Showing papers in "Iet Radar Sonar and Navigation in 2014"

Classification of human motions using empirical mode decomposition of human micro-Doppler signatures

Abstract: The ability to identify human movements can serve as an important tool in many different applications such as surveillance, military combat situations, search and rescue operations and patient monitoring in hospitals. This information can provide soldiers, security personnel and search and rescue workers with critical knowledge that can be used to potentially save lives and/or avoid dangerous situations. Most research involving human activity recognition employs the short-time Fourier transform (STFT) as a method of analysing human micro-Doppler signatures. However, the STFT has time-frequency resolution limitations and Fourier transform-based methods are not well-suited for use with non-stationary and non-linear signals. The authors approach uses the empirical mode decomposition to produce a unique feature vector from the human micro-Doppler signals following which a support vector machine is used to classify human motions. This study presents simulations of simple human motions, which are subsequently validated using experimental data obtained from both an S-band radar and a W-band millimetre wave (mm-wave) radar. Very good classification accuracies are obtained at distances of up to 90 m between the human and the radar.

Analysis of detection range of FM-based passive radar

Abstract: This study presents an analysis of the detection range of a passive bistatic radar (PBR) by using FM radio transmitters as the illuminators of opportunity and the analysis of a required analogue-front-end dynamic range. Firstly, the theoretical considerations are presented in which the power budget is analysed, by taking into account the specific features of the PBR such as instantaneous reception of the direct illumination signal and weak target echoes and direct path interference removal. In the second part of this study, measurements performed by using an FM-based PBR demonstrator PaRaDe (passive radar demonstrator) are presented. The PaRaDe is a deployable system operating in real time, developed at the Warsaw University of Technology, Poland. The measurements include a scan of a typical spectrum in the range of 88-108 MHz, and the analysis of the long range detection of the air targets.

Design and performance evaluation of a mature FM/DAB/DVB-T multi-illuminator passive radar system

Abstract: Passive radar (PR) systems use the target illumination by third-party transmitters, for example, from broadcast or cellular base stations, for target detection and localisation. Since PR does not use an own transmitter, it can be installed and operated at low cost and it is hard to detect and jam. These advantages and the increasing maturity of PR technology has led to growing interest in these systems over the last years. However, until now most PR systems have been rather experimental set-ups tailored to a single frequency band or implemented as laboratory test devices. This study in contrast describes the design, implementation and performance evaluation of a multi-band, multi-illuminator PR system developed at near-production stage. Starting out from a FM-broadcast-based approach, the step to DAB-based and DVB-T-based operation has already been made. As a result, a fully mobile FM/DAB/DVB-T multi-band PR system is now available, offering maximum flexibility for measurement campaigns with air, ground and sea targets. Experiments with a great variety of third-party transmitters and arbitrary transmitter-target-receiver geometries have been conducted. The design considerations and the resulting PR system concept are described, and the results of representative measurement campaigns with different types of ground and aerial targets are presented.

Phase-sensitive FMCW radar system for high-precision Antarctic ice shelf profile monitoring

Abstract: Ice shelves fringe much of the Antarctic continent, and, despite being up to 2 km thick, are vulnerable to climate change. Owing to their role in helping to control the ice sheet contribution to sea level change there is great interest in measuring the rate at which they are melting into the ocean. This study describes the development and deployment of an ice-penetrating phase-sensitive FMCW radar, sufficiently robust and with sufficiently low-power consumption to be run through the Antarctic winter as a standalone instrument, yet with the stability and mm-precision needed to detect the very slow changes in ice shelf thickness in this exceptionally demanding environment. A number of elegant processing techniques are described to achieve reliable, high-precision performance and results presented on field data obtained from the Larsen-C ice shelf, Antarctica.

