Emanuele Toscano

Multichannel Superframe Scheduling for IEEE 802.15.4 Industrial Wireless Sensor Networks

The IEEE 802.15.4 protocol offers great potential for industrial wireless sensor networks, especially when operating in beacon-enabled mode over star or cluster-tree topologies. However, it is known that beacon collisions can undermine the reliability of cluster-tree networks, causing loss of synchronization between nodes and their coordinator. For this reason, this paper proposes a Multichannel Superframe Scheduling (MSS) algorithm, a novel technique that avoids beacon collisions by scheduling superframes over different radio channels, while maintaining the connectivity of all the clusters. The paper describes the MSS algorithm and addresses the advantages it provides over the time-division superframe scheduling. Analytical results are shown which provide a quantitative estimation of how the schedulability space is improved, while simulation results show that the proposed technique increases the number of schedulable clusters and the maximum cluster density. Finally, this paper proves the feasibility of the proposed approach describing a working implementation based on TinyOS.

Coexistence Issues of Multiple Co-Located IEEE 802.15.4/ZigBee Networks Running on Adjacent Radio Channels in Industrial Environments

The characteristics of the IEEE 802.15.4 physical and medium access layers make such a protocol a suitable candidate to support communication between sensors and actuators in industrial environments. As industrial networks may comprise a large number of sensors and actuators and the delay increases with the increased number of nodes, a possible solution to keep the delay small is the use of multiple radio channels to implement different small low-latency communication cells. Although in IEEE 802.15.4 the radio channels do not overlap, recent literature showed that some interference may actually occur. This paper provides a better understanding of cross-channel interference in co-located IEEE 802.15.4 industrial networks and proposes a general methodology for the assessment of IEEE 802.15.4 performance under different cross-channel interference conditions. This methodology allows a network designer to perform on-site but accurate assessments and can be easily deployed in real industrial environments to perform measurements directly in the environment-under-test. A case study based on COTS IEEE 802.15.4 devices is presented to show how to apply our methodology to a real scenario and to discuss the results obtained with one or multiple interferers and varying some MAC level parameters.

An Adaptive Approach to Topology Management in Large and Dense Real-Time Wireless Sensor Networks

Topology management protocols play an important role in WSNs, managing the sleep transitions of the nodes to make data transmissions occur in an energy-efficient way, thus prolonging network lifetime. However, classical topology management protocols are not suitable for real-time WSNs, as they may introduce unbounded delays. In a previous work, we presented a static topology management protocol specifically designed for real-time WSNs which is able to provide bounded delay and routing fidelity. This paper extends such work, presenting a dynamic topology management protocol that surpasses the static approach introducing support for event-driven data transmissions and node joining at runtime and providing a novel adaptive technique for energy balancing among nodes to further increase network lifetime. This paper provides a detailed description of the dynamic protocol and simulation results on network lifetime and routing performance with comparative assessments.

Cross-channel interference in IEEE 802.15.4 networks

The growing spread of the IEEE 802.15.4 and ZigBee protocols to support communications in many contexts, such as industrial environments, home and building automation and wireless sensor networks, has led to the deployment of large complex monitoring networks, in which multiple PANs operate in parallel on different channels. In these contexts, network coexistence may be an issue, due to cross-channel interference. This paper addresses cross-channel interference in IEEE 802.15.4 networks. First, reasoning about the coding used by IEEE 802.15.4, we approximately assess the level of interference generated by ongoing transmissions on adjacent channels and thus the level of noise due to cross-channel interference. Secondly, we present and discuss experimental results obtained through an extensive series of measurements, which were run in order to assess the performance of IEEE 802.15.4 networks under different critical operating conditions.

Comparative assessments of IEEE 802.15.4/ZigBee and 6LoWPAN for low-power industrial WSNs in realistic scenarios

This paper addresses the low-power mechanisms provided by the IEEE 802.15.4/ZigBee and 6LoWPAN protocols, providing comparative assessments through experimental measurements performed on a real testbed. For a fair performance comparison, a special effort has been made to both tune the parameters of each protocol so as to make it able to properly operate in low-power mode and make the measurement scenarios equivalent in terms of traffic and energy efficiency. After addressing this tuning phase, the paper compares the protocols performance obtained on the same network, under the same workload and while working with the same duty cycle. The comparison focuses on the impact of the low-power mechanisms on the network performance. The experimental assessments highlight the strengths and weaknesses of both protocols when working in low-power mode.

A multichannel approach to avoid beacon collisions in IEEE 802.15.4 cluster-tree industrial networks

The IEEE 802.15.4 standard leaves the problem of beacon collisions in cluster-tree topologies unsolved. Some recent work tries to solve this problem, either drastically reducing scalability or introducing some non-determinism that make them unsuitable for industrial communications. In this paper we propose a novel multi-channel approach to the beacon collision avoidance problem. Thanks to the use of multiple radio channels in the same network, it enhances scalability of cluster-tree IEEE 802.15.4 networks while allowing contention-free scheduling. A Multichannel Super-frame Scheduling (MSS) algorithm is presented that, following the multichannel approach, can outperform single-channel algorithms under given analytical conditions.

A topology management protocol with bounded delay for Wireless Sensor Networks

In wireless sensor networks (WSNs) used in monitoring applications, the need to provide real-time traffic with an appropriate QoS typically clashes with the energy consumption constraints of the nodes, which have to work for long periods without the possibility of replacing their batteries. When both energy and QoS constraints are present, the role of topology control mechanisms is fundamental. This paper presents a topology control protocol to support energy-efficient real-time communication over WSNs. The aim of this work is to provide bounded delay for data traffic while reducing the energy consumption of the nodes. Detailed description of the protocol is given and both analytical and simulation results are presented that show the effects of our topology control protocol in terms of reduced energy consumption, increased network capacity and reduced packet loss rate.

Dynamic load balancing techniques for flexible wireless industrial networks

This paper deals with load management in flexible industrial networks, characterized by a hybrid wired/wireless architecture and mobile wireless nodes. Our target scenario is an industrial network, in which data is exchanged between sensors and actuators running on the wireless side and a wired automation network. As many unpredictable elements affect the performance of wireless data transmission, it is necessary to control the load over the different Access Points (AP) through dynamic balancing policies. In traditional WLANs, one station selects the AP to connect with on the basis of the received signal strength indicator (RSSI). This approach may cause all active mobile stations to connect to a small subset of the APs and saturate their capacity, while other APs may still be underloaded. This paper shows a dynamic technique to manage the unbalanced load caused by moving nodes and fluctuating channel characteristics. Simulation results highlight the advantage of the proposed technique over the standard AP selection mechanism and another load balancing approach in the literature.

A ZigBee-based network for home heating control

This paper presents a home monitoring system which enables a user to limit both methane (CH4) consumption and carbon dioxide (CO2) emissions by a proper control of the heating system. A case study on a real home automation scenario, where a wireless sensor network based on ZigBee is used for home heating control, is presented.

Bandwidth-efficient admission control for EDF-based wireless industrial communication

This paper proposes a bandwidth-efficient admission control mechanism for EDF-scheduled factory communication cells, which addresses the two main issues of industrial communication, i.e., reliability, which is affected by the intrinsic error-prone and non-deterministic behaviour of such networks, and timeliness, which depends on the transmission scheduling policy adopted. In our model, each real-time flow is associated a target success rate, which is the minimum fraction of messages that have to be delivered correctly and on time, and the methodology to calculate the feasibility of a flow set is provided, which takes explicitly into account message loss and retransmissions according to known statistics of the wireless link. Analytical results are then compared with simulation results to assess the effectiveness of the proposed approach.