| 1. |
- Johansson, Eija, 1982, et al.
(författare)
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Interpolation based on stationary and adaptive AR(1) modeling
- 2011
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Ingår i: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - 1520-6149. - 9781457705397 ; , s. 4052-4055
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Konferensbidrag (refereegranskat)abstract
- In this paper, we describe a minimal mean square error (MMSE) optimal interpolation filter for discrete random signals. We explicitly derive the interpolation filter for a first-order autoregressive process (AR(1)), and show that the filter depends only on the two adjacent points. The result is extended by developing an algorithm called local AR approximation (LARA), where a random signal is locally estimated as an AR(1) process. Experimental evaluation illustrates that LARA interpolation yields a lower mean square error than other common interpolation techniques, including linear, spline and local polynomial approximation (LPA).
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| 2. |
- Panahi, Ashkan, 1986, et al.
(författare)
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Basis pursuit over continuum applied to range-Doppler estimation problem
- 2014
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Ingår i: Proceedings of the IEEE Sensor Array and Multichannel Signal Processing Workshop. - 2151-870X. - 9781479914814 ; , s. 381-384
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Konferensbidrag (refereegranskat)abstract
- Sparse estimation and compressive sensing techniques have been recently considered for radar estimation problems. It is frequently observed that these methods are robust to model uncertainties and substantially improve performance in scenarios with a low signal-to-noise. However, since current sparsity-based techniques are computationally costly and require a suitable discretization (grid), which strongly restricts resolution, they practically receive less attention. In this work, we present an application of a new sparsity-based technique to the specific problem of range-Doppler estimation. The method, generalizing basis pursuit, is less computationally complex and its performance is independent of the grid selection. We demonstrate that the proposed technique can improve estimation performance in difficult cases, as compared to the SAGE technique.
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| 3. |
- Panahi, Ashkan, 1986, et al.
(författare)
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Wideband waveform design for robust target detection
- 2015
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Ingår i: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - 1520-6149. - 9781467369978 ; 2015-August, s. 3926-3930
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Konferensbidrag (refereegranskat)abstract
- © 2015 IEEE. Future radar systems are expected to use waveforms of a high bandwidth, with an advantage of an improved range resolution. Herein, a technique to design robust wideband waveforms is developed. The context is detection of a single object with partially unknown parameters. The technique achieves an optimal detection speed for a desired resolution, maintaining a high detection performance. Many radar systems also require fast adaptation to a variable environment. Hence, the technique is devoted to rapidly design waveforms. In terms of probabilities of detection and false alarm, numerical evaluation shows the efficiency of the method when compared with a chirp signal and a Gaussian pulse.
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| 4. |
- Rowe, W.L., et al.
(författare)
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Frequency division orthogonal waveforms for narrowband MIMO arrays
- 2013
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Ingår i: IEEE International Symposium on Phased Array Systems and Technology. ; , s. 421-427
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Konferensbidrag (refereegranskat)abstract
- Multiple-Input Multiple-Output arrays with closely spaced antennas typically utilize orthogonal waveforms to create a larger virtual aperture. Orthogonality between waveforms can be achieved using time, Doppler, coding, or frequency division. In this work we examine the method of generating frequency diverse waveforms. In general, the frequency division approach generates waveforms that have reduced bandwidth which results in reduced range resolution. To overcome this loss of range resolution more spectrum must be utilized which might not be compatible with narrowband arrays. Herein, we present an approach for generating a notched waveform set that preserves range resolution, is effectively orthogonal, and could be utilized by narrowband arrays.
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| 5. |
- Rowe, W.L., et al.
(författare)
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Robust adaptive beamforming for MIMO monopulse radar
- 2013
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819495051 ; 8714
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Konferensbidrag (refereegranskat)abstract
- Researchers have recently proposed a widely separated multiple-input multiple-output (MIMO) radar using monopulse angle estimation techniques for target tracking. The widely separated antennas provide improved tracking performance by mitigating complex target radar cross-section fades and angle scintillation. An adaptive array is necessary in this paradigm because the direct path from any transmitter could act as a jammer at a receiver. When the target-free covariance matrix is not available, it is critical to include robustness into the adaptive beamformer weights. This work explores methods of robust adaptive monopulse beamforming techniques for MIMO tracking radar.
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| 6. |
- Ström, Marie, 1984, et al.
(författare)
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Low PAPR waveform synthesis with application to wideband MIMO radar
- 2011
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Ingår i: Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP), 2011 4th IEEE International Workshop on. - 9781457721052 ; , s. 5-8
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Konferensbidrag (refereegranskat)abstract
- This paper considers the problem of waveform synthesis given a desired power spectrum. The properties of the designed waveforms are such that the overall system performance is increased. The metric used to evaluate the optimality of the synthesized time domain signals is the peak-to-average power ratio (PAPR). We discuss how to synthesize waveforms using the technique of partial transmit sequence (PTS). The key point is that the gradient can explicitly be derived from the objective function. Furthermore, the result is extended by allowing the power spectrum to deviate from its original shape, yielding a further reduction in the PAPR. The method is applied to derived power spectra for wideband multiple-input-multiple-output (MIMO) radar. It is shown that the proposed technique can achieve optimal or near optimal performance with PAPR below 0.5 dB.