On deception jamming for countering bistatic ISAR based on sub-Nyquist sampling

Abstract: Bistatic inverse synthetic aperture radar (ISAR) operates with spatially separated transmitting and receiving antennas. This study presents a method capable of generating deceptive images from a series of intercepted bistatic ISAR chirp pulses. It is demonstrated that deceptive false-target images will be induced by the under-sampled pulses which are retransmitted to a moving target and scattered by it under the principles of bistatic ISAR configuration. Additionally, the jamming idea is proved to be applicable based on the characteristics of the false-target images and the requirement of jamming power. A scattering model of Yak-42 plane with 330 point scatterers is adopted to verify the effectiveness of the jamming idea.

Two-dimensional location of moving targets within local areas using WiFi-based multistatic passive radar

Abstract: In this study the authors investigate the two-dimensional target localisation capabilities of a passive radar system based on WiFi transmissions. It is well known that the most straightforward way to achieve the target position estimation in the horizontal plane with a passive radar exploits the measurements either of a single bistatic range plus a direction of arrival (DoA) or of two bistatic ranges collected by two separate receivers. However, for a practical application it is interesting to clearly define which one of the two approaches provides the passive radar target localisation with a higher accuracy and whether combining both multiple bistatic range plus DoA measurements provides a further advantage. A multistatic configuration is considered which allows to collect a set of range/Doppler/angle measurements for a given target. Different target localisation strategies are devised and compared, based on subsets of the available measurements with the aim of understanding the localisation accuracies achievable using the different combinations of measurements. Experimental results are shown based on a passive radar prototype developed and fielded at the DIET Department - Sapienza University of Rome. This will contribute to demonstrate the fruitful application of the passive radar concept for short range surveillance.

Detection of high-speed and accelerated target based on the linear frequency modulation radar

Abstract: The high-speed movement of a target may cause range migration and Doppler frequency migration of the radar echo, which has a serious impact on the detection performance of the radar. To resolve the problem of detecting a high-speed target in linear frequency modulation radar, this study analyses the effect on the integration gain caused by range migration and Doppler frequency migration, and proposes a corresponding compensation method according to the different input signal-to-noise ratios (SNRs) of the echo signal. To compensate for range migration in high SNRs, two-dimensional median filtering and constant false alarm rate technology are combined to estimate the speed. For low SNRs, based on coarse valuations, the authors use the discrete Fourier transformation (DFT) to realise the fractional delay cell to improve speed accuracy. Furthermore, to compensate for Doppler frequency migration, an instantaneous cross-correlation method is proposed for high SNRs, which is combined with the fractional Fourier transform method to estimate the acceleration for low SNRs. The input SNR threshold for the different algorithms is then analysed using simulation data, and the theoretical reference value is shown. Finally, the study verifies the effectiveness of the proposed methods through simulation and measured data.

A frequency-domain three-stage algorithm for active deception jamming against synthetic aperture radar

Abstract: Efficient generation of jamming signal is an important but intractable issue in active deception jamming against synthetic aperture radar. Considerations must be given to both the computational complexity and the focus depth of the false scatterers of a deception template. However, existing methods cannot meet both demands mentioned above when generating jamming signal of an extended false scene or scattered false targets. In this study, a frequency-domain three-stage algorithm (FDTSA) is proposed. In theory, the jammer system is deliberately reformatted in the two-dimensional frequency domain. Accordingly, the implementation of the FDTSA can be effectively accelerated by fast Fourier transform and by separating the modulation process of a repeat jammer into three stages: the offline stage, the initialisation stage and the real-time modulation stage. Theoretical analyses and simulation results indicate that the FDTSA can get rid of severe focus deterioration of the false scatterers and reasonable computational load is required.

Improved method for synthetic aperture radar scattered wave deception jamming

Abstract: This study presents an improved scattered wave jamming method for synthetic aperture radar (SAR). The jammer adjusts the time-delay and the phase of the intercepted SAR signal. Then, a false scene is created to provide an effective protection for a certain area. It requires a lower jamming power than barrage jamming and has less computational complexity than direct-path deception jamming. Based on the performance analysis of scattered wave jamming, pulse repetition intervals to delay retransmission, and a modulation centre shift are proposed as improvements to enlarge the jamming area.

