Search results for " telecomunicazioni"

A software receiver adaptive phase lock loop method

2009

The aim of this paper is to introduce a new and relatively simple algorithm which is capable to tune the parameters of the loop filter in a phase lock loop, like the one that can be found in a global navigation satellite system receiver. The parameters are chosen while the system is running, in order to make the bandwidth of the filter adaptive with respect to the signal dynamic and strength. A wider bandwidth is obtained to make the filter more reactive when searching the carrier, while the bandwidth gets narrower when the system is in the tracking state, in order to cut off as much noise as possible. The algorithm is based on the observation of the estimated variance of the phase lock loo…

Sviluppo di dispositivi elettronici di misura innovativi per la gestione delle Smart Grid attraverso un'opportuna infrastruttura di comunicazione

2014

On the Flexibility of the IEEE 802.11 Technology: Challenges and Directions

2011

The original 802.11 standard, which is the de-facto standard for contention-based wireless data networks, has shown to give poor performance or to be scarcely suitable for dealing with new PHY-layer technologies, networking scenarios, or service contexts, thus boosting the proliferation of projects, technical solutions and dedicated task groups for extending the basic protocol operations. In this paper, starting from the evolution analysis of current 802.11 standard and de- vices, we propose an architectural solution for making the medium access protocol programmable. Our basic idea, pursued within the FP7 EU Project FLAVIA [1], started in July 2010, is changing the role of the wireless net…

Wireless card virtualization: from virtual NICs to virtual MAC machines

2012

Virtualization has been a hot topic in computer science this last 10 years, and a key enabler to the recent advances. By technically enabling the Cloud paradigm, virtualization is becoming an inspiring source for the whole IT industry. At the same moment the virtualization of commodity PC was envisioned, Software Defined Radio started as a huge promise of efficient wireless transmission hardware. Unfortunately, the pace of innovation has still to reach the one of the PC virtualization. Yet, there is a another option. The current state of the art of hardware and software of wireless adapter in standard PC reveals interesting capabilities in terms of unused wireless capacity, processing power…

Analysis of MAC-level throughput in LTE systems with link rate adaptation and HARQ protocols

2015

LTE is rapidly gaining momentum for building future 4G cellular systems, and real operational networks are under deployment worldwide. To achieve high throughput performance, in addition to an advanced physical layer design LTE exploits a combination of sophisticated mechanisms at the radio resource management layer. Clearly, this makes difficult to develop analytical tools to accurately assess and optimise the user perceived throughput under realistic channel assumptions. Thus, most existing studies focus only on link-layer throughput or consider individual mechanisms in isolation. The main contribution of this paper is a unified modelling framework of the MAC-level downlink throughput of …

Optimal Resource Allocation in Multi-Hop Networks: Contention vs. Scheduling

2014

CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) is actually the most used method in ad-hoc networks for transmitting on a contending medium, even if it shows poor performance in presence of hidden nodes. To increase performance, we propose an algorithm that combines CSMA and TDMA (Time Division Multiple Access) approaches. The adopted solution consists of grouping contending nodes in non-interfering subsets and granting a different numbers of time slots to different groups, while using the CSMA to manage medium access among nodes belonging to the same subset. An optimization procedure to assign the time slots to each subset of nodes and to find an equilibrium between contention …

Opportunistic Synchronization for Improving IEEE 802.15.4 MAC Performance in Chain Topologies

2010

The most effective solution for energy saving in low-rate wireless sensor networks is maintaining each node in a doze state as long as possible. In order to guarantee network connectivity, the intervals at which the network sensors are turned on and off have to be coordinated. Therefore, synchronization is a very critical function for sensor networks. In this paper, we analyze the IEEE 802.15.4 MAC performance in sensor networks deployed in a chain topology. For this topology, critical inefficiencies can arise in case of multi-hop packet deliveries. We evaluate the impact of different synchronization schemes on the network performance, both in terms of network throughput and in terms of ene…

A Channel-Aware Adaptive Modem for Underwater Acoustic Communications

2021

Acoustic underwater channels are very challenging, because of limited bandwidth, long propagation delays, extended multipath, severe attenuation, rapid time variation and large Doppler shifts. A plethora of underwater communication techniques have been developed for dealing with such a complexity, mostly tailoring specific applications scenarios which can not be considered as one-size-fits-all solutions. Indeed, the design of environment-specific solutions is especially critical for modulations with high spectral efficiency, which are very sensitive to channel characteristics. In this paper, we design and implement a software-defined modem able to dynamically estimate the acoustic channel c…

Leveraging Users' Likes in a Video Streaming P2P Platform

2014

This paper investigates how a p2p television platform can take advantage of the presence of frequent channel viewers to grant them a more satisfying service than to less regular spectators. The idea we explore is to learn beforehand about the users' interests, in order to cluster them in groups that display different behaviors; then, the neighborhood creation strategy and video chunk scheduling algorithm of the overlay is altered, with the aim of serving frequent spectators in a privileged manner, providing them with a faster access to the selected channel without overly penalizing less habitual customers. An analytical model is developed, to capture the difference in startup delay that the…

On the effects of transmit power control on the energy consumption of WiFi network cards

2009

Transmit power control has been largely proposed as a solution to improve the performance of packet radio systems in terms of increased throughput, spatial reuse and battery lifetime for mobile terminals. However, the benefits of transmit power control schemes on these different performance figures may strongly depend on the employed PHY technology and channel access mechanism. In this paper, we focus on the effects of power control on the energy consumption of WiFi network cards. By means of several experimental tests carried out under different operation conditions and modulation schemes, we try to justify why the reduction of the transmission power has a marginal effect on the overall en…