Research

Research activities have been almost devoted to radiocommunications and wireless systems, with special emphasis on development of i) theoretical frameworks for performance analysis, ii) algorithmic components and iii) protocol architectures in modern systems. Theory and engineering of communication systems being the core of research, a cross-disciplinary approach has been pursued since the early stage of research career, when a two-years long full time experience was carried out in a microelectronic research lab of the National Research Council (CNR) of Italy. More recently, strong and structured connections with the control and computer engineering communities have been established to develop activities in the networked embedded systems domain according to the emerging "triple C" (Computing, Communication and Control) paradigm. Furthermore, significant efforts have been spent to setup close cooperations with the national and international research community and with the industrial world along more than 25 years of academic career at the University of L'Aquila. A short description of major research tracks is provided in the following.

1. Satellite communication systems and technologies

This research field has been almost explored since the Master thesis, then during the Ph.D. program and the early stage of the academic career. A major activity has been concerned with development, prototyping and validation of superconducting technologies for millimeter waves radio communications front-ends: specifically, integrated low-noise frequency converters have been fabricated in a clean room facility with a complete sequence of processes, and tested in a series of prototypes that included on the same chip the mixer and the local oscillator for down conversion. Performance have been reported in a number of journal papers in the area of physics and technology. Moreover, application perspectives have been explored in cooperation with Telespazio, with interesting benefits in the field of long range communications and inter-satellite links. Nonetheless, the mmW band has become attractive in recent years for short range high capacity communications. Another activity undertaken at the beginning of the career is related to resource management and teletraffic performance evaluation in integrated terrestrial-satellite systems for mobile communications. In this frame, an extension of the recursive algorithm of the Erlang B formula has been developed in order to encompass the case of guard channels for priority traffic management. A latest activity in the field of satellite and space communications is concerned with all-digital processing for semi-transparent transponders, in cooperation with Thales Alenia Space - Italy: several papers have been published in major IEEE technical journals and conference proceedings, and on-going work is concerned with the design of digital transparent transponders for incoming satellite constellations and their integration with terrestrial networks in the 5G arena.

2. Handover algorithms and link quality statistics in land mobile cellular systems

This area has been a major topic of research for many years in 2G/3G systems and has been later reinforced in the 4G/5G perspective. Relevant contributions have been provided in a series of journal and conference papers that have been acknowledged and cited by top level researchers worldwide. The following major results have been achieved:

- development of cross-layer frameworks for joint analysis of handover initiation and execution, that include modelling of handover dwell time and queueing policies in several scenarios;

- novel algorithms for handover initiation, that are based on least square estimation of the path loss and have been developed in a general and adaptive version; our latest advance in this field is the result of a quite long work in cooperation with our colleagues at KTH and relies on novel approximations and modern tools for optimization; the adaptive framework that has been developed is very promising to cope with requirements of 4G/5G and beyond 5G systems, where heterogeneous and variable coverages are to be considered;

- modelling of effects of interference for accurate evaluation of performance indexes such as statistics of handovers and outages; in particular, significant theoretical contributions have been provided to derive approximate statistics for sums of log-normal variates with constant or random weights, and in terms of both first and second order statistics. Instead of resorting to bounds under simplyfied system assumptions, an approach has been undertaken that is oriented to derive accurate approximations for the signal-to (interference+noise) ratio without introducing simplifying assumptions in system settings (e.g. no cross correlations among channel components or composite channel settings); in this frame easy-to-use solutions  and also new models for cross-correlated shadowing components have been developed. This research line has represented the basis for many subsequent developments of the research team in the modern areas of wideband, ultrawideband and cooperative systems, the most recent ones related to network interference modelling through stochastic geometry. Modelling of interference is currently a transversal major activity in many wireless frameworks, e.g. the ones described in the following items (short range radios, 5G and post-5G NOMA schemes for multiple access).

3. Multiple access techniques and radio resource management for multimedia wireless systems

This area is basically concerned with capacity evaluation under optimal resource assignment in spread-spectrum systems for multimedia applications. Relevant contributions have been provided in defining and solving optimization problems and in development of adequate approximations for derivation of performance indexes. The following major results have been achieved:

- computation of outage statistics (of the first and second order) in FH-TDMA and DS-CDMA systems under various settings for channel statistics and power control imperfections;

- optimal power allocation for capacity maximization in multimedia DS-CDMA systems in single cell and multi-cell systems;

- modelling and performance optimization of nested control loops in wireless chains with cross-layer settings, in cooperation with our colleagues in control engineering; this activity has lead to some prospective research lines presented in journals and conferences in the area of embedded and networked control.

