Flavia Martelli

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.

Design of a body area network for medical applications: the WiserBAN project

This paper deals with some preliminary results achieved in the framework of the FP7 project WiserBAN (Smart miniature low-power wireless microsystem for Body Area Networks), aiming at the creation of a low-power and miniature microsystem targeting wearable and implanted devices for medical applications. The results achieved in the first year of the project, related to the radio channel characterization and protocol design, are reported. Different Medium Access Control protocols, based on existing and emerging standards, are proposed and their performance are compared. Results show that the proposed protocols allow to satisfy the end users requirements.

Link Adaptation in IEEE 802.15.4-based Wireless Body Area Networks

In this paper we consider an IEEE 802.15.4-based Wireless Body Area Network, where wearable sensor devices are distributed on a body and have to send the measured data to a coordinator. The Carrier Sense Multiple Access with Collision Avoidance algorithm defined by the standard is used as Medium Access Control protocol, whereas different modulation schemes are assumed to be available at the physical layer. We propose a novel Link Adaptation (LA) strategy, where nodes select the modulation scheme according to the experienced channel quality and level of interference. The novelty lays in the fact that in case of large Signal-to-Noise Ratio and low Signal-to-Interference Ratio nodes increase the bit rate, instead of reducing it, as largely done in the works present in the literature. The reduction of the bit rate, in fact, allows to decrease the time the channel is occupied and, therefore, the collision probability. Performance is evaluated in terms of packet error rate and results achieved with and without LA are compared. Results show that the proposed strategy improves performance.

Modeling Query-Based Wireless CSMA Networks Through Stochastic Geometry

A mathematical model for characterizing the performance of wireless access networks based on a carrier-sense multiple-access (CSMA) mechanism is derived. The model is developed through a statistical description of the interference power coming from stochastic geometry and by taking into account the hidden node problem. As an example of a specific application of the model, the IEEE 802.15.4 standard is considered. Nodes are assumed to be uniformly distributed according to a Poisson point process (PPP) in a 2-D infinite plane. They have to communicate with the network coordinator through direct links (star topology), following a query-based application. The total interference power is modeled considering the actual density of nodes that are simultaneously transmitting. This takes into account the operation of the CSMA with collision avoidance (CSMA/CA) algorithm used by nodes to access the channel, according to the IEEE 802.15.4 standard. Results show the impact of node density, packet length, and sensing range on the system performance, which is evaluated in terms of success probability in transmitting packets from nodes to the coordinator.

Link Adaptation in Wireless Body Area Networks

We consider a Wireless Body Area Network (WBAN) where wearable sensor devices are distributed on a body and have to send the measured data to a coordinator. The network uses the Carrier Sense Multiple Access with Collision Avoidance algorithm defined by the IEEE 802.15.4 standard as Medium Access Control protocol, whereas different modulation schemes are assumed to be available at the physical layer. We propose to use the Link Adaptation (LA) in this WBAN scenario, with the aim of reducing packet losses. Nodes select the modulation scheme according to the experienced channel quality: when the Signal-to-Noise Ratio is large, regardless of the actual interference, nodes increase the bit rate, in order to decrease the time the channel is occupied and, therefore, the collision probability. Performance is evaluated in terms of packet error rate and results achieved with and without LA are compared. Results show that the proposed strategy improves performance.

Application-Driven Analytic Toolbox for WSNs

In this paper we propose a Generic Analytical DesiGn EnvironmenT (GADGET) Toolbox for designing the most suitable MAC protocol for an arbitrary wireless sensor network (WSN) application. Furthermore, a model to weight the metrics in the design and a new single compound metric are proposed. Comparing performance curves produced by a number of metrics make it difficult to evaluate how well a given protocol suits for the purposes of an application. It may also be difficult to estimate, which of the protocols at hand would perform the best with respect to that application. Matching the application with the most appropriate protocols is critical for efficient WSN operation because the sensor nodes are resource constrained by nature. The analytic hierarchy process and a pair-wise weighted comparison of the protocols enable to emphasise application performance requirements and to produce a single performance curve either by combination of competing protocols (fractional) or per protocol (absolute). The former provides suitability of one protocol over others with respect to an application whereas the latter provides also insight on the absolute performance of the protocol.

Measuring and Understanding Opportunistic Co-presence Patterns in Smart Office Spaces

This paper presents the outcomes of a study that examines human interactions and mobility patterns in indoor spaces such as office environments. To this purpose, Bluetooth and IEEE 802.15.4-based fine grained traces have been collected through an extensive experimental measurement campaign in a heterogeneous Internet of Things (IoT) test bed, deployed in a real-life office environment. An initial analysis of these traces provides deeper insights into the encounter characteristics between human-held devices and human-held and static infrastructure devices. The study shows that due to lack of granularity, existing traces and the derived works, often neglect a significant portion of shorter-lived contacts that can be exploited for opportunistic communication. The presented findings also confirm that contact opportunities between mobile devices derived from observations of infrastructure devices can introduce significant errors into the modeling of such encounters. We believe that our traces and the derived models, together with our initial findings, are useful for the research community in supporting the design of future IoT solutions in such environments.