46 research outputs found
Waveform libraries: Measures of effectiveness for radar scheduling
Our goal was to provide an overview of a circle of emerging ideas in the area of waveform scheduling for active radar. Principled scheduling of waveforms in radar and other active sensing modalities is motivated by the nonexistence of any single waveform that is ideal for all situations encountered in typical operational scenarios. This raises the possibility of achieving operationally significant performance gains through closed-loop waveform scheduling. In principle, the waveform transmitted in each epoch should be optimized with respect to a metric of desired performance using all information available from prior measurements in conjunction with models of scenario dynamics. In practice, the operational tempo of the system may preclude such on-the-fly waveform design, though further research into fast adaption of waveforms could possibly attenuate such obstacles in the future. The focus in this article has been on the use of predesigned libraries of waveforms from which the scheduler can select in lieu of undertaking a real-time design. Despite promising results, such as the performance gains shown in the tracking example presented here, many challenges remain to be addressed to bring the power of waveform scheduling to the level of maturity needed to manifest major impact as a standard component of civilian and military radar systems.Douglas Cochran, Sofia Suvorova, Stephen D. Howard and Bill Mora
Fractional fourier transform based waveform for a joint radar-communication system
The increasing demand of spectrum resources and the need to keep the size, weight and power consumption of modern radar as low as possible, has led to the development of solutions like joint radar-communication systems. In this paper a novel Fractional Fourier Transform (FrFT) based multiplexing scheme is presented as joint radar-communication technique. The FrFT is used to embed data into chirp sub-carriers with different time-frequency rates. Some optimisation procedures are also proposed, with the objective of improving the bandwidth occupancy and the bit rate and/or Bit Error Ratio (BER). The generated waveform is demonstrated to have a good rejection to distortions introduced by the channel, leading to low BER, while keeping good radar characteristics compared to a widely used Linear Frequency Modulated (LFM) pulse with same duration and bandwidth
Bayesian reconstruction of gravitational wave burst signals from simulations of rotating stellar core collapse and bounce
Presented in this paper is a technique that we propose for extracting the
physical parameters of a rotating stellar core collapse from the observation of
the associated gravitational wave signal from the collapse and core bounce.
Data from interferometric gravitational wave detectors can be used to provide
information on the mass of the progenitor model, precollapse rotation and the
nuclear equation of state. We use waveform libraries provided by the latest
numerical simulations of rotating stellar core collapse models in general
relativity, and from them create an orthogonal set of eigenvectors using
principal component analysis. Bayesian inference techniques are then used to
reconstruct the associated gravitational wave signal that is assumed to be
detected by an interferometric detector. Posterior probability distribution
functions are derived for the amplitudes of the principal component analysis
eigenvectors, and the pulse arrival time. We show how the reconstructed signal
and the principal component analysis eigenvector amplitude estimates may
provide information on the physical parameters associated with the core
collapse event.Comment: 17 pages, 9 figure
Robust waveform design for multistatic cognitive radars
In this paper we propose robust waveform techniques for multistatic cognitive radars in a signal-dependent clutter environment. In cognitive radar design, certain second order statistics such as the covariance matrix of the clutter, are assumed to be known. However, exact knowledge of the clutter parameters is difficult to obtain in practical scenarios.
Hence we consider the case of waveform design in the presence of uncertainty on the knowledge of the clutter environment
and propose both worst-case and probabilistic robust waveform design techniques. Initially, we tested our multistatic, signaldependent
model against existing worst-case and probabilistic methods. These methods appeared to be over conservative and generic for the considered scenario. We therefore derived a new approach where we assume uncertainty directly on the radar cross-section and Doppler parameters of the clutters.
