Blunt S.D.,University of Kansas |
Chan T.,Johns Hopkins University |
Gerlach K.,US Radar
IEEE Transactions on Aerospace and Electronic Systems | Year: 2011
A new approach for spatial direction-of-arrival (DOA) estimation, denoted as re-iterative superresolution (RISR), is developed based upon a recursive implementation of the minimum mean-square error (MMSE) framework. This recursive strategy alternates between updating an MMSE filter bank according to the previous receive spatial power distribution and then subsequently applying the new filter bank to the received data snapshots to obtain a new estimate of the receive spatial power distribution. Benefits of this approach include robustness to coherent sources such as can occur in multipath environments, operation with very low sample support to enable "tracking" of sources with rapidly changing DOA (e.g., bistatic pulse chasing), intrinsic determination of model order, and robustness to array modeling errors by exploiting approximate knowledge of array calibration tolerances. From an implementation perspective RISR belongs to a class of recursive algorithms that includes Interior Point methods, the minimum-normbased FoCal underdetermined system solver (FOCUSS) algorithm, and the iterative reweighted least squares (IRLS) algorithm. However, the structure of RISR also enables the natural inclusion of spatial noise covariance information as well as a mechanism to account for array modeling errors which are known to induce degradation for existing superresolution methods. The inclusion of the latter is also found to facilitate an adaptive form of regularization that establishes a feasible (given model uncertainties) dynamic range for source estimates. © 2011 IEEE.
Raj R.G.,US Radar
2012 IEEE Statistical Signal Processing Workshop, SSP 2012 | Year: 2012
We introduce a novel methodology for calculating discriminative codes for different classes of vectors with respect to the same dictionary. This is accomplished by introducing and quantifying the concept of mutual exclusivity between two classes of vectors (endowed possibly with different probabilistic structures) in a manner amenable to convex programming. We study theoretical properties of our mutual exclusivity operator and experimentally demonstrate its capability in generating effective discriminative codes that successfully incorporate both intra-class and inter-class characteristics. We conclude with a brief discussion of a generalization our mutual exclusivity operator to handle arbitrary number of classes, together with future directions emanating from this work. © 2012 IEEE.
Chen R.C.,US Radar
IEEE National Radar Conference - Proceedings | Year: 2010
Optimal waveforms for minimum mean square error range profile estimation are investigated. An idealized measurement and waveform adaptation process is developed that yields optimal scene and range specific waveforms. This process is idealized in that during each cycle of the process, a large number of dwells are required. As part of our method, a modified version of the Adaptive Pulse Compression (APC) estimation method is used to estimate the range profile after each dwell cycle. The proposed method is analogous to the APC method in that it yields a set of range specific optimal waveforms, while the APC method yields a set of range specific optimal pulse compression filters. In certain scenarios, the measurement and waveform adaptation process yields range profile estimates that are significantly better than those derived by the APC method alone. © 2010 IEEE.
Henke D.,University of Kansas |
McCormick P.,University of Kansas |
Blunt S.D.,University of Kansas |
Higgins T.,US Radar
IEEE National Radar Conference - Proceedings | Year: 2015
The sensitivity impact of range straddling in the form of mismatch loss is well known. What is less appreciated, however, is the effect upon dynamic range, particularly for receive filtering that seeks to minimize range sidelobes. For FM-based waveforms, which are readily implementable in a high-power radar system, it is shown that least-squares (LS) mismatched filtering (MMF) realizes a penalty in sidelobe suppression when range straddling occurs. This degradation can be partially compensated through modification of the LS MMF implementation. Alternatively, adaptive pulse compression (APC), appropriately modified for application to FM waveforms, demonstrates robustness to both straddling and eclipsing effects. Simulated and experimentally measured results are provided to demonstrate the efficacy of these filtering approaches. © 2015 IEEE.
Raj R.G.,US Radar
IEEE National Radar Conference - Proceedings | Year: 2014
We apply our recently developed concept of mutual exclusivity  in the context of discriminative coding, to the problem of learning dictionary for representing signals drawn from N classes in a way that optimizes their discriminability. We first briefly review our mutual-exclusivity concept and then deploy it a simple discriminative dictionary learning algorithm that directly generalizes the well-known KSVD algorithm which is addressed for the traditional problem of signal coding. We demonstrate performance improvements over traditional KSVD based feature extraction schemes and conclude by describing avenues for future research. © 2014 IEEE.
Dorsey W.M.,US Radar |
Scholnik D.P.,US Radar
2016 IEEE Radar Conference, RadarConf 2016 | Year: 2016
Circular arrays are an appealing if underused option for radar systems that require 360° coverage in azimuth. They require no mechanical scanning and do not suffer from the high-Angle scan loss and beam broadening of linear and planar arrays. The circular geometry, along with suitable pattern synthesis techniques, enables some unique capabilities. On transmit they provide the flexibilty to synthesize a continuum of beam shapes, from omnidirectional to sector to high gain. On receive, simultaneous high-gain beams can be formed to cover any desired azimuth footprint. In this paper we explore the capabilities of circular arrays through a series of pattern synthesis design examples. © 2016 IEEE.
Farshchian M.,US Radar |
Raj R.G.,US Radar
IEEE National Radar Conference - Proceedings | Year: 2011
Track-Before-Detect (TBD) is a detection technique that simultaneously tracks and detects a target. The technique is specially useful for targets whose back-scattered return is significantly lower than the surrounding noise and background environments. Different algorithms proposed to perform TBD include particle filter, dynamic programming and Hough transform algorithms have been proposed. These techniques work well in a highly noise environment with constant velocity targets. However, some of these techniques are not applicable to targets that have acceleration as well as targets embedded in sea clutter. In this paper, we present a beamlet track-before-detect technique for maritime detection. Due to the sea clutter, two different adaptive sea clutter filtering methods are applied before the aforementioned TBD technique. Overall, the paper introduces and studies a beamlet TBD technique for maneuverable maritime targets in sea clutter. © 2011 IEEE.
Raj R.G.,US Radar |
Chen V.C.,US Radar |
Lipps R.,US Radar
IET Signal Processing | Year: 2010
The authors develop methods for the time-frequency (TF) analysis of human gait radar signals. In particular the authors demonstrate how knowledge of different motion classes can be obtained via a Markov chain model of state transitions based on the TF envelope structure associated with the motion sequence being analysed. The class-conditional knowledge thus obtained allows us to effectively extract the motion curves associated with different body parts via a non-parametric partial tracking algorithm that is coupled with an optimum Gaussian g-Snake modelling of the TF structure. The optimum segmentation of the TF structure into different half-cycles as well as the determination of the initial Doppler control points (corresponding to each half-cycle) is facilitated by a dynamic programming algorithm wherein the associated cost function involves a mean-square minimisation of the best quadratic fit to each segment together with a sparsity prior that enables us to control the smoothness of the approximation space in which the time series being analysed is effectively projected. Finally, the authors describe some of the limitations of our approach and point out future research directions that can overcome some of the difficulties associated with the complex interaction between the inherently non-linear dynamics of human gait motion and radar systems. © 2010 The Institution of Engineering and Technology.
US Radar | Date: 2015-03-02
A Ground Penetrating Radar (GPR) system makes use of digital circuitry for synchronizing the sampling of a received radar signal with a transmitted radar signal. The digital synchronization achieves improved waveform reproduction and greater receiver sensitivity. Furthermore, the system employs digital circuitry to control the gain of a receiver amplifier. The digitally controlled gain makes it possible to accurately calibrate the amplitude of received radar signals with great precision while achieving good dynamic range.