Tony O'Donovan

A context aware wireless body area network (BAN)

In monitoring a patients real-time vital signs through Body Area Networks (BAN), rich data sources are communicated to medical practitioners. The benefit of BANs may be negated if medical practitioners are overloaded with streams of BAN data. It is essential that data is delivered in a timely context aware manner. In this paper a BAN designed for falls assessment among elder patients (65+ years) is presented, with an emphasis on the communication scheme chosen. The FrameComm MAC protocol described in this paper employs three data management techniques, 1) message priority, 2) opportunistic aggregation and 3) an adaptive duty cycle, all of which are designed to ensure that patient vital signs (i.e. data packets) are delivered under a variety of network loads. The protocol is evaluated using a small laboratory network, initially configured to communicate Beat-to-Beat (continuous blood pressure) readings when a patient goes from a sitting to a standing position and then with added ECG (ElectroCardioGram) readings.

Car-Park Management using Wireless Sensor Networks

A complete wireless sensor network solution for carpark management is presented in this paper. The system architecture and design are first detailed, followed by a description of the current working implementation, which is based on our DSYS25z sensing nodes. Results of a series of real experimental tests regarding connectivity, sensing and network performance are then discussed. The analysis of link characteristics in the car-park scenario shows unexpected reliability patterns which have a strong influence on MAC and routing protocol design. Two unexpected link reliability patterns are identified and documented. First, the presence of the objects (cars) being sensed can cause significant interference and degradation in communication performance. Second, link quality has a high temporal correlation but a low spatial correlation. From these observations we conclude that a) the construction and maintenance of a fixed topology is not useful and b) spatial rather than temporal message replicates can improve transport reliability

The GINSENG system for wireless monitoring and control: Design and deployment experiences

Todays industrial facilities, such as oil refineries, chemical plants, and factories, rely on wired sensor systems to monitor and control the production processes. The deployment and maintenance of such cabled systems is expensive and inflexible. It is, therefore, desirable to replace or augment these systems using wireless technology, which requires us to overcome significant technical challenges. Process automation and control applications are mission-critical and require timely and reliable data delivery, which is difficult to provide in industrial environments with harsh radio environments. In this article, we present the GINSENG system which implements performance control to allow us to use wireless sensor networks for mission-critical applications in industrial environments. GINSENG is a complete system solution that comprises on-node system software, network protocols, and back-end systems with sophisticated data processing capability. GINSENG assumes that a deployment can be carefully planned. A TDMA-based MAC protocol, tailored to the deployment environment, is employed to provide reliable and timely data delivery. Performance debugging components are used to unintrusively monitor the system performance and identify problems as they occur. The article reports on a real-world deployment of GINSENG in an especially challenging environment of an operational oil refinery in Sines, Portugal. We provide experimental results from this deployment and share the experiences gained. These results demonstate the use of GINSENG for sensing and actuation and allow an assessment of its ability to operate within the required performance bounds. We also identify shortcomings that manifested during the evaluation phase, thus giving a useful perspective on the challenges that have to be overcome in these harsh application settings.

Opportunistic Aggregation over Duty Cycled Communications in Wireless Sensor Networks

To implement duty cycles with packet based transceivers, a sender transmits a trail of identical packets (which we call framelets) of which the receiver is able to catch one in its active listening phase. This communication concept is used in the standard low power listening (LPL) protocol shipped with TinyOS 2.x. This existing solution has many shortcomings which result in a very limited network performance. In this paper, we firstly present an alternative framelet based low power listening implementation called Framelet Communications (FrameComm) that eliminates these shortcomings. Secondly, we present a novel additional improvement to FrameComm - Interception and Aggregation of Framelet Communications (i-FrameComm) - that further improves network performance by opportunistically aggregating packets over the radio channel. A prototype implementation of the proposed FrameComm mechanism in TinyOS 2.02 on TelosB nodes is used for evaluation and comparison. The experiments show that the interception and aggregation method increases network throughput and lifetime as communication resources are used more efficiently.

