Passive Coherent Location 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.

Multi-passive coherent location radar system for detection range and range-doppler resolution in Tarakan

The presence of many radio frequency illuminators in an area provides an opportunity to be used as a transmission source for a passive radar system called a passive coherent locator (PCL). Unlike the active radar, the passive radar provides advantages such as low cost without an active transmitter, potential for broad range measurements, portable in construction, anti-detectable by active radar or electronic counter measures (ECM), etc. Just like other areas where there are many PCL in Tarakan such as FM radio transmission (RRI), many base-stations (BTS) from 4G-LTE network, digital TV transmission, access-point (AP) from wireless fidelity (WiFi), and so on. This paper will present and analyze all of these PCLs which include predictions of performance and ambiguity function (AF). Performance prediction is related to range detection which provides information about target detection range, radar cross section, and range-velocity resolution. While AF analyzes the transmit waveform of all PCL which gives a limit of resolution to the range and Doppler of adjacent targets. The results of the evaluation and analysis of performance predictions show that FM radio transmission (RRI) has a range and velocity resolution of 1 km and 12 m/s, respectively and the detection range at a maximum SNR of 15 dB is around 4 km. While the results of the AF evaluation on the PCL obtained range and Doppler resolution of around 2.73 km and 500 Hz, respectively.

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.

Revisiting the Spaceborne Illuminators of Opportunity for Airborne Object Tracking

This article reviews existing research for cooperative passive coherent location and tracking employing spaceborne opportunistic illuminators, highlighting the need for novel cooperative real-time object detection and tracking approaches and discussing the lack of multistatic experimental data for future research.

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.

The Impact of Channel Errors in Passive Coherent Location Radar using FM Base Stations

This paper presents the impact of channel errors for an FM based passive bistatic radar system mounted on mobile platforms for ground moving target indication (GMTI). Reciprocal filter, which is effective compared to conventional matched filter (MF), is performed for the pulse compression stage to remove the time-variant structure of the signal. The displaced phase centre antenna (DPCA) method is applied for the clutter cancellation and target detection. This technique is effective if the hardware is well calibrated. Thereby, the influences of calibration errors between the receiving channels are studied for different FM waveforms. The simulation results of the amplitude and phase errors are analysed separately.

Multichannel SDR Platforms for Mobile PCL Applications

This article presents a brief overview of hardware platforms with multiple RF input channels that can be employed in the area of passive coherent location (PCL) and passive synthetic aperture radar. Two families of the platforms are considered, i.e., field-programmable gate array based development boards and general-purpose software-defined radio receivers. Practical solutions that have been validated in field experiments are described: a high-performance four-channel platform and its lightweight version that perfectly suits the needs of low-power moving installations. The preliminary results of target detections are presented, which are obtained from the signals acquired with the lightweight PCL platform. Our results prove that, besides its simplicity, the small and low-power platform can be successfully used in PCL applications that use digital audio broadcasting transmitters as the source of illumination.

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.

Convolutional Neural Network-Based Target Detector Using Maxpooling and Hadamard Division Layers in FM-Band Passive Coherent Location

The constant false alarm rate (CFAR) has been widely used in radar systems to detect target echo signals because of its simplicity. With the recent development of different types of neural networks (NNs), NN architecture-based target detection methods are also being considered. Several studies related to NN-based target detectors have introduced multi-layer perceptron-based and convolutional neural network (CNN)-based structures. In this paper, we propose a CNN-based target detection method in frequency modulation (FM)-band passive coherent location (PCL). We improved the detection performance using a maxpooling layer and a Hadamard division layer, which are parallelly placed with a CNN layer. Moreover, in our method there is no need to determine the specific cell configuration (e.g., cell under test, reference cells, and guard cells) because the proposed method obtains the trained kernels by end-to-end learning. We show that the trained kernels help in the extraction of either signal or noise components. Through the simulations, we also prove that the proposed method can yield an improved receiver operating characteristic compared to that of a cell-averaging CFAR detector for FM-band PCL in a homogeneous environment.

DAB Signal Preprocessing for Passive Coherent Location.