Accordingly, we propose a clutter-specific stochastic optimization that, by using Taylor series approximations, is able to determine
robust waveforms with specific Signal to Interference and Noise Ratio (SINR) outage constraints
Coherent Network Analysis of Gravitational Waves from Three-Dimensional Core-Collapse Supernova Models
Using predictions from three-dimensional (3D) hydrodynamics simulations of
core-collapse supernovae (CCSNe), we present a coherent network analysis to
detection, reconstruction, and the source localization of the
gravitational-wave (GW) signals. We use the {\tt RIDGE} pipeline for the
analysis, in which the network of LIGO Hanford, LIGO Livingston, VIRGO, and
KAGRA is considered. By combining with a GW spectrogram analysis, we show that
several important hydrodynamics features in the original waveforms persist in
the waveforms of the reconstructed signals. The characteristic excess in the
spectrograms originates not only from rotating core-collapse, bounce and the
subsequent ring down of the proto-neutron star (PNS) as previously identified,
but also from the formation of magnetohydrodynamics jets and non-axisymmetric
instabilities in the vicinity of the PNS. Regarding the GW signals emitted near
at the rotating core bounce, the horizon distance extends up to 18 kpc
for the most rapidly rotating 3D model in this work. Following the rotating
core bounce, the dominant source of the GW emission shifts to the
non-axisymmetric instabilities. The horizon distances extend maximally up to
40 kpc seen from the spin axis. With an increasing number of 3D models
trending towards explosion recently, our results suggest that in addition to
the best studied GW signals due to rotating core-collapse and bounce, the time
is ripe to consider how we can do science from GWs of CCSNe much more seriously
than before. Particularly the quasi-periodic signals due to the
non-axisymmetric instabilities and the detectability should deserve further
investigation to elucidate the inner-working of the rapidly rotating CCSNe.Comment: PRD in pres
On model, algorithms and experiment for micro-doppler based recognition of ballistic targets
The ability to discriminate between Ballistic Missile warheads and confusing objects is an important topic from different points of view. In particular, the high cost of the interceptors with respect to tactical missiles may lead to an ammunition problem. Moreover, since the time interval in which the defence system can intercept the missile is very short with respect to target velocities, it is fundamental to minimise the number of shoots per kill. For this reason a reliable technique to classify warheads and confusing objects is required. In the efficient warhead classification system presented in this paper a model and a robust framework is developed, which incorporates different microDoppler based classification techniques. The reliability of the proposed framework is tested on both simulated and real dat
Waveform design for communicating radar systems using fractional Fourier transform
A novel waveform design technique for enabling a communication channel within a pulse radar is presented. The proposed waveform is composed of quasi-orthogonal chirp sub-carriers generated by means of the Fractional Fourier Transform (FrFT), with the aim of preserving the radar performance of a typical Linear Frequency Modulated (LFM) pulse while embedding data to be sent to a cooperative system. Waveform generation and demodulation are described, together with techniques aimed at optimising the design parameters and mitigating the Inter-Carrier Interference (ICI) caused by the quasi-orthogonality of the chirp sub-carriers. The proposed FrFT based communicating-radar (CoRadar) waveform design is compared with Orthogonal Frequency Division Multiplexing (OFDM) based CoRadar with respect to both radar and communication operations. Radar performance is evaluated through examination of the Ambiguity Function (AF) and by assessing the performance of a standard square law detector. Communication performance is shown in terms of Bit Error Ratio (BER) for different channel conditions. Results demonstrate that the proposed FrFT waveform presents performance close to a LFM pulse in terms of probability of detection and probability of false alarm, in exchange for slightly worse range and Doppler resolution. Furthermore, it is shown to maintain comparable communication performance with respect to the OFDM waveform. Finally, a hardware implementation is described that demonstrates the simultaneous radar and communication capabilities of the proposed system
High-Energy Gamma-Ray Observations of W Comae with STACEE
We report on observations of the blazar W Comae (ON+231) with the Solar Tower
Atmospheric Cherenkov Effect Experiment (STACEE), a wavefront-sampling
atmospheric Cherenkov telescope, in the spring of 2003. In a data set
comprising 10.5 hours of ON-source observing time, we detect no significant
emission from W Comae. We discuss the implications of our results in the
context of the composition of the relativistic jet in W Comae, examining both
leptonic and hadronic models for the jet. We derive 95% confidence level upper
limits on the flux at the level of 1.5--3.5 x 10^{-10} cm^{-2} s^{-1} above 100
GeV for the leptonic models, or 0.5--1.1 x 10^{-10} cm^{-2} s^{-1} above 150
GeV for the hadronic models.Comment: 9 pages, 7 figures, uses emulateapj.sty. Accepted to Ap
The Constant Information Radar
abstract: The constant information radar, or CIR, is a tracking radar that modulates target revisit time by maintaining a fixed mutual information measure. For highly dynamic targets that deviate significantly from the path predicted by the tracking motion model, the CIR adjusts by illuminating the target more frequently than it would for well-modeled targets. If SNR is low, the radar delays revisit to the target until the state entropy overcomes noise uncertainty. As a result, we show that the information measure is highly dependent on target entropy and target measurement covariance. A constant information measure maintains a fixed spectral efficiency to support the RF convergence of radar and communications. The result is a radar implementing a novel target scheduling algorithm based on information instead of heuristic or ad hoc methods. The CIR mathematically ensures that spectral use is justified