1,720,973 research outputs found
Tecniche innovative per la rivelazione e la separazione di segnali sovrapposti nel canale del radar secondario di sorveglianza
Full text linkIn questo lavoro è stato affrontato il problema della corretta ricezione di segnali a 1090 MHz in ambienti ad alta densità di traffico. I segnali oggetto degli studi sono quelli utilizzati dai sistemi per la sorveglianza del traffico aereo (ATC): il radar secondario di sorveglianza (SSR), il sistema ADS-B (Automatic Dependent Surveillance-Broadcast), i sistemi di multilaterazione (MLAT e WAM), il sistema TIS-B ed il sistema T-CAS (Traffic Collisions Avoidance System). Le sorgenti dei segnali sono: i transponder avionici, i transponder veicolari e le stazioni trasmittenti del sistema TIS-B (Traffic Information System – Broadcast). I transponder trasmettono segnali di modo convenzionale e di modo S a seguito di interrogazioni da parte del radar secondario di sorveglianza, da parte di sistemi MLAT/WAM attivi e da parte dei sistemi T-CAS. I transponder di modo S inoltre trasmettono anche dei segnali spontanei detti squitter. Le stazioni TIS-B trasmettono segnali di modo S con la funzione di aggiornare gli aeromobili dotati di ADS-B sul traffico di aeromobili non dotati di ADS-B. Un ricevitore a 1090 MHz collocato in un ambiente ad alta densità di traffico possiede una probabilità non trascurabile di ricevere segnali sovrapposti nel tempo, soprattutto se dotato di antenna ricevente omnidirezionale. Inevitabilmente una tale situazione impedisce la corretta ricezione e decodifica di tutti i segnali, pregiudicando l’integrità della sorveglianza. Le tecniche proposte per affrontare il problema della ricezione di segnali sovrapposti sfruttano la diversità di antenna per rivelare la presenza di segnali sovrapposti e separarli. Tali metodi prevedono l’uso di una antenna ad array ed un ricevitore multicanale. Viene proposta anche una soluzione basata sull’uso di un ricevitore mono canale ed antenna omnidirezionale. Gli algoritmi presentati sono stati valutati tramite dei test utilizzando segnali reali registrati. Infine viene mostrato come aumenta la capacità del canale a 1090 MHz grazie all’utilizzo delle tecniche proposte.This work addresses the reception problem of 1090 MHz signals in high traffic density environment. The 1090 MHz signals are used in air traffic control systems: The secondary surveillance radar (SSR), the ADS-B (Automatic Dependent Surveillance-Broadcast), the multilateration systems (MLAT and WAM ), the TIS-B (Traffic Information System - Broadcast) system and the T-CAS (Traffic Collisions Avoidance System). The signals sources are: the avionic transponder, the vehicular transponder and the TIS-B ground stations. The transponders transmit conventional and Mode S signals after receiving an interrogation by the secondary radar surveillance systems, by active MLAT / WAM and by T-CAS systems. Mode S transponders also transmit squitters, i.e. spontaneously emitted signals. The TIS-B ground-stations transmit Mode S signals in order to update the non-ADS-B traffic to the aircraft equipped with ADS-B (it is an ADS-B gap filler). A 1090 MHz receiver placed in a high traffic environment has a significant probability of receiving signals overlapping in time, particularly while using omnidirectional receiving antenna. Inevitably, this situation prevents the proper reception and decoding of all signals, compromising the integrity of surveillance. The thesis propose several methods to address the problem of overlapping received signal exploiting the antenna diversity, via an antenna array, for signals detection, separation, and decoding. These methods necessitate the use of an antenna array and a multichannel receiver, but also a mono-channel algorithm is proposed, which is useful for older systems that have only a single omnidirectional antenna. The presented algorithms have been assessed using real recorded signals. Finally the 1090 MHz channel capacity enhancement using the proposed methods is demonstrated
Scheduling Methods for a Conformal, Phased Array Multifunction Radar
No full textThis paper presents a method for the scheduling of a multifunction radar based on an active phased array of the conformal type (frustum of cone). This type of antenna obtains a 360 degrees horizontal coverage by a number M of sectors each one belonging to a sub-array, where different non overlapping sub-arrays can illuminate different targets at the same time. This operation has both the advantages of a rotating antenna and those of the electronic scan of a fixed-faces multifunction radar. In this context, a scheduling algorithm has to organize a number of parallel radar tasks respecting the constrains on the update intervals. The goal is to implement a scheduling algorithm for a system quite similar to a fixed-faces multifunction phased array radar, with the significant difference that the faces number and pointing directions are variable and adaptive to the scenario. An optimization model is presented and then a heuristic models is discussed with some computational results
