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Radar, Sonar & Navigation, IET

Issue 9 • Date Dec. 2011

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Displaying Results 1 - 13 of 13
  • Optimised complexity reduction for maximum likelihood position estimation in spread spectrum navigation receivers

    Publication Year: 2011 , Page(s): 911 - 923
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (795 KB)  

    In urban environments, spread spectrum radio navigation is subject to multipath propagation causing multipath errors of tens of metres. Low-complexity high-resolution channel delay estimation is crucial for position estimation in the receivers to mitigate the multipath errors. The main drawback of maximum likelihood (ML) channel delay estimation is the high computational complexity. Thus, recent publications present methods to decrease its computational complexity. These contributions assess the complexity reduction by means of signal subspace energy errors (SSEEs). This assessment of the complexity reduction is incomplete, as the relevant metric, that is, the relationship between complexity reduction and degrading position accuracy in terms of increasing root mean square error (RMSE) lacks. The authors main contribution is the derivation and analysis of this relation. The larger RMSE for complexity-reduced ML estimation algorithms compared to the implementation without complexity reduction consists of an increased noise variance and a non-zero bias. Thus, this contribution associates the SSEE and the RMSE for complexity-reduced ML estimators. Computer simulations confirm the revealed analytical relationships. Furthermore, the authors approach yields a novel method to minimise the increased noise variance of complexity-reduced ML estimation. Thus, the authors algorithms yield a lower RMSE. View full abstract»

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  • Super-resolution techniques for wind turbine clutter spectrum enhancement in meteorological radars

    Publication Year: 2011 , Page(s): 924 - 933
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1362 KB)  

    The Doppler resolution for wind turbine clutter (WTC) returns usually gets degraded when using the operational standard scanning mode of meteorological radars. Here, the use of super-resolution techniques for improving the Doppler resolution is proposed. This study concentrates on the spectral estimation based on auto-regressive coefficients and the multiple signal classification algorithm. The former usually brings to light the four components of WTC, that is, the tower and the three blades, hence outperforming the classical Fourier spectral estimation. The latter, on the contrary, may be improper for scenarios with weather returns. To derive the pertinent conclusions, both classical spectral estimation and the commented super-resolution approaches are applied to simulated and real data coming from both WTC and weather. View full abstract»

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  • Two novel methods for estimating the compound K-clutter parameters in presence of thermal noise

    Publication Year: 2011 , Page(s): 934 - 942
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (445 KB)  

    In this study, the authors present two novel methods to estimate the parameters of the compound K-clutter in presence of additive thermal noise. Based on the parametric fitting to the tail of the clutter distribution, the first method estimates simultaneously the unknown parameters. This is achieved by comparing the experimental cumulative distribution function, drawn from the recorded data intensity, to a set of curves derived from the mathematical model. To this effect, a multidimensional unconstraint non-linear algorithm; namely the Nelder-Mead method is used to minimise the residuals between the real data and the fitted curve with unknown parameters. Considering always the presence of thermal noise and based on the neuronal approaches and fuzzy inference systems, the second method also yields an accurate estimation and guarantees an inexpensive computation of the unknown parameters when the clutter-to-noise ratio (CNR), is known a priori. To assess the obtained results, the authors illustrate the effectiveness of these new methods through Monte-Carlo simulations. View full abstract»

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  • Classification of personnel targets by acoustic micro-doppler signatures

    Publication Year: 2011 , Page(s): 943 - 951
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (649 KB)  

    Classification of targets using their micro-Doppler signatures has attracted a growing interest in recent years. In addition to their main bulk translation, targets may exhibit additional motions, such as vibrations and rotations, which generate Doppler modulations in the echo that contain unique target features and thus can be used to perform target recognition. Although target classification by micro-Doppler signatures has been exploited in the radio frequency regime for radar systems, much less work has been done in acoustic. In this work, an ultrasound radar operating at 80 kHz has been developed to gather micro-Doppler signatures of personnel targets performing various actions. The performance of a range of classifiers and feature extraction algorithms in distinguishing between these micro-Doppler signatures is presented. View full abstract»

