Passive Coherent Location System Research Articles

Scalable multitarget tracking using PCL in SFN with 3D data association uncertainty

Passive coherent location (PCL) has attracted widespread attention due to its low cost, good concealment, and strong anti-stealth. When multiple illuminators operating in a single frequency network are used in a PCL system for multitarget tracking, the three-dimensional (3D) data association uncertainty among the illuminators, measurements and targets has to be dealt with because it will significantly increase computational complexity and reduce scalability. To solve this problem, a scalable multi-association belief propagation (MA-BP) approach for multitarget tracking is proposed. By factorizing the joint probability density function, the tracking problem is described by a factor graph, in which two new illuminator-target oriented and measurement oriented association variables are defined to describe the 3D data association uncertainty. Furthermore, under the Gaussian assumption, a Gaussian version of MA-BP, named as multi-association Gaussian belief propagation (MA-GaBP), is implemented with a generalized virtual measurement model. The MA-GaBP approach can further reduce memory requirements and computational complexity. Simulation results show that the proposed approach effectively solves the 3D data association uncertainty, and has satisfied tracking accuracy and scalability.

SSB-Based Signal Processing for Passive Radar Using a 5G Network

This paper presents an alternative processing chain for the passive radar using fifth-generation (5 G) standard technology for broadband cellular networks as illuminators of opportunity. The proposition is to use a 5 G synchronization signal block's (SSB) periodically transmitted modulated pulse in 5G-based passive coherent location (PCL) system processing. Although the SSB periodicity limits the velocity ambiguity, the paper describes a solution to tackle this problem in a single target scenario. The method is advantageous when there is a lack of transmission in the telecommunication channel, and the 5 G SSB is the only existing signal. The paper proposes a signal processing pipeline for 5G-based PCL that is inspired by passive radars using non-cooperative pulse radar as an illumination source. The method has been validated using simulated and real-life 5 G data measurements. The results presented in the paper show the possibility of detecting a moving target with a lack of data transmission in the 5 G network, using only the SSB when the classical passive radar signal processing fails. The presented results prove the possibility for a significant increase of 5 G network-based PCL utilization in short-range applications.

UWB Wire-Bowtie Array for FM-PCL Passive Radar

Passive coherent location (PCL) systems using commercial FM radio broadcast stations as illuminators of opportunity (FM-PCL) require an antenna system with a null in its radiation pattern for suppressing the direct path interference (DPI) from the selected FM broadcast station. To maximize the surveillance coverage of the FM-PCL, ideally, the antenna should have a cardioid radiation pattern, which can be obtained by the ideal couplet of isotropic radiators. We carry out a theoretical and experimental analysis to show that such a cardioid pattern cannot be realized by a couplet of cylindrical wire antennas. Therefore, we introduce an alternative array configuration and at the same time seek a simple and low-cost antenna solution for FM-PCL. The proposed antenna is a two-element array of UWB wire bowties, which has an ultrawide bandwidth, a stable main beam, a large beamwidth, and a fixed array setup within the FM-PCL frequency range (88–108 MHz), leading to a simple antenna implementation. At the same time, as it does not require expensive RF and mechanical parts, a low-cost antenna solution for FM-PCL is obtained. Hence, the proposed antenna satisfactorily meets the goal of this work, i.e., simple and low-cost antenna solution for the FM-PCL passive radar.

