A new look at the conditions for the synthesis of speed-independent circuits

This paper presents a set of sufficient conditions for the gate-level synthesis of speed-independent circuits when constrained to a given class of gate library. Existing synthesis methodologies are restricted to architectures that use simple AND-gates, and do not exploit the advantages offered by the existence of complex gates. The use of complex gates increases the speed and reduces the area of the circuits. These improvements are achieved because of (1) the elimination of the distributivity, signal persistency and unique minimal state requirements imposed by other techniques; (2) the reduction in the number of internal signals necessary to guarantee the synthesis; and finally (3) the utilization of optimization techniques to reduce the fan-in of the involved gates and the number of required memory elements.Peer ReviewedPostprint (published version

Hierarchical gate-level verification of speed-independent circuits

This paper presents a method for the verification of speed-independent circuits. The main contribution is the reduction of the circuit to a set of complex gates that makes the verification time complexity depend only on the number of state signals (C elements, RS flip-flops) of the circuit. Despite the reduction to complex gates, verification is kept exact. The specification of the environment only requires to describe the transitions of the input/output signals of the circuit and is allowed to express choice and non-determinism. Experimental results obtained from circuits with more than 500 gates show that the computational cost can be drastically reduced when using hierarchical verification.Peer ReviewedPostprint (published version

Efficient encoding schemes for symbolic analysis of Petri nets

Petri nets are a graph-based formalism appropriate to model concurrent systems such as asynchronous circuits or network protocols. Symbolic techniques based on Binary Decision Diagrams (BDDs) have emerged as one of the strategies to overcome the state explosion problem in the analysis of systems modeled by Petri nets. The existing techniques for state encoding use a variable-per-place strategy that leads to encoding schemes with very low density. This drawback has been partially mitigated by using Zero-Suppressed BDDs, that provide a typical reduction of BDD sizes by a factor of two. This work presents novel encoding schemes for Petri nets. By using algebraic techniques to analyze the topology of the net, sets of placesPeer ReviewedPostprint (published version

Building a safe and socially acceptable concept of operation for drones flying at the very low level

This work has been prepared by all CORUS partners: DLR, DFS, DSNA, ENAV, EUROCONTROL, HEMAV, NATS, Unifly and UPC. The list of authors would be too long to include them all, but we would like to acknowledge them now. This work has been partially funded by the SESAR Joint Undertaking, a body of the European Commission, under grant H2020 RIA-763551.As part of the Single European Sky ATM Research (SESAR) a number of projects related to the drones flying at the very low level (VLL) have been funded. At its core, the CORUS project is developing the concept of operations (ConOps) of these drones1. At the same time, the last European ATM Masterplan has proposed the “Roadmap for the safe integration of drones into all classes of airspace”2. This document proposes the set of services for the unmanned air traffic management, named as Uspace, together with a calendar for their deployment (from U1 to U4). The CORUS project integrates these services as pillars of the ConOps, with the objective of supporting the new businesses and jobs, improving the safety of the drones, and dealing with their public acceptance.Postprint (published version

U-space concept of operations: A key enabler for opening airspace to emerging low-altitude operations

Opening the sky to new classes of airspace user is a political and economic imperative for the European Union. Drone industries have a significant potential for economical growth according to the latest estimations. To enable this growth safely and efficiently, the CORUS project has developed a concept of operations for drones flying in Europe in very low-level airspace, which they have to share that space with manned aviation, and quite soon with urban air mobility aircraft as well. U-space services and the development of smart, automated, interoperable, and sustainable traffic management solutions are presented as the key enabler for achieving this high level of integration. In this paper, we present the U-space concept of operations (ConOps), produced around three new types of airspace volume, called X, Y, and Z, and the relevant U-space services that will need to be supplied in each of these. The paper also describes the reference high-level U-space architecture using the European air traffic management architecture methodology. Finally, the paper proposes the basis for the aircraft separation standards applicable by each volume, to be used by the conflict detection and resolution services of U-space.This work has been partially funded by the SESAR Joint Undertaking, a body of the European Commission, under grant H2020 RIA-763551 and by the Ministry of Economy and Enterprise of Spain under contract TRA2016-77012-R.Peer ReviewedPostprint (published version

A new technique based on mini-UAS for estimating water and bottom radiance contributions in optically shallow waters

