Eleonora Borgia

The Internet of Things vision: Key features, applications and open issues

Abstract The Internet of Things (IoT) is a new paradigm that combines aspects and technologies coming from different approaches. Ubiquitous computing, pervasive computing, Internet Protocol, sensing technologies, communication technologies, and embedded devices are merged together in order to form a system where the real and digital worlds meet and are continuously in symbiotic interaction. The smart object is the building block of the IoT vision. By putting intelligence into everyday objects, they are turned into smart objects able not only to collect information from the environment and interact/control the physical world, but also to be interconnected, to each other, through Internet to exchange data and information. The expected huge number of interconnected devices and the significant amount of available data open new opportunities to create services that will bring tangible benefits to the society, environment, economy and individual citizens. In this paper we present the key features and the driver technologies of IoT. In addition to identifying the application scenarios and the correspondent potential applications, we focus on research challenges and open issues to be faced for the IoT realization in the real world.

Wi-fi in ad hoc mode: a measurement study

In this paper we investigate the performance of IEEE 802.11b ad hoc networks by means of an experimental study. This analysis reveals several aspects that are usually neglected in simulation studies. Firstly, since different transmission rates are used for control and data frames, different transmission ranges and carrier-sensing ranges may exist at the same time in the network. In addition, the transmission ranges are in practice much shorter than usually assumed in simulation analysis, not constant but highly variable (even in the same session) and depends on several factors (i.e., mobile height, interference condition, etc.). Finally, exploiting our performance measurements, we present a channel model for an 802.11 network that indicates virtual carrier sensing is generally not necessary and the RTS/CTS mechanism only introduces additional overhead.

Understanding the real behavior of Mote and 802.11 ad hoc networks: an experimental approach

IEEE 802.11 and Mote devices are today two of the most interesting wireless technologies for ad hoc and sensor networks respectively, and many efforts are currently devoted to understanding their potentialities. Unfortunately, few works adopt an experimental approach, though several papers highlight that popular simulation and analytical approximations may lead to very inaccurate results. In this paper we discuss outcomes from an extensive measurement study focused on these technologies. We analyze the dependence of the communication range on several parameters, such as node distance from the ground, transmission data rate, environment humidity. Then, we study the extent of the physical carrier sensing zone around a sending node. On the basis of these elements, we provide a unified wireless link model for both technologies. Finally, by using this model we analyze well-known scenarios (such as the hidden node problem), and we modify the traditional formulations according to our experimental results.

Minimum-Delay Service Provisioning in Opportunistic Networks

Opportunistic networks are created dynamically by exploiting contacts between pairs of mobile devices that come within communication range. While forwarding in opportunistic networking has been explored, investigations into asynchronous service provisioning on top of opportunistic networks are unique contributions of this paper. Mobile devices are typically heterogeneous, possess disparate physical resources, and can provide a variety of services. During opportunistic contacts, the pairing peers can cooperatively provide (avail of) their (other peers) services. This service provisioning paradigm is a key feature of the emerging opportunistic computing paradigm. We develop an analytical model to study the behaviors of service seeking nodes (seekers) and service providing nodes (providers) that spawn and execute service requests, respectively. The model considers the case in which seekers can spawn parallel executions on multiple providers for any given request, and determines: 1) the delays at different stages of service provisioning; and 2) the optimal number of parallel executions that minimizes the expected execution time. The analytical model is validated through simulations, and exploited to investigate the performance of service provisioning over a wide range of parameters.

Experimental comparison of routing and middleware solutions for mobile ad hoc networks: legacy vs cross-layer approach

In this paper we present an experimental evaluation of a full ad hoc network architecture with particular attention to routing and middleware layers. In particular we set up a MANET prototype on which we performed a large set of experiments: in a first phase, we analyzed performances of a proactive and a reactive routing protocols in case of low mobility scenarios in small-medium scale ad hoc networks; then we studied the performances of a first prototype of an optimized p2p system for ad hoc networks (CrossROAD), based on a cross-layer interaction with a proactive routing protocol. Our analysis shows that the use of a proactive routing protocol does not negatively influence system performances, furthermore it allows the optimization of a structured p2p system on ad hoc networks, providing a complete and timely updated knowledge of the network topology. In this way, the overlay network is completely self-organizing and correctly manages network partitioning and topology changes.