Digital Audio Broadcast (DAB) transmitters can be successfully used as illumination sources in Passive Coherent Location (PCL). However, extending the integration time in such a configuration leads to the occurrence of periodical artifacts in the bistatic range/Doppler plots, resulting from the time structure of the DAB signal. In this paper, we propose some methods of signal preprocessing (based on symbol removal, substitution by noise, and duplication) that operate on the DAB transmission frame level and improve the received signal’s correlation properties. We also demonstrate that two of these methods allow us to avoid the mentioned artifacts and thus to improve the quality of the range/Doppler plots with detection results. We evaluate the performance of the proposed methods using real DAB signals acquired in an experimental PCL platform. We also provide the analysis of the Signal to Noise Ratio (SNR) during the detection of a moving target which shows that the proposed solution, based on symbol duplication, can offer around 3 dB of gain in SNR. Finally, we carry out the computational complexity analysis showing that the proposed method can be implemented with a minimal cost after some optimizations.

Geometric Clutter Analysis for Airborne Passive Coherent Location Radar

The paper presents detailed geometric analyses of ground clutter in bistatic passive airborne radars. Analytic closed-form solutions are derived for finding the intersection of iso-ranges and iso-velocities. This allows clutter bistatic coordinates to be easily converted to its Cartesian coordinates. Based on those solutions, a theoretical clutter map in the bistatic coordinates can be calculated assuming uniform clutter distribution on the Earth’s surface. This is done by first converting a resolution cell in the bistatic coordinates into a corresponding cell in the Cartesian coordinates. Next, the power distribution in the bistatic coordinates is calculated taking into account range dependency, incident angles, and the radiation patterns of the transmitter and the receiver. The aim of this analysis is to characterize clutter in terms of expected mean power map rather than in terms of statistical distribution. The obtained results provide insight into the expected characteristics of clutter, which can be helpful in designing signal processing algorithms for ground moving target indication (GMTI) and synthetic aperture radar (SAR). The theoretical clutter distribution on the range-velocity map is compared with real-life data acquired with a DVB-T-based passive radar, and good agreement between theory and measurement is presented.

Counter-Passive Coherent Locator (C-PCL)—A Method of Remote Detection of Passive Radars for Electronic Warfare Systems

Passive Coherent Location methods and techniques have an established position in the modern state-of-the-art radar. Inexpensive, easy to deploy and undetectable for other sensors, passive radars are growing in popularity. Due to that, a need arises to develop proper methods of any possible kind of countermeasure. In this work, a method of detection and localization of hidden PCL systems is proposed. Authors exploit certain physical features of an RF receiver in order to detect such a passive systems. Results of selected hardware measurements are presented as a proof of concept. Summarized findings are followed by an extensive discussion of conditions related with the method implementation in a real world scenarios.

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 •

Beamforming of LOFAR Radio-Telescope for Passive Radiolocation Purposes

This paper presents the results of investigations on the beamforming of a low-frequency radio-telescope LOFAR which can be used as a receiver in passive coherent location (PCL) radars for aerial and space object detection and tracking. The use of a LOFAR radio-telescope for the passive tracking of space objects can be a highly cost-effective solution due to the fact that most of the necessary equipment needed for passive radiolocation already exists in the form of LOFAR stations. The capability of the radiolocation of planes by a single LOFAR station in Borowiec is considered to be ‘proof of concept’ for future research focused on the localization of space objects. Beam patterns of single sets of LOFAR antennas (known as tiles), as well as for the entire LOFAR station, are presented and thoroughly discussed in the paper. Issues related to grating lobes in LOFAR beam patterns are also highlighted. A beamforming algorithm used for passive radiolocation purposes, exploiting data collected by a LOFAR station, is also discussed. The results of preliminary experiments carried out with real signals collected by the LOFAR station in Borowiec, Poland confirm that the appropriate beamforming can significantly increase the radar’s detection range, as well as the detection’s certainty.

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.

DVB-T Receiver Independent of Channel Allocation, With Frequency Offset Compensation for Improving Resolution in Low Cost Passive Radar

In this article, a commercial low cost solution for increasing DVB-T based passive radar (also referred to as passive coherent location) robustness with respect to channel allocation and range resolution, is designed. IDEPAR demonstrator is updated to include a new recording system in charge of DVB-T channels reallocation. The use of commercial hardware introduces frequency mismatching between acquired channels that compromises system operation. To face channel frequency alignment, fulfilling the requirements imposed by the high Doppler resolution typical of passive radars, a novel compensation algorithm is proposed, based on the minimization of signal dispersion in the Cross-Ambiguity Function domain. The well-known cyclic prefix van de Beek method is used as reference. Results show an increase in target signal to interference ratio and detection performances, as well as a reduction of clutter dispersion when the novel proposed algorithm is applied. The low cost solution is also compared to a high performance one capable of acquiring a wide bandwidth of sparse DVB-T channels, and performing channel reallocation by digital signal processing. Results show that both systems reached similar performances in terms of range resolution and SNR improvement.

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.