Sabato Manfredi

Synchronization of Networks of Non-Identical Chua's Circuits: Analysis and Experiments

This paper is concerned with the theoretical and experimental analysis of synchronization and pinning control of networks of non-identical Chuas circuits. The design and implementation is presented of an appropriate setup to carry out experiments on networks of these nonlinear circuits with easily reconfigurable parameter values. Then, the theoretical expectations are validated of the so-called Extended Master Stability Function approach to study the onset of synchronization in the presence of real parameter mismatches between the circuits at the network nodes. The validation is carried out both numerically and experimentally. For the first time, the EMSF is also used to investigate pinning synchronization in a network of non-identical circuits where a master node (or pinner) is used to drive the network dynamics towards some desired synchronous evolution. The numerical and experimental results confirm the viability of the EMSF as an effective analysis and design tool.

Reliable and energy-efficient cooperative routing algorithm for wireless monitoring systems

The recent increased interest in distributed and flexible wireless pervasive applications has drawn great attention to Wireless Networked Control Systems (WNCS) architectures based on Wireless Sensor and Actuator Networks (WSANs) and the resulting Quality of Service (QoS) obtained in specific applications. In wireless monitoring systems based on WSANs, providing certain QoS specifications in terms of reliability and energy efficiency is crucial for the sensors/actuators as they perform actions based on the data samples/received with a limited amount of energy to spend. To this aim the paper introduces the cooperative-based routing algorithm to guarantee a good performance trade-off between reliability and energy efficiency of the overall wireless monitoring system. Simulations have been carried out in order to quantify the impact of the proposed algorithm on the overall monitoring system reliability and energy efficiency and a comparison is presented with the existing Ad-hoc On-Distance Vector (AODV), the cooperation along the shortest non-cooperative path (CASNCP) and minimum-power cooperative routing (MPCR) algorithms. Finally it is shown the application of the proposed algorithm to healthcare monitoring system pointing out as the cooperation-based routing algorithms are suitable and rewarding for the management of the future generation of monitoring systems.

An algorithm for fast rendezvous seeking of wireless networked robotic systems

Abstract The recent development of wireless network architecture and distributed control algorithm allows the onset of large scale robotic application such as monitoring, formation control and flocking, coordination, exploration of unknown environments, and surveillance. In such applications there are many autonomous robots which have capabilities of sensing and acting on the environment and that can communicate with the other robot by wireless communication network defining a Wireless Networked Robotic Systems (in the follows briefly WNR). Usually a robot implements a cooperative algorithm to get some common WNR objective. A widely studied cooperative algorithm allows every robot automatically converge to a common position (consensus or rendezvous) using only local information received from its one hop neighboring robots. Therefore WNR brings together the cooperative control algorithm and the communication capabilities. Despite of a large body of research produced by robotics research community, it is a challenging problem to explore the analysis, the design and evaluation of cooperative algorithm in a more realistic scenario of wireless networked robotic application where the networking and protocol features might affect the overall closed loop WNR performance. In this direction the paper deals with the analysis and design of m -order cooperative control algorithm for fast rendezvous seeking over WNR. Specifically we give a sufficient stability condition of the control algorithm in the presence of heterogeneous time delays affecting the communication through the hops of the WNR. Moreover we analyze the effect of the packet collision phenomena and the presence of background disturbance traffic on the resulting WNR performance. The above sufficient stability condition and analysis, joining with the implementation issues can give a guideline about the design of the rendezvous control algorithm and wireless protocol parameters when we deal with a realistic network environment of WNR. Simulation experiments carried out by a realistic simulation confirm the theoretical findings.

A robust approach to active queue management control in networks

This paper is concerned with the design of improved AQM control schemes by means of an appropriate reduction method for time-delay systems. The aim is to stabilize the delay differential equations model of TCP (transmission control protocol) behavior. A robust observer is introduced to estimate online the transmission window resulting in a window-based congestion control scheme. The robust stability and dynamic behavior in the presence of network parameter uncertainties is validated and tested through numerical simulations on a single bottleneck.