Learning Resource Allocation in Active-Passive Radar Sensor Networks

Recent advances in Passive Coherent Location (PCL) systems make combined active and passive radar sensor networks very attractive for both military and civilian air surveillance. PCL systems seem promising as cost-effective gap fillers of active radar coverage especially in alpine terrain and also as covert early warning sensors. However, PCL systems are sensitive to changes of Transmitters of Opportunity (ToO). Many approaches for energy-efficient target detection have been proposed for active radar sensor networks. However, energy-efficiency and topology optimization of combined active-passive radar sensor networks in realistic scenarios have been poorly studied until today. We here propose an unsupervised learning approach for topology optimization and energy-efficient detection in combined active-passive radar sensor networks. The interdependence of active and passive sensors in the network and the given target scenario is naturally accounted for by our approach. Optimal power budget and detection sectors of active radars and the most useful ToOs for each PCL sensor are simultaneously learned over time. This is a critical contribution for minimizing the need for active radar power budget and PCL computational resources. The power budget of active radars is minimized in a way that the added value of PCL sensors is fully exploited. We also demonstrate how our approach dynamically relearns to achieve robust performance when changes in the ToO of PCL sensors occur. We test our approach in a simulation suite for active-passive radar sensor networks using real-world air surveillance data and ToOs under real-world topographical conditions.

Array Manifold Measurement and Verification for UCA Calibration in Multistatic PCL System based on FM Broadcasting

This study describes a method of measurement and verification of array manifold of uniform circular array antenna applicable to multistatic Passive Coherent Location(PCL) system using FM broadcasting. In an environment of outdoor test where FM broadcast signals are scattered, array manifold measurement methods using network analyzer and multi-channel digital receiver are introduced. Also, the descriptions and solutions for the test limits of each measurement method and the considerations affecting the measurement accuracy are presented. In addition, to verify the validity of the measured array manifold, the gain and phase difference were compared with the array manifold data obtained by EM simulation, and the effectiveness and accuracy of the measured array manifolds were compared and analyzed by estimating the direction of arrival of the FM broadcast signal received from the multistatic PCL system. Keywords: Multistatic PCL, Uniform Circular Array, Array Manifold, DOA Estimation Keywords: 멀티스태틱 PCL, 원형 배열 ì•ˆí Œë‚˜, ì–´ë ˆì´ 매니폴드, 도래각 ì¶”ì •

Design of a Wideband Coupled Feed Dipole Antenna for PCL Array Systems

This article proposes the design of a wideband coupled feed dipole antenna for Passive Coherent Location (PCL) systems. The proposed antenna consists of an internal direct feed dipole and an external coupled feed dipole. This coupled feed mechanism, which is often used in microstrip patch antennas, is applied to the dipole element for a wide matching bandwidth. To verify the operating principle of the proposed antenna, an equivalent circuit model is investigated along with some parametric studies of the coupling effect. The proposed antenna is then extended to an eight-element uniform circular array to confirm the beamforming performance for PCL systems. The results demonstrate that the coupled feed dipole element is more suitable to enhance the matching bandwidth compared to a conventional dipole antenna.

Array Antenna Design for Passive Coherent Location Systems with Non-Uniform Array Configurations

This study investigates non-uniform array configurations to maximize the beamforming performance of passive coherent location (PCL) systems. The proposed array consists of eight dipole elements that are divided into two groups with different distances from the array center. This double-layered non-uniform configuration is designed considering the array antenna characteristics (peak-to-side lobe ratio, first null bandwidth, null width, and null depth). The resulting antenna array can provide more appropriate patterns for PCL systems than a conventional uniform circular array. The target detection performance of the proposed array in PCL systems is tested in a certain scenario. The results demonstrate that the proposed antenna in PCL systems can detect the target with Doppler and range errors of 1 Hz and 1.2 km, respectively, in a given situation.

Design and analysis of an 8‐element dipole array for passive coherent location systems

AbstractThis article deals with a design and analysis of an 8‐element dipole array for passive coherent location (PCL) systems. The array is composed of eight identical dipole elements that are arranged at a radius of 0.5λ0 from the center to the elements. To verify the performance for the PCL system, the array is fabricated and measured in an outdoor test site. Array performances such as the antenna gain, peak to side lobe ratio (PSLR), half‐power beam width (HPBW), null width, and null depth are then analyzed. The results demonstrate that the proposed array has beam pattern characteristics suitable for PCL systems.

