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The definition of a virtual router layer allows the application of energy saving techniques based on the migration of virtual routers within the physical infrastructure as traffic conditions change. As traffic decreases, physical resources can be vacated through virtual router migration, thus, saving energy. Such resources can be reclaimed if needed because of traffic increase. Unfortunately, the migration of virtual routers involves reconfiguration costs depending on implementation details and characterized, for instance, by the revenue loss due to quality-of-service (QoS) degradation during the migration process. In this paper, we propose a methodology based on the Markov decision processes for the evaluation of optimal migration policies taking into account both the operation (in terms of energy consumption) and reconfiguration costs.

A new vision-based obstacle avoidance technique for indoor navigation of Micro Aerial Vehicles (MAVs) is presented in this paper. The vehicle trajectory is modified according to the obstacles detected through the Depth Map of the surrounding environment, which is computed online using the Optical Flow provided by a single onboard omnidirectional camera. An existing closed-form solution for the absolute-scale velocity estimation based on visual correspondences and inertial measurements is generalized and here employed for the Depth Map estimation. Moreover, a dynamic region-of-interest for image features extraction and a self-limitation control for the navigation velocity are proposed to improve safety in view of the estimated vehicle velocity. The proposed solutions are validated by means of simulations.

In this paper capture effect in IEEE 802.15.4 networks is studied, by means of mathematical analysis and experimentation. A Personal Area Network (PAN) composed of multiple nodes, which transmit data to a given sink by using the beacon-enabled mode of 802.15.4 Medium Access Control (MAC) protocol, is considered. Upon reception of the beacon transmitted by the PAN coordinator, the nodes transmit their packets using the slotted Carrier Sense Multiple Access with Collision Avoidance algorithm defined by the standard. A test-bed composed of 802.15.4-compliant Freescale devices is used to measure the protection ratio, that is the minimum Signal-to-Interference Ratio (SIR) which ensures the correct reception of majority of the packets. The result is, then, used to extend the developed mathematical model for beacon-enabled 802.15.4 networks. In contrast to the literature on the 802.15.4 MAC modelling, our model allows to compute the Packet Success Probability (PSP) of a node when capture effect is considered, in the scenario described. The impact of capture effect on the PSP, by varying the number of nodes, the propagation parameters and the protection ratio, is shown. The model is validated through simulations and experimental measurements. In both cases a very good agreement is found.

This paper introduces a new algorithm to prove contraction of nonlinear dynamical systems. The algorithm is then used to devise novel strategies to achieve synchronization and consensus of networked control systems. Numerical simulations illustrate the results on a set of representative examples.

Biomedical ultrasound (US) image quality is limited due to the blurring of tissue reflectivity introduced by the transducer point spread function (PSF). Deconvolution techniques can be used to eliminate this effect and to obtain the pure tissue response. In this paper we propose a new enhancement method based on recursive least squares (RLS) adaptive filtering. The method handles the spatial variability of the PSF by means of blind homomorphic characterization of the transducer. The results show that the RLS adaptation increases contrast and resolution by eliminating the spectral shaping of the backscattered echo and thus enhancing the diagnostic capability of US images.

Runs of benchmarks or a suite of benchmarks are inadequate to characterize parallel machines or to predict the execution time of applications with a computational kernel which is not included in the suite. Furthermore, the observed results are quite sensitive to the nature of the benchmark. In this paper, we present a new approach to the benchmarking of SIMD machines. The idea is to create and use a machine characterizer which measures the performance of given system in terms of high-level language instructions (e.g. Fortran 90 or TAO). The analyzer yields a set of parameters which provides the execution time for some primitive operations in the high-level language. This approach gives us considerable insight into both the machines and the programs, since the effects of individual parameters are immediately evident. We present experimental results on Quadrics machines.

A family of high performance processing elements has been conceived to implement flexible multiprocessor structures for real-time applications. The floating-point capabilities of the INMOS transputer components (T222-T805) have been improved, by using the AT&T floating-point Digital Signal Processors (DSP32-DSP32C), allowing to achieve up to 25 MFLOPS, 30 MIPS. In the paper, the design of a single board T800/DSP-32C based is presented and the simulation results of its specialization in signal processing applications are also reported. A comparative test between the traditional Cooley-Tukey FFT Algorithm (aA) and the Prime Factor Algorithm (PFA) shows that a 4096 complex points radix 4-CTA takes 16.6 ms. while for a 5040 complex points PFA about 32.3 ms are needed. A flexible development system has been also realized to allow a careful design of various "Strengthened Nodes", since it can be used as test-bed to compare the performance of different DSPs available on the market, when they are connected to components of the transputer family. "Strengthened Nodes" will be used in heterogeneous multiprocessor structures specialized for Synthetic Aperture Radar (SAR) data processing.