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Online ISSN 1751-8792 Print ISSN 1751-8784

IET Radar, Sonar & Navigation

Volume 5, Issue 5, June 2011

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Volume 5, Issue 5

June 2011

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    • Turbo architecture for multipath mitigation in global navigation satellite system receivers
      • Author(s): X. Chen ; F. Dovis ; M. Pini ; P. Mulassano
      • Source: IET Radar, Sonar & Navigation, Volume 5, Issue 5, p. 517 –527
      • DOI:  10.1049/iet-rsn.2010.0356
      • Type: Article
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      • p. 517 –527 (11)
        In this study a new multipath mitigation architecture for satellite navigation receiver, named coupled amplitude delay lock loops (CADLLs) is presented. This architecture exploits the ‘turbo principle’ to separately track the line-of-sight (LOS) signal and multipath signals in order to mitigate the effects of the multiple reflections. The delay lock loop (DLL) and the amplitude lock loop (ALL) are two basic elements in the structure. DLL is in charge of estimating and tracking the code delay of a specific ray in the incoming signal while ALL is in charge of estimating the corresponding amplitude. A pair of DLL and ALL makes a Unit, devoted to track LOS or a multipath signal. Several Units are incorporated in the CADLL structure, and then able to track the different component rays from the overall incoming signal. The feedback architecture and special working strategy of CADLL boost the performances of the parameter estimation accuracy, the noise tolerance ability and the error mitigation for short-range multipath.
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      Generalised likelihood ratio test detector for micro-motion targets in synthetic aperture radar raw signals
      • Author(s): B. Deng ; H.-Q. Wang ; X. Li ; Y.-L. Qin ; J.-T. Wang
      • Source: IET Radar, Sonar & Navigation, Volume 5, Issue 5, p. 528 –535
      • DOI:  10.1049/iet-rsn.2010.0223
      • Type: Article
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      • p. 528 –535 (8)
        Micro-motion targets are gaining an increased interest from the synthetic aperture radar (SAR) community. Their SAR returns can be modelled as sinusoidal frequency-modulated signals in the noise/clutter environment. A detector based on the generalised likelihood ratio test (GLRT) is proposed to detect such targets using SAR raw signals instead of SAR imagery. The GLRT detector entails searching three parameters for the maximum of a statistic, followed by comparison of the maximum with a threshold determined by the constant false alarm rate. It can also provide estimation of the micro-motion parameters. The detection performance is derived theoretically and demonstrated by both simulated and quasi-real data, showing favourable detection ability under low signal-to-noise/clutter ratios.
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      Use of XMTM radio satellite signal as a source of opportunity for passive coherent location
      • Author(s): L.-P. Gill ; D. Grenier ; J.-Y. Chouinard
      • Source: IET Radar, Sonar & Navigation, Volume 5, Issue 5, p. 536 –544
      • DOI:  10.1049/iet-rsn.2010.0065
      • Type: Article
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      • p. 536 –544 (9)
        This article investigates the use of an XMTM signal as a source of opportunity for passive coherent location. An analysis of the echo-to-direct signal ratio and the echo-to-noise ratio emphasises two major target detection problems: the masking effect of the direct signal and the low power of the echo from the reflected signal. First, a subspace-based method is proposed to suppress the direct signal by the projection of the received signal in subspaces orthogonal to direct signal. Then, to overcome the problem of low power of the echo, a directive gain technique is also proposed: an overlapped array is used to provide a directive gain while maintaining a sufficient resolution for using the subspaces method. The number of subarrays employed is optimised for maximum gain while avoiding the occurrence of nuls at the output of a filter matched to the direct path signal, for specific numbers of subarrays. The impact of the subtraction of the noise covariance matrix of noise is also studied. The integrated detection system is then tested through simulations to verify its effectiveness for the detection of moving targets.
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      Spatial-dependent waveform design for colocated uniform linear array multiple-input multiple-output radar
      • Author(s): Z. Jindong ; W. Kerang ; Z. Xiaohua
      • Source: IET Radar, Sonar & Navigation, Volume 5, Issue 5, p. 545 –550
      • DOI:  10.1049/iet-rsn.2009.0297
      • Type: Article
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      • p. 545 –550 (6)
        Multiple-input multiple-output (MIMO) radars have attracted considerable attention for their ability to transmit multiple waveforms. These waveforms affect the range, Doppler and spatial performance. Recently, the concept of ambiguity function, which is an important mathematical tool for analysing and designing radar signals, has been extended to the MIMO radar case. In this study, the authors investigate the range and spatial properties of colocated MIMO radar based on range-spatial ambiguity function. Owing to spatial dependence of the matched filter output of MIMO radar, the spatial detection region is divided into multiple sections by spatial resolution. A new algorithm for designing orthogonal frequency-hopping waveforms according to the spatial section where the target may appear is proposed. This algorithm improves the peak sidelobe level of the matched filter output.
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      Numerical study on the phase and amplitude statistics of backscattered signals from time-evolving sea surfaces
      • Author(s): X. Li  and  X. Xu
      • Source: IET Radar, Sonar & Navigation, Volume 5, Issue 5, p. 551 –560
      • DOI:  10.1049/iet-rsn.2010.0198
      • Type: Article
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      • p. 551 –560 (10)