4. Distributed wireless networks and networked embedded systems

This research area is quite broad: it has been almost developed within the Centre of Excellence DEWS and more recently in the recently funded Centre of Excellence Ex-EMERGE and its various connections to partners and projects. The following major results have been achieved along various research lines:

- advanced performance modelling of Impulse Radio UWB systems: along the track of earlier research work on modelling of SNR and SINR statistics, a framework based on Pearson Type IV distribution has been developed during the program of a brilliant Ph.D. student to compute the average bit error probability in UWB system setups of practical interest with both rake receivers and transmitted reference systems, without introducing preliminary simplifications in the system model (e.g. simplifying the channel model or neglecting the intra-pulse interference). Along with contributions on UWB channel sounding and optimal detection of UWB signals in the presence of interferers, this research topic has lead to a consistent number of papers in top level journals and conferences, with a good impact on the technical literature;

- distributed and cooperative algorithms for source coding and positioning in wireless sensor networks: a fundamental contribution has been provided to achieve novel results on i) theoretical frameworks for performance assessment of distributed source coding (DSC) under realistic system settings (multi-hop, error control coding and data aggregation), and ii) distributed and cooperative least squares algorithms for position estimation, with an original solution proposed and various settings tested in experimental contexts. Especially the last topic has lead to several publications, with a few of them achieving a significant number of qualified citations (e.g. by Moe Win's group);

- joint control-communication design in networked embedded control systems through advanced modelling and formal methods based on platform-based design: a fundamental and prospective activity has been done to define and develop the research agenda of this emerging and cross-disciplinary area, with results achieved on i) advanced modelling and optimization of a control-communication paradigm based on stochastic abstraction, ii) network design for application in industrial and process control, iii) development of cross layer models for wireless sensor and actuator networks relying on the widespread IEEE 802.15.4 stack and, more recently, for performance analysis of modern RFID systems based on passive tags and backscatter modulation;

- performance analysis of cooperative and cognitive communications: by resorting to the development of a Moment Generating Function (MGF)-based approach, the following specific contributions have been provided in a cooperative communication setting with multiple hops and multiple branches: i) important performance indexes as end-to-end SNR and average bit error probability are obtained in exact form for generalized fading channels, and ii) a simple bound is introduced to deal with some specific cases. This work was launched through a cooperation with a former Ph.D. student and has later evolved towards performance prediction in the presence of the network interference. A recent evolution of activities on relay networks, that is only documented in a conference paper published in April 2016, is targeted to address blockage events in millimeter waves systems;

- vehicular communication networks for automotive, rail and aeronautics. This topic is of crucial interest for effective implementation of ITS (Intelligent Transport Systems) and it requires at the same time high reliability and low latency, which is now encoded in the 5G paradigm of URLLC (Ultra Reliable Low Latency Communications). Our research activity has been focused on the shared channel capacity and MAC performance of IEEE 802.11p communication frameworks, with development of extensive simulation environments and experimental trials based on Cohda Wireless embedded platforms. A specific activity is related to performance analysis of cooperative communication setups that integrate RF wireless and optical wireless in vehicular networks. Finally, current activities are referred to research advances for URLLC in 5G and post-5G frameworks and are included in the specific mission of the Centre Ex-EMERGE and Radiolabs Consortium;

- security issues in networked embedded systems: this research topic has been launched and developed in the research group as an internal project and has later become strategic as it has attracted many funds from both EU and national agencies; significant research results have been obtained in terms of proposal of i) a novel hybrid cryptographic scheme and ii) of low complexity intrusion detection mechanism based on weak process models. The activities have also included the development of more than one middleware platforms for actual implementation on a test-bed: an alternative is based on mobile agents, a more recent one is based on the Service Oriented Middleware (SOM) approach and is specifically developed on a IEEE 802.15.4 protocol stack. This research track has recently evolved towards cryptographic schemes based on elliptic curves with particular emphasis on its application to vehicular communication networks.