approach for determining the HF radar cross-section of a volume ... more We present a numerical modelling approach for determining the HF radar cross-section of a volume displacement in the ocean surface. This displacement, for example, might be from a non-conductive wooden-hulled boat with no metal structure or fittings. Such a vessel typically has too small a radar cross-section to be detected considering only the scattering properties of the boat in isolation. Our modelling technique is approximate but indicates wooden, or other non-conductive material boats may be detectable by skywave radar in some instances, solely due to their displacement in the ocean. Our results suggest new radar management strategies to improve the likelihood of detecting these targets. However, we continue to require the preferred ship detection criteria of low sea-state and low doppler-spread ionospheric propagation conditions. We also assume the boat is moving at speed and heading combinations such that the target Doppler is separated from the ocean first-order Bragg scatter.
half a dozen countries, along with several expressions of regret from people who wished to contri... more half a dozen countries, along with several expressions of regret from people who wished to contribute but were prevented from doing so by government or corporate constraints. If most of the papers were to survive peer-review, then we would be on course for a double issue. After the rigorous two-stage peer-review process, we ended up with thirteen accepted papers. We, as Guest Editors, have decided to arrange the resulting twopart Special Issue such that the first part contains the seven papers dealing primarily with HF skywave radar. The second part contains six papers, with the focus on HF surface wave radar and on hybrid systems. To reflect this organization, we have opted to call the first part Special Issue on HF Skywave Radar and the second part Special Issue on HF Radar, for ease of reference, but of course there is an extensive commonality of technology and scientific principles. While we cannot claim to have achieved a truly comprehensive account of the global state of HF radar, this Special Issue contains papers from Australia, Canada, China, Germany, Singapore and the United States, with technical exposition and scientific results from some of the world's most advanced HF radar systems, written by the key researchers involved. The papers in this first collection address a diverse range of issues that confront designers and users of HF radars. The opening article, by Anderson, is a cri de coeur for greater recognition of the need to employ physical models whose fidelity is commensurate with the dynamic range of modern HF radars. His argument is illustrated with examples from both skywave and surface wave radar systems. Next, Francis, Cervera and Frazer describe a methodology for designing a network of HF skywave radars, where the radar siting and system parameters must be optimized for the mission objectives, taking account of the propagation and noise environments. Not only must HF radars manage to achieve their objectives in a challenging interference environment, they must also be responsible citizens of the HF band. McKerracher,
Models of radar systems are required for a variety of reasons. The sophistication of these models... more Models of radar systems are required for a variety of reasons. The sophistication of these models is highly dependent on their purpose; for instance, microwave radar models, which are designed to be integrated into existing wargaming simulation frameworks, will often be low-fidelity models. The development of similar models of over-the-horizon (OTH) radar is particularly challenging. This is due to the highly variable propagation environment in which such systems are required to operate: even the lowest fidelity model of an OTH radar must model the environmental conditions appropriately. The base level environmental modeling required to accurately characterize OTH radar performance is the climatology, that is, diurnal, seasonal, and solar cycle variations. In this paper we detail a climatological model of OTH radar developed using high-frequency radio wave ray tracing techniques. We discuss how this model may be used to provide initial assessments of the viability of candidate OTH radar networks to meet particular missions and how it may be used in sophisticated radar network design methodologies.
Multiple-Input Multiple-Output (MIMO) radar has been an active topic in the radar research commun... more Multiple-Input Multiple-Output (MIMO) radar has been an active topic in the radar research community for more than a decade [1]–[3]. MIMO based approaches have been investigated for improving target detectability, improving target localization, achieving higher spatial resolution, and clutter reduction using transmit or joint transmit-receive beamforming. This paper describes two series of experiments undertaken by the author and coworkers in learning how we might apply MIMO radar techniques to challenges in skywave Over-the-Horizon Radar (OTHR).
IEEE International Conference on Acoustics Speech and Signal Processing, 1993
Abstract Time-varying higher order spectra (TVHOS) based analysis is an emerging technique for an... more Abstract Time-varying higher order spectra (TVHOS) based analysis is an emerging technique for analyzing signals which are non-stationary, non-Gaussian and nonlinear. Most TVHOS are derived from the Wigner-Ville distribution (WVD), and in particular, retain the lag centering property of the WVD. When extended to third and higher orders, calculation of TVHOS can be complicated by the need for signal interpolation, imposed by the requirement for lag centering. The authors derive a phase product relationship which allows the lag ...
