This paper proposes an improvement of the random multiple access scheme for satellite communication named Multislot coded ALOHA (MuSCA). MuSCA is a generalization of Contention Resolution Diversity Slotted ALOHA (CRDSA). In this scheme, each user transmits several parts of a single codeword of an error correcting code instead of sending replicas. At the receiver level, the decoder collects all these parts and includes them in the decoding process even if they are interfered. In this paper, we show that a high throughput can be obtained by selecting variable code rates and user degrees according to a probability distribution. With an optimal irregular degree distribution, our system achieves a normalized throughput up to 1.43, resulting in a significant gain compared to CRDSA and MuSCA. The spectral efficiency and the implementation issues of the scheme are also analyzed.
Research and Development in a peculiar field such as Satellite Communications (as well as Space science/technology in general) is known to be the ideal stage both for large, transnational companies with the functions of large integrators and system/service providers, and for Small-Medium Enterprises (SMEs) specialized in vertical technologies and/or services. Both kinds of actors, and SMEs in particular, may take advantage of different forms of regional networking on a smaller-than-national scale to create synergies and exploit complementarities at a local level. This paper reports on a very recent experience of this kind, namely, the newborn no-profit regional association ToscanaSpazio, based in Tuscany, Italy. The association, through a number of networking, dissemination, and lobbying actions, helps creating and strengthening competence, and prevents the brain drain and the possible slow decay of the technological, scientific, and entre-preneurship assets of the region. In addition to describing the association, the paper also identifies and informs about the different opportunities of region-to-region business for similar regional networks or districts that may arise in Europe with the help of the European Commission, of national and regional Space Agencies, and of international large companies.
The design of efficient and effective techniques for security policy analysis is a crucial open problem in modern information systems. Significant attention has been dedicated in the past to the use of logical tools for the analysis of security policies, but this work has produced a limited impact on enterprise information systems. Important reasons of the limited success of past research were the difficult integration of these approaches with the technological scenario and the limited scalability of many proposals. Nowadays Semantic Web tools are increasingly used in modern information systems. We show how the tools provided by Semantic Web and ontology management technologies offer an adequate basis for the realization of techniques able to support conflict analysis in security policies. Based on the use of these techniques, we propose a solution for two different variants of conflict analysis: (a) Policy Incompatibility, and (b) Separation of Duty Satisfiability. Experiments that test the techniques on large security policies demonstrate the scalability of the approach.
Broadband Satellite Communication links have been proposed as an effective solution for backhaul links in access networks. Moreover, the ever increasing demand for high data rates has led to the use of frequencies above 10GHz. At these frequency bands, rain attenuation is the dominant fading mechanism and the only atmospheric phenomenon exhibiting significant spatial inhomogeneity. The cooperation of hybrid satellite-terrestrial systems and the Multiple-Input Multiple-Output (MIMO) techniques have been proposed in order to support high throughput and overcome the fading effects. In this work, the performance of a hybrid satellite-terrestrial MIMO system is studied and the outage capacity is analytically calculated. The antenna gains are adjusted to the different path losses of the satellite and terrestrial links resulting in a balanced MIMO system in terms of the Equivalent Isotropically Radiated Power (EIRP). Extended numerical results illustrate the performance gain of the spatial multiplexing techniques compared to a single satellite (SISO) system.
This paper aims at defining the role of a satellite component in an integrated communications, localization and monitoring system, which can be used in all emergency management phases. Particular attention will be given to the integration of the satellite and terrestrial components and of the different functionalities.
This paper provides an overview of some demonstration projects, which utilize Satellite Earth Observation, Navigation and Telecommunications technologies to the benefits of user communities in different domains with a high potential economic/societal impact. The main objective of the European Space Agency Integrated Applications Promotion (IAP) program is to foster the development of sustainable user-driven services integrating multiple space technologies. The presented applications are related to agriculture (GrapeLook), energy management (INTOGENER) and the maritime domain (SEMAFORS). For each project the user communities and their needs, the selected technical solution, the innovative elements and the operational prospects are discussed.
