Performance tradeoff in a unified multi-static passive radar and communication system

In this paper, we consider the problem of tracking multiple targets in a passive multi-static radar system using Doppler-only measurements. The number of targets is assumed unknown and time-varying. The Doppler measurements are subject to additive noise, clutter, and missed detections. Doppler-only measurements from a single sensor provide incomplete information about the target state, commonly referred to as single-sensor unobservability. In a passive multi-static radar system, the availability of multiple bistatic links naturally lends itself to the fusion of measurements from spatially distributed sensors. However, data fusion emerges as a computationally intensive problem in multi-sensor multi-target tracking algorithms. We propose a two-step sequential approach to solve the underlying problem. We first cast the underlying problem as a group sparse problem in a discretized position-velocity space. A group sparsity based algorithm is applied to simultaneously exploit the multi-static Doppler frequency measurements to directly obtain the instantaneous target state estimates in the Cartesian coordinate system. These estimates are then fed as inputs to the linear Gaussian mixture probability hypothesis density (GMPHD) filter, which removes the false measurements, compensates for missed detections and reduces the localization error. The optimal sub-pattern assignment metric, which jointly comprises a weighted contribution of cardinality error and localization error, is used to evaluate the performance of the proposed method. Simulation results show that the proposed method successfully handles the multi-target tracking problem and outperforms the existing random receiver selection based multi-sensor implementation of the GMPHD filter.

In multistatic passive radar systems, the Cramer–Rao lower bound (CRLB) can be used to select the optimal illuminator of opportunity so that it provides the best estimation accuracy for target parameters. In this Letter, the monostatic and bistatic modified Cramer–Rao lower bound (MCRLB) for the Advanced Television Systems Committee (ATSC) signal, which is the pervasive digital television signal of opportunity for North American passive radar systems, is derived using the relationship between the ambiguity function of a signal and its CRLB. It is shown that the derived bistatic MCRLB for the range and velocity measurements can be used to select the optimal illuminator that exhibits the lowest bounds at each region. Examples are provided in the Columbus, OH area where the Ohio State University passive radar is located.

Passive radar systems operate by exploiting signals of opportunity that are designed for other applications, such as broadcasting, communications, and satellite navigation. Passive radars have recently attracted attention in military applications, mainly because of their covertness, low-cost implementation, and no requirement of signal emissions [1], [2]. Whereas the primary use of passive radars is in the defense sector, these same features make them attractive in commercial applications. Unlike conventional active radar systems, which typically operate in a monostatic mode, passive radar can operate in a multistatic mode (thus called passive multistatic radar, or PMR) by using multiple transmitters. Multiple networked receivers can also be exploited for an expanded PMR network size.

Passive coherent location (PCL), passive covert radar (PCR), passive bistatic radar (PBR), passive radar, parasitic radar, and hitchhiking radar are all common names for passive radar systems exploiting cooperative, noncooperative transmitters, or transmitters of opportunity, [1, pp. 3]. Recent review of the various names resulted in the compromise PBR, [2, pp. 248]. However, it should be noted that the PCL name is still being used for full systems like Lockheed Martin's - Silent Sentry [3], [4], Thales' - Homeland alerter 100 [5], [6] seen in Figure 1, and Airbus “Passive Radar” [7]–[15]. The PCL systems may be considered as systems of PBR systems. This work focuses on the system perspective of the technology, i.e. PCL, while relying on the technical depths of the PBR technology.

Distributed passive radars confront the high dynamic range challenge by splitting the receiver physically to provide high SNR samples of the transmitter as well as reduced cochannel interference. The receivers are mutually coherent and must therefore exchange voltage level data for computation of the cross-ambiguity function. The data bandwidth required for full- precision (16 bit) data is about 2 Mbps to support for a single channel. This data bandwidth demand can stress the cost and latency of distributed passive radars. Therefore we investigate the effect the sensitivity of a passive radar system using several methods to compress the voltage level samples prior. (4 pages)

The present work illustrates the Fraunhofer FHR contribution to the MAPIS project field trials held in Livorno in June 2017. The MAPIS project, funded by EDA, aims at demonstrating radar imaging capability of passive radar systems in a (military) maritime scenario. In particular, two different Passive Bistatic Radar (PBR) systems, one exploiting Digital Video Broadcasting - Terrestrial (DVB-T) signals, the other one exploiting Digital Video Broadcasting - Satellite (DVB-S) signals have been used to experimentally assess the imaging performance. This paper describes the systems developed by Fraunhofer FHR and used during the trials. In addition, a small overview of the trial itself is provided together with some preliminary results concerning the passive radar imaging.

