Jonathan P. Benson

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 development of a novel minaturized modular platform for wireless sensor networks

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. In this paper, the development of a highly modular and miniaturized wireless platform for sensor networks is described. The system incorporates a radio transceiver (in the 2.4 GHz ISM Band) with embedded protocol software to minimize power consumption and maximize data throughput. Additional input capability for sensor and actuator integration can be incorporated seamlessly due to the modular nature of the system. The total system is packaged in a modular 25 mm cubed form factor. A smaller, (10 mm cubed), prototype is currently under development. Ongoing development of highly miniaturized nodes is discussed.

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 DSYS25 sensor platform

In this demonstration, a new sensor platform named DSYS25 is presented. The platform has a unique hardware design and runs a customized version of the TinyOS operating system. Transceiver hardware and packaging distinguish the D-Systems platform from other available designs.

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.

On the Effects of Aggregation on Reliability in Sensor Networks

Data collected in a sensor network is transported hop-by-hop to a sink for further analysis. The quality of the analysis depends on the amount of data reaching the sink. Hence, data transport reliability influences the quality of the analysis. Data aggregation is a common 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. Therefore, data aggregation significantly influences the overall data transport reliability observed at the sink. This influence is analyzed and described analytically and by experiment within this paper. Furthermore it is shown how the influence of data aggregation on data transport reliability can be controlled for a particular class of data gathering application

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.

Self-adaptive framelet-based communication for wireless sensor networks

Wireless sensor nodes employ a duty cycle to conserve energy. To implement a duty cycle, a sensor node constantly switches the communication transceiver between listen and sleep states. If a listen/sleep cycle of the receiver is known, a sender can transmit a trail of identical packets, called framelets, of which the receiver is guaranteed to receive one. Such framelet-based communication mechanisms are currently used in sensor networks. However, the framelet communication mechanisms that are currently used are static and unable to adapt to changing traffic requirements or traffic bursts. In this paper, we present three new framelet communication enhancements that can be used to overcome this limitation and allow us to construct a self-adaptive framelet-based communication protocol. Our framelet mechanisms are evaluated using testbed and simulation experiments. The results show that our self-adaptive communication protocol is able to accommodate varying traffic patterns with low energy cost.