The D-Systems Project - Wireless Sensor Networks for Car-Park Management

Wireless sensor networks are collections of autonomous devices with computational, sensing and wireless communication capabilities. Research in this area has been growing in the past few years given the wide range of applications that can benefit from such a technology. This paper reports on a joint project between The Tyndall National Institute and the Computer Science Department at University College Cork, Ireland in developing a novel miniaturised modular platform for wireless sensor networks. The system architecture, hardware and software are discussed as well as details of the deployment scenario chosen for the project - a car park management system. Results and problems encountered during deployment are presented

Reliability Control for Aggregation in Wireless Sensor Networks

The IP multimedia subsystem (IMS) provides a framework that accommodates current and future services in wired and wireless networks. However, IMS does not handle non-3G elements such as wireless local area networks (WLANs). In order to provide interconnection at the service layer between 3G and WLANs, interworking between IMS and WLAN is necessary. Extending IMS beyond 3G to WLANs is a crucial step towards the evolution of a seamless universal next generation wireless network, commonly known as 4G. In this paper, a novel architecture for service layer interworking between WLAN and 3G is presented. The architecture takes into consideration the interaction of WLAN Application SIP servers with the IMS call session control functions (CSCFs) and the extensibility of application servers (ASs) beyond the core IMS network. A WLAN AS is introduced into the IMS network and an SIP server into the WLAN. These act as interworking arbitrators and communicate with each other to provide service and session continuity. The main advantage of this architecture is its feasibility within the standard. It is also non-intrusive to the IMS core or the WLAN.Data aggregation is a method used in sensor networks to reduce the amount of messages transported. By aggregating, the data contained in several messages is fused into one single message. If such a message, containing the equivalent of many individual messages, is lost due to transmission errors then this has a detrimental effect on the application quality experienced. In many sensor network applications a constant supply of data is needed and therefore application quality is severely effected by excessive data loss. This paper proposes and evaluates the use of an in-network control mechanism to offset this disadvantageous effect. The control mechanism analytically calculates the correct reliability that an aggregate of given size must be forwarded at in order to meet application specific goals.

WSN evaluation in industrial environments first results and lessons learned

The GINSENG project develops performance-controlled wireless sensor networks that can be used for time-critical applications in hostile environments such as industrial plant automation and control. GINSENG aims at integrating wireless sensor networks with existing enterprise resource management solutions using a middleware. A cornerstone is the evaluation in a challenging industrial environment — an oil refinery in Portugal. In this paper we first present our testbed. Then we introduce our solution to access, debug and flash the sensor nodes remotely from an operations room in the plant or from any location with internet access. We further present our experimental methodology and show some exemplary results from the refinery testbed.

Detailed diagnosis of performance anomalies in sensornets

We address the problem of analysing performance anomalies in sensor networks. In this paper, we propose an approach that uses the local flash storage of the motes for logging system data, in combination with online statistical analysis. Our results show not only that this is a feasible method but that the overhead is significantly lower than that of communication-centric methods, and that interesting patterns can be revealed when calculating the correlation of large data sets of separate event types.

Priority interrupts of Duty Cycled communications in wireless sensor networks

FrameComm is a contention based, duty cycled, MAC protocol that ensures a message will be transmitted during the receiverpsilas listen phase by sending a packet, followed by a short gap, repeatedly for a precalculated number of times or until an acknowledgment is received. While introducing duty cycled communications can yield large power savings it does so at the cost of increased delay and decreased throughput. Many WSNs may incorporate several distinct message types of varying priority. A node with a high priority message to send may find the channel to be busy with a lesser priority message from another node and must therefore dasiaback-offpsila leading to further delays. In a multi-hop environment, these delays are compounded and may become unacceptably large. This paper proposes adding a high priority interrupt message to FrameComm that allows a node with important data to send to interrupt another nodepsilas lesser priority transmission giving immediate access to the channel. The priority interrupt mechanism is evaluated using an implementation in TinyOS 2 on a small laboratory testbed.

Deployment alternatives for performance debugging in wireless sensor networks

A common approach for performance monitoring and diagnosis in wireless sensor networks (WSNs) is to send meta-data to a sink node to process. WSN radio constraints limit the amount of this meta-data that can be sent. Logging it to the nodes onboard storage can also aid in long-term performance debugging. Using the stored data it is possible for nodes to do statistical analysis for the detection of performance anomalies in the network, rather than at the sink. In this paper we compare the cost and accuracy of performing anomaly detection in the network and at the sink.