ADS-B vulnerability to low cost jammers: Risk assessment and possible solutions
No full textAutomatic 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
Clustering methods for Mode S stations: Evaluation and perspectives
Full text linkGrouping of a set of Secondary Surveillance Radar (SSR) Mode S stations into functional entities called clusters has significant operational facets; it calls for a constrained optimization, an important significant constraint being the scarcity of Interrogation Identifier (II) codes. This clustering problem can be approached by two ways, i.e., integer programming methods and heuristic approaches. The definition of a general, usable decision support tool to build up and evaluate clustering strategies in any operational airspace, e.g. the one of a nation or, even more complicated, of a system such as the European one, is a very challenging task. This paper describes some steps toward this envisaged result proposing a mathematical formulation and a heuristic approach for the problem
Multiple sources discrimination by array processing
No full textAn array system solution is adopted in the paper to face the problem of separation of superimposed signals by performing blind source separation. A five channels receiving station has been implemented to provide a large dynamic range, wide bandwidth and fast sampling, with a proper array of six independent antenna elements properly designed to give a sufficiently wide covering pattern. The source separation algorithm is fully described and the experimental results concerning the characterization of the array elements are discussed
ADS-B degarbling and jamming mitigation by the use of blind source separation
No full textAutomatic Dependent Surveillance-Broadcast system is a pillar of the future air traffic system. Equipped aircraft utilize the on-board navigation system (based on the GPS unit) to calculate their position and velocity and then broadcast this information on a common RF channel using an on board emitter. Ground-based sensors receive these messages that are used by the ATC centers to produce an image of the traffic on the controller's display. This system uses a data-link protocol called "1090 Extended Squitter (1090ES)": each aircraft periodically transmits messages PPM modulated on L-band (1090 MHz) with random access to the channel with a transmitter called transponder. This protocol is affected by two important limitations: the throughput of the channel is limited by the garbling effect (i.e. the reception of superimposed messages in dense scenario) and the fact that the 1090 MHz RF channel can be prone to jamming (that is the transmission of high power signals superimposing the aircraft messages). A method to mitigate these two effects using a multichannel ADS-B receiver and a Principal Component Analysis (PCA) based Blind Source Separation (BSS) technique is proposed in this work. The proposed method is evaluated using real signals both in jamming and garbling cases
Time for a change in phased array radar architectures - part I: Planar vs. conformal arrays
No full textThe 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
Coherent source separation based on sparsity: an application to SSR signals
Full text linkSystems 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 being planned. In this frame, high-density traffic leads to the reception of a mixture of several overlapping SSR replies. By nature, SSR sources are sparse, i.e. with amplitude equal to zero with significantly high probability. While in the literature several algorithms performing sources separation with an m-element 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, although we present in this study two algorithms to separate the complex-valued SSR sources. Recorded signals in a live environment are used to demonstrate the effectiveness of the proposed techniques. Copyright © Cambridge University Press and the European Microwave Association 2009
Time for a change in phased array radar architectures- part II: The d-radar
No full textA 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
Separation of multiple secondary surveillance radar sources in a real environment for the near-far case
Full text linkMultilateration systems based on Secondary Surveillance Radar (SSR) systems and omni-directional antennae are operational today [1,2]. Assuming the replacement of the single-element antenna by an array, we proposed new algorithms to discriminate overlapped signals in previous works [3,4,5]; other solutions were also proposed in the literature [6,7,8]. Unfortunately, all have either some shortcomings, or an expensive computational cost, or no simple practical implementation. Therefore, we proposed in [9] a reliable, simple, and effective projection algorithm. Nevertheless, some issues were overlooked: in particular the relative power ratio between the signals to be separated may be important, which we study in this paper with real-life signals
- …
