Roberta Cardinali

Cancellation of clutter and multipath in passive radar using a sequential approach

The paper deals with the cancellation of direct signal, multipath and clutter echoes in passive radar, where the transmitted waveform is not under control of the radar designer and the sidelobes of the ambiguity function mask even targets largely displaced in range and Doppler from the disturbance. A sequential approach is presented for disturbance cancellation and target detection based on projections of the received signals in a subspace orthogonal to both disturbance and previously detected targets. Modeling the clutter spread on few Doppler bins allows complete clutter cancellation. The approach is shown to be effective against typical scenarios with a limited number of iterations.

Comparison of Clutter and Multipath Cancellation Techniques for Passive Radar

In this paper we address the problem of clutter and multipath cancellation in passive radar. Different adaptive techniques are considered based on both well known approaches and innovative strategies proposed by the authors. The performance comparison allows to understand the particular behaviour of each technique in a practical scenario. The proposed innovative strategies are shown to be very appealing solutions for disturbance cancellation in passive radar.

UWB ranging accuracy in high- and low-data-rate applications

The Cramer-Rao lower bound (CRLB) was determined for different ultra-wideband (UWB) signal formats and, in particular, for the two UWB high-data-rate (HDR) signal formats proposed within the IEEE 802.15.3a Task Group, that is, the impulsive direct-sequence UWB (DS-UWB) and the nonimpulsive multiband orthogonal frequency-division multiplexing (MB-OFDM), and an impulsive time hopping (TH) UWB format close to the format for UWB low data rate (LDR) of the forthcoming IEEE 802.15.4a standard. The analysis was carried out for both ideal and multipath channels under power constraints as set by emission masks. Results obtained for HDR formats showed that DS-UWB has better ranging accuracy than does MB-OFDM, thanks to its potentially larger bandwidth and higher frequency of operation. In addition, the degree of multipath strongly affected ranging accuracy, although differently for DS-UWB versus MB-OFDM. When incorporating a correlation receiver structure as well as an Early Late gate synchronizer in the model, ranging performance proved to be related to features of the synchronization sequence. For specific synchronization sequences, in particular, the best ranging accuracy was obtained with MB-OFDM. In the case of LDR, the study analyzed the effect of pulse shape on CRLB. Results showed that a suboptimal choice of the pulse shape reduces the ranging accuracy achievable by TH-UWB signals.

Array optimization and adaptive processing for sub-array based thinned arrays

In this work a new approach is proposed for the optimized design of a thinned array, based on a small set of different sub-array types (with assigned properties), properly disposed on a planar surface. The small number of different sub-array shapes is relevant for industrial production, to reduce design and manufacturing costs, as well as to allow scalable antenna designs for different applications. The optimization of the design is based on the maximization of an objective function, involving the side lobe level and/or the main lobe width. The possibility to split the obtained thinned array antenna in a set of sub-apertures is investigated, corresponding to an integer number of sub-arrays connected to independent receiving channels. This is required to apply adaptive processing techniques to cancel external e.m. interferences and/or clutter echoes. The performance obtained by using the adaptive techniques with sub-apertures taken from the optimized thinned array are evaluated with reference to assigned clutter and jamming scenarios, and compared to the sub-array based filled array.

UWB ranging accuracy for applications within IEEE 802.15.3a

The definition of ultra wide band (UWB) signals released by the Federal Communications Commissions (FCC) opened the way to both impulse and non-impulse UWB signal formats, as reflected within the IEEE 802.15.3a TG, devoted to the definition of a standard for UWB-based high bit rate WPANs. The two main proposals considered in this group are a multi band OFDM approach, based on the transmission of non-impulse OFDM signals combined with frequency hopping (FH), and the direct-sequence (DS) UWB approach, based on impulse radio transmission of UWB DS-coded pulses. In this paper, the ranging capabilities of the two proposals are investigated by determining the Cramer-Rao lower bound (CRLB) for the distance estimation error. The CRLB is evaluated with both ideal and real, multipath-affected, channel models and the impact of multipath on ranging accuracy is quantified. Results show that DS-UWB is, in general, best suited for ranging, thanks to its larger bandwidth and its higher frequencies of operation, although multipath may affect in a different way DS-UWB and MB-OFDM signals.

Lower bounds for ranging accuracy with multi band OFDM and direct sequence UWB signals

The definition of ultra wide band (UWB) signals set by the Federal Communications Commissions (FCC) opened the way to both impulse and non-impulse UWB signal formats. This is reflected within the IEEE 802.15.3a TG, aiming at the definition of a standard for UWB-based high bit rate WPANs. The two main proposals considered in this group are in fact a multi band OFDM approach, based on the transmission of non-impulse OFDM signals combined with frequency hopping (FH), and the direct-sequence (DS) UWB approach, based on impulse radio transmission of UWB DS-coded pulses. In this paper we analyze the ranging capabilities of the two proposals by first determining the Cramer-Rao lower bound (CRLB) for the error in distance estimation using both an ideal channel model and a real channel model taking into account the effect of multipath. Next, we investigate the impact of receiver structure and synchronization sequences adopted in the two proposals on the ranging accuracy. Results show that synchronization sequences play a key role in determining the ranging accuracy. Although the DS-UWB signal is in general best suited for ranging, thanks to its larger bandwidth and its higher frequencies of operation, specific synchronization sequences may in fact lead to better ranging accuracy for the MB-OFDM signal.

Active and passive radar sensors for airport security

In this paper, a new concept for increasing the airport security is proposed. The proposed innovative system is studied and developed in the ATOM (Airport detection and Tracking Of dangerous Materials by active and passive sensors arrays) project, funded by the European Commission. It foresees the definition of a multi-sensor approach that integrates active and passive radar sensors with currently used surveillance systems. The conceived system covers not only the access to the gate area but also the terminal area, actually monitored mainly by Closed Circuit Television (CCTV), aiming at increasing the security level in that area. The enhanced capability of detecting and tracking dangerous tools and materials without passengers collaboration is another key point of ATOM concept. The fusion of data coming from the different innovative sensors aims at enhancing the situation awareness, thus allowing an automatic alert provided to security operators to neutralize the threat. This work is focused on some activities performed by SESM - a Finmeccanica Company - and DIET Dept. of University of Rome “La Sapienza”. Specifically, the overall architecture of ATOM system is described, together with an overview of the WiFi-based Passive Bistatic Radar (PBR) tracking sub-system.

Track Fusion in a New Security System for Airports

This paper proposes a new concept for increasing airport security. The key point of this innovative system is the definition of a new airport security system architecture that covers not only the access to the sterile area, but also to the public area (currently monitored mainly through CCTV). The proposed architecture achieves such by increasing the security capability by using innovative sensors able to detect metallic and non-metallic objects without the passengers collaboration. The fusion of the information obtained from sensors with different physical characteristics enhances the understanding of the monitored surroundings and provides the basis for planning and decision-making. The core of the new system is therefore the means through which it executes data management and data fusion. In this paper a feasible track fusion strategy is proposed and its performance analyzed.

Localization in airport enviroment exploiting only-Doppler passive radar data

This paper proposes a new concept for increasing airport security. The proposed architecture achieves such by increasing the security capability by using innovative sensors able to detect metallic and non-metallic objects without the passengers collaboration. In this paper the focus is on the target localization exploiting only Doppler information, mainly coming from Passive Radar system.