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Online ISSN 1751-8792 Print ISSN 1751-8784

IET Radar, Sonar & Navigation

Volume 3, Issue 2, April 2009

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Volume 3, Issue 2

April 2009

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    • Efficient direct position determination of orthogonal frequency division multiplexing signals
      • Author(s): O. Bar-Shalom  and  A.J. Weiss
      • Source: IET Radar, Sonar & Navigation, Volume 3, Issue 2, p. 101 –111
      • DOI:  10.1049/iet-rsn:20080097
      • Type: Article
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      • p. 101 –111 (11)
        The authors present an efficient method for positioning of orthogonal frequency division multiplexing (OFDM) signals. The method, called direct position determination (DPD), enables one to determine the emitter position in a single search operation. In formerly published articles on DPD, the signal was assumed to be a narrowband Gaussian source, which was subjected to a rather simple flat-fading channel model. Here, the authors extend the DPD algorithm to handle the OFDM signals that propagate through a frequency-selective channel, and derive the least squares estimator (LSE) for the problem. In addition, the authors present a method for a fine 2D position estimation, which enables one to reduce the DPD computational complexity without compromising on its estimation accuracy.
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      Ionospheric clutter mitigation using one-dimensional or two-dimensional wavelet processing
      • Author(s): F. Jangal ; S. Saillant ; M. Hélier
      • Source: IET Radar, Sonar & Navigation, Volume 3, Issue 2, p. 112 –121
      • DOI:  10.1049/iet-rsn:20070095
      • Type: Article
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      • p. 112 –121 (10)
        Ionospheric clutter mitigation is an important issue for high-frequency surface wave radar (HFSWR) signal processing. Clutter results from a sky wave propagation mode, which is backscattered by ionospheric ionisation irregularities. The random behaviour and the high strength of clutter signals can strongly limit the HFSWR detection capabilities. Here, an ionospheric clutter mitigation processing using wavelets is described. This new approach is founded on the ability of wavelets to separate signals having different variation scales or different directions of variations. The results obtained on real clutter signals with simulated targets are reported. Using the proposed method, one can expect, at mid-latitude, an improvement of the target-to-clutter ratio of 20–30 dB.
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      Orthogonal frequency-division multiplexing radar signal design with optimised ambiguity function and low peak-to-average power ratio
      • Author(s): M.A. Sebt ; A. Sheikhi ; M.M. Nayebi
      • Source: IET Radar, Sonar & Navigation, Volume 3, Issue 2, p. 122 –132
      • DOI:  10.1049/iet-rsn:20080106
      • Type: Article
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      • p. 122 –132 (11)
        Considering the important role of the ambiguity function (AF) of a signal regarding the performance of a matched filter bank for the detection of targets and the estimation of their ranges and velocities, the thumbtack shape is assumed to be the desirable shape of the AF and the method of least squares for the synthesis of the AF is introduced. Then, an iterative method for the allocation of a proper phase to the desired AF is proposed to obtain better results. This method is then applied to select the proper codes for the synthesis of pulsed orthogonal frequency-division multiplexing signals. It is also shown how this method can reduce sidelobes, almost uniformly, throughout the entire ambiguity plane. Finally, an efficient algorithm is presented, which modifies the produced codes in order to reach a lower peak-to-average power ratio suitable for transmission.
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      Two-dimensional pulse-to-pulse canceller of ground clutter in airborne radar
      • Author(s): X.-M. Li ; D.-Z. Feng ; H.-W. Liu ; M.-D. Xing ; D. Luo
      • Source: IET Radar, Sonar & Navigation, Volume 3, Issue 2, p. 133 –143
      • DOI:  10.1049/iet-rsn:20080108
      • Type: Article
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      • p. 133 –143 (11)
        It is well known that in the airborne radar, the location of the ground clutter spectrum in the angle-Doppler space is dependent mainly on the platform velocity and radar parameters. The authors propose a two-dimensional pulse-to-pulse canceller (TDPC) that can make full use of such prior information. The more detailed formulations of the ground clutter model and the signal model are given in a matrix–vector form. The least-squares-typical cost function associated with the filter coefficient matrix of the TDPC is established on the basis of the ground clutter model and the signal model. Like the classical displaced phase centre antenna (DPCA) processing, the proposed TDPC is also a spatial-temporal suppressor of ground clutter and can decrease the ground clutter signals, even though the DPCA condition is not satisfied. The proposed TDPC can also be used as an efficient pre-filtering tool before the conventional moving target indication (MTI) processing and the classical adaptive processing. Moreover, if only the TDPC plus the conventional MTI is used, it takes less computational time than the adaptive canceller. Experimental results show that the proposed TDPC has the satisfactory ground clutter suppression capability by using both simulated data and measured data.
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      Direction of arrival estimation for uncorrelated and coherent signals with uniform linear array
      • Author(s): Z. Ye ; Y. Zhang ; X. Xu ; C. Liu
      • Source: IET Radar, Sonar & Navigation, Volume 3, Issue 2, p. 144 –154
      • DOI:  10.1049/iet-rsn:20080041
      • Type: Article
