A Unifying Approach for Disturbance Cancellation and Target Detection in Passive Radar Using OFDM

Abstract

International audienceThis paper addresses the problem of mobile target detection in multipath scenarios with a passive radar using DVB-T transmitters of opportunity. For such emissions, it has been shown the interest in implementing ``mismatched'' correlators, reducing both the zero Doppler contribution (ZDC) masking effects and the false alarm rate. A very efficient mismatched reference signal is obtained with the reciprocal filter (or inverse filter) which consists in a modulus frequential equalization of the transmitted signal. We propose here to revisit the reciprocal filter-based correlator and to reinterpret it as a so-called Doppler channel detector (CHAD). This new interpretation allows a direct rejection of the ZDC, unifying in one and the same step the main disturbance mitigation and the detector construction. We provide a statistical theoretical study of the performance and a comparison with the matched correlator, i.e., the classical cross-ambiguity function (CAF). We demonstrate that CHAD has a random pedestal (a clutter floor level) significantly lower than that of the classical CAF for low Doppler frequency shifts. Numerical experiments on simulated and real data as well validate the mathematical derivations

Adaptive Target Detection Techniques for OFDM-Based Passive Radar Exploiting Spatial Diversity

“…In the range-Doppler plane, the theoretical location of the target echo of interest (17.1km,-173.0Hz) is marked by a black circle. Such a range value corresponds to a relative bistatic delay more than twice as large as the CP duration and a slight discrimination loss (about 10 log 10 ((32 2) 2 /32 2 ) = 0.57dB, see [18]) is expected using CHAD with respect to CAF. To tackle dynamic range issues between the different target returns, we adjusted, in each following 3D surveillance map, the colorscale so that the highest peak with a unit normalized level, appears with a black color while the clutter floor has always the same gray/blue color.…”

“…As introduced in [18], the previous model (1) can be rewritten as a sum of F differently frequency shifted ("Dopplerized") contributions and one has using the convolution operator ⇤:…”

“…It corresponds to a 70km relative bistatic coverage for the largest guard interval duration in European DVB-T emissions and to 8.75km for the shortest one. Now, it has been stated in [18] that this limitation can reasonably be overridden in return for a gradual detection loss due to the proportion of samples outside the guard interval. Note that this is the case for the experimental results at the end of this paper where relative bistatic delays up to three time the guard interval duration are explored.…”

“…The idea is that reciprocal filter outputs being theoretically "signalindependent", presence of ghost targets (false alarms) caused by the DVB-T signal structure (cyclic prefix, transmission parameter signalling, pilot data, see [17]) is naturally eliminated. In [18], a new interpretation of such an approach was stated in term of channel-based detector (CHAD). Note that a similar interpretation can be found in [19] for the particular case of DAB signals.…”

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

“…In recent years, there has been ongoing development of aircraft with low-probability-of-intercept (LPI) capabilities, which are difficult to track using conventional radar systems. To counter these technologies, passive coherent location (PCL) radars using commercial low-frequency broadcast signals, such as frequency modulation (FM) radio [1,2], digital TV [3][4][5][6], analog TV [7], satellites [8,9], and mobile communications [10], have been studied extensively. In particular, PCL radars using low-frequency bands, including the very high frequency (VHF) band of FM broadband signals, can effectively counter long-range targets with radar absorbing material (RAM) or radar absorbing structure (RAS).…”