Chiara Buratti

A ZigBee Smart Energy Implementation for Energy Efficient Buildings

Energy efficiency in buildings is one of the promising fields of application of wireless sensor networks. Simple affordable sensors can be used to monitor the power consumption of appliances in buildings to implement smart algorithms in order to conserve energy. The ARTEMIS Joint Undertaking project eDIANA (Embedded Systems for Energy Efficient Buildings) funded by the European Commission aims to improve energy efficiency in buildings by using embedded technologies. In the eDIANA platform the energy consumed by household or office appliances is monitored by using IEEE 802.15.4/Zigbee-compliant devices. In this paper we describe the prototype that we have developed by using ZigBee Smart Energy Profile in order to realize the eDIANA application scenarios. Moreover we provide latency statistics and packet error rate obtained through our test-bed in different monitoring scenarios.

An IEEE 802.15.4/ZigBee based wireless sensor network for Energy Efficient Buildings

Realizing energy efficient control strategies in the buildings is one of the innovative and challenging field of application for wireless sensor networks. To achieve the goal of reduced energy consumption and optimized use of energy in the buildings, the deployment of sensors and actuators is crucial. Simple affordable sensors can be used to monitor the power consumed by each appliance in the building in order to turn them on/off when it is efficient in the use of energy. The ARTEMIS Joint Undertaking project eDIANA (Embedded Systems for Energy Efficient Buildings) funded by the European Commission aims to improve energy efficiency in buildings by using embedded technologies. In the eDIANA platform the energy consumed by household or office appliances is monitored by using IEEE 802.15.4/Zigbee-compliant devices. The aim of the study is to show the feasibility of the IEEE 802.15.4/Zigbee technology to the eDIANA application scenario and to provide guidelines for the network design. For this purpose two studies have been carried out: (i) a simulation analysis of a large apartment where many nodes are deployed; (ii) a real test-bed composed of IEEE 802.15.4/ZigBee-compliant devices. In the first case performance, in terms of packet error rate, average delay and energy consumption, is evaluated by varying the number of nodes in different traffic conditions. In the second case, instead, the statistics of the delay is provided. The study shows that simulation results are in line with the results achieved through the measurements. Moreover results fulfil the eDIANA requirements.

Capture effect in IEEE 802.15.4 networks: Modelling and experimentation

In this paper capture effect in IEEE 802.15.4 networks is studied, by means of mathematical analysis and experimentation. A Personal Area Network (PAN) composed of multiple nodes, which transmit data to a given sink by using the beacon-enabled mode of 802.15.4 Medium Access Control (MAC) protocol, is considered. Upon reception of the beacon transmitted by the PAN coordinator, the nodes transmit their packets using the slotted Carrier Sense Multiple Access with Collision Avoidance algorithm defined by the standard. A test-bed composed of 802.15.4-compliant Freescale devices is used to measure the protection ratio, that is the minimum Signal-to-Interference Ratio (SIR) which ensures the correct reception of majority of the packets. The result is, then, used to extend the developed mathematical model for beacon-enabled 802.15.4 networks. In contrast to the literature on the 802.15.4 MAC modelling, our model allows to compute the Packet Success Probability (PSP) of a node when capture effect is considered, in the scenario described. The impact of capture effect on the PSP, by varying the number of nodes, the propagation parameters and the protection ratio, is shown. The model is validated through simulations and experimental measurements. In both cases a very good agreement is found.

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.

Decentralized detection in IEEE 802.15.4 wireless sensor networks

We present a mathematical model to study decentralized detection in clustered wireless sensor networks (WSNs). Sensors and fusion centers (FCs) are distributed with the aim of detecting an event of interest. Sensors are organized in clusters, with FCs acting as cluster heads, and are supposed to observe the same common binary phenomenon. A query-based application is accounted for; FCs periodically send queries and wait for replies coming from sensors. After reception of data, FCs perform data fusion with a majority-like fusion rule and send their decisions to an access point (AP), where a final data fusion is carried out and an estimate of the phenomenon is obtained. We assume that sensors are IEEE 802.15.4-compliant devices and use the medium access control (MAC) protocol defined by the standard, based on carrier-sense multiple access with collision avoidance. Decentralized detection and MAC issues are jointly investigated through analytical modelling. The proposed framework allows the derivation of the probability of decision error at the AP, when accounting for packets losses due to possible collisions. Our results show that MAC losses strongly affect system performance. The impact of different clustering configurations and of noisy communications is also investigated.

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.

Optimum Topology in Clustered IEEE 802.15.4 Sensor Networks with Decentralized Detection

In this paper, we present a mathematical framework to study decentralized detection in IEEE 802.15.4-compliant clustered wireless sensor networks (WSNs). Sensors are organized in clusters, with fusion centers (FCs) acting as cluster heads, and are supposed to observe the same common binary phenomenon. The FCs periodically send queries to sensors and wait for replies. Once data are received, the FCs perform majority fusion. Decisions are sent to an access point (AP), where a final data fusion is carried out and an estimate of the phenomenon is obtained. A data aggregation strategy at sensors is also investigated. The goal of this paper is to jointly investigate decentralized detection, medium access control (MAC), and data aggregation issues. Our results show that an optimum WSN clustering configuration exists and it depends on the data aggregation strategy used and the MAC parameters.

On the Capacity of a CSMA-Based Multi-Hop Linear Network with Poisson Distributed Nodes

In this paper we consider a multi-hop ad hoc network where nodes are distributed according to a Poisson point process (PPP) over a line. A slotted Carrier Sense Multiple Access protocol is used to transmit data from a source to a destination node, through multiple relays. Due to the hidden terminal node problem interferences are present and reduce the network capacity. Performance is evaluated in terms of mean ergodic capacity of the generic link. Results show that there exists an optimum value of nodes density maximizing the performance and this value changes when varying the source-destination distance.