Petr Jurcik

A Simulation Model for the IEEE 802.15.4 protocol: Delay/Throughput Evaluation of the GTS Mechanism

The IEEE 802.15.4 protocol has the ability to support time-sensitive wireless sensor network (WSN) applications due to the guaranteed time slot (GTS) medium access control mechanism. Recently, several analytical and simulation models of the IEEE 802.15.4 protocol have been proposed. Nevertheless, currently available simulation models for this protocol are both inaccurate and incomplete, and in particular they do not support the GTS mechanism. In this paper, we propose an accurate OPNET simulation model, with focus on the implementation of the GTS mechanism. The motivation that has driven this work is the validation of the network calculus based analytical model of the GTS mechanism that has been previously proposed and to compare the performance evaluation of the protocol as given by the two alternative approaches. Therefore, in this paper we contribute an accurate OPNET model for the IEEE 802.15.4 protocol. Additionally, and probably more importantly, based on the simulation model we propose a novel methodology to tune the protocol parameters such that a better performance of the protocol can be guaranteed, both concerning maximizing the throughput of the allocated GTS as well as concerning minimizing frame delay.

Real-Time Communications Over Cluster-Tree Sensor Networks with Mobile Sink Behaviour

Modelling the fundamental performance limits of wireless sensor networks (WSNs) is of paramount importance to understand the behaviour of WSN under worst case conditions and to make the appropriate design choices. In that direction, this paper contributes with a methodology for modelling cluster tree WSNs with a mobile sink. We propose closed form recurrent expressions for computing the worst case end to end delays, buffering and bandwidth requirements across any source-destination path in the cluster tree assuming error free channel. We show how to apply our theoretical results to the specific case of IEEE 802.15.4/ZigBee WSNs. Finally, we demonstrate the validity and analyze the accuracy of our methodology through a comprehensive experimental study, therefore validating the theoretical results through experimentation.

Dimensioning and worst-case analysis of cluster-tree sensor networks

Modeling the fundamental performance limits of Wireless Sensor Networks (WSNs) is of paramount importance to understand their behavior under the worst-case conditions and to make the appropriate design choices. This is particular relevant for time-sensitive WSN applications, where the timing behavior of the network protocols (message transmission must respect deadlines) impacts on the correct operation of these applications. In that direction this article contributes with a methodology based on Network Calculus, which enables quick and efficient worst-case dimensioning of static or even dynamically changing cluster-tree WSNs where the data sink can either be static or mobile. We propose closed-form recurrent expressions for computing the worst-case end-to-end delays, buffering and bandwidth requirements across any source-destination path in a cluster-tree WSN. We show how to apply our methodology to the case of IEEE 802.15.4/ZigBee cluster-tree WSNs. Finally, we demonstrate the validity and analyze the accuracy of our methodology through a comprehensive experimental study using commercially available technology, namely TelosB motes running TinyOS.

Models and Tools

An accurate planning and dimensioning of the network parameters and resources is paramount for the overall system to behave as expected. This is particularly important when there are more demanding quality-of-service requirements to be met, namely related to the correct and timely execution of the tasks and transmission of messages. This chapter outlines a set of analytical and simulation models and tools to help the system designer to setup and fine tune all relevant settings and parameters, as well as to anticipate hardware problems and identify the network behavior and its performance limits.

Simulation study of energy efficient scheduling for IEEE 802.15.4/ZigBee cluster-tree Wireless Sensor Networks with time-bounded data flows

The simulation analysis is important approach to developing and evaluating the systems in terms of development time and cost. This paper demonstrates the application of Time Division Cluster Scheduling (TDCS) tool for the configuration of IEEE 802.15.4/ZigBee beacon-enabled cluster-tree WSNs using the simulation analysis, as an illustrative example that confirms the practical applicability of the tool. The simulation study analyses how the number of retransmissions impacts the reliability of data transmission, the energy consumption of the nodes and the end-to-end communication delay, based on the simulation model that was implemented in the Opnet Modeler. The configuration parameters of the network are obtained directly from the TDCS tool. The simulation results show that the number of retransmissions impacts the reliability, the energy consumption and the end-to-end delay, in a way that improving the one may degrade the others.