Seventh International Symposium on Signal Processing and Its Applications, 2003. Proceedings., 2003
Page 1. TIME-FREQUENCY ANALYSIS FOR MANEUVERING TARGET DETECTION IN OVER-THE-HORIZON RADARS Yamin... more Page 1. TIME-FREQUENCY ANALYSIS FOR MANEUVERING TARGET DETECTION IN OVER-THE-HORIZON RADARS Yamin Zhangt, Moeness G. Amint, BehzadMohammadi Dogahet, and Gordon J. Frazed + Center for Advanced ...
Advanced Signal Processing Algorithms, Architectures, and Implementations XIV, 2004
By exploiting the reflective and refractive nature of high-frequency (HF) radiowave propagation t... more By exploiting the reflective and refractive nature of high-frequency (HF) radiowave propagation through the ionosphere or the conducting sea surface, over-the-horizon radar (OTHR) systems perform wide-area surveillance at long range well beyond the limit of the horizon of conventional line-of-sight (LOS) radars. Improved characterizations of the targets can be achieved by using multiple OTHRs operating simultaneously as compared to a single OTHR operating alone. In this paper, we consider concurrent operations of two OTHR systems that occupy the same frequency band with different chirp waveforms. The objective is to respond to the advanced wide-area surveillance needs without reducing the wave repetitive frequency. For this purpose, a new cross-radar interference cancellation technique is developed and its effectiveness is verified through both analytical and simulation results.
IEEE International Conference on Acoustics Speech and Signal Processing, 2002
We address the problem of characterizing the power attributed to local near-field scattering for ... more We address the problem of characterizing the power attributed to local near-field scattering for the case of a linear equi-spaced array of sensors. The proposed method uses what we have termed the quadratic sensor angle distribution (SAD), previously called the spatial Wigner distribution. This distribution is a characterization of the power at every angle for each sensor in the array. In this distribution near-field sources have different angle for each sensor. The SAD is a joint-variable distribution and a dual in sensor number and angle to Cohen's class of time-frequency distributions. We use a known test source to illuminate the local scatterer distribution we wish to characterize and modify the received array snapshots to remove, via orthogonal projection, the direct propagation path from the test source so as to reveal the less powerful local scatter. An example is provided to demonstrate our technique.
This chapter presents a comprehensive treatment of the hybrid area of time-frequency distribution... more This chapter presents a comprehensive treatment of the hybrid area of time-frequency distributions (TFDs) and array signal processing. The application of quadratic ‘l’F’Ds to sensor signal processing has recently become of interest, and it was necessitated by the need to address important problems related to processing nonstationary signals incident on multiantenna receivers. Over the past few years, major contributions have been made to improve direction finding and blind source separation using time-frequency signatures. This improvement has cast quadratic TFDs as a key tool for source localization and signal recovery, and put bilinear transforms at equal footing with second-order and higher-order statistics as bases for effective spatial-temporal signal processing. This chapter discusses the advances made through time-frequency analysis in direction-of-arrival estimation, signal synthesis, and near-field source characterization.
An experimental multi-static HF radar is described that augments conventional over-the-horizon ra... more An experimental multi-static HF radar is described that augments conventional over-the-horizon radar (OTHR) by placing multiple forward-based receiver systems within line-of-sight of targets of interest. With sufficient and appropriately located forward-based receiver sites the radar can generate target tracks that are independent of the uncertain ionospheric state and the system has low incremental cost compared with a complete OTHR. Each site in the multi-static system consists of a ten element linear array with a direct digital HF receiver per element architecture and the receiving components have sufficient dynamic range and spectral purity to operate in the footprint of the direct OTHR transmitter signal. The system uses custom receivers that integrate the frequency management function with the radar receiver function. Signal processing algorithms include real-time STAP and adaptive CFAR. Inter-site communications is achieved using a low-cost 802.11 b wireless communications network where the longest path in this network is 37 km. The system has performed beyond expectation for the desired target class.
2014 48th Asilomar Conference on Signals, Systems and Computers, 2014
This paper considers the problem of range-folded spread clutter mitigation in parallax (geographi... more This paper considers the problem of range-folded spread clutter mitigation in parallax (geographically remote) transmit (Tx) and receive (Rx) high-frequency (HF) over-the-horizon radar (OTHR). We demonstrate that MIMO radar technology could be applied to provide the required level of spread range-folded clutter.