A Passive Radar System for Monitoring of Coastal Areas Ship Traffic Using Satellite Illumination Signals

Introduction. Increasing requirements for improving of information systems for ensuring navigation safety in coastal areas of marine waters determine the search of new engineering and scientific solutions. The creation of a passive coherent location systems (PCL), based on existing sources of electromagnetic radiation (in particular, global navigation satellite system (GNSS) signals) as radar illumination of the monitored space is of particular interest. During development and implementation of the systems, there are a number of problems related to the search of highly efficient processing algorithms, to the optimization of structure and functioning modes when the system is a part of a complex multi-position monitoring system in coastal areas. Aim. Rationale of the structure of bistatic PCL system with GNSS illumination signal, analysis of methods for increasing of the level of reflected signals, development of a general signal processing algorithm of the system receiver unit, formation of proposals for the creation of multi-position radar system (MP radar) for coastal areas navigation monitoring. Materials and methods. Mathematical modeling, theory of signals, methods of digital signal processing. Results. The structure of the bistatic PCL with GNSS illumination signal for monitoring in coastal areas of marine waters to ensure navigation safety has been developed. Methods for increasing the power level of satellite signals at the input of the receiving device have been proposed. General signal processing algorithm and the algorithm of CAF calculation in the bistatic PCL system using GPS C/A code satellite signal for sea surface coastal areas monitoring have been developed. Conclusion. The considered bistatic PCL system with GNSS illumination may be applied as a part of MP radar for monitoring in areas of heavy vessel traffic to ensure the safety, for operational control of marine operations in the high seas, for quick analysis of the situation at sea in an emergency.

Polarimetric Passive Radar: A Practical Approach to Parametric Adaptive Detection

Polarimetric diversity has been recently shown to significantly improve the target detection performance in the passive radar systems if properly exploited to mitigate the competing interference. An adaptive processing scheme is presented in this article, leveraging the information conveyed using multipolarized receiving antennas and modeling the disturbance as a multichannel autoregressive process. Despite the fact that this approach operates with a limited number of the adaptive degrees of freedom, the long integration time exploited by a passive radar typically requires a substantial computational cost and ad hoc expedients for its application. Therefore, a modified cost-effective implementation of the conceived solution is proposed in order to reduce the computational burden while controlling the resulting loss. The authors extensively demonstrate the effectiveness of the proposed solution against the experimental data collected by an FM radio-based passive coherent location system. The experimental results show that the proposed processing scheme yields a remarkable improvement with respect to both the conventional processing at the single polarimetric channel and the state-of-the-art strategies exploiting the polarization diversity in passive radars.

Pilot‐based detection for DVB‐T passive coherent location radars

This study investigates the feasibility of pilot-based detection for passive coherent location (PCL) radars exploiting digital video broadcasting-terrestrial (DVB-T) signals. The DVB-T signal is formed by two parts: a data signal and a pilot signal. The parameters of the pilot signal are known thanks to the DVB-T standards that permit the generation (at the receiver) of the pilot signal. The pilot recovery technique, based on the known DVB-T standard, is utilised in DVB-T based PCL systems to reduce the number of the reception channels by considering a locally generated pilot signal as a reference signal. Consequently, no reference channel is required, which reduces the cost and the complexity of the resulting PCL system. In this work, the authors propose a signal processing method to achieve this goal. They consider theoretical analysis, simulations and real-data results to validate the feasibility of such a system.

Design and Performance Prediction of a Dual-Band Coupled-Fed Dipole Array Antenna for PCL Systems in the VHF Band

This article proposes the design of a dual-band coupled-fed dipole antenna for passive coherent location (PCL) systems in the very high frequency (VHF) band. The proposed indirect coupled feed mechanism, which is often employed in microstrip patch antennas, is first applied to VHF band dipole elements for dual-band matching. To confirm the effectiveness of the proposed design, we fabricate the coupled-fed dipole element and measure antenna characteristics, such as the voltage standing wave ratio (VSWR) and the antenna gain. The proposed antenna element is then applied to an eight-element circular array to form the reference and surveillance beams for PCL systems. Finally, the target location is estimated by constructing amplitude-range doppler (ARD) maps for one frequency modulation (FM) and two terrain digital multimedia broadcasting (T-DMB) illuminators in the Seoul-Gyunggi urban area. The results confirm that the proposed element is suitable for dual-band PCL systems in the VHF band compared to a conventional dipole antenna.