Decentralized Queue Balancing and Differentiated Service Scheme Based on Cooperative Control Concept

In this paper, we introduce the concept of a bottleneck-routers cooperation in the explicit rate-control framework of communication networks in order to mitigate congestion effects on the network performance and balance the queues. The proposed controller at each router (server or switch) regulates the rates of the heterogeneous source classes leveraging on the cooperation of neighboring bottlenecks. We consider the model of multibottleneck network in the presence of time delay and formulate global stability conditions suitable for network parameters and controller gains design. The proposed approach guarantees good performance in terms of link utilization, packet loss and fairness. Additionally it is guaranteed queue balancing without requiring rerouting or hop-by-hop operation differently from the existing approaches. A validation is carried out by a discrete packet experiment simulator in a realistic multibottleneck scenario to demonstrate the effectiveness of the key idea of the paper. Finally the proposed scheme is compared to some of well-known network controller-type presented in the literature in both steady-state and dynamic network scenario.

Small world effects in networks: an engineering interpretation

In this paper, an engineering interpretation of small world effects in networks is given. After briefly summarizing the main features of small world networks, an attempt is made to investigate the relevance that small world effects can have in communication networks. The aim is that of investigating the relationship between small world behaviour and some of the characteristic parameters associated to the overall performance of the network. It is shown that the performance of a communication network is indeed affected by the presence or absence of small world effects. Namely, the link between these effects and the average throughput and delivery time on the network is established and assessed through numerical simulations.

Robust output feedback active queue management control in TCP networks

This paper is concerned with the design of improved AQM control schemes. An appropriate robust H/sup /spl infin// controller for time-delay systems is proposed and hence used to design a suitable AQM control scheme. A robust observer is used to estimate online the transmission window resulting in a novel output feedback stabilization scheme for AQM. The resulting control law is first validated and tested firstly through numerical and experimental methods.

Frozen state conditions for asymptotic consensus of time-varying cooperative nonlinear networks

In this paper we present new results on asymptotic consensus for continuous-time nonlinear time varying cooperative networks. We endow the well known assumption of integral connectivity proposed by Moreau with a remarkable additional feature of being frozen in state variables, making its direct verification more straightforward. Moreover, we give an estimate of the exponential rate of convergence towards the agreement manifold.

A theoretical analysis of multi-hop consensus algorithms for wireless networks: Trade off among reliability, responsiveness and delay tolerance

Recently great attention has been posed on the consensus protocols in networks of agents. A widely studied consensus algorithm allows every agent automatically converge to a common consensus state using only local information received from its one hop neighboring agents. We study the problem of reaching a consensus in network of mesh nodes under m-hop protocols where each node-agent can access to the state of its m-steps neighboring agents. Moreover we consider also the presence of heterogeneous time delays affecting the communication through the different hops. The first aim of the paper in the WMNs research theoretical foundations is to give a sufficient condition for the multi hop network consensus protocol stability in the presence of heterogeneous time delays that explicitly relates the network and algorithm features (e.g. time delay tolerance, topology, the number of hop). The second aim is to point out by the previous analytical condition the interplay between the network performance/features (i.e. reliability, the delay tolerance, the communication topology) and the effectiveness of the distributed consensus algorithms/communication protocols (i.e. in terms of complexity, amount of the information to be managed, responsiveness and steady state error performance). This trade off must be taken into account in the performance evaluation and algorithm design for WMNs. Finally, the theoretical result has been validated by simulation experiments using a realistic evaluation environment.

On global and local consensusability of multi-agent systems with input constraint and uncertain initial conditions

In this paper we consider the consensuability problem of linear multi agent systems in the presence of input constraint and uncertain state initial conditions. By employing Lyapunov stability theory and linear matrix inequality (LMI) technique, we present low computationally on demanding LMI conditions to explicitly design a distribute protocol to guarantee network consensuability. Input norm bound constraint is full-filled despite of the uncertain network initial conditions. This is of practical interest in a real applications of consensus protocol because the input bound (i.e. due to actuator saturation) may not be easily fulfilled as the control at each node depends on the state and its uncertain initial value of the neighboring agents. The results hold for both undirected and directed graph. A numerical example about the leader-follower scenario is shown to validate the theoretical findings. From the computational point of view, the LMI conditions have the merit to be easily solved by the MATLAB toolbox as their number and size do not depend on network size. This enables their use to control large scale multi agent systems.