Median matrices and their application to radar training data selection

Abstract: This study deals with the problem of covariance matrix estimation for radar signal processing applications. The authors propose and analyse a class of estimators which do not require any knowledge about the probability distribution of the sample support and exploit the characteristics of the positive definite matrix space. Any estimator of the class is associated with a suitable distance in the considered space and is defined as the median matrix of some basic covariance matrix estimates obtained from the available secondary data set. Then, the new devised estimators are applied to the problem of secondary data selection and their performances are compared with those obtained using geometric barycenters. The results show that data selectors exploiting geometric medians can outperform those based on geometric barycenters but the former requires a computational complexity higher than the latter.

Review and classification of vision-based localisation techniques in unknown environments

Abstract: This study presents a review of the state-of-the-art and a novel classification of current vision-based localisation techniques in unknown environments. Indeed, because of progresses made in computer vision, it is now possible to consider vision-based systems as promising navigation means that can complement traditional navigation sensors like global navigation satellite systems (GNSSs) and inertial navigation systems. This study aims to review techniques employing a camera as a localisation sensor, provide a classification of techniques and introduce schemes that exploit the use of video information within a multi-sensor system. In fact, a general model is needed to better compare existing techniques in order to decide which approach is appropriate and which are the innovation axes. In addition, existing classifications only consider techniques based on vision as a standalone tool and do not consider video as a sensor among others. The focus is addressed to scenarios where no a priori knowledge of the environment is provided. In fact, these scenarios are the most challenging since the system has to cope with objects as they appear in the scene without any prior information about their expected position.

Sparse subband fusion imaging based on parameter estimation of geometrical theory of diffraction model

Abstract: This study focuses on sparse subband fusion imaging. A method based on high-precision parameter estimation of geometrical theory of diffraction (GTD) model is given. Considering the incoherence problem in each subband data, a coherent processing method is adopted in the paper. Based on an all-pole model, it makes use of the phase difference of pole and scattering coefficient between each sub-band to effectively estimate the incoherent components. After coherent processing, the high and low frequency subband data can be expressed as a uniform all-pole model. The gapped-data amplitude and phase estimation algorithm is adopted to fill up the gapped band. Finally, fusion data is gained by high precision parameter estimation of GTD-all-pole model with full-band data, such as scattering center number, scattering center type and amplitude. The experimental results of simulated data with fixed-points indicate that the resolution of one-dimensional (1D) range profile and 2D inverse synthetic aperture radar (ISAR) image based on this method is better than that of each sub-band. In this way, the validity of the proposed method is proved.

Mitigating interference via spatial and spectral nulling

Abstract: Phase-only transmit nulling may help the next generation of radar systems operate in an over-crowded radio frequency spectrum. The reiterative uniform weight optimisation (RUWO) algorithm generates constant modulus radar waveforms with spatial, frequency or space-frequency nulls for multiple-input multiple-output (MIMO) transmit arrays by utilising the maximum signal-to-interference plus noise ratio framework in a reiterative fashion. This study presents loop-back and open air experimental results, obtained using an eight-channel X-band coherent MIMO radar test bed, that demonstrate the use of RUWO to generate constant modulus waveforms that possess spatial and/or frequency nulls. The RUWO algorithm is first used to deterministically generate phase-only weights that produce spatial, frequency or space-frequency nulls at baseband in a loop-back configuration. The algorithm is then utilised to generate weights to produce spatial nulls, both deterministically and adaptively, for the full eight-channel test bed in an open air configuration. The deterministic and adaptive strategies are compared; results demonstrate that RUWO can be used to create spatial nulls and highlight the need for careful calibration of both the transmitter and the receiver.

