%0 Journal Article
%T A Sub-A Ultrasonic Wake-Up Trigger with Addressing Capability for Wireless Sensor Nodes
%A Emanuele Lattanzi
%A Matteo Dromedari
%A Valerio Freschi
%A Alessandro Bogliolo
%J ISRN Sensor Networks
%D 2013
%R 10.1155/2013/720817
%X Wireless sensor nodes spend most of the time waiting either for sensed data or for packets to be routed to the sink. While on board, sensors can raise hardware interrupts to trigger the wake-up of the processor, incoming packets require the radio module to be turned on in order to be properly received and processed; thus, reducing the effectiveness of dynamic power management and exposing the node to unintended packets cause energy waste. The capability of triggering the wake-up of a node over the air would makes it possible to keep the entire network asleep and to wake up the nodes along a path to the sink whenever there is a packet to transmit. This paper presents an ultrasonic wake-up trigger for ultra-low-power wireless sensor nodes developed as a plug-in module for VirtualSense motes. The module supports a simple out-of-band addressing scheme to enable the selective wake-up of a target node. In addition, it makes it possible to exploit the propagation speed of ultrasonic signals to perform distance measurements. The paper outlines the design choices, reports the results of extensive measurements, and discusses the additional degrees of freedom introduced by ultrasonic triggering in the power-state diagram of VirtualSense. 1. Introduction The reduction of power consumption through the adoption of low-power design solutions and dynamic power management policies is mandatory in order to meet the needs of wireless sensor networks (WSNs). The average power consumption of on-board transceivers, at the time of writing, can be estimated to be around 20£żmA (either in receiver or transmitter mode), which is commonly recognized as the main contribution to the energy drain of sensor nodes [1]. Since the radio module has to be powered on to enable the reception of incoming packets, strategies and techniques have been developed with the aim of limiting the impact of idle listening on power consumption. Current state-of-the-art solutions make use of pseudoasynchronous rendez-vous schemes or purely asynchronous methods that exploit ad hoc hardware. The former, in all their variants, are protocols developed in order to allow efficient communication between duty-cycle-based receivers, which typically trade off latency for power consumption. The latter are techniques that exploit separate low-power wake-up receivers that are devoted to continuous monitoring of the communication channel in order to enable the main radio module to be switched off while idle to avoid energy waste. A further possible approach to the problem entails the adoption of global clock
%U http://www.hindawi.com/journals/isrn.sensor.networks/2013/720817/