Erico Leão

Superframe Duration Allocation Schemes to Improve the Throughput of Cluster-Tree Wireless Sensor Networks

The use of Wireless Sensor Network (WSN) technologies is an attractive option to support wide-scale monitoring applications, such as the ones that can be found in precision agriculture, environmental monitoring and industrial automation. The IEEE 802.15.4/ZigBee cluster-tree topology is a suitable topology to build wide-scale WSNs. Despite some of its known advantages, including timing synchronisation and duty-cycle operation, cluster-tree networks may suffer from severe network congestion problems due to the convergecast pattern of its communication traffic. Therefore, the careful adjustment of transmission opportunities (superframe durations) allocated to the cluster-heads is an important research issue. This paper proposes a set of proportional Superframe Duration Allocation (SDA) schemes, based on well-defined protocol and timing models, and on the message load imposed by child nodes (Load-SDA scheme), or by number of descendant nodes (Nodes-SDA scheme) of each cluster-head. The underlying reasoning is to adequately allocate transmission opportunities (superframe durations) and parametrize buffer sizes, in order to improve the network throughput and avoid typical problems, such as: network congestion, high end-to-end communication delays and discarded messages due to buffer overflows. Simulation assessments show how proposed allocation schemes may clearly improve the operation of wide-scale cluster-tree networks.

Real-Time Communication for Smart Sensor Networks: A CAN Based Solution

Due to the increased availability of low cost network technology, the use of networks to interconnect sensors, actuators and controllers is now widely accepted. Such increased availability is one of the driving factors for the implementation of smart sensor networks. To ensure the correctness of the supported applications, the communication network must provide a reliable and timely communication service. Aside from the medium access control (MAC) protocol, one of the components that has a high impact in the communication delays is the local communication stack. Therefore, the usage of an adequate communication stack is of utmost importance to guarantee the timing correctness of the supported smart sensor applications. In this paper, we analyze the real-time aspects of a CAN-based smart sensor network. We assess the use of well established realtime scheduling algorithms to manage the outgoing queue of each of the local communication stacks. We show that it is possible to improve the responsiveness of applications supported by the CAN communication protocol, by using just a light scheduling middleware to adequately schedule each of the outgoing queues. We also show that implementing such middleware upon COTS communication hardware, it is possible to reduce the occurrence of priority inversions in the communication medium. Therefore it becomes possible to decrease the number of deadline misses even for highly loaded network scenarios. As a consequence, we advocate that CAN networks can be an interesting solution to support event-triggered smart sensor networks.

An Event-Triggered Smart Sensor Network Architecture

A smart transducer is the integration of a sensor/actuator element, a processing unit and a network interface. Smart sensor networks are composed of smart transducer nodes interconnected through a communication network. This paper proposes a new architecture for smart sensor networks, that is driven by events (asynchronous data). The events are derived from a data compression algorithm embedded in the smart sensor, which compresses data from the sensor. The proposed architecture also provides configuration and monitoring data to manage the distributed system.

Alternative Path Communication in Wide-Scale Cluster-Tree Wireless Sensor Networks Using Inactive Periods

The IEEE 802.15.4/ZigBee cluster-tree topology is a suitable technology to deploy wide-scale Wireless Sensor Networks (WSNs). These networks are usually designed to support convergecast traffic, where all communication paths go through the PAN (Personal Area Network) coordinator. Nevertheless, peer-to-peer communication relationships may be also required for different types of WSN applications. That is the typical case of sensor and actuator networks, where local control loops must be closed using a reduced number of communication hops. The use of communication schemes optimised just for the support of convergecast traffic may result in higher network congestion and in a potentially higher number of communication hops. Within this context, this paper proposes an Alternative-Route Definition (ARounD) communication scheme for WSNs. The underlying idea of ARounD is to setup alternative communication paths between specific source and destination nodes, avoiding congested cluster-tree paths. These alternative paths consider shorter inter-cluster paths, using a set of intermediate nodes to relay messages during their inactive periods in the cluster-tree network. Simulation results show that the ARounD communication scheme can significantly decrease the end-to-end communication delay, when compared to the use of standard cluster-tree communication schemes. Moreover, the ARounD communication scheme is able to reduce the network congestion around the PAN coordinator, enabling the reduction of the number of message drops due to queue overflows in the cluster-tree network.

CT-SIM: A simulation model for wide-scale cluster-tree networks based on the IEEE 802.15.4 and ZigBee standards:

The IEEE 802.15.4/ZigBee set of standards is one of the most used wireless sensor network technologies. This set of standards supports cluster-tree networks, which are suitable topologies for wide-scale deployments. The design of wide-scale wireless sensor networks is a challenging task because it is difficult to test, analyse and validate new designs in real scenarios. Thus, simulation becomes a convenient and feasible method for its assessment before deployment. Within this context, we provide a set of simulation models for IEEE 802.15.4/ZigBee-based networks, which are able to deal with wide-scale cluster-tree wireless sensor networks and to address their major challenges. The provided simulation models implement important mechanisms for the assessment of wide-scale cluster-tree networks and associated data communication mechanisms, enabling an easier design and test of wide-scale wireless sensor network implementations.

An opportunistic approach to deal with real-time mesh communication in wireless sensor networks

In this paper we propose a novel approach, named Real-Time Alternative-Route Definition (RT-ARounD), to support real-time message streams over large-scale wireless sensor networks. Starting from a standard cluster-tree topology, where each cluster has active and inactive periods, the proposal selects a set of nodes to build a mesh topology which is used during the inactive periods of the respective clusters to transmit messages with real-time requirements. This new topology is built considering shortest path routes between source and sink nodes. In that way, the number of hops that a real-time message needs to transverse can be drastically reduced, thereby improving the real-time responsiveness of the overall network. Moreover, the use of the inactive period guarantees that the normal cluster-tree operation remains unaffected.

Implementation of an event-triggered smart sensor network architecture based on the IEEE 802.15.4 standard

Abstract A smart transducer is the integration of a sensor/actuator element, a processing unit, and a network interface. Smart sensor networks are composed of smart transducer nodes interconnected through a communication network. This paper presents an event driven smart sensor network architecture (asynchronous data) and its respective implementation based in the IEEE 802.15.4 standard. The events are derived from a data compression algorithm embedded into the smart sensor, which compresses data from the sensor. The architecture also supports configuration and monitoring activities for the over all distributed system.

An allocation scheme for IEEE 802.15.4-ZigBee cluster-tree networks

The IEEE 802.15.4/ZigBee standards support the implementation of cluster-tree networks, which are a suitable topology to deploy wide-scale networks. In this type of topology, an important issue is the configuration of the superframe duration that is allocated to each of the network clusters. In this paper, we propose an allocation scheme for setting-up these superframe duration values. The proposed scheme allocates adequate duration values for each cluster coordinator, based on the message load originated from its child nodes (including child coordinators and its descendants). The target of the proposed allocation scheme is to improve the network throughput and to reduce network congestion and dropped messages. Its main advantages are: 1) to have a balanced allocation of network resources to the different clusters; 2) the message generation at the application layer does not need to be synchronised with the beacon arrival; and 3) the message periods do not need to be multiple of the beacon interval.