1,721,011 research outputs found
DVB-T-Based passive forward scatter radar: Inherent limitations and enabling solutions
Full text linkThis article investigates the target detection capability of a passive forward scatter radar (PFSR) exploiting a digital video broadcasting-terrestrial (DVB-T) transmitter as illuminator of opportunity. By means of theoretical and simulated analyses, it is shown that conventional processing schemes might suffer from significant performance degradation when exploiting orthogonal frequency division multiplexing (OFDM) waveforms of opportunity compared to other broadcast transmissions (e.g., frequency modulation radio broadcast). Specifically, the direct application of conventional processing approaches to the case of a DVB-T PFSR is demonstrated to yield: 1) a nonnegligible increase of the competing background level and 2) a steeper fading of the target response due to the intrinsic characteristics of the exploited waveforms of opportunity, above all the modulation scheme and the signal spectral characteristics. Therefore, appropriate signal processing techniques are proposed to avoid these effects which jeopardize the target detection capability. The conceived processing scheme exploits the digital nature of the employed waveforms and a subband approach for improving both the interference cancellation stage and the target signature extraction. The benefits of the proposed approach are illustrated by means of theoretical and simulated analyses. The application of the resulting processing scheme against experimental data proves its effectiveness in practical scenarios
Exploiting polarimetric diversity in passive radar
No full textRadar polarimetry has been widely used in radar systems aiming at the detection,
discrimination, and recognition of targets of interest among other interfering sources.
It becomes an essential tool in challenging radar scenarios where the achievable
performance is not under control of the radar designer. This is certainly the case of
passive radar whose performance largely varies with the radiative properties of the
transmitter of opportunity as well as with the severity of the electromagnetic (EM)
scenario that typically includes many interfering sources.
Passive radar, also known as passive coherent location (PCL), technology has
been attracting significant research interest over the past two decades. The
wide interest received by PCL sensors allowed them to increasingly reach a point of
maturity. Nevertheless, by relying on signals emitted by illuminators of opportunity
(IOs) to detect and localize targets, the performance of PCL sensors might be largely
time-varying
and leading to an unreliable surveillance system. The main limitations
stem from the lack of control over the exploited waveform structure as well as from
the strong direct signal and multipath contributions. In addition, significant
interference can be experienced due to co-channel
or adjacent-channel
transmissions,
especially when broadcast emitters are exploited as IOs.
Recently, among the advanced processing strategies devised to overcome these
limitations, the exploitation of polarization diversity has been considered as a mean
to increase the reliability of passive radar with particular reference to the target
detection task. Specifically, the availability of multi-polarimetric
channels
on receive has been demonstrated to provide robustness against the target echo fading
that results from the induced variable polarization. Moreover, a
proper combination of signals received via differently polarized antennas has been
shown to improve the target identification capability against the interfering sources,
thanks to the wave polarization diversity.
In this chapter, we take this perspective and illustrate practical multi-polarimetric
passive radar architectures together with the corresponding signal processing techniques.
Different approaches are compared both in terms of achievable performance
and based on considerations regarding the resulting system complexity. The aim is to
offer the interested reader with an overview of existing solutions and to provide hints
for the identification of the most suitable architecture for the application at hand.
The discussion is supported by results from real-world
tests performed by means of
experimental passive radar receivers operating at different frequency bands
Experimental results for a passive forward scatter radar based on OFDM waveforms of opportunity
No full textRecently, it has been demonstrated that OFDM waveforms of opportunity have a non-negligible impact on the performance of a passive forward scatter radar (PFSR) when employing conventional processing schemes. Therefore, ad-hoc signal processing techniques have been proposed for improving both the interference cancellation stage and the target signature extraction in OFDM-based PFSR. This paper reports on the performance obtained with the resulting PFSR sensor in dedicated experimental tests. To this purpose a Digital Video Broadcasting - Terrestrial transmitter is employed as illuminator of opportunity and the detection capability of a commercial off-the-shelf (COTS) based receiver is investigated against aerial targets. The results demonstrate the benefits of the proposed approach in a real-world scenario
Multi-channel SAR experiments from the space and from ground: Potential evolution of present generation spaceborne SAR
No full textAfter presenting the multi-channel SAR and the multistatic SAR constellations as the evolutions of present-generation SAR systems, two sets of experiments are proposed to assess their potential applications and validate them, before designing fully operational systems. The experiments from the space are based on the use of the existing SAR together with one or more receiving-only sensors on board of mini-satellites. The experiments from the ground are based again on the exploitation of the existing SAR as the radar illuminator and by the use of one or more ground-base receivers appropriately positioned in high elevation location. The proposed experiments are highly recommended for a fast evaluation of the potential applications achievable by both multichannel and multistatic potential evolutions of the modern SAR