Construction of the bounded application-layer multicast tree in the overlay network model by the integer linear programming

The geographically distributed system can be interconnected via an overlay multicast network. In this overlay network the multicast data are routed and replicated on the application layer along a multicast tree. This paper presents the techniques of the network reduction and the multicast tree construction. The multicast tree in the form of shortest path tree (SPT) can be build up upon the linear programming formulation. To control the load of each host, the additional constraints on the maximal number of directly outgoing connections and integer variables are added and subsequently form the degree-bounded shortest path tree problem (db-SPT). This theoretically based problem is formulated in integer linear programming framework

Energy-Efficiency in Data Centers

Moving from a still on-going work [1], this section reports the progress being developed towards energy-efficient operations and the integrated management of cyber and physical aspects of data centers. In particular, an integrated system composed by wired and wireless sensors is presented: it monitors power consumptions of the servers and environmental conditions, with the goal of achieving an overall reduction of data centers’ energy consumptions. As like as the EMMON system ( Chap. 8), the architecture proposed is intended to be hierarchical, modular and flexible enough to achieve high temporal and spatial resolution of the sensor measurements, with negligible latencies of sensors’ reports to the data center management control station.Overall, the advantage of having fine-grained power and environmental measurements in this application scenario is twofold: (i) measuring the power consumption at the single server level has enormous benefits for the business logic of data centers’ owners, since they can offer services and billing to their customers based on the actual consumption, and (ii) although there are in literature models to predict heat-flows used in commercial Computer Room Air Cooling (CRAC) systems, those models often lack of spatial resolution, so the availability of micro-climate conditions would help improving those models as well as continue feeding them with real data will improve the reliability and accuracy of their forecasts. Fine-grained measurements are also the basis to provide different views of the system, each of them customized to different users. The proposed architecture allows to set the desired resolution of the readings upon user’s requests, for example to investigate some problems in a specific area (row, room or floor) of the data center building. Every single sensor can be configured by setting user defined alarms and trigger measurements reports adaptively, by changing or (re-)configuring specific thresholds at run-time.

Amendments to the IEEE 802.15.4 Protocol

This chapter presents specific amendments to the IEEE 802.15.4, so that some of the open issues that have been previously identified. In particular, a new implicit GTS allocation mechanism (i-GAME) is proposed that over performs the default one. Then, a node grouping mechanism (H-NAMe) is proposed so that the hidden nodes problem is mitigated and consequently energy-efficiency, throughput and latency are improved. Also, we present a very simple mechanism to exploit differentiate the traffic based on multiple priority. Finally, an overview of several improvements affecting the security and privacy of the messages against external attacks and spoofing is presented. Importantly, all these mechanisms have been implemented and integrated in the 15.4 protocol stack and experimentally validated.

Structural Health Monitoring

This chapter proposes an extension of our preliminary work [1] to address COTS-based accurate and scalable Structural Health Monitoring (SHM) systems by means of WSN, trying to overcome most if not all of the limitations identified in this field, namely by: (i) using adequate synchronization between all nodes in the network; (ii) relying on standard communications protocols, while most proposals use IEEE 802.15.4-compliant devices that neither implement the IEEE 802.15.4 medium access control (MAC) nor ZigBee protocols; (iii) building upon a standard de facto operating system (OS) for WSNs platforms (TinyOS); (iv) relying on COTS technologies (more cost-effective); and (v) providing adequate scalability to monitor large infrastructures in an effective way, i.e., with a consistent time correlation of samples.

Snapshot of the IEEE 802.15.4 and ZigBee Protocols

This chapter presents the most important features of the IEEE 802.15.4 and ZigBee protocols. It particularly focuses on the Data Link and Network Layers, which are the most relevant in the context of this book. Finally, a brief discussion on the issues that the standards still leave open is presented. A possible set of solutions to those problems will be formulated as amendments in the second part of the book.