Demo Abstract: A Sensornet-inspired Underwater Acoustic Modem for Wake-up and Data ⁄

Sensor networks are changing how data is collected in many applications on earth today. However, today’s sensornets do not address the 71% of the earth’s surface that is covered by water. Just as sensornets benefit environmental monitoring and industrial control on land, environmental monitoring in oceans and lakes, and control of underwater industrial processes can benefit from sensor networks [4, 2]. While underwater sensornets can exploit the same computation and storage approaches of terrestrial sensornets, radio networks are simply not viable underwater because water absorbs most radio frequencies. Acoustic modems are a viable alternative, but most commercial acoustic modems today target long-distance, point-to-point communication with high-power consumption and high costs. While matched for some vertical applications that are fielded today, these modems are the antithesis of a sensornet, which calls for short-range, low-power, many-to-many communications, and small, inexpensive platforms. We are developing a new underwater acoustic modem targeted at the needs of sensor networks [8]. Our design targets low cost (∼$100, plus hydrophones), short range (less than 500m), and relatively low bit rates (1kbaud). As with sensornet radios, we support transmit power control and exploit CPU capabilities to get the flexibility of software-level bit decoding. A unique feature of our modem is an ultralow-power wake-up circuit (100μA at 5V), which can be activated by a short wake-up tone. We exploit wake-up tones by developing T-Lohi, an underwater media access protocol that is efficient in both energy and throughput [7]. This demonstration will show both data transfer and wakeup tone activation. We will show end-to-end data transmission (PC-to-PC, through motes operating as NICs, modems, and hydrophones in water). This demonstration is an extension of a demonstration that will be shown at Sensys 2008 [6]. We will show tone-triggered modem wakeup, high∗This work is supported by the National Science Foundation (NSF) under grants number NeTS-NOSS-0435517, CNS0708946, and CNS-0821750, and by CiSoft (the Center for Interactive Smart Oilfield Technologies), a joint venture between the University of Southern California and Chevron Corporation. Portions of this abstract are common with the Sensys