2003 IEEE International Conference on Acoustics, Speech, and Signal Processing, 2003. Proceedings. (ICASSP '03).
A coarray-based synthetic aperture beamformer using stepped-frequency signal synthesis and post-d... more A coarray-based synthetic aperture beamformer using stepped-frequency signal synthesis and post-data acquisition processing is presented for wideband imaging of near-field scenes. The proposed beamformer formulation and implementation finds key applications in through-the-wall microwave imaging and landmine detection problems. While coarray techniques offer significant reduction in array elements for a given angular resolution, stepped-frequency realization of wideband systems simplifies implementation and offers flexibility in beamforming. Proof of concept is provided using real data collected in an anechoic chamber. Comments Comments
2017 XXXIInd General Assembly and Scientific Symposium of the International Union of Radio Science (URSI GASS), 2017
Models of radar systems are required for a variety of reasons. The sophistication of these models... more Models of radar systems are required for a variety of reasons. The sophistication of these models is highly dependant on their purpose; for instance microwave radar models which are designed to be integrated into existing wargaming simulation frameworks will often be low-fidelity models. The development of similar models of over-the-horizon radar is particulary challenging. This is due to the highly variable propagation environment in which such systems are required to operate: even the lowest fidelity model of an OTH radar must model the environmental conditions appropriately. The “base level” environmental modelling required to accurately characterise OTH radar performance is the climatology, i.e. diurnal, seasonal and solar cycle variations. In this paper we detail a climatological model of OTH radar (CMOR) developed using high frequency (HF) radio wave raytracing techniques. We discuss how this model may be integrated into low-fidelity wargaming simulations, used to provide init...
Transmission of spatially diverse orthogonal waveforms in radar to support enhanced illumination ... more Transmission of spatially diverse orthogonal waveforms in radar to support enhanced illumination control and surveillance timeline management has been recently discussed in the radar literature. Such use of orthogonal waveforms in radar (sometimes referred to as MIMO radar) is potentially attractive in modern HF over-the-horizon (skywave) radar systems. However, HF radar implementation of orthogonal waveforms present some special challenges to waveform design. HF radars operate over several octaves of RF frequency, have array inter-element spacing which deviates significantly from one half-wavelength, use nonlinear power amplifiers, and have stringent spectral occupancy requirements. Implementation of specific orthogonal waveform types present their own particular design requirements, but some issues are generic and span a wide range of waveform classes. In particular, operation with over-sampled arrays can give rise to excessive reactive power. This can be mitigated by the use of a...
[1991] Conference Record of the Twenty-Fifth Asilomar Conference on Signals, Systems & Computers
Abstract The authors demonstrate the application of the Wigner-Ville time-frequency distribution,... more Abstract The authors demonstrate the application of the Wigner-Ville time-frequency distribution, the bispectrum, the time-varying bispectrum, and Gerr's third-order Wigner distribution to some underwater acoustic data. They also demonstrate the merit of including higher-order spectral information when signaturing underwater acoustic sources. It is pointed out that conventional signal analysis procedures do not utilize all the information available in many practical signal analysis problems. It is shown that the use of higher- ...
A challenging task in over-the-horizon radar (OTHR) is the tracking of target altitude. It has be... more A challenging task in over-the-horizon radar (OTHR) is the tracking of target altitude. It has been shown that the micro-multipaths due to ocean/ground reflections may reveal important information about the elevation maneuvering of a target. The Doppler signature of such micro-multipath signals is typically composed of three components having close nonlinear time-frequency behaviors. In this paper, we develop novel timefrequency analysis techniques for the characterization of Doppler effect of micro-multipath signals. The proposed method is based on the local analysis of the signal phase, followed by a stationarization operator. In the warped representation domain, the multi-component nonlinear Doppler signatures become stationary, thus allowing the application of spectral analysis tools. The results presented are based on real data and illustrate the potential of the proposed methods.