Passive radar for GMTI
No full textThe 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
Multi‐carrier and multi‐polarimetric model based adaptive target detector for passive radar systems
Full text linkAbstract A new adaptive detection strategy for passive radar systems that fruitfully capitalizes on signals, simultaneously emitted by the same transmitter of opportunity at different carrier frequencies and collected by a set of differently polarized surveillance antennas is derived. Based on recent results that demonstrated the benefits provided by proper strategies to exploit polarimetric diversity, the authors aim at further improving the target detection performance by combining polarimetric and frequency diversity. Real data collected through an FM radio‐based passive radar prototype is used to extensively demonstrate the effectiveness of the derived strategy with respect to state‐of‐the‐art approaches. The conceived solution is proved to successfully enhance the capability to discriminate targets, thanks to an effective disturbance rejection performed at each frequency channel as well as a target echo enhancement and an increased robustness to the time‐varying characteristics of the exploited source of opportunity
DVB-T based Forward Scatter Radar for Small Target Surveillance
No full textThis paper investigates the target detection capability of a Passive Forward Scatter Radar (PFSR) exploiting a DVB-T transmitter as illuminator of opportunity. Specifically, it is shown that conventional processing schemes adopted in PFSR might suffer from significant performance degradation when dealing with OFDM waveforms of opportunity compared to the case of FM radio broadcast. In fact, a non-negligible increase of the disturbance background is observed in the final spectrogram, which yields an undesired masking effect on weak target echoes. Therefore, we propose a signal-based processing technique to mitigate the observed effect and improve the target detection capability. The proposed approach exploits the possibility to recover a good copy of the transmitted signal based on its digital nature; this is then used to cancel the fluctuating component of the output arising from the adopted modulation of the waveform of opportunity. The effectiveness of the proposed approach is proved against simulated data
A simple NULA design strategy for target detection and DoA estimation in mobile passive radar
No full textThis paper explores the advantages of Non-Uniform Linear Array (NULA) configurations for target detection and Direction of Arrival (DoA) estimation in mobile passive radar space-time adaptive processing (STAP). The limited number of receiving channels and the low directivity of antennas, typical of passive radar systems, may limit the moving target detection and angular localization capabilities. Therefore, the use of non-uniform distributions of antennas is encouraged, aimed at making the most of the available channels, by leveraging on spatial diversity. However, selecting a suitable NULA configuration represents a difficult task, being characterized by competing requirements. On the one hand, maximizing the array total length shrinks the clutter notch and reduces the DoA estimation error. On the other hand, increasing the inter-element spacings may lead to the appearance of statistical ambiguities, associated to sidelobes of the array beampattern, resulting in large estimation errors, as well as detection performance degradations. We propose a simple strategy for the selection of suitable NULA configurations, based on a requirement on the maximum peak-to-sidelobe ratio, which guarantee satisfactory performances in terms of both target detection and DoA estimation. The resulting array configuration are tested, via numerical analysis, addressing the case of a mobile passive radar exploiting DVB-T as a signal of opportunity
Reciprocal-filter-based STAP for passive radar on moving platforms
No full textThis paper addresses the problem of clutter cancellation and slowly moving target detection in digital video broadcast-terrestrial-based passive radar systems mounted on moving platforms. First, we show that conventional processing approaches based on the availability of multiple receiving channels might be ineffective in the considered scenarios due to the impossibility to control the employed waveform of opportunity. Therefore, an appropriate space-time adaptive processing scheme is proposed to cope with the Doppler spread clutter returns aiming at ground moving target indication applications. It 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 and then tested against experimental data collected by multichannel passive radar on a maritime moving platform
Pilot tones injection in Golay sequences for PAPR reduction in OFDM-based JRC systems
No full textThis paper investigates the integration of pilot carriers into Golay complementary sequences for peak-toaverage power ratio (PAPR) reduction in joint radar and communications (JRC) systems employing Orthogonal Frequency Division Multiplexing (OFDM) waveforms. While using Golay sequences as OFDM codewords allows to achieve PAPR values of 3 dB, the insertion of pilot tones can disrupt their optimal properties. This study focuses on the importance of careful consideration of pilot carrier integration in Golaybased PAPR reduction techniques for efficient JRC system design. Two approaches are proposed to address this challenge: restricting the transmitted codeword set to Golay sequences sharing desired pilot tone configurations or forcing predetermined pilot sequences onto Golay sequences to create Quasi-Golay sequences. Analysis reveals a trade-off between PAPR reduction and communication throughput: the Golaybased approach offers optimal PAPR but reduced data rates, whereas the Quasi-Golay-based approach provides higher data rates at the expense of slightly higher PAPR values. Evaluation through simulations demonstrates the performance of these approaches and their implications for JRC systems
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