Emilio G. Piracci

Separation of SSR Signals by Array Processing in Multilateration Systems

Location and identification of cooperating aircraft in the airport area (and beyond) may be implemented by multilateration (MLAT) systems using the secondary surveillance radar (SSR) mode S signals. Most of these signals, spontaneously emitted from on-board mode S transponders at a fixed carrier frequency, arrive randomly at the receiving station, as well as many mode A/C replies from legacy transponders still in use. Several SSR signals are, then, overlapped in multiple aircraft situations. Therefore, the aim of this work is the separation of overlapped SSR signals, i.e., signals superimposed in time at receiving stations. We improve the MLAT receiving station by replacing the single antenna by an array of m elements and using array signal processing techniques. In the literature, several algorithms address the general source separation problem, but a very few of them are specifically designed for a mixture of overlapping SSR replies. Unfortunately, all of them have either some shortcomings, or an expensive computational cost, or no simple practical implementation. In this paper, we use the time sparsity property of the sources to propose more reliable, simpler, and more effective algorithms based on projection techniques to separate multiple SSR signals. Real recorded signals in a live environment are used to demonstrate the effectiveness of our method.

ADS-B vulnerability to low cost jammers: Risk assessment and possible solutions

Automatic Dependent Surveillance-Broadcast (ADS-B) systems provide to the air traffic control centers flight and status information of the cooperating targets. Problems due to jamming and/or spoofing of the ADS-B channel are under study, as well as verification and validation techniques. In this paper, we show how a low cost jammer can affect an ADS-B receiver. Three types of threats were evaluated. A multichannel receiver permitted to evaluate the received signal stream with and without jammer. The measurements were carried out coupling the receiver antenna with the in-cable jammer radio frequency (1090 MHz) signal. The results show the detection loss as a function of jammer range and jammer type. Finally, possible solutions are proposed to mitigate the effects. Some trials to evaluate their effectiveness are described.

The transponder data recorder: Implementation and first results

We have designed, implemented, and tested a flexible receiving and processing multichannel system for signals in the 1,090-MHz band with significant air traffic management applications in surveillance and communication. Thanks to a wide bandwidth and a large dynamic range, with four linear channels plus a logarithmic channel, this TDR allows us to record the signals of interest with minimal distortion, from sources whose distance from the antenna sys-tem ranges from a few tens of meters up to hundreds of kilometers. From the recorded signals, it is possible: 1) to characterize the traffic in the 1,090-MHz band, and 2) to test the effectiveness of different source separation algorithms, either based on space diversity or based on frequency diversity. The system permits a higher degree of automation and higher quantity of data acquisition than some previous experimental systems.

Time for a change in phased array radar architectures - part I: Planar vs. conformal arrays

The well-known phased array radar architecture with four planar faces presents significant limitations for the azimuth coverage of 360 degrees due to the beam scanning up to 45 degrees. Today, a better time and energy efficiency can be obtained by circularly-symmetrical arrays having cylindrical or conical shape. Using separate transmit/receive (Tx/Rx) arrays with Digital Beam Forming in the Rx array adds some further operational flexibility in terms of coverage and revisit time.

Time for a change in phased array radar architectures- part II: The d-radar

A novel multifunction phased array radar is introduced, characterized by conformal arrays, extensive usage of digital beam forming and separation between Tx and Rx arrays. Some significant design trade-off and radar operating aspects are described, including the radar management and scheduling, showing the main differences with respect to the classical, four faces phased array multifunction radar architecture.

Secondary Surveillance Radar: Sparsity-based sources separation in a real environment

Secondary surveillance radar (SSR) based on multilateration principle and omni-directional antennae are operational today [1], [2]. We proposed several new algorithms to separate a mixture of overlapping SSR replies on a M-elements antenna in previous works [3], [4], [5], [6], other solutions were also proposed in the literature [7], [8], [9]. Unfortunately, a rare event, but important, has not yet been resolved: the impinging of more sources than sensors with an approximate similar time of arrival. This preliminary work studies the use of the SSR sources sparsity property, as in [10], [11], [12]. Real recorded signals in a live environment will be used to demonstrate the effectiveness of the proposed techniques.

Coherent sources separation based on sparsity: an application to SSR signals

Systems based on Secondary Surveillance Radar (SSR) downlink signals, both with directional and with omni- directional antennae (such as in Multilateration) are operational today and more and more installations are planned. In this frame, high-density traffic leads to the reception of a mixture of sev- eral overlapping SSR replies. By nature, SSR sources are sparse, i.e. with amplitude equal to zero with significantly high probabil- ity. While in the literature several algorithms performing sources separation with a -elements antenna have been proposed, none has satisfactorily employed the full potential of sparsity for SSR signals. Most sparsity algorithms can separate only real-valued sources, while we present in this study two algorithms to sepa- rate the complex-valued SSR sources. Recorded signals in a live environment are used to demonstrate the effectiveness of the pro- posed techniques. Index Terms - Secondary Surveillance Radar, Array processing, Blind Source Separation, Sparsity, Air Traffic Control.

High resolution, millimeter-wave radar applications to airport safety

A millimeter-wave (mmw: 3 mm wavelength, W-band) radar permits short-range, high-resolution detection and imaging of the airport movement area. The main safety-related applications, which have been tested in Marco Polo (Venice) and Urbe (Roma) airports respectively, are the prevention of runway incursions and the management of Foreign Object Debris (FOD). Other potential applications, to be studied, are Bird-strike prevention and Intruder detection.

Improved MDA, a case for de-garbling SSR mode S replies

Multilateration (MLAT) and Automatic Dependent Surveillance - Broadcast (ADS-B) systems exploiting the Secondary Surveillance Radar (SSR) channel suffer from garbling. This means that if two or more mode S signals impinge on the receiver at the same or very near time they could not be decoded. To alleviate this problem, many solutions have been proposed, one in particular [1] is effective for a large variety of scenarios, but excluding the cases when the replies are too much separated in time. Recently a paper [2] focused on linear algebra presented a potential solution for this case. In this work we present a practical application for the case of two mode S signals.

Single-antenna projection algorithm to discriminate super-imposed Secondary Surveillance Radar Mode S signals

This paper presents a novel, effective algorithm to discriminate and separate super-imposed SSR (Secondary Surveillance Radar) Mode S signals. Our goal is a blind separation of multiple SSR sources using a single channel receiver. Other algorithms perform sources separation exploiting space diversity or statistical properties, but with the practical inconvenience of the need for a multi-channel receiver. As today SSR stations are equipped with single-channel receivers (for Multilateration and Wide Area Multilateration applications, M-LAT, WAM) the proposed algorithm is aimed to be operationally useful.