        A statistical analysis based on modulated compound Gaussian (CG) fields is performed on the phase and amplitude of backscattered signals, numerically generated using the method of ordered multiple interactions (MOMIs) for time-evolving one-dimensional (1D) Creamer surfaces. According to CG fields, theoretical models are revisited to investigate the statistics of phase difference and amplitude ratio as a function of time lag to reveal the modulation mechanisms of the backscattered signals. Numerical results demonstrate good agreements between the numerically generated statistics and the theoretical counterparts, providing with clear evidence that the numerically generated backscattered fields are jointly Gaussian distributed on short time-scales but, are modulated in amplitude by the long surface waves, which make the clutter returns departing from joint Gaussian model gradually. Such modulation mechanisms are coincident with the findings from the analysis of radar measurements published in references, further validating the applicability of the MOMI-based electromagnetic modelling process for sea clutter.
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      Multipath synthetic aperture radar imaging
      • Author(s): J. DeLaurentis
      • Source: IET Radar, Sonar & Navigation, Volume 5, Issue 5, p. 561 –572
      • DOI:  10.1049/iet-rsn.2010.0225
      • Type: Article
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      • p. 561 –572 (12)
        In this report we develop a method for removing the distortions produced by multipath synthetic aperture radar (SAR) imaging. In conventional SAR systems, multipath scattering superimposes blurring artefacts on the radar image and diminishes resolution. We exploit a non-linear phase shift introduced in the multipath scattering term, of a slightly translated imaging aperture, to remove the effects of multiple scattering in an image obtained from a non-translated aperture. The multipath distortion removal is accomplished while still maintaining the resolving power of single scattering SAR.
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      Mismatched filter for analogue TV-based passive bistatic radar
      • Author(s): H. Wang ; J. Wang ; L. Zhong
      • Source: IET Radar, Sonar & Navigation, Volume 5, Issue 5, p. 573 –581
      • DOI:  10.1049/iet-rsn.2010.0136
      • Type: Article
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      • p. 573 –581 (9)
        This study examines the problem of solving the range ambiguity in analogue TV (ATV)-based passive bistatic radar (PBR). When matched filter (MF) is applied to ATV-based PBR, a range ambiguity at 19.2 km will be produced because of the 64 µs line fly-back time of the ATV signal. The relatively short range and the severity of this ambiguity make application of this type of waveform much more likely to be limited. A novel mismatched filter (MMF) algorithm is developed for solving the problem of range ambiguity. In this new MMF algorithm, the MMF factor is acquired based on minimising the overall impact of the SNR loss (SL) compared to MF and the range sidelobes energy that the authors want to suppress. And a batch version with much computational saving is also introduced. Then the performance of this batch version is studied in detail. Finally, its effectiveness is demonstrated with the application to real data acquired with an experimental PBR system.
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      Motion parameter estimation of multiple ground fast-moving targets with a three-channel synthetic aperture radar
      • Author(s): J. Qian ; X. Lv ; M. Xing ; L. Li ; Z. Bao
      • Source: IET Radar, Sonar & Navigation, Volume 5, Issue 5, p. 582 –592
      • DOI:  10.1049/iet-rsn.2010.0111
      • Type: Article
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      • p. 582 –592 (11)
        This study presents a novel motion parameters estimation technique for moving targets, including those with velocities beyond the Nyquist limit in multi-channel synthetic aperture radar data. The technique proposed in this study exploits the linear dependence between the fold factor of the cross-track velocity and the slope of the moving target trajectory in the range-compressed and azimuth time domain after performing Keystone transformation in the range frequency and azimuth time domain. The velocity ambiguity thus can be overcome. The along-track velocity can be retrieved from the chirp rate estimated by applying a new time-frequency analysis method called Keystone-Wigner transform. The algorithm of motion parameter estimation efficiently converts the two-dimensional (2-D) search into the two separate 1-D cases. The proposed method can robustly estimate the motion parameters of the fast-moving targets, which are illustrated both with simulated and real data.
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      Spectral slope-based approach for mitigating bistatic space-time adaptive processing clutter dispersion
      • Author(s): F. Colone
      • Source: IET Radar, Sonar & Navigation, Volume 5, Issue 5, p. 593 –603
      • DOI:  10.1049/iet-rsn.2010.0264
      • Type: Article
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      • p. 593 –603 (11)
        In this study, the effects of bistatic clutter spectral dispersion on space-time adaptive processing (STAP) techniques are considered. A robust spectral slope-based approach is presented for mitigating the bistatic geometry-induced performance loss by pre-processing the secondary data used for covariance estimation. Owing to its capability to compensate both the clutter spectral centres misalignment and the trace slope variability over range, this approach is shown to yield further dispersion reduction with respect to previously proposed strategies, thus improving the performance of STAP. An adaptive version of the proposed approach is also introduced, which is able to extract the required parameters from the same data set used for the covariance matrix estimation, without requiring prior knowledge or ancillary data. The performance analysis against synthetic clutter data shows that the proposed slope-based compensation technique is rather robust with respect to the spectral trace shape and estimation errors, providing equal or better performance with respect to previously derived techniques, depending on the specific bistatic geometry.
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