The mapping of nearshore bathymetry based on spaceborne radiometers is commonly used for QC ocean colour products in littoral waters. However, the accuracy of these estimates is relatively poor with respect to those derived from Lidar systems due in part to the large uncertainties of bottom depth retrievals caused by changes on bottom reflectivity. Here, we present a method based on mini unmanned aerial vehicles (UAS) images for discriminating bottom-reflected and water radiance components by taking advantage of shadows created by different structures sitting on the bottom boundary. Aerial surveys were done with a drone Draganfly X4P during October 1 2013 in optically shallow waters of the Saint Lawrence Estuary, and during low tide. Colour images with a spatial resolution of 3 mm were obtained with an Olympus EPM-1 camera at 10 m height. Preliminary results showed an increase of the relative difference between bright and dark pixels (dP) toward the red wavelengths of the camera's receiver. This is suggesting that dP values can be potentially used as a quantitative proxy of bottom reflectivity after removing artefacts related to Fresnel reflection and bottom adjacency effects.Peer ReviewedPostprint (published version

NtoM: a concept of operations for pilots of multiple remotely piloted aircraft

The concept of operations proposed here pursues the feasibility, from a human factors perspective, of having a single pilot/aircrew controlling several remotely piloted aircraft systems at once in non-segregated airspace. To meet such feasibility, this multitasking must be safe and not interfere with the job of the air traffic controllers due to delays or errors associated with parallel piloting. To that end, a set of measures at several levels is suggested, which includes workload prediction and balance, pilot activity monitoring, and a special emphasis on interface usability and the pilot’s situational awareness. The concept relies greatly on the exploitation of the potential of Controller-Pilot Data Link Communications, anticipating future widespread implementation and full use. Experiments comparing the performance of the same pseudo-pilots before and after the implementation of part of the measures showed a decrease in the number of errors, oversights and subjective stress.Peer ReviewedPostprint (published version

Dynamic workload management for multi-RPAS pilots

This document describes a key aspect of NtoM, a concept of operations (ConOps) currently under development, which focuses on the awareness, productivity and safety of Remotely Piloted Aircraft System (RPAS) pilots controlling several flights at once in non-segregated airspace. An explanation will be given of how the ConOps suggests capturing, representing, managing and predicting the workload of the pilots. To illustrate some of the features of the concept, it was necessary to define a representation of the workload associated to the tasks. A synthetic task environment that used the NtoM prototype was built and used to evaluate the requirements of time and attention of pseudo-pilots based on their performance while executing the tasks and task overlaps, determine the top threshold of workload allowed for a pilot and detect incompatibilities among tasks. These values served as a reference to design demanding test scenarios, which helped to reveal weaknesses and inspire improvements that were addressed in the following stage of development.Peer ReviewedPostprint (published version

Symbolic analysis of bounded Petri nets

This paper presents a symbolic approach for the analysis of bounded Petri nets. The structure and behavior of the Petri net is symbolically modeled by using Boolean functions, thus reducing reasoning about Petri nets to Boolean calculation. The set of reachable markings is calculated by symbolically firing the transitions in the Petri net. Highly concurrent systems suffer from the state explosion problem produced by an exponential increase of the number of reachable states. This state explosion is handled by using Binary Decision Diagrams (BDDs) which are capable of representing large sets of markings with small data structures. Petri nets have the ability to model a large variety of systems and the flexibility to describe causality, concurrency, and conditional relations. The manipulation of vast state spaces generated by Petri nets enables the efficient analysis of a wide range of problems, e.g., deadlock freeness, liveness, and concurrency. A number of examples are presented in order to show how large reachability sets can be generated, represented, and analyzed with moderate BDD sizes. By using this symbolic framework, properties requiring an exhaustive analysis of the reachability graph can be efficiently verified.Peer ReviewedPostprint (published version

Improving real-time drone detection for counter-drone systems

The number of unmanned aerial vehicles (UAVs, also known as drones) has increased dramatically in the airspace worldwide for tasks such as surveillance, reconnaissance, shipping and delivery. However, a small number of them, acting maliciously, can raise many security risks. Recent Artificial Intelligence (AI) capabilities for object detection can be very useful for the identification and classification of drones flying in the airspace and, in particular, are a good solution against malicious drones. A number of counter-drone solutions are being developed, but the cost of drone detection ground systems can also be very high, depending on the number of sensors deployed and powerful fusion algorithms. We propose a low-cost counter-drone solution composed uniquely by a guard-drone that should be able to detect, locate and eliminate any malicious drone. In this paper, a state-of-the-art object detection algorithm is used to train the system to detect drones. Three existing object detection models are improved by transfer learning and tested for real-time drone detection. Training is done with a new dataset of drone images, constructed automatically from a very realistic flight simulator. While flying, the guard-drone captures random images of the area, while at the same time, a malicious drone is flying too. The drone images are auto-labelled using the location and attitude information available in the simulator for both drones. The world coordinates for the malicious drone position must then be projected into image pixel coordinates. The training and test results show a minimum accuracy improvement of 22% with respect to state-of-the-art object detection models, representing promising results that enable a step towards the construction of a fully autonomous counter-drone system.Peer ReviewedPostprint (published version