Programming a Sensor Network as an Amorphous Medium

In many sensor network applications, the network is deployed to approximate a physical space. The network itself is not of interest: rather, we are interested in measuring the properties of the space it fills, and of establishing control over the behavior of that space. Consider, for example, deploying a network of devices to manage a large farm. The tasks to be carried out by the devices—irrigation, pest management, and fertilization, for example—are naturally specified in terms of regions of the farm (e.g. “a potato field is watered every so-many hours during hot weather”). An applications programmer for farms should be able to write code at this level, rather than having to specify in depth how the sensor network will be deployed in the fields or how the devices will coordinate to carry out the programs. The spatial nature of sensor network applications means that many can be expressed naturally and succinctly in terms of the global behavior of an amorphous medium—a continuous computational material filling the space of interest. Although we cannot construct such a material, we can approximate it using a sensor network. Using this amorphous medium abstraction separates sensor network problems into two largely independent domains. Above the abstraction barrier we are concerned with longrange coordination and concise description of applications, while below the barrier we are concerned with fast, efficient, and robust communication between neighboring devices. We apply the amorphous medium abstraction with Proto, a high-level language for programming sensor/actuator networks. Existing applications, such as target tracking and threat avoidance, can be expressed in only a few lines of Proto code. The applications are then compiled for execution on a kernel that approximates an amorphous medium. Programs written using our Proto implementation have been verified in simulation on over ten thousand nodes, as well as on a network of Berkeley Motes.