Double phase estimator: new unambiguous binary offset carrier tracking algorithm

Abstract: Several new global navigation satellite system modulations adopt a binary offset carrier (BOC) subcarrier to shape the signal spectrum, increase the frequency separation and improve the tracking performance. BOC modulated signals are, however, characterised by ambiguous multi-peaked correlation functions and several techniques have been proposed in the literature to solve the problem of locking into secondary peaks. In this study, a novel unambiguous BOC tracking technique, the double phase estimator (DPE), is designed to account for the effect of signal bandlimiting. The DPE is an effective alternative to the double estimator (DE) tracking technique where the subcarrier lock loop is replaced by a subcarrier phase lock loop. In the presence of signal bandlimiting, the DPE is able to generate local signal replicas matched in a better manner to the input components, outperforming the DE. The performance of the DPE is thoroughly characterised and the processing of real wideband BOC signals is used to demonstrate the effectiveness of the algorithm proposed. In addition to this, the DPE requires a lower computational load than the DE and thus should be adopted for the processing of wideband BOC signals.

Maximum-likelihood-based approach for single-pass synthetic aperture radar tomography over urban areas

Abstract: Synthetic aperture radar (SAR) tomography (TomoSAR) is one of the key techniques in remote sensing for a sophisticated, three-dimensional (3D) analysis of complex scenes such as forests or urban areas. During recent years, much progress has been made in order to deal with unfavourable data conditions and to further enhance the achievable resolutions. Since TomoSAR has essentially be seen as a spectral estimation problem in the context of array signal processing, most of the methods investigated until now rely on a relatively large tomographic aperture and a relatively high number of receiving antennas in order to be able to separately reconstruct scatterers below the Rayleigh resolution limit. In contrast to that, this study proposes a maximum-likelihood-based approach for tomographic SAR inversion, which provides a better height resolution than conventional array signal processing approaches even if the number of antennas or the overall baseline size is limited. The algorithm is tested on real multi-baseline SAR data acquired over an urban area by an airborne single-pass four-antenna system operating in the millimetre-wave domain. First results show the feasibility of the method both with respect to 3D scatterer reconstruction and 3D SAR focusing.

Marginal unscented kalman filter for cross-correlated process and observation noise at the same epoch

Abstract: The independence of the process and observation noises is the prerequisite of many Kalman-type filters. However, the fact is that these two noises may be correlated with each other in actual applications. The filtering of the non-linear systems with cross-correlated process and observation noises at the same epoch is studied. First, a decorrelated scheme is introduced and a pseudo non-linear process equation is reconstructed in which the corresponding pseudo process noise is no longer cross-correlated with the observation noise; so a celebrated non-linear filter, that is, the unscented Kalman filter (UKF) can be used to filter the non-linear problem. Second, the (conditionally) linear substructure in the above non-linear system is exploited and a refined filter called marginal UKF is employed so as to reduce computational load without deteriorating the accuracy. The performance of the standard UKF for the original system equations, the standard and marginal unscented UKFs for the reconstructed system equation are compared in the simulation. From the results of the simulation, the theoretical statements are validated, and some interesting but not surprising phenomena are also founded, that is, the performance of the conventional filter actually does not degenerate, whereas that of the proposed filters become better when cross-correlation exists and increases. This phenomenon can be due to the fact that the proposed filters exploited the extra information buried in the cross-correlation, whereas the conventional filter fails to do so.

Space–time interference analysis and suppression for airborne passive radar using transmissions of opportunity

Abstract: This study presents the space-time snapshot models for the interfering passive signals received by the airborne passive radar which uses a ground-based stationary non-cooperative transmitter. The random range sidelobes couplings of the direct path and of the strong clutter signals into further range cells are major concerns in moving target detection performance. The least squares-based adaptive interference cancellation technique is proposed to efficiently suppress the direct path, strong clutter and Doppler-shifted strong clutter signals present at each antenna element prior to matched filter processing. In mitigating the interfering signals, their corresponding random range sidelobes will also be suppressed by the same amount. Ground-based moving passive radar trials were conducted to validate and ascertain the effectiveness of the proposed adaptive interference cancellation algorithm.