Controlling complex systems, containing nonlinearities and constraints, is always a domain of interest for researchers. Different schemes such as Nonlinear Model Predictive Control (NMPC) have been proposed but these are usually computationally demanding and complex by themselves. Nowadays two powerful techniques, Fuzzy Modeling and Model Predictive control, are being blended together in different ways to attain the advantages of controlling delayed, non-minimum phase, nonlinear and constrained systems efficiently. The paper discusses this novel technique to control a class of nonlinear systems, the Hammerstein models. In order to control the Hammerstein model containing static nonlinearity with linear GPC algorithm a 0th order TS adaptive fuzzy inverse model controller is used with feedback. This strategy makes the scheme powerful enough to be used with different Hammerstein models containing different types of static nonlinearities and different linear dynamics. Furthermore the GPC algorithm is developed by using Toeplitz/Hankel matrices rather than Diophantine equation to reduce computational complexity. The scheme has been tested in MATLAB/Simulink for different kinds of nonlinearities and different parameters of system dynamics, and has produced good control results. Simulation results show that in any case, the optimization remains convex and single layer of optimization is sufficient to optimize the cost function.
User's privacy protection is a very important issue which can seriously affect the usability of a biometric system, and prevent its successful establishment. In order to perform people verification while providing security and privacy to the employed characteristics, several biometric template protection schemes have been recently proposed. Unfortunately, when deploying a biometric cryptosystem, a significant intra-class variability, combined with the lack of enrollment data for estimating the templates' statistics, may prevent the users' verification due to the limits on error correction capability of the employed codes. In this paper we propose a feature-level fusion technique which can significantly reduce the intra-class variability of feature-based templates, thus allowing to reach low false recognition rates in protected systems. The benefits of the proposed approach are evaluated over a novel video-based face verification system relying on Universal Background Models and adapted user model eigen-projections. Tests over the BANCA database show good performance of the proposed features for face verification, and improved template protection when the proposed feature fusion approach is applied.
In this paper we describe a framework of resources and procedures for critical infrastructure disaster recovery. The aim is to create an asset management system consisting of the necessary resources (services, human resources, equipment,) for providers to restore communications in disasters using satellite technology. The latter provides service to a wide coverage without restrictions to location and access technologies used. The proposed system will check the compatibility and interactivity of these resources and shall provide a disaster recovery plan when needed, a useful tool for civil protection services of the European countries and the European Union in general.
During a seismic swarm masonry buildings suffer stresses which often give rise to permanent deformation and, in extreme cases, lesions, and sometimes unavailability. When a large area is hit by a swarm, the number of buildings affected by this phenomenon, and potentially vulnerable, amounts to several thousand, giving rise to huge monitoring activity needs [1]. According to this reason, we decided to explore the methodology of differential SAR interferometry, which allows, in principle, to detect deformations of the order of a few millimeters within a comprehensive picture of a whole area.
This paper describes the main outcomes of Sistemi Software Integrati (SSI) R&D activities addressing Network-centric software architecture for autonomous systems. Specifically, the studies and products focus on Swarm-centric architectures, a specialized branch of Network-centric systems where system features such as autonomy, fractionation, and (self-) organization gain a primary role in the system design guidelines. The Real-Time Swarm Intelligence Platform (RT-SIP) is described as SSI product and application integration platform which implements the Swarm paradigm.
Communication satellite payload has redundancy networks with multi port switches connecting input units to output units. In case of a probable failure at an output unit, connected input unit must be re-routed to a redundant output unit via changing the positions of switches. This paper proposes a mathematical model to represent the redundancy networks and a recursive algorithm to find all paths connecting input units to output units. Simulation results of an example payload, receiver redundancy network demonstrate the efficiency of the proposed approach.