We present a numerical modelling approach for determining the HF radar cross-section of a volume ... more We present a numerical modelling approach for determining the HF radar cross-section of a volume displacement in the ocean surface. This displacement, for example, might be from a non-conductive wooden-hulled boat with no metal structure or fittings. Such a vessel typically has too small a radar cross-section to be detected considering only the scattering properties of the boat in isolation. Our modelling technique is approximate but indicates wooden, or other non-conductive material boats may be detectable by skywave radar in some instances, solely due to their displacement in the ocean. Our results suggest new radar management strategies to improve the likelihood of detecting these targets. However, we continue to require the preferred ship detection criteria of low sea-state and low doppler-spread ionospheric propagation conditions. We also assume the boat is moving at speed and heading combinations such that the target Doppler is separated from the ocean first-order Bragg scatter.
half a dozen countries, along with several expressions of regret from people who wished to contri... more half a dozen countries, along with several expressions of regret from people who wished to contribute but were prevented from doing so by government or corporate constraints. If most of the papers were to survive peer-review, then we would be on course for a double issue. After the rigorous two-stage peer-review process, we ended up with thirteen accepted papers. We, as Guest Editors, have decided to arrange the resulting twopart Special Issue such that the first part contains the seven papers dealing primarily with HF skywave radar. The second part contains six papers, with the focus on HF surface wave radar and on hybrid systems. To reflect this organization, we have opted to call the first part Special Issue on HF Skywave Radar and the second part Special Issue on HF Radar, for ease of reference, but of course there is an extensive commonality of technology and scientific principles. While we cannot claim to have achieved a truly comprehensive account of the global state of HF radar, this Special Issue contains papers from Australia, Canada, China, Germany, Singapore and the United States, with technical exposition and scientific results from some of the world's most advanced HF radar systems, written by the key researchers involved. The papers in this first collection address a diverse range of issues that confront designers and users of HF radars. The opening article, by Anderson, is a cri de coeur for greater recognition of the need to employ physical models whose fidelity is commensurate with the dynamic range of modern HF radars. His argument is illustrated with examples from both skywave and surface wave radar systems. Next, Francis, Cervera and Frazer describe a methodology for designing a network of HF skywave radars, where the radar siting and system parameters must be optimized for the mission objectives, taking account of the propagation and noise environments. Not only must HF radars manage to achieve their objectives in a challenging interference environment, they must also be responsible citizens of the HF band. McKerracher,
Models of radar systems are required for a variety of reasons. The sophistication of these models... more Models of radar systems are required for a variety of reasons. The sophistication of these models is highly dependent on their purpose; for instance, microwave radar models, which are designed to be integrated into existing wargaming simulation frameworks, will often be low-fidelity models. The development of similar models of over-the-horizon (OTH) radar is particularly challenging. This is due to the highly variable propagation environment in which such systems are required to operate: even the lowest fidelity model of an OTH radar must model the environmental conditions appropriately. The base level environmental modeling required to accurately characterize OTH radar performance is the climatology, that is, diurnal, seasonal, and solar cycle variations. In this paper we detail a climatological model of OTH radar developed using high-frequency radio wave ray tracing techniques. We discuss how this model may be used to provide initial assessments of the viability of candidate OTH radar networks to meet particular missions and how it may be used in sophisticated radar network design methodologies.
Multiple-Input Multiple-Output (MIMO) radar has been an active topic in the radar research commun... more Multiple-Input Multiple-Output (MIMO) radar has been an active topic in the radar research community for more than a decade [1]–[3]. MIMO based approaches have been investigated for improving target detectability, improving target localization, achieving higher spatial resolution, and clutter reduction using transmit or joint transmit-receive beamforming. This paper describes two series of experiments undertaken by the author and coworkers in learning how we might apply MIMO radar techniques to challenges in skywave Over-the-Horizon Radar (OTHR).
IEEE International Conference on Acoustics Speech and Signal Processing, 1993
Abstract Time-varying higher order spectra (TVHOS) based analysis is an emerging technique for an... more Abstract Time-varying higher order spectra (TVHOS) based analysis is an emerging technique for analyzing signals which are non-stationary, non-Gaussian and nonlinear. Most TVHOS are derived from the Wigner-Ville distribution (WVD), and in particular, retain the lag centering property of the WVD. When extended to third and higher orders, calculation of TVHOS can be complicated by the need for signal interpolation, imposed by the requirement for lag centering. The authors derive a phase product relationship which allows the lag ...