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| 7. |
- Ström, Marie, 1984, et al.
(författare)
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Mapping colors from paintings to tapestries: Rejuvenating the faded colors in tapestries based on colors in reference paintings
- 2012
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489425 ; 8291, s. Art. no. 82911F-
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Konferensbidrag (refereegranskat)abstract
- We addressed the problem of recovering or "rejuvenating" colors in a faded tapestry (the target image) by automatically mapping colors from digital images of the reference painting or cartoon (the source image). We divided the overall computational challenge into several subproblems, and implemented their solutions in Matlab: 1) quantizing the colors in both the tapestry and the referent painting, 2) matching corresponding regions in the works based on spatial location, area and color, 3) mapping colors from regions in the source image to corresponding regions in the target image, and 4) estimating the fading of colors and excluding color mapping of areas where color has not faded. There are a number of semi-global design parameters in our algorithm, which we currently set by hand, for instance the parameter that balance the effects of 1) matching color areas in the two images and 2) matching the spatial locations between the two images. We demonstrated our method on synthetic data and on small portions of 16th-century European tapestries of cultural patrimony. Our first steps in a proof-of-concept work suggest that future refinements to our method will lead to a software tool of value to art scholars.
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| 8. |
- Ström, Marie, 1984
(författare)
-
Robust Transceiver Design and Waveform Synthesis for Wideband MIMO Radar
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the problem of designing and synthesizing waveforms that are optimal, both in a signal-to-noise-and-interference ratio (SNIR), and in a system hardware design perspective, i.e., to synthesize time domain waveforms with a low peak-to-average power ratio (PAPR), or even constant modulus.In the first part of the thesis, we investigate the possibility to suppress interference for wideband multiple-input multiple-output radar, by exploiting the spectral properties of the transmit signals. The idea is to use tunable filters at the transmitter and receiver sides, and to derive the optimal power spectral density that enhances the system performance in terms of the SNIR, for a given scenario. Herein, the focus is to suppress active jamminginterference, and especially deceptive jamming. The proposed method is extended to invoke imperfections in the given scenario. Two robust optimization methods are evaluated: one that utilizes a Taylor series expansionof the SNIR, and one that exploits a worst-case SNIR maximization. In the second part of the thesis, we utilize the results obtained in the first part to synthesize time domain signals that achieve certain hardware restrictions. By using the technique of partial transmit sequence, we synthesize signals that achieve optimal spectral properties and that experience a low PAPR. Finally, we show that if we allow the power spectrum to deviatesomewhat from its desired shape, a further reduction of the PAPR, or even a constant modulus signal is possible. The proposed method can be used to design a time domain signal with any predefined power spectrum, if there is no design restriction except for the PAPR on the time domainsignal waveform.
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| 9. |
- Ström, Marie, 1984, et al.
(författare)
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Robust transceiver design for wideband MIMO radar utilizing a subarray antenna structure
- 2013
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Ingår i: Signal Processing. - : Elsevier BV. - 0165-1684. ; 93:12, s. 3541-3552
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we investigate the possibility to suppress interference in wideband multiple-input multiple-output radar. The idea is to employ tunable filters at the transmitter and the receiver sides, and to derive filter coefficients that result in optimal transmitted signals from a system performance point of view, for a given radar scenario. The system performance is measured in signal-to-interference-and-noise ratio (SINR) at the receiver output, from which the filter properties are derived. The focus is to suppress active jamming interference, and especially deceptive jamming interference. We discuss two ways to derive the transmit and the receive filters. Each procedure utilizes two different power constraints related to the transmit filters. To incorporate imperfections in the given scenario, a robust extension to the design problem is proposed. Two different robust methods are evaluated: one that utilizes a Taylor series expansion of the SINR, and one that exploits a worst-case SINR maximization. Numerical validation illustrates the possibility to suppress interference without actually forming a spatial null in the direction towards interference, and the necessity to design transmit filters that are robust to uncertainties in the given scenario. (C) 2013 Elsevier B.V. All rights reserved.
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| 10. |
- Ström, Marie, 1984, et al.
(författare)
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Transmit and receive filter optimization for wideband MIMO radar
- 2011
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Ingår i: Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP), 2011 4th IEEE International Workshop on. - 9781457721052 ; , s. 9-12
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Konferensbidrag (refereegranskat)abstract
- In this paper, we discuss the possibility to suppress interference for wideband multiple-input-multiple-output (MIMO) radar, using only the temporal properties of the signals. The idea is to use tunable filters each connected to a wideband waveform generator, and to derive the optimal power spectral density (PSD) of the resulting signals in a known environment. The metric used to evaluate the enhancement in the system performance is the signal-to-noise and interference ratio (SNIR), from which the optimal transmit and receive filter properties are derived. We discuss two optimization approaches: one alternating and one joint algorithm. Each method is separated into two cases: for a total power constraint and for an individual power constraint on the transmit filters, respectively. Numerical validation illustrates the possibility to suppress the interference in the temporal domain, without actually forming a spatial null in the direction of the interference.
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