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  • Improved Gerschgorin disk estimator for source enumeration with robustness against spatially non-uniform noise

    Publication Year: 2011 , Page(s): 952 - 957
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (245 KB)  

    In this study, a characteristic equation-based Gerschgorin disk estimator (CE-GDE) is proposed for source enumeration. In CE-GDE, the diagonal averages of the array output covariance matrix of a uniform linear array are used to form a new data matrix, whose rank equals the number of the incident signals. Then the signal number is estimated by detecting the rank of this matrix with the Gerschgorin disk estimator. Numerical examples show that CE-GDE surpasses existing methods in scenarios of both spatially uniform and non-uniform noise. View full abstract»

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  • Squaring and cross-correlation codeless tracking: analysis and generalisation

    Publication Year: 2011 , Page(s): 958 - 969
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (790 KB)  

    In this study, squaring and cross-correlation codeless phase lock loops (PLLs) for global navigation satellite systems (GNSS) applications are at first reviewed. It is shown that the discriminators of squaring and cross-correlation PLLs are special solutions of the maximum likelihood (ML) equation for the estimation of the L2 P(Y) signal phase. A generalised codeless PLL (GCPLL), combining squaring and cross-correlation processing, is then derived as general solution of the ML equation. Approximate expressions for the tracking jitter of the considered codeless techniques are provided and validated using Monte Carlo simulations. The analysis is further supported by results obtained using live global positioning system (GPS) L1 and L2 signals. View full abstract»

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  • Adaptive range-spread target detection based on modified generalised likelihood ratio test in non-Gaussian clutter

    Publication Year: 2011 , Page(s): 970 - 977
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (517 KB)  

    Adaptive detection of a range-spread target is addressed for a possibly singular estimated covariance matrix, in non-Gaussian clutter modelled as a spherically invariant random vector. Firstly, a modified generalised likelihood ratio test with recursive estimator (MGLRT-RE) is derived. To improve the adaptability and to reduce the computational complexity of MGLRT-RE, a simplified MGLRT (SMGLRT) is proposed and is proved to be constant false alarm rate (CFAR) to the statistics of the texture theoretically. Based on secondary data, the heuristic SMGLRT-CA (cell-averaging) and MGLRT-RE-CA are also designed. The SMGLRT outperforms the MGLRT and MGLRT-RE; similarly, the SMGLRT-CA with fully CFAR properties outperforms the MGLRT-CA and MGLRT-RE-CA. The performance assessment conducted by Monte Carlo simulation confirms the effectiveness of the proposed detectors. View full abstract»

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  • Continuous-discrete estimation for tracking ballistic missiles in air-surveillance radar

    Publication Year: 2011 , Page(s): 978 - 986
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    A problem of tracking tactical ballistic missiles (TBMs) in a long-range air-surveillance radar is considered. An effective tracking algorithm is presented, which is based on continuous-time dynamic models of object motions and on a discrete-time model of measurement process. The estimator utilises an innovative combination of kinematic models of TBM movements in radar 'range-azimuth-elevation' coordinates, continuous-discrete extended Kalman filtering, interacting multiple-model state estimation and probabilistic data association. The performance and robustness of the new algorithm was proved by extensively testing using real and simulated radar data. For the purpose of this study its properties are illustrated using simulations. View full abstract»

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  • Oversampling gain in adaptive normalised matched filter detector

    Publication Year: 2011 , Page(s): 987 - 993
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (390 KB)  

    In radar target detection, the adaptive normalised matched filter (ANMF) detector is often used to detect moving targets in sea and land clutter environment. Its performance depends on estimation of clutter covariance matrix. The sample covariance matrix (SCM) estimator has been thoroughly analysed for independent and identically distributed Gaussian clutter vectors. Many radar systems on service use range-oversampling receivers. Referred to the range-oversampling model in the weather and oceanic radars, the spatial correlation model of range-oversampled clutter vectors is established, the error of the SCM estimator is analysed, and the range-oversampling gain, relevant to the oversampling factor and the receiver's bandwidth, is derived. The experiments using raw radar clutter data are made to verify the range-oversampling gain, showing that the range oversampling improves the performance of the ANMF detector. View full abstract»