Seventh International Symposium on Signal Processing and Its Applications, 2003. Proceedings., 2003
Page 1. TIME-FREQUENCY ANALYSIS FOR MANEUVERING TARGET DETECTION IN OVER-THE-HORIZON RADARS Yamin... more Page 1. TIME-FREQUENCY ANALYSIS FOR MANEUVERING TARGET DETECTION IN OVER-THE-HORIZON RADARS Yamin Zhangt, Moeness G. Amint, BehzadMohammadi Dogahet, and Gordon J. Frazed + Center for Advanced ...
Advanced Signal Processing Algorithms, Architectures, and Implementations XIV, 2004
By exploiting the reflective and refractive nature of high-frequency (HF) radiowave propagation t... more By exploiting the reflective and refractive nature of high-frequency (HF) radiowave propagation through the ionosphere or the conducting sea surface, over-the-horizon radar (OTHR) systems perform wide-area surveillance at long range well beyond the limit of the horizon of conventional line-of-sight (LOS) radars. Improved characterizations of the targets can be achieved by using multiple OTHRs operating simultaneously as compared to a single OTHR operating alone. In this paper, we consider concurrent operations of two OTHR systems that occupy the same frequency band with different chirp waveforms. The objective is to respond to the advanced wide-area surveillance needs without reducing the wave repetitive frequency. For this purpose, a new cross-radar interference cancellation technique is developed and its effectiveness is verified through both analytical and simulation results.
IEEE International Conference on Acoustics Speech and Signal Processing, 2002
We address the problem of characterizing the power attributed to local near-field scattering for ... more We address the problem of characterizing the power attributed to local near-field scattering for the case of a linear equi-spaced array of sensors. The proposed method uses what we have termed the quadratic sensor angle distribution (SAD), previously called the spatial Wigner distribution. This distribution is a characterization of the power at every angle for each sensor in the array. In this distribution near-field sources have different angle for each sensor. The SAD is a joint-variable distribution and a dual in sensor number and angle to Cohen's class of time-frequency distributions. We use a known test source to illuminate the local scatterer distribution we wish to characterize and modify the received array snapshots to remove, via orthogonal projection, the direct propagation path from the test source so as to reveal the less powerful local scatter. An example is provided to demonstrate our technique.
This chapter presents a comprehensive treatment of the hybrid area of time-frequency distribution... more This chapter presents a comprehensive treatment of the hybrid area of time-frequency distributions (TFDs) and array signal processing. The application of quadratic ‘l’F’Ds to sensor signal processing has recently become of interest, and it was necessitated by the need to address important problems related to processing nonstationary signals incident on multiantenna receivers. Over the past few years, major contributions have been made to improve direction finding and blind source separation using time-frequency signatures. This improvement has cast quadratic TFDs as a key tool for source localization and signal recovery, and put bilinear transforms at equal footing with second-order and higher-order statistics as bases for effective spatial-temporal signal processing. This chapter discusses the advances made through time-frequency analysis in direction-of-arrival estimation, signal synthesis, and near-field source characterization.
An experimental multi-static HF radar is described that augments conventional over-the-horizon ra... more An experimental multi-static HF radar is described that augments conventional over-the-horizon radar (OTHR) by placing multiple forward-based receiver systems within line-of-sight of targets of interest. With sufficient and appropriately located forward-based receiver sites the radar can generate target tracks that are independent of the uncertain ionospheric state and the system has low incremental cost compared with a complete OTHR. Each site in the multi-static system consists of a ten element linear array with a direct digital HF receiver per element architecture and the receiving components have sufficient dynamic range and spectral purity to operate in the footprint of the direct OTHR transmitter signal. The system uses custom receivers that integrate the frequency management function with the radar receiver function. Signal processing algorithms include real-time STAP and adaptive CFAR. Inter-site communications is achieved using a low-cost 802.11 b wireless communications network where the longest path in this network is 37 km. The system has performed beyond expectation for the desired target class.
2014 48th Asilomar Conference on Signals, Systems and Computers, 2014
This paper considers the problem of range-folded spread clutter mitigation in parallax (geographi... more This paper considers the problem of range-folded spread clutter mitigation in parallax (geographically remote) transmit (Tx) and receive (Rx) high-frequency (HF) over-the-horizon radar (OTHR). We demonstrate that MIMO radar technology could be applied to provide the required level of spread range-folded clutter.
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Papers by Gordon Frazer