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      • p. 144 –154 (11)
        A novel direction of arrival (DOA) estimation method is proposed with uniform linear array when uncorrelated and coherent signals coexist. The DOAs of uncorrelated signals are first estimated using a new method of modified total least squares estimation of signal parameters via rotation invariance techniques. Afterwards, the contributions of uncorrelated signals are eliminated and a new matrix is constructed based on the spatial difference matrix. Then, the coherent signals can be resolved by performing the forward spatial smoothing scheme on the new matrix. The proposed method can resolve more signals than the array elements with good performance. Simulation results demonstrate the effectiveness and efficiency of the proposed method.
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      Application of the Radon transform to detect small-targets in sea clutter
      • Author(s): J. Carretero-Moya ; J. Gismero-Menoyo ; A. Asensio-López ; Á. Blanco-del-Campo
      • Source: IET Radar, Sonar & Navigation, Volume 3, Issue 2, p. 155 –166
      • DOI:  10.1049/iet-rsn:20080123
      • Type: Article
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      • p. 155 –166 (12)
        The authors present a novel and heuristic approach for the detection of low radar cross-section targets in high-resolution sea clutter. The proposed technique is based on the application of the Radon transform to range–time matrices formed by column-wise storage of consecutive range profiles. The objective of this paper is 2-fold: to analyse the effect of the transform on real high-resolution sea clutter and to describe a detection scheme based on the insight obtained. The proposed technique emulates the behaviour of traditional motion target detection algorithms without the need for reliable Doppler information. It also constitutes a powerful non-coherent integration strategy of the target's energy along its specific path on the range–time plot. The performance of the detection technique has been tested against real high-resolution sea clutter data, acquired at the south coast of Spain with an in-house developed continuous wave linear frequency modulated millimetre-wave radar system. Monte Carlo simulations show a significant improvement over the conventional cell averaging constant false alarm rate schemes.
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      Joint time difference of arrival/angle of arrival position finding in passive radar
      • Author(s): Y. Norouzi  and  M. Derakhshani
      • Source: IET Radar, Sonar & Navigation, Volume 3, Issue 2, p. 167 –176
      • DOI:  10.1049/iet-rsn:20080069
      • Type: Article
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      • p. 167 –176 (10)
        Several target position finding methods are proposed in various papers mainly regarding sensor networks. However, the problem of position finding in passive radar systems is somewhat different from the general case of sensor networks. Generally, in a passive radar system, there are few receivers located at short distances when compared with the it distance from the target. In this case, a problem known as geometric dilution of precision (GDP) occurs, which considerably increases the error of many proposed methods. This phenomenon can even make the position finding equations non-solvable. Regarding this fact, we have developed a least mean square error (LMSE) based method, which uses both the angle of arrival (AOA) and time difference of arrival (TDOA) measurements to estimate almost precisely the position of very distant targets in a passive radar system. A simple equation is derived here to compare the TDOA and AOA accuracies. Then, it is shown that whenever the accuracies of these two measurements are comparable, the proposed method estimates the target position more precisely than the conventional AOA-only and TDOA-only methods. It also avoids the non-convergence behaviour encountered in TDOA-only methods.
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      Bistatic point target reference spectrum in the presence of trajectory deviations
      • Author(s): R. Wang ; O. Loffeld ; H. Nies ; A. Medrano-Ortiz ; S. Knedlik
      • Source: IET Radar, Sonar & Navigation, Volume 3, Issue 2, p. 177 –185
      • DOI:  10.1049/iet-rsn:20080053
      • Type: Article
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      • p. 177 –185 (9)
        The point target reference spectrum (BPTRS) of bistatic SAR in the presence of trajectory deviations based on Loffeld's bistatic formula (LBF) is developed. The presented BPTRS is suitable for the general air-borne bistatic configuration. For the air-borne bistatic SAR, both the transmitter and the receiver will contribute to the trajectory deviation. The compensation of trajectory deviations becomes more complex because of the separate locations of the transmitter and receiver. The authors focus on the effects of trajectory deviations on the point target spectrum of bistatic SAR. The proposed BPTRS is verified by simulation experiments performed in the azimuth-invariant configuration.
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      Novel joint time delay and frequency estimation method
      • Author(s): X.F. Zhang  and  D.Z. Xu
      • Source: IET Radar, Sonar & Navigation, Volume 3, Issue 2, p. 186 –194
      • DOI:  10.1049/iet-rsn:20080032
      • Type: Article
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      • p. 186 –194 (9)
        A novel algorithm has been proposed for joint time delay and frequency estimation of sinusoidal signals received at multiple separated sensors. The joint time delay and frequency estimation problem is linked to a trilinear model. Exploiting this link, it derives a trilinear decomposition-based joint time delay and frequency method algorithm. The simulation results reveal that the algorithm performance is close to that of the Cramer–Rao lower bound, and the proposed algorithm even supports small sample sizes.
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