GSM passive coherent location system: performance prediction and measurement evaluation

Abstract: This study describes the processing scheme of the FKIE (Fraunhofer Institute for Communication, Information Processing and Ergonomics) GSM-based passive coherent location (PCL) system, which consists of an antenna and signal processing adapted to the GSM waveform and of target tracking based on multi-hypothesis tracking. To overcome the limitations from a single bistatic transmitter-receiver pair, fusion of the measurements from different geometries is the key component of a GSM PCL system. The authors demonstrate a significant improvement in target position estimation from the tracking process on the basis of real data and theoretical performance bounds. The impact of the transmitter-target-receiver geometry is discussed and the effect of the exploitation of prior context knowledge (e.g. clutter and land maps) on maritime traffic surveillance is shown.

Exploiting multiple a priori spectral models for adaptive radar detection

Abstract: This study deals with the problem of adaptive radar detection when a limited number of training data, due to environmental heterogeneity, is present. Suppose that some a priori spectral models for the interference in the cell under test and a lower bound on the power spectral density (PSD) of the white disturbance term are available. Hence, generalised likelihood ratio test-based detection algorithms have been devised. At the design stage, the basic idea is to model the actual interference inverse covariance as a combination of the available a priori models and to account for the available lower bound on the PSD. At the analysis stage, the capabilities of the new techniques have been shown to detect targets when few training data are available as well as their superiority with respect to conventional adaptive techniques based on the sample covariance matrix.

Power allocation for range-only localisation in distributed multiple-input multiple-output radar networks - a cooperative game approach

Abstract: Power allocation in distributed multiple-input multiple-output radar is investigated for range-only target localisation such that the determinant of Bayesian Fisher information matrix (B-FIM) is maximised. The B-FIM is derived from a signal model that incorporates the propagation path loss, the target reflectivity, the transmitted power and target prior information. The authors model the problem as a cooperative game and exploit the solution concept of Shapley value to distribute a given power budget among all transmitting radars for localisation and integrate the algorithm with a sequential Bayesian estimator to localise target. In numerical simulations, it is shown that uniform power allocation is not in general optimal. They illustrate the impact of the radar antenna geometry and target location prior density on the allocation results and demonstrate the superior performance of the proposed optimal power allocation scheme via Monte Carlo simulations.

Amplitude scintillation effects on SAR

Abstract: Space-based low-frequency synthetic aperture radar (SAR) is affected by the ionosphere, which induces both phase and amplitude fluctuations, known as scintillation, into the radar signal. This paper describes the effect of amplitude scintillation on SAR imagery. The two-way amplitude and intensity probability density functions (pdf) for both monostatic and bistatic SAR are derived from the one-way Nakagami-m distribution. The moments are then used to determine the SAR radiometric calibration error and image contrast from the one-way S 4 index. It is also shown that monostatic SAR experiences an S 4-dependent radar cross-section (RCS) enhancement that is not experienced by bistatic SAR. The anisotropy of the ionospheric irregularities strongly affects the degree to which amplitude scintillation will be visible in SAR imagery. The description of anisotropic effects is reviewed and extended to cover SAR. The variation over the Earth is illustrated, showing that a sun-synchronous satellite will experience the strongest effect near Brazil. Two PALSAR images of the same area of Brazilian rainforest are compared, one of which shows azimuthal streaking, corresponding to an amplitude modulation of ± 1 dB. The one-way S 4 index is determined from this imagery using both the RCS enhancement and image contrast measures of S 4, which produce similar results.

