Daniele Puccinelli

Wireless sensor networks: applications and challenges of ubiquitous sensing

Sensor networks offer a powerful combination of distributed sensing, computing and communication. They lend themselves to countless applications and, at the same time, offer numerous challenges due to their peculiarities, primarily the stringent energy constraints to which sensing nodes are typically subjected. The distinguishing traits of sensor networks have a direct impact on the hardware design of the nodes at at least four levels: power source, processor, communication hardware, and sensors. Various hardware platforms have already been designed to test the many ideas spawned by the research community and to implement applications to virtually all fields of science and technology. We are convinced that CAS will be able to provide a substantial contribution to the development of this exciting field.

Routing in ad hoc networks: a case for long hops

For multihop wireless networks, a fundamental question is whether it is advantageous to route over many short hops (short-hop routing) or over a smaller number of longer hops (long-hop routing). Short-hop routing has gained a lot of support, and its proponents mainly produce two arguments: reduced energy consumption and higher signal-to-interference ratios. Both arguments stem from a simplified analysis based on crude channel models that neglects delay, end-to-end reliability, bias power consumption, the impact of channel coding, mobility, and routing overhead. In this article we shed more light on these issues by listing 18 reasons why short-hop routing is not as beneficial as it seems to be. We also provide experimental evidence to support this claim. The conclusion is that for many networks, long-hop routing is in every aspect a very competitive strategy.

Sensorless Sensing in Wireless Networks: Implementation and Measurements

Multipath fading and shadowing are usually regarded as negative phenomena hindering proper radio communication. Adopting a completely different stance, this paper illustrates that such phenomena enable information harvesting from received signal strength leading to a number of original applications requiring no conventional sensing hardware. The radio itself, provided that it can measure the strength of the incoming signal, is the only sensor we use; with this sensor-less sensing approach, any wireless network becomes a sensor network. We show that motion of the nodes in the network or motion of bodies external to the network leaves a characteristic footprint on signal strength patterns, which may be exploited for motion detection. We illustrate a technique to extract an estimate of velocity from signal strength, and we leverage on the spatial memory properties of wireless links to present a method for spatial configuration recognition.

Multipath fading in wireless sensor networks: measurements and interpretation

Multipath fading heavily contributes to the unreliability of wireless links, causing fairly large deviations from link quality predictions based on path loss models; its impact on wireless sensor networks is considerable. Although analytical models provide a probabilistic description, multipath fading is a deterministic phenomenon. Moreover, in the case of static nodes, fading is time-invariant. We illustrate its spatial nature with experimental evidence obtained using lower-end sensing node hardware. We also show the limitations of the supposed immunity of wideband radios to multipath fading in indoor deployments.

Sensor node lifetime: An experimental study

Node lifetime is a key performance metric in wireless sensor network (WSN) research. Simplistic assumptions and naïve lifetime estimation techniques invariably prove to be extremely unreliable in practice, to the point that premature battery depletion notoriously affects real-world deployments. In this paper we adopt an experimental approach and employ various types of real-world batteries to determine the actual lifespan of a sensor node under common operating conditions. We present a rich set of results from an extensive experimental campaign based on the widely used TelosB platform running TinyOS. We have measured the actual node lifetime using various brands of commercial batteries as a function of different combinations of application parameters. Some of our observations match previously published results that are often neglected, while others underscore less known properties of low-power radios.

Reliable data delivery in large-scale low-power sensor networks

In data collection applications of low-end sensor networks, a major challenge is ensuring reliability without a significant goodput degradation. Short hops over high-quality links minimize per-hop transmissions, but long routes may cause congestion and load imbalance. Longer links can be exploited to build shorter routes, but poor links may have a high energy cost. There exists a complex interplay among routing performance (reliability, goodput, energy efficiency), link estimation, congestion control, and load balancing; we design a routing architecture, Arbutus, that exploits this interplay, and perform an extensive experimental evaluation on testbeds of 100-150 Berkeley motes.

Arbutus: Network-Layer Load Balancing for Wireless Sensor Networks

The hot spot problem is a typical byproduct of the many-to-one traffic pattern that characterizes most wireless sensor networks: the nodes with the best channel to the sink are overloaded with traffic from the rest of the network and experience a faster energy depletion rate than their peers. Routing protocols for sensor networks typically use a reliability metric to avoid lossy links and thus directly exacerbate the problem. Significant advantages can be obtained by embedding a load balancing scheme at the network layer, as we show with the design and implementation of Arbutus, a novel routing protocol for wireless sensor networks with a built-in load balancing scheme. By imposing a special structure on the collection tree, privileging longer hops, and accounting for network load in the route selection process, Arbutus reduces the impact of hot spots on network lifetime without a deterioration of the end-to-end reliability performance. An implementation of Arbutus on Berkeley motes and the MoteLab testbed shows a 30% reduction in the network traffic load needed to achieve the same packet delivery rate as an existing mote-oriented protocol. This provides key benefits such as a significant lifetime gain and increased fault tolerance.

SCAMPI: service platform for social aware mobile and pervasive computing

Allowing mobile users to find and access resources available in the surrounding environment opportunistically via their smart devices could enable them to create and use a rich set of services. Such services can go well beyond what is possible for a mobile phone acting alone. In essense, access to diverse resources such as raw computational power, social networking relationships, or sensor readings across a set of different devices calls for distributed task execution. In this paper, we discuss the SCAMPI architecture designed to support distributed task execution in opportunistic pervasive networks. The key elements of the architecture include leveraging human social behavior for efficient opportunistic interaction between a variety of sensors, personal communication devices and resources embedded in the local environment. The SCAMPI architecture abstracts resources as service components following a service-oriented model. This enables composing rich applications that utilize a collection of service components available in the environment.

The impact of network topology on collection performance

The network topology has a significant impact on the performance of collection protocols in wireless sensor networks. In this paper, we introduce an unobtrusive methodology to quantify the impact of the topology on the performance of collection protocols. Specifically, we propose a protocol-independent metric, the Expected Network Delivery, that quantifies the delivery performance that a collection protocol can be expected to achieve given the network topology. Experimental evidence obtained with two collection protocols on numerous topologies on testbeds shows that our approach enables a systematic evaluation of protocol performance.

OpenVLC: software-defined visible light embedded networks

Though there has been a lot of interest in Visible Light Communication (VLC) in recent years, a reference platform based on commercial off-the-shelf components is still missing. We believe that an open-source platform would lower the barriers of entry to VLC research and help the VLC community gain momentum. In this paper we take an initial step toward the goal of a VLC reference platform - OpenVLC, and present our design and implementation. Built around a credit-card-sized embedded Linux platform with an LED front-end, OpenVLC offers a basic physical layer, a set of essential medium access primitives, as well as interaction with Internet protocols. We investigate the performance of OpenVLC and show how it can be used along with standard networking diagnostics tools.