Multistatic Doppler Estimation Using Global Positioning System Passive Coherent Location

In previous works, methods were explored for position estimation utilizing satellite-borne signals of opportunity, mainly the global positioning system (GPS). The GPS signal was exploited for use in a multistatic passive coherent location (PCL) system. The GPS signal is especially attractive for PCL applications because of the native capability to produce position and velocity estimation. This paper examines the signal specifications for PCL implementation and explores the potential limitations of the proposed solutions. GPS specific methods are developed for multistatic PCL velocity estimation in a three-dimensional plane. The method developed is combined with previously completed work of GPS PCL position estimation for a complete system design in range and Doppler. The PCL system is evaluated against conventional GPS position estimation and velocity estimation and proves to have comparable metrics of performance. Analysis and simulation are performed for verification and validation of the developed methods.

TDOA‐based adaptive observer trajectory optimisation algorithm for tracking in passive coherent location system

In the passive coherent location system with fixed observers, the target tracking performance is limited by the inappropriate localisation geometry. This study proposes an adaptive observer trajectory optimisation (AOTO) algorithm in terms of minimising the geometric dilution of precision (GDOP) based on the time difference of arrival (TDOA) measurements gained from multiple emitters. The target states are estimated by the extended Kalman filter (EKF) algorithm. Simulation results demonstrate that the AOTO algorithm can effectively improve the tracking accuracy compared with the corresponding tracking approaches with fixed observers.

Performance analysis of the reference signal reconstruction for DVB-T passive radars

Abstract The present work investigates the reference signal reconstruction method for passive coherent location (PCL) radars exploiting Digital Video Broadcasting-Terrestrial (DVB-T) signals. The reference signal reconstruction improves the signal-to-noise ratio (SNR) of the reference signal, which enhances the detection probability for DVB-T based PCL systems. The existing approach for the reference signal reconstruction is performed by demodulating the received reference signal to retrieve the transmitted quadrature amplitude modulation (QAM) symbols and modulate them to obtain the reconstructed signal. For low SNR values, the QAM symbol detection is accompanied with a significant error, which leads to a mismatch between the reconstrued signal and the exact one. Consequently, the expected improvement due to the signal reconstruction is limited. In this work, we propose an optimum reconstruction method which filters the detected QAM symbol prior to the remodulation step. To validate the proposed method, we retrieved analytic expressions for the detection and false-alarm probabilities and verified them through Monte-Carlo simulations. In addition, real-data sets were used to evaluate the proposed method performances. The results show that the proposed method outperforms the conventional one by extending the feasibility of the reference signal reconstruction for low SNR values.

Maximum‐likelihood angle estimator for multi‐channel FM‐radio‐based passive coherent location

Frequency-modulation-based (FM-based) passive coherent location (PCL) systems can estimate the target location/velocity by exploiting a single FM channel. In order to improve the performance of PCL systems, multi-channel-single-transmitter setup-based PCL systems have been studied recently. However, it has not yet been considered for direction of arrival estimation based on the multi-channel configuration. Thus, the authors propose a maximum-likelihood angle estimator exploiting the multiple FM-radio channels and derive the Cramer-Rao bound for verifying the convergence of the proposed method in the sense of root-mean-square error (RMSE). In addition, they propose a target association algorithm for solving the ambiguity problem in selecting the steering vectors of each target. Computer simulations are included to show the estimation performance of the proposed method and to compare the RMSE of the single-channel case with that of the multi-channel case.