This study presents an analysis of micro‐Doppler signatures of helicopters obtained using a network of passive radar receivers utilising multistatic geometry. In the multistatic scenario, for each passive radar receiver the target is visible from different bistatic angles, which results in different micro‐Doppler signatures. This feature allows additional information on the observed helicopter target to be obtained. The presented concept has been successfully verified by the authors using the real micro‐Doppler signatures of a helicopter collected during the measurement campaign. As an illuminator of opportunity for the passive radar network a commercial digital video broadcasting‐terrestrial (DVB‐T) transmitter was used. The results of the applied micro‐Doppler analysis for the real multistatic passive radar measurement carried out are presented in this study. In addition, some examples of inverse synthetic aperture radar (ISAR) images of helicopter rotor blades based on micro‐Doppler analysis in the multistatic configuration are shown in this study.

This paper investigates the problem of low probability of intercept-based optimal power allocation (LPI-OPA) for an integrated multistatic radar and communication system, which consists of multiple transmitters operating at different frequencies, a radar receiver, and a communication receiver (CR). The integrated multistatic radar and communication system is capable of fulfilling the requirements of both radar and communication subsystems. The key tenet of the integrated system is to minimize the total power consumption by optimizing the transmit power allocation at each transmitter for radar waveforms and information signals, which is constrained by a predetermined target detection performance for the RR and a desired information rate for the CR. Since the analytical closed-form expression of the probability of detection is not tractable, its upper bound is derived. We analytically show that the resulting optimization problem can be reformulated as two subproblems, which can be solved by an efficient solution procedure based on the approach of linear programming and the Karush–Kuhn–Tuckers optimality conditions. Simulation results are provided to show that the LPI performance of the integrated multistatic radar and communication system can significantly be enhanced by employing our proposed LPI-OPA scheme.

Passive radar systems are proposed as ground traffic control and monitoring tools in modern urban areas. These radars use communication networks transmitters available in the area of interest, instead of dedicated ones. The absence of a transmitter reduces dramatically the cost of development, deployment and maintenance, making feasible passive radar sensor networks for covering modern cities complex scenarios. They do not generate electromagnetic compatibility problems, and, more important, they are not associated with health issues. The illuminator selection is one of the most important tasks. The transmitted waveform, the transmitted power, the availability or the coverage areas are critical elements that are out of the control of the radar designer. The IDEPAR demonstrator is used in an urban environment to prove the traffic monitoring capabilities of passive radars exploiting Direct Video Broascasting -Terrestrial transmitters.

Passive radar permits inexpensive and stealthy detection and tracking of aerospace and geoscience targets. Transmitters of opportunity such as commercial FM broadcast, DTV broadcast, and cell phone towers are already illuminating many populated areas with continuous power. Passive radar receivers can be located at a distance from the transmitter, and can sense this direct transmission as well as any reflections from ground clutter, aircraft, ionospheric turbulence and meteoroids. The 100% duty cycle allows for long coherent integration, increasing the sensitivity of these instruments greatly. Presented here is a new passive radar receiver designed to analyze any transmission of opportunity with frequencies up to 1.5 GHz without the use of a front end analog downconverter. The receiver centers around a Reconfigurable Open Architecture Computing Hardware (ROACH) board developed by the Collaboration for Astronomy Signal Processing and Electronics Research (CASPER) group. The radar is designed for mobile operation. It fits within a 19 rack, it is equipped with solid state hard drives, and can run off an uninterruptible power supply (UPS) for up to 1 hour of continuous operation. In this paper we describe technical details of the hardware, firmware, and software of the system including the use of polyphase filtering in lieu of traditional digital downconversion. We describe the use of the cross-ambiguity function as a detection mechanism. We present preliminary results of detections from this radar. In stationary operation, the same helicopter has been detected using two different DTV transmissions. We present early results of mobile operation, in which the doppler-spread ground clutter and possible detection of aircraft can be seen, again with the use of DTV broadcast. Finally, we detail future developments to exploit the full capabilities of this versatile new system.