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  • Low-frequency ultra-wideband synthetic aperture radar ground moving target imaging

    Publication Year: 2011 , Page(s): 994 - 1001
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (498 KB)  

    A method for low-frequency ultra-wideband synthetic aperture radar (SAR) imaging of ground moving targets is proposed in this study. This method can deal with large range migration of the moving target. A first-order keystone transform is used to correct range walk (first-order range migration), and range curvature (second-order range migration) is compensated by using a second-order keystone transform. Both the first-order and second-order keystone transform parameters are independent of the motion parameters, so that this method can correct the range migration for all targets without knowing their velocity. The advantage of this method is that it can correct range curvature for all targets in one processing step, so that it is simple to implement. Simulation and experimental SAR data processing results are shown to demonstrate the validity of the proposed method. View full abstract»

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  • Inverse synthetic aperture radar rotation velocity estimation based on phase slope difference of two prominent scatterers

    Publication Year: 2011 , Page(s): 1002 - 1009
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (471 KB)  

    In order to rescale an inverse synthetic aperture radar image into a homogeneous range cross-range domain, a novel method is proposed to estimate rotation velocity (RV) by exploiting the phase slope difference of two prominent scatterers on a complex image. Firstly, two prominent scatterers are automatically extracted in a range-Doppler image via watershed method. Subsequently, the signal obtained by the two scatterers is divided into two equal segments, each of which provides an estimation of the phase slope via phase unwrapping and the least-square fitting. Finally, the target RV can be estimated based on the difference of the two phase slopes. The proposed method can be implemented automatically and is more computationally efficient than the traditional methods. Finally, the results based on simulation data and real data are provided to demonstrate the effectiveness of the proposed method. View full abstract»

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  • Doppler/XNAV-integrated navigation system using small-area X-ray sensor

    Publication Year: 2011 , Page(s): 1010 - 1017
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (446 KB)  

    To reduce the area of an X-ray sensor, a Doppler/XNAV (X-ray pulsar-based navigation)-integrated navigation system is proposed. The Doppler navigation, which utilises the radial velocity relative to the Sun as the measurement information, can provide highly accurate velocity information. However, this method is completely unobservable, and cannot be used to navigate alone. The XNAV system utilising three or more pulsars is completely observable, but its navigation accuracy is low when the area of the X-ray sensor is small. As two methods are complementary to each other, a federated filter is utilised here to fuse the information from the XNAV and the Doppler navigation subsystems. As both the state and the measurement equations of two methods are non-linear, the UKF (Unscented Kalman Filter) is used as the local filters of the federated filter. Compared with XNAV, this integrated navigation method can provide better navigation performance. The simulation results demonstrate the feasibility and accuracy of this navigation method with a small-area X-ray sensor. View full abstract»

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  • Modelling roughness effects on propagation of electromagnetic waves in a maritime environment: a hybrid approach

    Publication Year: 2011 , Page(s): 1018 - 1025
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (741 KB)  

    This study presents work on radar links in the maritime environment. In order to understand and to optimise these links, the author have modelled electromagnetic wave propagation in the maritime environment, including in the presence of evaporation ducts. This modelling requires good propagation domain characterisation (maritime atmosphere, evaporation ducts etc.) and good modelling of the reflective effects of the sea surface (smooth or rough surface). In this study the author present a new method based on sea surface generation using sea spectra developed to model the sea surface roughness effects on electromagnetic wave propagation. Numerical results are given, in different configurations (duct height, transmitter altitude atmospheric conditions etc.), which enable the proposed model to be checked and highlight the interest of accurate roughness modelling in electromagnetic propagation over the sea surface. View full abstract»

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Aims & Scope

IET Radar, Sonar & Navigation covers the theory and practice of systems involving the processing of signals for radar, radiolocation, radionavigation and surveillance purposes.

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