Experimental evaluation of ad hoc routing protocols

In this paper we report an experimental comparison between two ad hoc routing protocols on real networks. Specifically, we evaluate performance of OLSR and AODV either in indoor and. outdoor environments on networks of 2-4 hops size with up to 8 nodes, representing realistic scenarios of few people exploiting the ad hoc network to share documents. In fact, as pointed out in the work of P. Gunningberg et al., with current technology, benefits of ad hoc network will vanish beyond the ad hoc horizon of 2-3 hops and 10-20 nodes. Our analysis shows that with semi-static topology the proactive approach performs much better than the reactive from the efficiency and QoS standpoint, and it introduces a limited overhead. On the other hand, even in this simple scenario, AODV performances are often poor introducing delays of seconds in order to ping a node few hops away. To avoid possible proactive-protocol scalability problems, we also discuss our ongoing work to develop a proactive protocol with partial dissemination.

A Hybrid Adaptive Protocol for Reliable Data Delivery in WSNs with Multiple Mobile Sinks

In this paper, we deal with reliable and energy-efficient data delivery in sparse wireless sensor networks (WSNs) with multiple mobile sinks (MSs). This is a critical task, especially when MSs move randomly, as interactions with sensor nodes are unpredictable, typically of short duration and affected by message losses. In addition, multiple MSs can be simultaneously present in the sensor contact area making the minimum energy data delivery a complex optimization problem. To solve the above issues, in this paper we propose a novel protocol that efficiently combines erasure coding with an Automatic Repeat reQuest (ARQ) scheme. The key features of the proposed protocol are as follows: (i) the use of redundancy to cope efficiently with message losses in the multicast environment and (ii) the ability of adapting the level of redundancy based on feedbacks sent back by MSs through acks. We observed by simulation that our protocol outperforms an alternative protocol that relies only on an ARQ scheme, even when there is a single MS. We also validated our simulation results through a set of experimental measurements based on real sensor nodes. Our results show that the adoption of encoding techniques increases the lifetime of the sensor in the range (40–55%) compared with standard simple ARQ approaches when applied to WSNs with MSs.

Effects of unstable links on AODV performance in real testbeds

A link between a pair of nodes is defined unstable if it is characterized by a packet loss which is not negligible in one or both directions. The presence of unstable links in multihop ad hoc networks is very likely and it depends on several factors (e.g., different transmission capabilities of the devices, interferences caused by additional wireless devices). Their management by the routing protocols is of paramount importance since they negatively affect applications performance. In our previous experimental studies, we found that AODV is characterized by very low performance in some specific situations and, in this work, we demonstrate that it mainly depends on the wrong management of unstable links as valid routes. We present some policies that have been proposed in literature to avoid this problem, and we validate two of them through experimental results, exploiting also a direct comparison with the proactive routing protocol OLSR. Our results show that AODV is not able to avoid the use of unstable links, even when an alternative stable route exists. In the same conditions, OLSR outperforms AODV by correctly managing unstable links. In fact, it is able to guarantee a higher packet delivery ratio to the application by using the most stable path to reach the destination.

Autonomic detection of dynamic social communities in Opportunistic Networks

In this paper we focus on approaches which aim at discovering communities of people in Opportunistic Networks. We first study the behaviour of three community detection distributed algorithms proposed in literature [1], in a scenario where people move according to a mobility model which well reproduces the nature of human contacts, namely HCMM [2]. By a simulation analysis, we show that these distributed approaches can satisfactory detect the communities formed by people only when they do not significantly change over time. Otherwise, as they maintain memory of all encountered nodes forever, these algorithms fail to capture dynamic evolutions of the social communities users are part of. To this aim we propose ADSIMPLE, a new solution which captures the dynamic evolution of social communities. We demonstrate that it accurately detects communities and social changes while keeping computation and storage requirements low.

MobileMAN: integration and experimentation of legacy mobile multihop ad hoc networks

Although research on mobile ad hoc networks has been ongoing for some time, there are relatively few experiences with real ad hoc networks in laboratory testbeds, and users never use multihop ad hoc networks. This seems due to a gap between what end users might find useful, and what research is currently addressing. Indeed, a large portion of research activities concentrate on the development of novel solutions to optimize lower-layer protocols in often unrealistic settings, while little attention is devoted to the quality of service (QoS) these networks may provide to end users in realistic applicative scenarios. The MobileMAN project tried to contribute to reduce this gap by promoting a research plan aimed at combining theoretical research with the integration of developed solutions in prototypes to be used for validating them in realistic small- and medium-scale scenarios (few hops and 10‐20 nodes). The aim is to design and integrate a full protocol stack and experimentally quantify the QoS the system is able to provide to the users. This research approach points out that, also in this limited setting, several problems still exist to construct efficient multihop ad hoc networks. In the next article [1] we discuss how cross layering can be exploited to fix some performance problems identified in our analyses.