Protocol stacks for power-aware wireless microsensor networks

Abstract

In a distributed wireless sensor system, a need to prolong the lifetime of the network is crucial and limited by battery capacity. As communication traffic among sensor nodes is triggered by sensing events, the network can exploit these time-varying scenarios to obtain power savings by adjusting its operating conditions accordingly. A coherent design of application-specific network protocol stacks is the key. Specifically, embedding power aware features in the link layer and media access control (MAC) layer promises to extend the lifetime of the sensor network. The power-aware design will be illustrated on [mu]AMPS sensor node prototypes. With the integrated design framework, lower layers of the network stack provides configurable power-aware features to be controlled by higher network layers that maintain broaderview knowledge of the environment. TDMA has been chosen as a MAC Layer protocol for its inherited power-aware mechanism of radio shutdowns outside its TDMA slot and in absence of sensing events. Another level of power-aware features can be deployed in MAC ID and TDMA slot assignments. In a field of scattered sensor nodes, not all the nodes are in radio range of one another or of the base station. Hence, assigning N TDMA slots for the network of N sensor nodes that are not all in radio range will waste the receiver energy and link bandwidth. An algorithm for a re-use of MAC ID and MAC time slot is proposed based on the number of neighboring nodes. Hence, varying the number of neighboring nodes by varying the transmit power can optimize the system lifetime and bandwidth. An implementation of the Link and MAC infrastructure is completed. Power scalability is illustrated on [mu]AMPS node prototypes, with TDMA Media Access and a vehicle tracking application demonstration.