Conventional methods such as matched filtering, fractional lower order statistics cross ambiguity function, and recent methods such as compressed sensing and track-before-detect are used for target detection by passive radars. Target detection using these algorithms usually assumes that the background noise is Gaussian. However, non-Gaussian impulsive noise is inherent in real world radar problems. In this paper, a new optimization based algorithm that uses weighted and norms is proposed as an alternative to the existing algorithms whose performance degrades in the presence of impulsive noise. To determine the weights of these norms, the parameter that quantifies the impulsiveness level of the noise is estimated. In the proposed algorithm, the aim is to increase the target detection performance of a universal mobile telecommunication system (UMTS) based passive radars by facilitating higher resolution with better suppression of the sidelobes in both range and Doppler. The results obtained from both simulated data with stable distribution, and real data recorded by a UMTS based passive radar platform are presented to demonstrate the superiority of the proposed algorithm. The results show that the proposed algorithm provides more robust and accurate detection performance for noise models with different impulsiveness levels compared to the conventional methods.

The tasks of clutter suppression and ground moving target indication are a typical and also very challenging problem for airborne radar systems for both defence and civilian applications. Nowadays, research aims at applying these tasks for passive radar systems on moving platforms. This chapter addresses the problem of clutter cancellation and slowly moving target detection in orthogonal-frequency-division-multiplex-based passive radar systems mounted on moving platforms. Conventional signal processing approaches which exploit multiple receiving channels can be ineffective for the considered application due to the impossibility to control the employed waveform of opportunity. Therefore, a processing scheme, which aims at ground moving target indication needs to address this issue. The space-time adaptive processing scheme, proposed in this Chapter, exploits the benefits of the reciprocal filtering strategy applied at a range compression stage together with a flexible displaced phase center antenna approach. The effectiveness of the proposed scheme is demonstrated via application to a simulated dataset as well as on experimental data collected by a multichannel passive radar on an airborne moving platform.

By using the transmitters of opportunity, passive radar systems allow target detection and tracking without transmitting any RF energy. This approach ensures covert operation of the radar thus decreasing the risks of enemy detection and electronic countermeasures. In a nutshell, the passive radar utilizes the existing broadcast signals from multiple FM radio and TV transmitters, detects backscattered signals from targets, and employs advanced DSP algorithms to provide real time target position/speed estimation and tracking. In the first part of this work, the problem of estimating the true target position from three bi-static ranges is formulated and its solution is implemented using non-linear optimization tools. In the second part, the feasibility of using the passive radar approach for accurate target position detection is experimentally evaluated at 2.4 GHz. It is shown that the target range can be estimated with 50 feet resolution when a 6 MHz wide broadcast signal is used.

This paper examines the feasibility of 4G (LTE)-based passive radar for detecting ground moving targets. Specifically, the focus of this paper is to describe the proposed LTE-based passive radar system and to conduct an experiment using a real LTE eNB transmitter as an illumination source. Seven scenarios were carried out to investigate the detection performance of the proposed system on moving targets. Each scenario had different types of ground targets moving with a variety of speeds and directions. The experimental results showed that the LTE-based passive radar system has the capability to detect typical ground targets/objects like cars, motorbikes and humans moving with different speeds, trajectories and ranges. The positive results opened up a new frontier for passive radar systems to be used in many potential applications, including border protection, microwave fences, monitor of buildings and others.

Non-contact breathing monitoring systems are very attractive for a range of e-Healthcare applications. This paper proposes a passive radar based system for measuring human breathing rate. A novel signal processing method is introduced to extract breathing rate based on micro Doppler derived from cross ambiguity function (CAF). The passive radar system is built within a software defined radio (SDR) platform. The proposed system uses opportunistically energy harvesting transmitter as an illumination signal. Passive detection is compared and verified using the ground truth from clinical chest belt respiration detector. Two experiments have been conducted to show the feasibility of passive detection system in the line of sight and also through-wall conditions. We conclude that a low frequency narrow band signal with non-contact passive detection can offer a realistic alternative to UWB based radars for future e-Healthcare passive sensing applications.