Rain attenuation is the dominant fading mechanism for Future Broadband Satellite Communication Systems (operating at Ku band and above). In this paper, hitting time statistics of rain attenuation process are presented using a well accepted dynamic model. Hitting time gives the time needed for a stochastic process to exit an interval of thresholds given the initial value. The expression to compute analytically the Complementary Cumulative Distribution Function (CCDF) of hitting times for rain attenuation is given. Moreover, the employment of hitting time statistics in designing Fade Mitigation Techniques (FMTs) is proposed and a discussion of how these statistics can be used for the FMT control loop is made. The FMTs under consideration for the application of hitting time statistics are the power control, adaptive coding and modulation (ACM) and time diversity. Furthermore, numerical results are presented showing that the theoretical model actually reproduces the hitting time statistics and finally some useful conclusions are drawn.
The development of location based services for indoor environment has been limited by the lack of a GPS equivalent positioning system. In fact indoor localization technologies are installed in specific contests and usually requires dedicated terminals. Some location systems relay on the communication technologies available on mobile phones such as WiFi or Bluetooth. However these solutions are standalone systems and usually can't collaborate or can't be integrated with other solutions. In this paper we introduce the CAMMEO system that aims to overcome the limitation of existing location infrastructures. CAMMEO proposes well-defined interfaces among the actors involved in the localization: the wireless technologies, the positioning algorithms and the applications. These interfaces are implemented in a distributed system comprising mobile devices, servers and wireless infrastructures. The main goals of the system are to provide: i) a direct interface toward various wireless technologies, ii) a modular integration of existing localization frameworks and positioning engines and iii) a standard interface for application developers including also a maps management facility. We present a prototyping implementation of the CAMMEO system integrating WiFi, Bluetooth and RFID wireless technologies.
In this paper it is shown that bifilar of a Quadrifilar Helix Antenna (QHA) when designed in side-fed configuration at a given diameter and length of helical arm, effectively becomes equivalent to combination of a loop and a dipole antenna. The vertical and horizontal electric fields caused by these equivalent antennas can be made to vary by changing the turn angle of the bifilar. It is shown how the variation in horizontal and vertical electric field dominance is seen until perfect circular polarization is achieved when two fields are equal at a certain turn angle where area of the loop equals product of pitch of helix and radian length i.e. equivalent dipole length. The antenna is low profile and does not require ground plane and thus can be used in high speed aerodynamic and platform bodies made of composite material where metallic ground is unavailable. Additionally not requiring ground plane increases the isolation between the antennas with stable radiation pattern and hence can be used in MIMO systems.
This paper suggests a low cost design of MIL-STD-1553 bus terminal devices used in various Avionics and Aerospace applications. The design involves the implementation of MIL-STD-1553 bus core functionality on Digital Signal Processor (DSP) having on chip Multichannel Buffered Serial Port (MCBSP). The DSP acts as a host processor and MIL-STD-1553 bus compliant packet generator. Device specific software and the hardware design technique adopted to interface MCBSP with bus transceiver have also been discussed. With the successful implementation of the idea the terminal device host processor (DSP) could be used for performing all the necessary functions of 1553A/B protocol eradicating the need of a dedicated and an expensive bus core IC, parallel I/O lines and different control logic ICs. The work proves to be a low cost and reduced hardware design for 1553A/B based devices in Avionics and Aerospace systems.
When multiple flying vehicles collaborate in locating a target, their formation design is an important factor to the error of location. Based on the analyses of contribution that formation design made to the location error, Effective Observing Area is defined as a criterion to assess formation design. An evaluation method for formation design is then proposed in this paper, which can serve as a guide in further formation design. Digital simulation results have proved the effectiveness and correct of this concept.
This paper characterizes a recently proposed anonymous file sharing system, OneSwarm. This characterisation is based on measurement of several aspects of the OneSwarm system such as the nature of the shared and searched content and the geolocation and number of users. Our findings indicate that, as opposed to common belief, there is no significant difference in downloaded content between this system and the classical BitTorrent ecosystem. We also found that a majority of users appears to be located in countries where anti-piracy laws have been recently adopted and enforced (France, Sweden and U.S). Finally, we evaluate the level of privacy provided by OneSwarm, and show that, although the system has strong overall privacy, a collusion attack could potentially identify content providers.