Adaptive robust ultra-tightly coupled global navigation satellite system/inertial navigation system based on global positioning system/BeiDou vector tracking loops

Abstract: With the development of global navigation satellite system (GNSS), the GNSS/inertial navigation system (INS) integrated system offers the users better positioning or navigation performance. This paper proposes an adaptive robust ultra-tightly coupled GNSS/INS system based on a novel vector tracking strategy for combining both global positioning system (GPS) L1 and BeiDou B1 signals' tracking together. The inherent mechanism of the vector tracking approach has been analysed to describe the relationship between the replica signals and user's dynamic state. Then, an adaptive robust filter is used to gain the accurate estimates of vehicle states when the vehicle is under a weak-signal or large manoeuvring environment. Finally, the experimental platform is set up using a GPS/BeiDou signal simulator and an inertial measurement unit simulator and the test results show that the proposed ultra-tightly coupled system can keep the tracking loops from the high dynamic perturbations, which saves the cost time of signal reacquisition. Moreover, the presented adaptive robust ultra-tightly coupled system can obtain a higher accuracy than Kalman filtering in a simultaneous weak-signal and large manoeuvring environment.

Iterative least-squares-based wave measurement using X-band nautical radar

Abstract: In this study, an existing iterative least-squares (LS) method for determining ocean surface currents from X-band nautical radar images is modified for extracting ocean wave information from the same data. Within each iterative step, the image spectra samples are classified as containing contributions from fundamental, first-order and higher harmonic waves or noise. Based on the classification result, a new scheme is proposed to increase the robustness of current estimation. This involves automatically adjusting the first threshold that is used for obtaining an initial guess of the current velocity in the iterative LS method. The proposed wave algorithm directly uses the classified fundamental and first-order harmonic wave components for wave spectra and parameter retrieval. Unlike previous wave analysis techniques in which a bandpass filter is required to eliminate the non-wave contributions after the current velocity is obtained, the proposed algorithm simplifies the wave retrieval without such a bandpass filter. Algorithm verification is first conducted by using simulated radar images. Subsequently, the method is applied to field radar data and the results are compared with wave-buoy measurements. Wave parameters from both types of data show that the modified wave algorithm produces results that are close to those achieved using traditional algorithms.

Fast factorised backprojection algorithm in elliptical polar coordinate for one-stationary bistatic very high frequency/ultrahigh frequency ultra-wideband synthetic aperture radar with arbitrary motion

Abstract: The precise disposal of azimuth variance of range cell migrations and motion errors in the one-stationary bistatic very high frequency/ultrahigh frequency ultra-wideband synthetic aperture radar imaging is a real challenge for efficient frequency-domain algorithms, but can be precisely managed by time-domain approaches. In this study, a novel bistatic fast factorised backprojection (BFFBP) algorithm is presented, which can deal with these two effects accurately and achieve the computational performance in parity with frequency-domain algorithms. First, the imaging geometry with arbitrary motion in elliptical polar coordinate is provided, and the analytical expression of the bistatic backprojection algorithm in this coordinate system is derived, which provides a theory basis for the proposed algorithm. Then, based on the subaperture imaging geometry, the sampling requirements considering motion errors is deduced, which offers the optimal tradeoff between the imaging quality and computational speed. The advantage of using elliptical polar coordinate system for implementing the BFFBP algorithm is analysed. Finally, the implementation and computational burden of the BFFBP algorithm are discussed. Simulation results are shown to prove the correctness of the theory analysis and validity of the proposed approach.

Persymmetric detectors with enhanced rejection capabilities

Abstract: In this study, the authors deal with the problem of adaptive detection of point-like targets in Gaussian disturbance with unknown but persymmetric structured covariance matrix induced by the space and/or time symmetry of the sensing system. In this framework, they devise and assess two selective receivers exploiting the Rao test and the generalised likelihood ratio test design criteria. The performance assessment, conducted by Monte Carlo simulation, has shown that the proposed receivers can significantly outperform their unstructured counterparts and guarantee enhanced rejection performance of unwanted signals with respect to their natural competitors.

Wideband-scaled Radon-Fourier transform for high-speed radar target detection

Abstract: High target speed, long pulse duration or wide signal bandwidth may cause noticeable scale effect on radar echoes, for which the conventional narrowband matched filter may introduce an obvious signal-to-noise ratio (SNR) loss for target detection. To obtain the ideal SNR gain in the above scenarios, a novel long-time coherent integration method has been proposed, namely wideband-scaled Radon-Fourier transform (WSRFT). The proposed WSRFT can compensate the scale effect not only on the single pulse but also among the multiple pulses in a long coherent integration time. Furthermore, the performance comparison between the proposed WSRFT and the existing Radon-Fourier transform method is given. Finally, some numerical experimental results are also provided to demonstrate the effectiveness of the proposed WSRFT method.

