Roberto Verdone

An Overview on Wireless Sensor Networks Technology and Evolution

Wireless sensor networks (WSNs) enable new applications and require non-conventional paradigms for protocol design due to several constraints. Owing to the requirement for low device complexity together with low energy consumption (i.e., long network lifetime), a proper balance between communication and signal/data processing capabilities must be found. This motivates a huge effort in research activities, standardization process, and industrial investments on this field since the last decade. This survey paper aims at reporting an overview of WSNs technologies, main applications and standards, features in WSNs design, and evolutions. In particular, some peculiar applications, such as those based on environmental monitoring, are discussed and design strategies highlighted; a case study based on a real implementation is also reported. Trends and possible evolutions are traced. Emphasis is given to the IEEE 802.15.4 technology, which enables many applications of WSNs. Some example of performance characteristics of 802.15.4-based networks are shown and discussed as a function of the size of the WSN and the data type to be exchanged among nodes.

A Survey on Wireless Body Area Networks: Technologies and Design Challenges

Interest in Wireless Body Area Networks (WBANs) has increased significantly in recent years thanks to the advances in microelectronics and wireless communications. Owing to the very stringent application requirements in terms of reliability, energy efficiency, and low device complexity, the design of these networks requires the definition of new protocols with respect to those used in general purpose wireless sensor networks. This motivates the effort in research activities and in standardisation process of the last years. This survey paper aims at reporting an overview of WBAN main applications, technologies and standards, issues in WBANs design, and evolutions. Some case studies are reported, based on both real implementation and experimentation on the field, and on simulations. These results have the aim of providing useful insights for WBAN designers and of highlighting the main issues affecting the performance of these kind of networks.

Mathematical Evaluation of Environmental Monitoring Estimation Error through Energy-Efficient Wireless Sensor Networks

In this paper, the estimation of a scalar field over a bidimensional scenario (e.g., the atmospheric pressure in a wide area) through a self-organizing wireless sensor network (WSN) with energy constraints is investigated. The sensor devices (denoted as nodes) are randomly distributed; they transmit samples to a supervisor by using a clustered network. This paper provides a mathematical framework to analyze the interdependent aspects of WSN communication protocol and signal processing design. Channel modelling and connectivity issues, multiple access control and routing, and the role of distributed digital signal processing (DDSP) techniques are accounted for. The possibility that nodes perform DDSP is studied through a distributed compression technique based on signal resampling. The DDSP impact on network energy efficiency is compared through a novel mathematical approach to the case where the processing is performed entirely by the supervisor. The trade-off between energy conservation (i.e., network lifetime) and estimation error is discussed and a design criterion is proposed as well. Comparison to simulation outcomes validates the model. As an example result, the required node density is found as a trade-off between estimation quality and network lifetime for different system parameters and scalar field characteristics. It is shown that both the DDSP technique and the MAC protocol choice have a relevant impact on the performance of a WSN.

Performance Analysis of IEEE 802.15.4 Non Beacon-Enabled Mode

In this paper a mathematical model for the non-beacon enabled mode of the IEEE 802.15.4 Multiple access control (MAC) protocol, is provided. A wireless sensor network (WSN) composed of nodes which transmit data to a sink through direct links, is considered. Upon reception of a query from the sink, the nodes transmit their packets by using the carrier sensing multiple access with collision avoidance algorithm defined by IEEE 802.15.4. The model allows the evaluation of the statistical distribution of the traffic generated by the nodes, the success probability for the transmission of a packet, and the mean energy spent by a node for a transmission. The results are validated through simulations. The model differs from those previously published by other authors in the literature as it precisely follows the MAC procedure defined by the standard, in the context of the WSN scenario described above. Performance obtained by varying the parameters of the backoff algorithm, are evaluated and compared. Results show that a tradeoff between energy efficiency and reliability is needed.

Intelligent transportation systems: the role of third generation mobile radio networks

A synthetic review is given of the research developed in the past 10 years in the field of short-range communications for intelligent transportation systems. Moreover, the role of new packet mobile radio (such as the General Packet Radio Service) and third-generation systems in the possible provision of services for the field of ITS is discussed; more precisely, the services for driving safety are addressed. The research programs under development in Italy and Japan which can have an impact on the selection of suitable techniques for ITS services are presented.

