Event Stream Processing in Wireless Ad hoc Sensor Networks
In recent years, technical advances in wireless communication have enabled the development of many applications of sensor networks. In addition, sensor nodes and small-scale embedded computing devices used in wireless sensor and actuator networks (WSANs) have become progressively intelligent with advances in processors, memories, and communication facilities. WSANs can be employed in diverse applications such as fire detection, environment monitoring, object tracking, and so on.
However, WSANs have some characteristics that are distinct from those of ad hoc wireless networks, for example, limited resources, large and dense deployment, dynamic topology, etc. Due to the presence of low-rate and error-prone wireless links in the sensor networks, communication overheads should be minimized, particularly when the sensor nodes continuously produce a large volume of data. To achieve this goal, event processing systems should be designed so as to enhance the flexibility and responsiveness of the infrastructure of a wireless sensor network. Furthermore, the event processing systems should be able to increase the efficiency of resource utilization, to enable on-demand computing and to suppress the collection of unnecessary data from the physical world.
Most applications involving WSANs deal with long-standing queries, which are tasks to be accomplished in the networks. It is important to assign the tasks correctly in the networks and perform the assigned tasks in an energy-efficient manner since the sensor nodes can afford to use only a limited amount of energy from a battery. To achieve this, WSANs need efficient protocols for task assignment and load balancing.
- Design of a Distributed Event Processing Framework
First, we identify use cases for the WSAN and requirements for the use cases. Next, we design a novel distributed event processing framework for the WSAN and define its functional entities.
- Development of a Task Assignment Scheme
Task assignment is of particular importance for designing the distributed event processing framework for the WSAN. We consider several designing issues. The first issue is regarding the way of describing the task since the task description affects the complexity of the WSAN. The second issue is regarding how to validate the task to be assigned toeach sensor, which is a critical problem for deploying sensor networks. The third issue is regarding how to change the assigned task into a new task. Although the processing of a long-standing query (or task) in the WSAN takes a long time, some tasks should be changed according to application requirements.
- Development of a Load-balancing Scheme
We consider long-lived queries in large-scale wireless sensor networks with multiple gateways. In such an environment, sensory data are continuously delivered through the gateways therefore, it is important to prolong the overall system lifetime by distributing the sensory data through the multiple gateways. In this study, we design a task assignment scheme that enables load balancing among the multiple gateways. In addition, balanced energy consumption at the sensor nodes around the gateways is investigated.
- We identify key requirements for the distributed event processing framework in WSANs from realistic use cases, and these requirements can be used as guidelines for designing new event processing techniques.
- We propose a task assignment scheme in WSANs which is meeting the given application requirements such as long standing query and maintenance awareness. Furthermore, the proposed data aggregation scheme seeks to satisfy the latency and reliability requirements. A load-balancing scheme is also introduced for WSANs with multiple gateways, which improves system availability as well as system lifetime.
- We implement a WSAN prototype to evaluate the proposed data aggregation and task assignment schemes. Specifically, we will build up a multi-hop WSAN that consists of Crossbow Mote sensor nodes.
¡¤ International Journal
Jaekyu Cho, Yoonbo Shim, Sangheon Pack, Taekyoung Kwon, Yanghee Choi, and Sooyeon Kim, ¡° SARIF: A Novel Framework for Integrating Wireless Sensor and RFID Networks,¡± IEEE Wireless Communications, December 2007.
¡¤ Technical Report
Sangheon Pack, Jongsu Lee, Taekyoung Kwon, Yanghee Choi, and Sooyeon Kim, ¡°A Dynamic Load Balancing Scheme in Multi-Sink Wireless Sensor Networks.¡±
Last Modified: Tuesday, Dec 4, 2007