Wireless Sensor Network Protocols

Efficient design and implementation of wireless sensor networks has become a hot area of research in recent years, due to the vast potential of sensor networks to enable applications that connect the physical world to the virtual world. By networking large numbers of tiny sensor nodes, it is possible to obtain data about physical phenomena that was difficult or impossible to obtain in more conventional ways. In the coming years, as advances in micro-fabrication technology allow the cost of manufacturing sensor nodes to continue to drop, increasing deployments of wireless sensor networks are expected, with the networks eventually growing to large numbers of nodes (e.g., thousands). Potential applications for such large-scale wireless sensor networks exist in a variety of fields, including medical monitoring [1, 2, 3], environmental monitoring [4, 5], surveillance, home security, military operations, and industrial machine monitoring. To understand the variety of applications that can be supported by wireless sensor networks, consider the following two examples. Surveillance. Suppose multiple networked sensors (e.g., acoustic, seismic, video) are distributed throughout an area such as a battlefield. A surveillance application can be designed on top of this sensor network to provide information to an end-user about the environment. In such a sensor network, traffic patterns are many-to-one, where the traffic can range from raw sensor data to a high level description of what is occurring in the environment, if data processing is done locally. The application will have some quality of service (QoS) requirements from the sensor network, such as requiring a minimum percentage sensor coverage in an area where a phenomenon is expected to occur, or requiring a maximum probability of missed detection of an event. At the same time, the network is expected to provide this quality of service for a long time (months or even years) using the limited resources of the network (e.g., sensor energy and channel bandwidth) while requiring little to no outside intervention. Meeting these goals requires careful design of both the sensor hardware and the network protocols. Medical Monitoring. A different application domain that can make use of wireless sensor network technology can be found in the area of medical monitoring. This field ranges from monitoring patients in the hospital using wireless sensors to remove the constraints of tethering patients to big, bulky, wired monitoring devices, to monitoring patients in mass casualty situations [6], to monitoring people in their everyday lives to provide early detection and intervention for various types of disease [7]. In these scenarios, the sensors vary from miniature, body-worn sensors to external sensors such as video cameras or positioning devices. This is a challenging environment in which dependable, flexible, applications must be designed using sensor data as input. Consider a personal health monitor application running on a PDA that receives and analyzes data from a number of sensors (e.g., ECG, EMG, blood pressure, blood flow, pulse oxymeter). The monitor reacts to potential health risks and records health information in a local database. Considering that most sensors used by the personal health monitor will be battery-operated and use wireless