Simulation analysis and experimentation study on sea clutter spectrum for high-frequency hybrid sky-surface wave propagation mode

Abstract: This study simulated the broadening first-order sea clutter spectrum and analysed the influence of ionosphere and bistatic angle on sea clutter spectrum for high-frequency (HF) hybrid sky-surface wave radar based on the mechanism of sea clutter broadening. Firstly, according to the propagation characteristics of HF waves in the ionosphere and the mechanism of the ionosphere contamination, a method of dynamic ionospheric phase contamination simulation is introduced. Secondly, the formula of the Bragg frequency of first-order sea clutter is presented derived from the system configuration, and a simulation method of broadening sea clutter is given. The influence of bistatic angle and different ionosphere state on the first-order sea clutter spectrum is further analysed. Finally, the results of theoretic analysis are examined with the experimental results based on the newly developed integrated HF sky-surface wave radar experimental system, and the dominant factor of sea clutter broadening is studied. Simulation results show that the results of experiment consist with that of theoretic analysis, simulated broadening sea clutter can better describe the characteristics of measured sea clutter.

Robust radar waveform recognition algorithm based on random projections and sparse classification

Abstract: To solve the limitations existing in the feature-based recognition method in information completeness and redundant of the representation and the noise robustness, a radar waveform recognition algorithm based on random projections and sparse classification (SC) is presented. Construction of the framework of the proposed algorithm consists of two phases. In the first phase, the compressed signals by random projections are used instead of traditional signal features to represent the original signal. In the second, the robust SC approach is investigated to the radar waveform recognition. Compared with the existing feature-based recognition method, the random projections and sparse classification-based algorithm can improve the information completeness, efficiency and the noise robust. The validity of the recognition algorithm is demonstrated with the analysis and simulations.

Detection of a distributed target with direction uncertainty

Abstract: In this study, the authors deal with the problem of detecting a distributed target in coloured noise with unknown covariance matrix. The target echoes are all assumed to come from the same direction. However, the exact direction is unknown a priori. Precisely, the signal steering vector lies in a certain known subspace, but with unknown coordinate. They derive the Wald test and two-step Wald test and also show that there is no meaningful Rao test or its two-step variation. Moreover, it is found that the two-step Wald test is equivalent to an existing direction detector. Additionally, it is shown that the Wald test possesses the constant false alarm rate property. Some numerical examples are given to compare the detection performance of the novel direction detector with its counterparts, both in the cases of matched and mismatched signals.

Cramér-Rao lower bound with P d < 1 for target localisation accuracy in multistatic passive radar

Abstract: By exploiting the sources of opportunity not designed for radar applications, the passive radar system often operates with a P d in the range from 60 to 85% for acceptable false alarm rates. Multistatic radar networks can be used to both increase detection capability and localisation accuracy. The standard Cramer-Rao lower bound (CRLB) cannot be used for a realistic assessment of the target localisation accuracy in a surveillance area since it provides optimistic predictions. In this study, the authors derive the CRLB with missing observations, namely for P d < 1, for the multisensory case. The results are illustrated for the case study of a multistatic passive radar exploiting FM radio transmissions where each bistatic pair within the network is assigned with a detection probability for each target position in the surveillance area. The obtained CRLB with P d < 1 is then employed to compare the localisation performance achievable by a multistatic passive radar when using different sets of measurements: (A) only range measurements, (B) range and Doppler frequency measurements and (C) Doppler frequency measurements only. The reported results show that the proposed CRLB with P d < 1 yields a more reliable prediction of the achievable performance thus allowing a fair comparison of the above different strategies for target localisation.