Multihop R-ALOHA for intervehicle communications at millimeter waves

With reference to road transport information (RTI) applications, such as cooperative driving, short-range intervehicle communications in a highway environment are investigated in this paper. The research in this field indicates the suitability of the 60-64-GHz band. Due to the distributed nature of the intervehicle communication system, an R-ALOHA protocol is considered; multihop (MH) and single-hop (SH) strategies are compared. Network performance is assessed by considering the joint impact of random access, interference, thermal noise, propagation, and packet capture effect. Several figures of merit are analyzed and discussed: packet success probability (PSP), system stabilization time (SST), first success time (FST), and deadline failure probability (DFP). Network performance is evaluated either by an analytical approach or by a software tool able to simulate a one-lane highway scenario. Both steady-state and transition situations are considered. System performance in terms of PSP (in the presence of two-way Rice fading, noise, and interference with antenna diversity and selection combining) is analytically evaluated to validate the simulation tool and to prove the suitability of an MH network strategy. The simulation approach allows the evaluation of the impact of protocol parameters on network performance, with reference to nonsteady-state situations.

A sociability-based routing scheme for delay-tolerant networks

The problem of choosing the best forwarders in Delay-Tolerant Networks (DTNs) is crucial for minimizing the delay in packet delivery and for keeping the amount of generated traffic under control. In this paper, we introduce sociable routing, a novel routing strategy that selects a subset of optimal forwarders among all the nodes and relies on them for an efficient delivery. The key idea is that of assigning to each network node a time-varying scalar parameter which captures its social behavior in terms of frequency and types of encounters. This sociability concept is widely discussed and mathematically formalized. Simulation results of a DTN of vehicles in urban environment, driven by real mobility traces, and employing sociable routing, is presented. Encouraging results show that sociable routing, compared to other known protocols, achieves a good compromise in terms of delay performance and amount of generated traffic.

Coalition formation games for femtocell interference management: A recursive core approach

Overlaying low-power, low-cost, femtocells, over existing wireless networks has recently emerged as a means to significantly improve the coverage and performance of next-generation wireless networks. While most existing literature focuses on spectrum sharing and interference management among non-cooperative femtocells, in this paper, we propose a novel cooperative model that enables the femtocells to improve their performance by sharing spectral resources, minimizing the number of collisions, and maximizing the spatial reuse. We model the femtocell spectrum sharing problem as a coalitional game in partition form and we propose a distributed algorithm for coalition formation. Using the proposed algorithm, the femtocells can take autonomous decisions to cooperate and self-organize into a network partition composed of disjoint femtocell coalitions and that constitutes a stable partition which lies in the recursive core of the considered game. Whenever a coalition forms, the femtocells inside this coalition can cooperatively pool the occupied spectral resources. Additionally, the members of any given coalition jointly schedule their transmissions in order to avoid collisions, in a distributed way. Simulation results show that the proposed coalition formation algorithm yields a performance advantage, in terms of the average payoff (rate) per femtocell reaching up to 380% relative to the non-cooperative case.

Outage probability analysis for short-range communication systems at 60 GHz in ATT urban environments

In the context of a short-range communication system for advanced transport telematics (ATT) applications, this paper presents an analytical method to derive outage probability in the presence of Rice fading, noise, interference, and antenna diversity with selection combining; the approach is exploited to evaluate the performance of beacon-to-vehicle communications in urban environments. ATT applications are becoming more and more relevant for the purpose of designing a road traffic management system, either in urban or highway environments. The interest of researchers in this field mainly indicated two different frequency ranges for system operability, i.e., the 5.8and 60-64-GHz bands. The advantage of using millimeter waves is discussed with reference to efficient spatial filtering effects, having chosen a suitable model for channel characterization at 60 GHz. The validity of the analytical method is checked by means of Monte Carlo simulation. The role of oxygen and rain absorption on system performance is also investigated. By considering a monodimensional topology and a Manhattan scenario, system availability is evaluated in a multiuser context by taking the role of interfering signals on downlink performance into account. As an example of application, a time-division multiple-access (TDMA) scheme is assumed for channel access. The methodology exploited allows the definition of suitable design criteria; numerical results give the optimum value of distance between beacons as a function of system parameters and link budget.

Millimeter waves for short-range multimedia communication systems

A framework for the performance characterization of short-range communications systems is developed with the intention of investigating the feasibility of new multimedia wireless services at millimeter waves (MMWs). Both narrow- and wide-band systems are considered for mobile and/or fixed users. This paper aims at defining and evaluating proper metrics to characterize the service quality for the user and jointly takes the propagation characteristics, the transmission techniques, and the multiple access protocols into account. The definition of service-oriented metrics is emphasized. Three different real scenarios operating at MMW are investigated with a unified perspective: intelligent transport systems, wide-band local-area networks, and local multipoint distribution systems for interactive video services. The role played by the MMW band in the development of these services is discussed. In each scenario, accurate propagation analysis is carried out and suitable countermeasure techniques are pointed out in order to join suitable service-quality levels. The methodology considered is based on both analytical and semianalytical tools for performance evaluation.