JIE for a class of MD systems

In multi-detection (MD) systems including over-the-horizon radar (OTHR) systems, the forward-based receivers systems and passive coherent location systems, resolvable multiple detections of one target due to the multi-path propagation will be received, in which both identification (including measurement association and propagation mode/transmitting origin identification) and estimation (including path-conditional state estimation and multi-path track fusion) are deeply coupled and affect each other. Up to present, all corresponding methods fall into the scope of sequential identification orientated or estimation orientated processing, and hence the solutions are not satisfactory. Here the joint identification and estimation scheme for the MD systems (MD-JIE) is developed based on the generalized Bayes risk considering both identification and estimation performance. The likelihood-ratio function and the conditional probability density function as the identification cost and estimation cost are recursively calculated, respectively. Taking the data-association constraints into consideration, the proposed MD-JIE scheme is implemented via online constrained optimization technology. Compared to the identification-then-estimation (ITE) method and the estimation-then-identification (ETI) method, the proposed MD-JIE method prevails in the joint performance measure with the higher correct identification rate than the ETI method and the smaller root MSE than the ITE method. Besides, the robustness of the proposed method is verified.

Global positioning system processing methods for GPS passive coherent location

This study addresses processing methods for the use of the global positioning system (GPS) as a signal of opportunity in a multistatic passive coherent location (PCL) system. The signal properties of the GPS signal are designed for position estimation, which makes it particularly suited for GPS PCL applications. The signal specifications are examined and the potential limitations of a proposed system are explored. Conventional GPS processing techniques are implemented in the framework of multistatic GPS PCL. GPS specific methods are developed for target position estimation of a multistatic PCL system in a three-dimensional plane. The PCL system has comparable performance metrics to conventional GPS positioning. Two methods are developed utilising measurements available in a conventional GPS system. The first involves a short time scale, which is in the order of milliseconds. The second involves a long time scale method, which is on the order of seconds. Simulation and analysis are performed to verify the methods. Experimental validation was also conducted using a hardware in the loop approach, as well as, an active radar calibrator.

Experimental results of polarimetric detection schemes for DVB‐T‐based passive radar

This study investigates the potential advantages conveyed by the exploitation of polarimetric diversity in Passive Coherent Location (PCL) system exploiting Digital Video Broadcasting – Terrestrial (DVB-T) signals. To this purpose, different polarimetric detection schemes are considered that jointly exploit the signals collected at different receiving channels characterised by differently polarised antennas. A performance analysis has been carried out using experimental data collected by a passive radar system developed by Fraunhofer, namely PARASOL. This PCL system employs two orthogonal linearly polarised receiving channels (horizontal and vertical). The results obtained against cooperative targets demonstrate that a Polarimetric Generalised Likelihood Ratio Test (P-GLRT) detection scheme provides a remarkable improvement in terms of target detection capability as compared to the single-polarisation operation and the non-coherent integration of the results obtained at the available polarimetric channels.

Traffic density monitoring using passive radars

Today the main applications of ground based passive coherent location (PCL) systems are in the domain of air traffic surveillance–air target detection, tracking, and localization. Interest in using PCL radars in these applications is expressed primarily by military users, mainly because of the great advantages of silent and covert operation that passive radars provide. In this regard, passive radars benefit from the fact that they operate by using emissions already present (e.g. FM radio, DAB, DVB-T, GSM, Wi-Fi, etc.) rather than their own. Other advantages of passive radars relate to the possibilities of stealth target detection and gap filling in areas not covered by active radars. Another huge advantage of the passive radar lies in the fact that there is no need for requirements for spectrum allocation or powerful transmitters. Consequently, as the aforementioned points make passive radars great representatives of “green” technology, one can install them in “sanctuaries”–specific or specialized places such as high-density urban areas, sites located in the vicinities of hospitals, and/or other places where electromagnetic emissions are limited by law because of the risk of interference or simply through the public's fear of electromagnetic fields. Also, it is worth mentioning that PCL systems can be cheaper than active ones as the passive radar does not have its own transmitter and typically consists of a simple radio receiver with commercial off-the-shelf (COTS) hardware, and uses a commercially available PC as a computation.